CHAPTER 2CHAPTER 2THE HUMANTHE HUMAN

INFLUENCE...INFLUENCE...

Image Credit :http://www.jersey.com

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The global debate on climate change is over,

most governments now accept that emissions

from human sources are largely responsible for

global warming. Over the last 150 years our

activities have changed the way the earth’s

climate behaves and this chapter discusses the

science behind the theory of global warming

and the evidence that supports it.

CHAPTER 2 - THE HUMAN INFLUENCE

The Science of Climate Change

2.1 An Introduction to Climate Change

2.2 ‘What are Global Warming’ and the‘Greenhouse Effect’?

A Changing World

2.3 The Intergovernmental Panel onClimate Change

2.4 How do we Measure Global ClimateChange

2.5 How has Global Climate Changed inRecent Times?

Jersey’s Climate Through the 20th Century

2.6 Have we Observed Changes to theLocal Climate?

2.7 Is the local Marine ClimateChanging?

Alternative Climate Change Theories

2.8 Are Greenhouse Gases Really toBlame?

CHAPTER 2 - THE HUMAN INFLUENCE

Science advances byconstructing theories andtesting them using dataas supporting evidence.

Climate change theory isno different. It arguesthat human influencehas altered thecomposition of theatmosphere and in doingso has changed the wayit absorbs radiation fromthe sun.

This theory is not new. Asearly as 1895 Swedishchemist and Nobellaureate SvanteArrhenius argued thatincreased atmosphericCO2 could lead to awarmer climate, with arise of 5 to 6°C with CO2

doubled.

The degree of warmingrecently observed hasincreased the urgency ofthe debate.

This chapter reviews thescience behind theclimate change debate,showing that humaninfluence hascontributed to observedwarming, particularly inthe last 30 to 40 years.

Finally, a review ofseveral commonarguments used by‘climate sceptics’ isprovided, exposing thelack of evidence tosupport their arguments.

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The Science of Climate Change

The magnitude of this rise can perhaps bebetter understood if we consider that thedifference between the middle of an iceage and the middle of a warm periodbetween ice ages is about 5 or 6°C, whilethe temperature rose by a mere 0.6°Cbetween 1900 and 2000.

EMISSIONS OF CARBON DIOXIDE INTOTHE ATMOSPHERE

Emissions of CO2 into the atmosphere byburning fossil fuels are currently nearly 7billion tonnes a year and rising rapidly.Unless urgent measures are taken they couldreach two or three times this level thiscentury. To stabilise CO2 concentrations,emissions need to reduce to a fraction of thepresent level well before the end of thecentury.

The reduction in emissions will need aconcerted world-wide effort, but the issue iscomplicated by big differences ingreenhouse gas emissions from one countryto another. In tonnes per person per year,they vary from about 5.5 in the USA to 2.5tons in Europe to 0.7 tonnes in China and 0.2tonnes in India (Box 1). Ways will need to befound to achieve realistic and equablereductions.

Developed countries have benefited fromabundant fossil fuel energy over many years,so the demands on their stewardship take ona special poignancy, because the adverseimpacts of global warming are likely to falldisproportionately on poorer nations and

‘Greenhouse’ gases, such as water vapourand carbon dioxide (CO2), act as blanketsover the Earth’s surface, keeping it warmerthan it would otherwise be. They do this byabsorbing infra-red radiation or ‘heat’emitted from the earth’s surface. Theexistence of this natural ‘greenhouse effect’has been known for nearly 2000 years and isessential if we are to maintain the climate towhich ecosystems and humans haveadapted.

Since the beginning of the IndustrialRevolution around 1750, CO2 has increasedby nearly 40% and is now more highlyconcentrated in the atmosphere than formany thousands of years. Chemical analysisshows the increase is due largely to burningof fossil fuels - coal, oil and gas. If no actionis taken to curb these emissions, by the endof the century, CO2 concentration is forecastto reach two to three times the pre-industriallevel.

The climate record over the last thousandyears shows a good deal of naturalvariability, as highlighted in Section 1, but theincrease in global average temperatures(and the rate of rise) particularly in the last 30to 40 years is well outside the range of thisknown natural variability.

This century the global average temperatureis projected to rise by between 2 and 6°Cfrom the pre-industrial level. The rangedepends on two factors a) differingassumptions as to the levels of emissions overthe next century and b) the sensitivity ofclimate models used to make the estimates.

2.1 AN INTRODUCTION TO CLIMATE CHANGEAndrew Casebow

Climate change due to human activities represents the biggestchallenge facing the world in the 21st century.

Box 1

Carbon dioxide emissions in theyear 2000. The area of each bar isrepresentative of total emissions i.e.China and OECD Europe emit simi-lar amounts of carbon dioxide intotal due to China’s much largerpopulation.

Graph Credit: M Grubb, 2003 and Planet Guernsey, 2007

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tend to exacerbate an increasingly largedivide between rich and poor.

The aim must be to stabilise carbon emissionsto as low a level as possible to avoid adamaging change in climate. In 1996 theEuropean Commission proposed a 2°C limiton the rise in average global temperaturefrom the pre-industrial level. This implies astabilisation level for CO2 at about 430 partsper million (ppm) allowing for the effect ofother greenhouse gases at their 1990 levels.Without action to secure this stabilisationatmospheric CO2 could go much higher - seeBox 2.

If carbon dioxide is stabilised at 500 ppm andthe effect of other greenhouse gases at their1990 levels is added, it is about equivalent todouble the carbon dioxide at its pre-industriallevel, and will therefore produce a rise inglobal average temperature of about 2.5°C .

Although global warming may eventually behalted, the impacts at such a level would belarge. A steady increase in sea level wouldcontinue, heat waves such as experienced inEurope in 2003 would be more common,floods and droughts would also be morecommon. The aim should be to stabilise at alower level. But is this possible?

The UK government has taken a lead on thisissue, agreeing to a modest target of

reducing greenhouse gas emissions by 80% by2050. The cost will not be great if action istaken quickly. UK Government Treasuryeconomists have estimated the cost to the UKeconomy, assuming growth of 2.25% perannum, as no more than the equivalent of 6months growth over the 50-year period.

The need for action on global warming isurgent for three reasons:

1: Scientