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Alec, Horton (2010) Temperature Dynamics, Volatility, and the UK Demand for Natural Gas. [Dissertation (University of Nottingham only)] (Unpublished)
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Temperature Dynamics, Volatility, and the UK Demand for Natural Gas
By
Alec John Michael Horton
2010
A Dissertation presented in part consideration for the degree of MA Finance and Investments.
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Abstract
The purpose of this paper is to consider how changes in temperature affect the volatility of the
financial markets and overall demand for natural gas as released by the National Grid. Parts 1 to
3 of this paper provide an overview of the gas markets and the literature. Parts 4 and 5 provides
the reader with an in depth analysis into temperature, demand and the financial markets. Part 4
finds a strong relationship between temperature and the demand for natural gas and clear
evidence of seasonality in natural gas demand. Part 5 focuses on volatility and the financial
markets. There is significant evidence that market volatility is greater during the winter months
in comparison to the summer months. The market is also found to be largely inefficient, which is
confirmed when testing the Efficient Market Hypothesis in part 5.1.
Acknowledgements
I would first like to thank my supervisor Dr Monica Giulietti who throughout the preparation of
my dissertation has kept in constant communication and provided me with sound advice. This
dissertation has been completed for Advisory Group AG, I would like to thank all the people at
Advisory Group who helped me obtain my data and have remained in constant communication
throughout this process, and I would also like to thank Advisory Group for several very enjoyable
trips to Zurich throughout the writing of my thesis.
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CONTENTS List of Terms............................................................................................................................................5
1 Introduction .........................................................................................................................................7
1.1 Theoretical view of the Natural Gas Markets ............................................................................... 7
1.12 The Spot‐Futures Parity and Efficient Market Hypothesis...................................................... 7
1.2 What is Natural Gas? .................................................................................................................... 9
1.3 Background on the UK Natural Gas Market................................................................................ 10
1.31 The UK Import Market .......................................................................................................... 11
1.4 An overview of UK Weather ....................................................................................................... 12
1.41 Climate Change ..................................................................................................................... 14
1.5 Why are the energy markets so volatile? ................................................................................... 14
4.1 Data and Methodology ........................................................................................................... 21
4.2 Model Specification ................................................................................................................ 22
4.3 Estimation Results................................................................................................................... 23
4.4 National Grid Demand and Seasonality .................................................................................. 27
5.1 Testing the EMH...................................................................................................................... 30
5.2 Which Market is more responsive to changes in temperature? ............................................31
5.3 Data and Methodology ........................................................................................................... 31
5.3 ARMA ‐ Model Specification and Results................................................................................ 34
5.4 GARCH ‐ Model Specification and Results .............................................................................. 37
5.5 T‐GARCH ‐ Model Specification and Results ........................................................................... 40
5.6 Seasonal Analysis .................................................................................................................... 41
5.61 Monthly GARCH Analysis ...................................................................................................... 41
5.62 Spot Price Volatility and Seasonality..................................................................................... 42
7 Bibliography .......................................................................................................................................46
7.1 References ..............................................................................................................................46
7.2 Appendices..............................................................................................................................49
LIST OF FIGURES AND TABLES
FIGURE 1 – WORLDWIDE MARKETED NATURAL GAS ENERGY CONSUMPTION (QUADRILLION BTU), IEO 2010. .........10 FIGURE 2 – NATIONAL DEMAND INDEX VS. LONDON DAILY LOW TEMPERATURE.................................................. 11 FIGURE 3 – FUTURES PRICE VS. BIRMINGHAM DAILY LOW, DECEMBER 2009 – JANUARY 2010.............................15 FIGURE 4 – NATIONAL GRID ESTIMATED DEMAND (MCM),.............................................................................. 29
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FIGURE 5 – PRICE BEHAVIOUR AND THE EFFICIENT MARKET HYPOTHESIS, BREALEY ET AL (2008)...........................36 FIGURE 6 – HURRICANE’S KATRINA AND RITA, AND THEIR PATH TOWARD THE US MAINLAND, AUGUST‐SEPTEMBER 2005. WELLS, 2006 .................................................................................................................................55 FIGURE 7 – DAILY NATURAL GAS PRODUCTION FROM THE GULF OF MEXICO FOLLOWING LANDFALLS OF HURRICANES KATRINA AND RITA. WELLS, 2006 ............................................................................................................... 55 FIGURE 8 – UK LOCAL DISTRIBUTION ZONES, NATIONAL GRID 2009................................................................. 56 FIGURE 9 – ACF AND PACF OF SPOT PRICE RETURNS. .................................................................................... 56
TABLE 1 – SUMMARY OF DEMAND, SPOT AND FUTURES DATA. ......................................................................... 19 TABLE 2 – AUGMENTED DICKEY FULLER TEST FOR UNIT ROOTS ........................................................................ 23 TABLE 3 – REGRESSION COEFFICIENTS AND N‐W S.E. ..................................................................................... 24 TABLE 4 – NATIONAL GRID DEMAND AND SEASONALITY ESTIMATED COEFFICIENTS..............................................28 TABLE 5 – EVIDENCE OF SEASONAL DEMAND FOR NATURAL GAS. ..................................................................... 28 TABLE 6 – SPOT AND FUTURES SUMMARY STATISTICS. .................................................................................... 30 TABLE 7 – ADF, JAN 2006 – MAY 2010. ..................................................................................................... 33 TABLE 8 – PORTMANTEAU TEST FOR WHITE NOISE, JAN 2006 – MAY 2010. ..................................................... 34 TABLE 9 – AKAINE’S INFORMATION CRITERION – AR COMPONENT.................................................................... 34 TABLE 10 ‐ AKAINE’S INFORMATION CRITERION – MA COMPONENT. ................................................................ 35 TABLE 11 – AKAINE’S INFORMATION CRITERION ‐ ARMA (P,Q) ....................................................................... 35 TABLE 12 – TEST FOR ARCH EFFECTS ........................................................................................................... 37 TABLE 13 – AIC FOR GARCH (P,Q) MODELS.................................................................................................. 38 TABLE 14 – SPOT RETURNS, NOTE THAT (Α1 + Β1=0.983
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LIST OF TERMS
95% Conf. 95 percent confidence
interval GARCH (p,q)
Generalised Autoregressive Conditional Heteroscedasticity
AIC Aikaike Information
Criterion GWh Gigawatt Hour
ADF Augmented Dickey
Fuller Test HDD Heating Degree Days
ACF Autocorrelation
Function ICE Intercontinental Exchange
AR (p) Autoregressive IEO International Energy Outlook
ARCH (q) Autoregressive Conditional Heteroscedasticity
LDZ Local Distribution Zones
ARIMA (p,q) Autoregressive Integrated Moving Average
MMcm Million Cubic Meters
AUT Autumn
MDV Monthly Dummy Variable
BBL Balgzand‐Bacton‐Line MA (q) Moving Average
Bcm Billion Cubic Meters NBP National Balancing Point
LM Breusch Godfrey Test NTS National Transmission System
BTU British Thermal Units
N‐W Newey West
CLRM Classical Linear Regression Model
OTC Over‐the‐Counter
CLRM Classical Linear Regression Model
PACF Partial Autocorrelation Function
CHV Composite Heating Degree Day Variable
GBP Pound Sterling
CHV Composite Weather
Variable R2 R‐Squared, measure of model fit
CWV Composite Weather
Variable NBP97 Short Term Flat NBP Trading Terms and
Conditions 1997
CDD Cooling Degree Days
SPR Spot Prices (EMH)
UGASDEMD Daily Actual National Grid Demand for Natural Gas
SPRN Spring
MEAN Daily Average
Temperature S.E. Standard Error
NBPG1MON Daily Front Month NBP Closing Prices (Futures)
SUM Summer
HIGH Daily High
Temperature UK The United Kingdom
MIN Daily Low
Temperature Thm Therm
GA1NB Daily Prompt NG Closing Prices (Spot)
T‐GARCH (p,q)
Threshold Generalised Autoregressive Conditional Heteroscedasticity
DTI Department of Trade and Industry
DD Total Degree Days, HDD + CDD
DW Durbin Watson Test WSJ Wall Street Journal
EMH Efficient Market WSD Weather Surprise Dummy Variable
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Hypothesis
EIA Energy Information Administration
WSV Weather Surprise Variable
FPR Futures Prices (EMH)
WINT Winter
The first part of this paper will be devoted to an overview of the Natural Gas markets and key
issues that will provide the foundation for analysis in future sections. Sections two and three will
provide a summary of the literature and obtained data. Parts four and five will provide detailed
analysis of both the level of demand and the financial markets for Natural gas, with a focus on the
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temperature and volatility. Within section six are conclusions to the analysis in sections four and
five.
1 INTRODUCTION
1.1 THEORETICAL VIEW OF THE NATURAL GAS MARKETS
When analysing the relationship between temperature and the price of commodities past
literature has generally preferred the use of either Spot or Futures prices. This part of the paper
will briefly discuss the Spot‐Futures parity condition and its implications for analysis in further
parts. Fama and French (1987) find that good spot‐price data is not available for most
commodities and prefer the use of futures, they state that futures are regulated through organised
regulated exchanges and thus can be assumed to be a true reflection of the market. Spot prices
data is released by reporting agencies such as Bloomberg, Reuters and Platt’s and these prices
often differ across reporting agencies. Mu (2004) verifies Fama and French’s observations and
also prefers the use of futures.
1.12 THE SPOTFUTURES PARITY AND EFFICIENT MARKET HYPOTHESIS The theoretically correct relationship between the spot and futures price is known as the Spot‐
Futures Parity, if this relationship fails to hold, arbitrage opportunities arise. There are essentially
two ways to acquire a commodity such as Natural gas. Market participant can purchase the
physical commodity today and store it, or can choose to take a long position in futures, these
two strategies must have the same market determined costs. Commodities are physical goods
and thus have different properties to financial assets, for example, a Natural Gas processing
plant is not purchasing a futures contract to speculate but to consume. In absence of storage
costs, the forward price of a commodity, such as Natural Gas is given by Equation 1. Where F0 is
the Forward Price, S0 the Spot Price, r the risk‐free rate of return and T the time period. This
equation must hold to prevent risk free arbitrage profits.
Equation 1
If a term ‘u’ is introduced, which represents the present value of all the known storage costs that
will be incurred over the contract period, absorbing funds, it follows Equation 1 that
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Equation 2
There are also advantages to owning a physical commodity, if a Natural Gas processing plant is
long futures and there is some unforeseen shock, such as an extremely cold winter, this will
cause an increase in demand for gas, but, the plant cannot convert the futures contracts into
physical delivery before contract maturity. The advantage to the plant of holding the physical
commodity is difficult to quantify, but Hull (2002) prefers the term ‘convenience yield’, denoted
by y and shown in Equation 3.
Equation 3
The convenience yield essentially represents market expectations in regards to the future
availability of the commodity. The greater the likelihood of shortages for example, the higher
the convenience yield. The difference between the futures price and the spot price is called the
‘Basis’, overtime the basis will be volatile but eventually converge. If today’s Futures price is
equal to the expected spot price at maturity then;
Equation 4
Over an extended time period, in rational markets, expectations about futures spot price will
adjust upward as often as downward. Telser (1958) finds that futures prices display no trend as
they approach maturity and accepts the hypothesis that the futures price equals the expected
spot price, Gray (1961) verified Telser’s findings and Dusak (1973) also supports Equation 4.
The spot‐futures parity condition is consistent with the Efficient Market Hypothesis (EMH)
(Fama, 1970) which states that the financial markets are informationally efficient. In an efficient
market, new information is reflected instantly in commodity prices, which implies that the futures
price is the optimal forecast of the spot price. No other topic has produced as many articles as
the EMH in the area of finance1. The spot futures parity condition is based on the assumption
that market participants are able to trade in the spot and futures markets at the same time, i.e.
traders can utilize any spot/futures price differentials. If the EMH holds then price patterns are
random and no system based on past market behaviour can earn excess returns. 1 Malkiel (1973) famously stated that a blindfolded chimpanzee throwing darts at the WSJ could select a portfolio that would so as well as the experts.
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Walls (1995) founds that the spot price of natural gas was co integrated with the futures price,
that each price conveys the same information about the present and expected underlying value,
that is, the markets are efficient and Shawky (2002) found that many of the characteristics of
the electricity market can be viewed to be broadly consistent with efficient markets.
However, Chang (1985) found that ‘large wheat speculators’ possessed some superior
forecasting ability and provides statistical evidence that is inconsistent with the hypothesis that
commodity futures prices are unbiased estimates of the corresponding future spot prices,
Houthakker (1957) also finds evidence of definite forecasting skill. In terms of the Natural Gas
markets, Herbert (1993) was first to look at markets for US Natural Gas futures and found
inefficiency in the market. Chinn et al (2005) found that futures prices were unbiased predictors
of future spot prices, with the exception those in the natural gas markets at the 3‐month
horizon, and Mazighi (2003) rejects the hypothesis of efficiency in the futures markets for
natural gas and concludes that forward prices are far from being optimal predictors of spot
prices.
1.2 WHAT IS NATURAL GAS?
Natural gas is a colourless, odourless and shapeless fossil fuel found underground that is
generated through the slow decomposition of ancient organic matter. This gas is generally found
trapped in pockets of porous rock which is supported by impermeable rock, although natural gas
is also found within oil reservoirs (Associated Natural Gas) or coal deposits (Coal‐Bed methane).
Natural gas is extracted through the use of wells drilled into the porous rock and is largely
composed of methane, all other by‐products must be removed at a processing plant before being
moved through pipelines to the end consumer.
Natural gas is highly combustible and emits a great deal of energy when burned. Once delivered to
homes it is used for a range of purposes, although in the UK it is primarily used to power central
heating systems, boilers and gas powered ovens and increasingly Natural gas is being used to
generate electricity. Consumers require space conditioning to create a comfortable living and
working environment, electricity drives devices such as fans, air conditioners, chillers, cooling
towers and electric boilers (Gellings, 2009) and energy use in buildings accounts for 53 percent
of total electricity use (Harvey, 2010). Figure 1 illustrates that since 1990 Natural gas
consumption has increased from 75.4 quadrillion Btu in 1990 to an estimated 162.3 quadrillion
Btu in 2035 (International Energy Outlook 2010) and Harvey (2010) states that there are
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enough Natural gas reserves to last for 80‐217 years depending on supply and demand
approximations.
Figure 1 – Worldwide marketed Natural gas Energy Consumption (quadrillion Btu), IEO 2010.
1.3 BACKGROUND ON THE UK NATURAL GAS MARKET
In the early 1980’s the UK gas industry began to liberalise and restructure2, which began with
the privatisation of British Gas in 1986 and the ‘demerger’ of its activities in 1991. Prior to the
liberalisation of Britain’s energy markets British Gas and 14 regional public electricity suppliers
had a monopoly to supply gas and electricity to every domestic energy consumer. Today the
market is very competitive and the demand for Natural gas in mainland UK is categorized
between Local Distribution Zones (LDZs), of which there are thirteen in the National
Transmission System (NTS). Ofgas was created to ensure a smooth transition from a vertically
integrated state owned monopolistic market to a competitive market in which consumer
interests were protected.
The UK is one of the ‘big six’ major European gas markets along with Germany, Italy, France,
Netherlands and Spain. The UK market is the largest volume market and is completely
liberalised, because of this the UK market is also the most active, competitive and volatile gas
trading market in Europe. Approximately 40% of the UK’s primary energy comes from gas, and
there are large summer/winter swings due to ‘central heating’ demand, this is shown in Figure
2, which clearly shows that when temperatures are at their lowest, the demand for natural gas
is highest and vice versa.
2 The 1982 Oil and Gas Act gave the government the power to dispose of British Gas assets and open up pipelines to the market.
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Figure 2 – National Demand Index vs. London Daily Low Temperature
The majority of gas in Europe is priced on a long‐term contract, and a per country basis, short‐
term fluctuations tend to be due to traders trading out daily imbalances, these gas prices are
based on ‘market values’ and competition at the National Balancing Point (NBP). In the UK
market, the majority of demand for natural gas is during the winter months, summers are
usually the lowest demand periods. However, abnormally hot periods can cause an increase in
demand, as consumers demand electricity to cool their homes, this is usually found to be the
case in the US market. Recent Natural Gas market volatility and the changeover of the UK from a
net exporter to a net importer mean that security of supply is also a top priority for the UK.
1.31 THE UK IMPORT MARKET The UK has historically been a net exporter of Natural Gas, however recently is became a net
importer. In 2008 natural gas production was 70 Billion cubic meters (Bcm) and consumption
was 96Bcm (CIA World Fact Book, 2010). The UK is home to the most developed and liquid hub
in Europe, the NBP, which started trading in 1996. The NBP is a virtual trading hub which
covers the whole British transmission grid, it is a notional point which does not have an
identifiable physical location. It is the trading point of UK short‐term natural gas and is key to
the price that domestic consumers pay and unlike the conventional European trading hubs,
trades made at the NBP are not required to be balanced, there is no fixed fee for being out of
balance. The NBP can be seen as the UK equivalent of the Henry Hub in the US, it is the pricing
and delivery point for Natural Gas futures in the UK that are traded on the Intercontinental
Exchange (ICE).
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The UK has a growing import capacity, the majority of gas enters the NBP system passing
through the five beach terminals in the North Sea, but there are also direct pipelines to Europe.
Langeled is a crucial 1200km pipeline that brings Natural Gas from Norway, and is able to
supply about 26Bcm per year, the Balgzand‐Bacton‐Line (BBL) from the Netherlands is also able
to supply about 16Bcm per year. Zeebrugge is a physical trading point located in Belgium, this
hub is joined to the Bacton terminal of the NBP through an interconnector pipeline that started
operations in 1998 and has recently been upgraded to be able to supply 17Bcm per year. These
three pipelines are able to meet a large part of the UK’s current demand. The original intention
of the Zeebrugge pipeline for example, was to export gas from the UK North sea to Europe, but
the flow of the Interconnector is often reversed to import gas to the UK market during winter
months. Holz et al (2008) find that this increased pipeline import volume will compensate for
the decline in UK domestic production.
Natural Gas is traded on either the spot or futures markets in the UK. Spot trading is primarily
used by traders who have short‐term physical gas imbalances to trade out. The Over‐the‐
Counter (OTC) market is an unregulated market which generally consists of bilateral
transactions between shippers, although the terms applicable to these transactions are specified
in the ‘Short Term Flat NBP Trading Terms and Conditions 1997, or ‘NBP97’. The spot market is
generally representative of the physical side of trading, whereas the futures markets are
favoured by speculators, or ‘paper side’ of the market. The exchange markets generally give the
best transparency of pricing as there is a great deal of day settlement pricing for gas.
This paper is focusing on the demand side of Natural Gas, although the supply side is also a key
issue. To meet the projected growth in demand for natural gas worldwide, producers will need
to increase annual production in 2035 to a level that is 46 percent higher than the 2007 total
(IEO 2010). This could prove a problem for the UK market, although Holz et al (2008) finds that
the competitive UK wholesale market will enable UK consumers to maintain their consumption
levels in the future.
1.4 AN OVERVIEW OF UK WEATHER
The UK market differs from the US in regards to the demand for natural gas. In the US market
the industrial sector is the largest consumer, but in the UK the single largest component of
natural gas demand is the domestic consumer, this is largely because about 90% of UK homes
have central heating systems of which 80% are gas‐fired (Stewart, 2004). Taylor et al (1977)
find that demand in both industrial and residential sectors are price inelastic in the short‐run,
but highly elastic in the long‐run. Al‐Sahlai (1989) confirms this and finds that industrial,
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residential and commercial demand are inelastic with respect to price and income in the short‐
run.
The UK market for Natural Gas is highly seasonal and because industrial demand for natural gas
is relatively unresponsive in the immediate short‐term, the weather is the single most
important factor that causes short‐term demand and price volatility. Weather data reaches the
market very quickly, and is available to all participants, thus ‘weather surprises’ will be quickly
reflected in the price of natural gas. If for example there was a sudden freeze in the North East,
consumers in cities such as Newcastle and Sunderland would turn on their central heating
systems. If this low temperature is unexpected, traders will be caught short Natural Gas and
look to the spot market to buy Natural Gas for immediate consumption. This increase in demand
would be reflected by a higher price, ceteris paribus.
Natural Gas used to power UK central heating systems is the most significant demand factor,
although over recent years the power generation market sector has been through considerable
changes. Natural Gas used to generate electricity increased from a market share of 0% in 1990
to a market share of 38% in 2002, displacing coal as the principal fuel for power generation in
the UK (Stewart, 2004). This implies that extremely hot weather surprises, such as a summer
heat wave, may instigate a spike in electricity demand used to power air conditioning systems,
which could have a similar effect on the demand for gas. Mu (2004) finds that in the US market
there is a ‘local peak’ in July and August as cooling demand increases the electric power use of
natural gas. Although this is certainly found to be the case in the US market, section three of this
paper will look to see if this thought can be applied to the UK market.
Two measures of relative temperature that are common in the market place are that of Heating
Degree Days (HDD) and Cooling degree Days (CDD). A day’s HDD is used to quantify the volume
of energy required for heating during the day, and a CDD the volume of energy for cooling
during the day, this is shown in equations 5 and 6.
Equation 5
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Equation 6
In the US, heating and cooling degree days are primarily used in the valuation of weather
derivative contracts and generally have a threshold temperature of 65°F, for this reason 18°C
will be used as the threshold temperature in future analysis.
1.41 CLIMATE CHANGE Natural gas is one of the world’s three principal fossil fuels and is the Earths most abundant
fossil fuel (Cocks, 2009). When conducting a study on weather and fossil fuel, climate change
needs a mention, but it is beyond the scope of this paper to look at climate change in great
detail, this paper will be concentrating on short‐term, intra‐month volatility, so climate change
is not entirely relevant. Harvey (2010) states that global average temperature warming ranges
from 3.5°C to as high as 6.5°C, but refers to the next century, not the next year or decade. In an
attempt to estimate future demand forecasts the National Grid created a ‘Composite Weather
Variable’ (CWV) using 2‐hourly temperatures and 4‐hourly wind speeds which includes factors
such as Wind chill, cold weather upturn and ‘effective temperature’, but even this complex
variable currently fails to incorporate the effects of climate change.
1.5 WHY ARE THE ENERGY MARKETS SO VOLATILE?
A highly volatile market is one in which prices are changing rapidly and unexpectedly, there is
an extensive range of literature available that examines whether market fundamentals or other
random factors determine price volatility. The price of Natural Gas, like any other commodity, is
fundamentally determined by supply and demand, and volatility, by nature, is a response to
shocks (Engle, 2001). The short‐term price paid for gas is determined by various factors, which
include the availability of supply, storage levels and alternative fuel prices. Henning et al (2003)
find that the Natural gas market is one of the most volatile commodity markets, even more so
than the crude oil markets. They also conclude that near‐term wellhead production is generally
inelastic, and because the demand for natural gas depends on the weather, which can shift
quickly and unexpectedly, this can creates a demand imbalance that amplifies price volatility.
In the US, ‘weather surprises’ such as hurricanes often cause vast amounts of volatility in the
market for Natural gas. Figures 6 and 7 show the impact that these hurricanes had on wellhead
production during the hurricane season of 2005. Shortly before Katrina and Rita hit, the
demand for Natural gas was already above normal, due to higher‐than average late summer
temperatures in the South. This increased the demand for gas to generate electricity, which
consumers then used to cool their homes, when combined with the supply disruptions that
followed, these hurricanes caused a significant spike in prices. Weather incidents can cause
large intra‐day price volatility, although in the UK area tropical hurricanes are not possible.
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Winter of 2009‐10 was the coldest on record for some years (see section three). Figure 3 show
the daily low temperature in Birmingham, against both spot and futures prices over the period
December 2009 to January 2010. It shows clearly that this ‘weather surprise’ caused market
volatility and the price paid for Natural gas to both increase. During the period 7th‐8th of January,
temperature was at its lowest level and spot prices were at their peak, this is consistent with the
theory that short‐term spot prices are largely determined by demand fundamentals and traders
trading out short‐term imbalances.
20
25
30
35
40
45
50
02/12
/2009
09/12
/2009
16/12
/2009
23/12
/2009
30/12
/2009
06/01
/2010
13/01
/2010
20/01
/2010
27/01
/2010
Spot/Futures Price
-12-10-8-6-4-202468
Temperature
Spot Prices Futures Price Birmingham Daily Low
Figure 3 – Futures Price vs. Birmingham Daily Low, December 2009 – January 2010.
2 LITERATURE REVIEW The data analysis part of this paper will first look at temperature and its relationship to the
demand for Natural gas. Then a brief test of the EMH will be conducted, and if rejected, further
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analysis will be conducted to see which financial market is more sensitive to temperature
volatility. There is very little literature on weather and the demand for natural gas, the majority of
the literature is based around the US market and concentrates on either the spot or futures
markets. Literature in regards to the UK Natural gas market tends to be composed by government
departments (see DTI, 2001) or the National Grid (see National Grid, 2007). There are clear gaps
in current research on the weather, temperature and their relationships to the UK market for
Natural gas, and the European Gas market has only just recently began to liberalise, thus literature
is scarce.
The EMH is one of the most discussed topics of finance; academics have disputed the theories of
the EMH for decades. The commodity markets are largely unregulated in comparison to the
capital markets, this makes the commodity markets a prime candidate for EMH testing and is
the reason for the extensive range of literature in this area. In general early literature suggests
that the inter‐market price behaviour and relative volatility are consistent with the theory of
storage, accepting the hypothesis that the futures price equals the expected spot price (see
Telser, 1958, Gray, 1961, and Dusak, 1973). The EMH has also been tested and confirmed in
markets such as the Electricity markets (see Shawky, 2002) and the wheat markets (Chang,
1985). The majority of studies have focused on long‐run properties, arguing that in the long‐run
inefficiencies will be traded out via arbitrage (Garbade and Silber, 1983) or that spot and futures
contracts share common stochastic trends (Lien and Root, 1999). However, Houthakker (1957)
found evidence of inefficient markets in the Wheat, Corn and Cotton commodity markets and
Roll (1984) came to the conclusion that Florida Orange Juice futures prices were
informationally inefficient.
The futures markets for commodities such wheat have been studied for decades, but the Natural
gas markets were largely regulated and monopolised by domestic governments until recently,
the US futures markets for example started trading in 1990. Only in recent years has data
become available in the UK market, and continental Europe has only just embarked upon fully
liberalising its markets. Herbert (1993) was the first to study the markets for US Natural gas
futures and found early examples of inefficiency in the markets, Chin et al (2005) and Mazighi
(2003) also reject the hypothesis of efficient markets in their Natural gas data. Whilst there is a
great deal of literature rejecting market efficiency, there is also a wide range of academic studies
that accept market efficiency. Walls (1995) adopted Herbert’s methodology, focusing on co
integration and found the spot and futures prices to be co integrated where Modjtahedi and
Movassagh (2005) observed that trends are due to positive drifts in the random‐walk component
of the price. It is clear that various authors agree and disagree on different aspects of the EMH, and
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for this reason part five of the paper will first test the EMH before conducting further analysis into
the markets for Natural gas, but, whereas all the literature thus far has focused on the US markets,
this paper will test the UK market. Further research in this area is also needed, particularly
focusing on the European and UK markets for Natural gas. Analysis in future sections will be
largely based on work by Mu (2004) and Ates and Wang (2007) who both favoured the use of
GARCH models to measure volatility in their data series.
Mu selected 766 weather stations east of the Rocky mountains from 1949‐2000 which were then
used to define a weather surprise variable. The weather surprise variable was then implemented
into a GARCH model. Mu found that the weather surprise variable has a significant effect on the
conditional volatility of natural gas prices. Mu also concluded that the inclusion of the weather
surprise variable in the conditional variance equation has significant effects on volatility
persistence. Ates and Wang define a more complex ARMA X‐Threshold GARCH model to define
volatility in their data series. They find that conditional volatility shocks are more persistent in
the futures market than in the spot market and propose that this is because informed traders
prefer to trade in the futures market because of its low trading costs relative to the spot market.
Their analysis also finds that extreme cold weather surprises affect the variation in basis, spot
and futures prices, that the conditional volatility of natural gas spot and futures are higher in
winter and lower in summer months, and the conditional correlations between spot and futures
markets are lower in winter and high in summer months, all of which will be tested in parts 4
and 5 of this paper. Suenaga et al (2006) and Brown and Yucel (2008) both come to similar
conclusions to Ates and Wang and Mu, that volatility is greater in the winter than in the
summer. The reasons they give is because the high marginal cost of natural gas production and
the inelastic winter mean that shocks of even a small magnitude can cause a large price swings.
The authors all agree that there is more volatility and higher prices in the winter than the
summer and the large majority find that the weather, particularly cold temperature has a very
significant impact on Natural Gas prices. This paper will largely adopt the GARCH
methodologies adopted by past literature. The only part of past studies that may have to be
amended is when defining the weather surprise variable, this is because all of the studies are in
the US markets, which are markets for both heating and cooling degree days, this paper expects
to find cooling degree days to be largely insignificant in comparison to heating demand in the
UK markets, thus, the composite weather variable may have to be redefined.
There are clear gaps in the current research, for example, the majority of literature focuses on
the US markets, this may mean that there are some factors overlooked or overstated in past
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18
studies that need to be included or excluded in future studies of the European and UK natural
gas markets. The reasons why there is very little literature on the UK markets and European
literature is non‐existent is because the markets have only recently been liberalised so further
research into this area is definitely required as the Natural gas markets continue to expand in
upcoming years.
3 GENERAL DATA SUMMARY This paper obtained daily actual National Grid Demand figures from 1st Jan 2003 until the 31st
May 2010 and daily front month NBP closing prices from the 5th of September 2005 until the
28th of May 2010, both were obtained from Bloomberg. Daily British prompt Natural gas closing
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19
prices from 1st Jan 2003 until the 31st May 2010 were also obtained from Reuters. Natural Gas is
measured in pence per therm where the demand figures are measured in million cubic meters
(MMcm). The data is summarized in table 1, the daily demand figures are reported daily, spot
and futures prices are reported on trading days only.
Observations
(excl missing
values)
Min Max Mean Standard
Deviation Skewness Kurtosis
Demand
‘UGASDEMD’ 2,630 130.52 465.46 280.82 67.25 0.14 2.02
Spot Prices
‘GA1NB’ 1,932 5 168 35.20 17.73 1.80 8.59
Futures Prices
‘NBPG1MON’ 1,189 14.7 113.53 43.34 17.75 0.78 3.37
Table 1 – Summary of Demand, Spot and Futures data.
The highest demand recorded over the periods was on 8th January 2010, at a time when
temperatures were at a record lows. The smallest demand recorded over the period was on the
30th July 2006, at a time when 60% of the US was experiencing drought conditions (McKenzie,
2006) and the UK was in the midst of a cool summer day relative to previous weeks (Deakin,
2006). The lowest recorded spot price in the periods was the 3rd of September 2006, at a time
when the UK had experienced the warmest September since records began, following the
warmest month on record, July 2006 (Forster, 2006). The highest recorded spot price was also
the day of the highest recorded futures price, the 22nd of November 2005. Prices were high
around this time largely because of supply‐side issues, this period was in the midst of Russia‐
Ukraine gas disputes and coincided with the time when cold winter weather began to hit large
parts of the UK.
Although this paper has obtained daily demand figures for the whole of the UK mainland, the
national grid segments the UK into thirteen different LDZs (see Figure 8). The methodology
employed when attaining weather data was to select the largest consumer, where possible, in
each LDZ and attain daily weather data3. Gas sales and customer data were obtained from the
National Grid, and the following cities were selected, Glasgow, Carlisle, Sunderland, Manchester,
Nottingham, Birmingham, Wrexham, Cardiff, South end‐on‐sea, Hammersmith and Fulham,
Brighton and Hove, Southampton and Bristol, this data is summarised in table 18.
3 Hammersmith and Fulham although not the largest consumer in the ‘North Thames’ LDZ, is the closest large urban area to the chosen weather station.
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20
Based on these locations, weather data was obtained from Bloomberg from 1st January 1973
until the 28th June 2010. To remain as consistent as possible across the dataset and to reduce
basis risk4 all of the data was taken from the closest Airport and all the temperature
measurements were taken in mid afternoon, between 13.20 and 13.50, this methodology is
summarised in table 19. The dataset consists of observations on temperature, detailed in Table
20: daily maximum (.HIGH), minimum (.MIN), average (.MEAN), heating degree days (.HDD) and
cooling degree days (.CDD). The data set contains occasional missing observations due to failure
of measuring stations to report to Bloomberg, although this is rare and largely insignificant as
there are almost 900,000 data points within the historical weather data. ‘Wrexham’ has been
removed entirely from future analysis as the data set was largely inconsistent and suffered from
clear misreporting of data, tables 21‐32 provide summary statistics of the selected locations.
The reasons for collecting such as vast amount of data will become more apparent when a
‘weather shock’ variable is defined in later sections. Although the market in the UK isn’t as
geographically broad as the US market for Natural Gas (Mu, 2004, selects 766 weather stations
east of the Rocky Mountains from 1949‐2000) the rationale for selecting weather stations at
various locations is to ultimately create a variable that includes all of the locations specified
above.
4 THE DEMAND FOR NATURAL GAS AND TEMPERATURE This part of the analysis will look at temperature and Natural Gas demand. Mu (2004) states that
the weather impacts about fifty percent of U.S. natural gas demand, and as explained in previous
sections, the UK markets is much more reliant on Natural Gas than the US market. UK Households
are now kept warmer than in the past. In 1970 5.6m homes were centrally heated, this increased
to 21.7m by 2000, likewise, average internal temperatures increased from 13°c in 1970 to 18°c in
2000 (DTI, 2001). With living standards expected to increase over time, a similar trend is likely to 4 The risk that the temperature differs in the measurement station to that of the main rural area which was selected based on consumption data.
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continue in the future, for this reason this paper expects to find a strong relationship between
temperature and demand in the UK market.
4.1 DATA AND METHODOLOGY National Grid actual demand figures from the 1st Jan 2003 until the 31st May 2010 were
obtained from Bloomberg, summary statistics are provided in Table 1. As explained in section 3,
the majority of the weather stations are located at airports closest in proximity to the highest
consuming area in that particular LDZ. Although every feasible step has been taken to ensure the
reliability of the weather data some issues may still persist, for example, when estimating their
CWV the National Grid notes that one weather station is on the top of an office building and is
affected by the heat from the building in very cold weather (pg 25, Gas Demand Forecasting
Methodology 2007). To ensure complete accuracy of the data, each location would have to be
checked individually and any anomalies adjusted for, this is beyond the scope of this paper.
Ates and Wang (2007) use just one city, Chicago, in their regression analysis. Chicago is generally
favoured as it is the third most populous city in the US and one of the largest consumers of Natural
Gas. Mu (2007) uses ‘total degree days’ as the explanatory variable in the regression analysis,
similar to that shown in Equation 7.
Equation 7
The reason why ‘total degree days’ (DD) are favoured when using historical data from cities such
as Chicago is because the summers are comparatively much warmer that those of the UK’s largest
cities, and thus consumers require more cooling energy. The historical July and August average
high in Chicago is about 7‐8°c higher than in London, this is a significant enough variation to have
differing impacts on CDD’s across these two locations. Table 33 shows that Heating Degree Days
have the highest correlation to Natural gas demand and Cooling Degree Days the lowest across all
the chosen UK cities, it is for this reason that HDD’s will be preferred in further analysis. A
Classical Linear Regression Model similar to that implemented by the National Grid will be first
estimated using OLS. Each location will be regressed against the demand data, in addition to this a
‘Composite HDD Variable’ (CHV) will also estimated, representing the sum of all the locations. The
reasons behind regressing each location in addition to the CHV is to discover if any one location,
London for example, is as accurate as using a composite variable. Ates and Wang (2007) elected to
use only one location in their analysis into the weather and temperature, this is in comparison to
Mu (2004) who, as explained briefly above, choose to use numerous locations.
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22
The formulated research question is ‘Do low temperatures have a significant impact on National
Grid demand data?’ the Null hypothesis is that HDD’s at each location do not impact national grid
demand.
4.2 MODEL SPECIFICATION The methodology preferred by the National Grid when evaluating the relationship between
demand and the CWV is shown in Equation 8, where A&B are constants, CWVi the estimated
Composite Weather Variable and ui the error term and i a ‘non‐holiday weekday’.
Equation 8
A similar simple regression model will be estimated using OLS, see Equation 9, where
UGASDEMDi is the actual daily demand for Natural Gas, in MMcm. nHDDi the Heating Degree Days
at location n, and εi the error term.
Equation 9
This regression will be estimated against each location and the CHV (see Equation 11), where
UGASDEMDi is the actual daily demand for Natural Gas, CHVi the Composite Heating Degree Day
Variable, and εi the error term.
Equation 10
The CHV is an arithmetic mean and is computed using the methodology shown in Equation 11,
where n represents the number of weather stations, with each locations Heating Degree Days
denoted by HDDi.
Equation 11
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23
As the dataset contains two leap years, the 29th of February 2004 and 2008 have been removed from
the analysis to insure that the CHV is consistent across the dataset. Section 4.3 interprets the
estimation results. Firstly the Augmented Dickey Fuller (ADF) test was conducted to check for
stationarity. The Breush‐Pagan and White tests were then employed to test for heteroscedasticity.
Finally, the Durbin Watson (DW) and Breusch‐Godfrey (LM) tests were used to check for serial
correlation.
4.3 ESTIMATION RESULTS An important assumption in regression analysis with regards to time series data is that the data
fluctuates around a mean, that is, the data is stationary. Running OLS on a non‐stationary series can
lead to a spurious regression, to avoid this all variables in the model are required to be stationary.
For example, generally one would expect commodities to be stationary, over time they are expected
to follow an upward trend, this is because as world population grows, people demand more food
and more energy and people generally expect their standard of living to increase, all of these factors
imply and upward trend in future years. The EMH implies that the behaviour of commodity prices
should follow a random walk, that the data should be non‐stationary, thus, the following hypothesis
will be tested;
H0: δ=0 Non‐Stationarity
H1: δ
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24
demand for Natural gas increases in all locations. All of the p‐values on the estimated coefficients
are very significant and all regressions show evidence of strong model fit, based on R2 values.
The location with the largest Model fit is London, the London Metropolitan area is the most highly
populated area and is responsible for the biggest demand for Natural gas in the UK, so the fact that
London explains more of the variation in Natural gas demand is not surprising. Introducing the
CHV as the dependent variable increases model fit slightly, but it is clear that choosing one large
city, such as London or Chicago (Ates and Wang, 2007), will produce results similar to creating a
composite weather variable, but creating a CHV generates a slightly more efficient slope
coefficient.
95% Conf. Coefficients NW S.E. tvalue Model Fit, R2
199.2084 1.359501 146.53 London 11.49701 0.1394825 82.43
0.8430
188.6218 1.480893 127.37 Birmingham 11.54471 0.141975 81.32
0.8228
178.5206 1.843107 96.86 Glasgow 1.89268 0.1817026 64.45
0.7531
178.3121 0.1716902 100.32 Sunderland 11.93757 1.777476 69.53
0.7758
185.1597 1.665936 111.14 Manchester 11.82768 0.1652612 71.57
0.8044
191.2574 1.4648 130.57 Nottingham 11.76738 0.14637 80.39
0.8304
185.2261 1.517523 122.05 Cardiff 12.66905 0.1562882 81.06
0.8305
200.6933 1.285398 156.13 South end 11.77499 0.1375053 85.63
0.8347
191.2164 1.413662 135.26 Brighton 12.16372 0.1448235 83.99
0.8256
187.0117 1.517392 123.25 Bristol 1.92083 0.1522111 78.32
0.8350
193.3418 1.483988 130.29 Southampton 11.82598 0.1478421 79.99
0.8005
193.2944 1.500767 128.80 Carlisle 11.76573 0.1644963 71.53
0.8013
184.1587 1.463701 125.82 CHV 12.46919 0.1542591 80.83
0.8490
Table 3 – Regression Coefficients and N‐W S.E.
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25
The Breusch‐Pagan and White tests will be conducted to test for Heteroscedasticity. The Null
Hypothesis is that the error term has a constant variance, the error term is homoscedastic
(Equation 12) and the alternate hypothesis is that the error variance varies with the dependent
variables (Equation 13).
H0: Homoscedasticity
Equation 12
H1:Heteroscedasticity
Equation 13
Table 34 illustrates that, with the exception of Manchester, all of the chosen locations either fail
the Breusch‐Pagan or White test, with Glasgow, Nottingham, Cardiff and Carlisle failing both
tests. These two tests were also applied to the CHV regression, heteroscedasticity was found to
be present using the White test, but the error term was found to be homoscedastic using the
Breusch‐Pagan test. Problems with heteroscedasticity cannot be ignored, it causes the
estimators to be inefficient and have much larger variance, changing according to different
values of the explanatory variables, hetero‐consistent Standard Errors (S.E.) will be calculated
after the models have been tested for serial correlation. As the regression is of AR (1) in nature,
the Durbin Watson test of Serial Correlation will be applied to the above regressions. Equation
14 will be tested, with the following hypothesis;
H0: ρ=0
H1:ρ≠0
Equation 14
If the error term is genuinely a random error term, ut, no serial correlation would imply that ρ=0.
Table 35 illustrates that in all of the tests there is evidence of positive serial correlation, which
indicates that errors from the previous day carry over into the future, this could cause an
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26
overestimate in one day, leading to an overestimate in succeeding days. The OLS standard errors will
be smaller than the true standard errors and the parameter estimates will give the impression of
being more precise than they really are.
‘Under both heteroscedasticity and autocorrelation the usual OLS estimators, although linear,
unbiased, and asymptotically normally distributed, are no longer minimum variance among all linear
unbiased estimators. In short, they are not efficient relative to other linear and unbiased estimators.
Put differently, they may not be BLUE. As a result, the usual, t, F, and χ2 may not be valid’ (pg 442,
Gujarati, 2003).
If conclusions are drawn and inferences made despite heteroscedastiity they may be misleading,
although ‘Heteroscedasticity has never been a reason to throw out a good model’ (Mankiw, 1990).
Further statistical testing can be conducted post‐regression to test whether or not the coefficients
are biased, future analysis in this section will test only the Compounded Weather Variable (CHV).
In regards to the CHV, the null hypothesis of Homoscedasticity is not rejected using the Breusch‐
Pagan test and only just rejected using the white test, a p‐value of 0.007 is only slightly below the
0.01 rejection region. The White test results suggest that the coefficients are biased and are no
longer valid to construct t‐statistics and make inferences. White developed an estimator for
standard errors that is robust to the presence of heteroscedasticity, although a large sample size is
required, with a sample size of 2,472 in this analysis this solution is acceptable. Before calculating
the hetero‐robust S.E. a test of serial correlation will be conducted to determine whether to use
Robust or Newey‐West adjusted S.E.
Time series data are, by definition, ordered in time, what occurs at time t is the best indicator of
what will occur at time t+1, as a result the difference between the predicted and actual error in one
time period are related to the error in the text time period. The DW test above tested for serial
correlation of an AR (1) nature, the estimated statistic fell into the reject region suggesting strong
positive autocorrelation, this suggests that the OLS estimators are no longer efficient and the
estimated R2 is not a reliable estimate of the true R2. To check for serial correlation of a higher than
AR (1) nature the DW is not suitable, for this the Breusch‐Godfrey (LM) test will be favoured, which
is statistically a more powerful tool than the DW. For this part of the analysis three lagged variables
were chosen, the LM tests confirms that there is a problem with autocorrelation as all the p‐values
are extremely significant. As a result of these tests this paper considered implementing lagged
variables into a regression, this analysis will be conducted in part five. As a result of the above tests,
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27
the Newey‐West method will be implemented, which corrects the standard errors for serial
correlation and heteroscedasticity, these corrected standard errors can then be used for inference.
The Newey ‐West p‐value’s came in very significant, (see Table 3) so we can conclude that the
relationship between the CHV and Natural Gas demand is true and strong.
The formulated research question at the start of this analysis was ‘Do low temperatures have a
significant impact on National Grid demand data?’ Although the CLRM may overestimate the effects,
the above analysis and previous literature (see Ates and Wang, 2007, Mu, 2004) clearly
demonstrates that temperature has a significant impact on the demand for Natural gas. The basic
laws of Supply and Demand dictate that if demand increases, price should increase, ceteris paribus.
Part 3.4 of the paper will look at National Grid Demand and Seasonality.
4.4 NATIONAL GRID DEMAND AND SEASONALITY The methodology preferred in this part of the analysis will involve estimating National Grid Demand
against the Weather Surprise Dummy Variable (see Equation 21) and the Monthly Dummy Variable
(see Equation 41).
Equation 15
Where Dt is National Grid actual demand at time t, WSVt the Weather surprise variable at time t and
μDVt the Monthly Dummy Variable at month μ and time t. Eleven dummy variables were included in
the analysis to capture the twelve months, table 4 shows the estimation results where β2 is the
coefficient for January, β3 for February... and β13 Decembers coefficient, August was omitted from
the regression to prevent problems of perfect multicollinarity.
Demand Coefficients Std. Err. t Robust S.E Robust t VIF
β0 189.8395 2.679182 70.86 1.975296 96.11
β1 33.01779 2.529292 13.05 2.453172 13.46 2.94
β2 148.0643 4.312705 34.33 4.59691 32.21 3.00
β3 139.8438 4.435837 31.53 4.319888 32.37 2.94
β4 112.9477 4.329204 26.09 4.15421 27.19 2.95
β5 83.39094 3.870468 21.55 3.019107 27.62 2.26
Equation 15
Estimation
Results
β6 55.93134 3.624846 15.43 2.94491 18.99 2.07
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β7 17.26326 3.777905 4.57 2.661994 6.49 1.86
β8 9.340919 3.746121 2.49 2.578551 3.62 1.88
β9 (omitted)
β10 20.27319 3.768107 5.38 2.777722 7.30 1.87
β11 67.40618 3.866743 17.43 2.875138 23.44 1.97
β12 96.40087 4.25406 22.66 3.386343 28.47 2.33
β13 135.7499 4.461677 30.43 4.795564 28.31 2.45
Table 4 – National Grid Demand and Seasonality Estimated Coefficients.
The model specification was then tested, tests of multicollinarity, heteroscedasticity and
autocorrelation were conducted equivalent to those implemented in the earlier section. VIF values
were estimated to check for multicollineratity, no VIF value was found to be above 10 so it appears
there is no problem of multicollinearity. The Breusch‐Pagan statistics came in significantly below
0.05 and the White test came significantly below 0.01, both tests conclude there are problems of
heteroscedasticity. The Breusch‐Godfrey (LM) test was implemented with various lengths of lags,
there was no evidence of serial correlation. To correct for heteroscedasticity, robust standard errors
were calculated and are displayed in table 4.
Month Estimated Natural Gas Demand
(β0 + βi)
Estimated Demand with Weather
Surprise
(β0 + βi + β1)
January 337.9038 370.9216 February 329.6833 362.7011 March 302.7872 335.805 April 273.2304 306.2482 May 245.7708 278.7886 June 207.1028 240.1206 July 199.1804 232.1982
August 189.8395 222.8573 September 210.1127 243.1305 October 257.2457 290.2635 November 286.2404 319.2582 December 325.5894 358.6072
Table 5 – Evidence of Seasonal Demand for Natural Gas.
Table 5 is constructed using the results from table 4 and the following inferences can be made.
January is the month with the highest demand for Natural gas, August the lowest and ‘weather
shock’ increases the demand for Natural gas by an estimated 33 Mcm, a visual representation is
shown below in Figure 4, with total demand shown on the vertical axis and the date shown on the
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29
horizontal. Mu (2004) finds evidence of a demand ‘spike’ around June and July (hot weather causes
an increase in Cooling Demand), although figure 4 suggests that there is no evidence to suggest that
this exists in the UK market for Natural Gas
150
200
250
300
350
National Grid Estimated Demand (Mcm)
National Grid Estimated Demand (Mcm)
Figure 4 – National Grid Estimated Demand (Mcm),
Further analysis was also conducted to include Macroeconomic factors and domestic heating prices,
to test if the weather was the most significant determinant of Natural Gas demand. The majority of
the variables added were found to be insignificant in the short‐term, only domestic prices affected
consumer demand, but there were large lags and thus are largely beyond the scope of this paper.
5 THE FINANCIAL MARKETS AND TEMPERATURE As explained in the above sections, theoretically, as Natural Gas can be stored, any disparity
between spot and futures prices create arbitrage opportunities, this should ensure a close
relationship between spot and futures prices. The aim of this section of the paper is to find if
temperature is a key reason for abnormal disparity, or volatility, in the markets, and if so which
market is most sensitive to changes in temperature, the spot or futures market. The second part
of this section will then look to examine Campbell and Diebold (2000) findings that the winter
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30
months are more volatile than summer months, and that prices are higher in the winter than the
summer. But, before we can conduct any of the above analysis we first need to test the EMH.
5.1 TESTING THE EMH The spot and future prices should behave similarly over time, they should be co‐integrated,
Herbert (1993) was the first to test the relationship between spot and futures contracts in the
Natural Gas markets, Herbet’s methodology will be adopted for this part of the analysis.
The first step is to estimate the simple regression, using OLS, shown in equation 16.
Equation 16
Where Sprt are daily British prompt natural gas prices and Fprt daily first month NBP Natural
Gas prices. If the estimated coefficient for c is not statistically different from zero and the
estimated coefficient for d is not significantly different from one, this suggests that the market is
efficient.
Equation 17
Herbert found that both series needed to be differentiated twice before a white noise series was
obtained and thus concluded that both series are integrated of order two, the results of Herbert
(1993) regression is reported in Equation 18.
Equation 18
Table 6 provides some summary statistics on the Spot and Futures prices for British natural gas,
obtained from Bloomberg and Reuters, prices are quoted in GBP per Therm.
Sept 05May 10 GA1NB Spot Prices NBPG1MON Futures Prices Mean 40.98 43.24 Standard Deviation 18.82 17.75 Variance 354.12 315.06 Skewness 1.50 0.77 Kurtosis 7.52 3.37
Table 6 – Spot and Futures Summary Statistics.
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31
Some observations at the end of 2005 were inconsistent and possibly misreported, for this
reason 1,108 observations were selected from January 2006 until May 2010. Campbell and
Diebold (2000) looked at temperature data in the US from the 1960’s until the early part of
2001 and found that all of their distributions had moderate skewness and moderate excess
kurtosis. The most likely reason for the large Kurtosis in this data set, particularly the spot data,
as explained in section three, is that the Russia‐Ukraine gas dispute caused very large daily
movement in the spot markets in late 2005, for this reason it is excluded from the above
analysis. This data was used to run a regression similar to Herbert (1993). The results are
shown in Equation 19.
Equation 19
The estimated coefficients are both significant and it can be concluded that the coefficients c and
d are statistically different from 0 and 1 at the 5% level. The results above are consistent with
Herbert (1993) findings and demonstrate that the market is inefficient. The following section
will now test which market is most sensitive to temperature volatility.
5.2 WHICH MARKET IS MORE RESPONSIVE TO CHANGES IN TEMPERATURE? Many of the more public critics, such as your daily newspapers, often blame the low cost of
trading in the futures markets for excess speculation, and thus market volatility. This may be
the case, but in terms of the weather, recent literature, most notably Campbell and Diebold
(2000), find that low temperatures have stronger effects on the volatility of spot price changes
then on futures price changes, Henning et al (2003) also find that the volatility of prices in the
futures market has the propensity to be much lower than the volatility in the spot market..
The next section will focus on the relationship between temperature and price volatility. In
particular it will test if conditional volatility shocks are more persistent in the futures than the
spot market (Ates and Wang, 2007) or vice versa (Campbell and Diebold, 2000). Further
analysis of the hypothesis that volatility is higher in the winter and lower in the summer (Ates
and Wang, 2007) and thus prices are higher in the winter than the summer (Campbell and
Diebold, 2000, Brown and Yucel, 2008 and Suenaga et al, 2006) will also be considered.
5.3 DATA AND METHODOLOGY The terms conditional variance and volatility will be used interchangeably, and price volatility is
defined as the returns on daily price movements. Both the spot and futures data display signs of
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32
excess skewness and kurtosis, as prices are bounded by zero on the downside but are limitless
on the upside, the distribution of price data is often skewed. In order to create a more normal
data distribution the continuously compounded log return will be used to measure intra‐day
volatility, shown in Equation 20, this methodology is generally favoured across the literature.
Equation 20
Non‐trading days are excluded from the analysis, these include weekends and holiday periods
such as the Christmas and Easter periods. A weather surprise variable (WSV) will be created
similar to that generated by Mu (2004) and Ates and Wang (2007). Equation 21 defines the
criteria that is used to establish the thresholds of what constitutes a ’weather surprise’.
Equation 21
Where CHVt denotes the sum of Heating Degree Days at all locations at time t and HDD.AV is an
integer which represents an approximate average HDD figure across all locations from 1970 to
June 2010. The reason why data as far back as 1970 is used to estimate the ‘shock’ factor is
because this period includes many shocks and is a much more efficient predictor of future
weather patterns, more effective than using the last two years of temperature data for example.
Historically Bristol has the lowest HDD’s at 7.17, Sunderland the highest of 9.77, to keep the
Weather Surprise Variable estimations simple HDD.AV will take the value of ‘8’ in future
analysis. As a fixed integer has been selected it is easier to see that the more the temperature
deviates from normal, the greater is the weather surprise. A ‘WSV Dummy variable’ will also be
created, the variable takes a value of 1 if the WSV at time t is greater than zero, i.e. there is a
‘cold weather surprise’ and a value of 0 is taken if the WSV at time t is zero, i.e. there is no
weather surprise, see Equation 22. As HDD’s cannot be negative, the downside of the ‘weather
surprise’ is limited to zero.
Equation 22
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33
Firstly, each price series is tested for the presence of a unit root using the Augmented Dickey‐
Fuller (ADF) test. It is important to check for stationarity as, if energy consumption is stationary
shocks will be transitory whereas if energy consumption is non‐stationary (i.e. contains a unit
root), shocks will be permanent. This is important when predicting future forecasts as if energy
consumption is stationary, then the past behaviour of energy consumption serves a role in the
generation of forecasts. On the other hand, if energy consumption is non‐ stationary, then the
past behaviour of energy consumption serves little or no use in forecasting (Apergis et al, 2010).
In part three of this paper tests of stationarity were conducted on HDD’s and Demand data, a
similar ADF test for unit root will be conducted below. In this section an ARIMA model will be
estimated to determine the optimal number of lags required to test for stationarity (Said and
Dickey, 1984, used a similar approach). In all instances, the null hypothesis of non‐stationarity
is tested. Table 7 shows that in all three time series the null is rejected, all are found to be
stationary, which is consistent with results in the US markets (Brown and Yucel, 2008).
Variable Number of Lags Test Statistic Reject the Null?
Spot Returns 7 ‐15.047 Yes
Future Returns 3 ‐17.492 Yes
WSV 9 ‐4.332 Yes
Table 7 – ADF, Jan 2006 – May 2010.
Graphical analysis was also conducted, correlogram and partial correlograms were estimated to
check for evidence of autocorrelation. Mu (2004) provides an autocorrelation function (ACF)
table with coefficient estimates of 10 lags, Gujarati (2003) states that a rule of thumb is to
compute Autocorrelation Functions (ACF) up to one‐third to one‐quarter the length of the time
series. As the time series in this study are so large the portmanteau test for white noise, which
tests whether the selected group of autocorrelations are different from zero will be favoured.
Table 8 reports the Portmanteau test statistics, both Spot return and the WSV are found to be
significant, but Futures prices display random walk characteristics. That is, futures price returns
today are not correlated with returns from previous periods. As the main aim of this paper is to
ultimately provide a future prognosis for these markets futures price returns will be excluded
from further analysis based on the results displayed in table 8.
Number of
Lags Spot Prob > Chi2 Futures Prob > Chi2 WSV Prob > Chi2
Q(2) 16.02 0.0003 1.55 0.4617 1536 0.0000
Q(20) 54.76 0.0000 15.17 0.7615 8142 0.0000
Q(150) 224.25 0.0001 170.88 0.1167 20763 0.0000
-
34
Q(300) 343.60 0.0042 338.36 0.0629 36829 0.0000
Table 8 – Portmanteau test for White Noise, Jan 2006 – May 2010.
5.3 ARMA MODEL SPECIFICATION AND RESULTS Before using any statistical modelling, a measure of volatility must first be defined. Equations 23
explain the basic steps in defining spot price volatility in this paper
Equation 23
Where dY*t is the relative change in spot returns and Xt is the mean‐adjusted relative change in spot
returns. X2t will be used as a measure of volatility. Autocorrelation and Partial Autocorrelation
graphs were first constructed, there was strong evidence of both in the Spot Price volatility variable
Xt. A correlogram was then examined to identify the nature of the time series process(es).
An ARMA model allows Yt to be explained by the past, or lagged, values of Y itself and stochastic
error terms. An ARMA (1,0) model was first constructed and is shown in Equation 24.
Equation 24
This model was estimated and the coefficients were found to be significant. To determine the
optimal lag length of this model the Alkaike Information Criterion (AIC) will be implemented, which is
used to find the model that helps best fit the data with the minimum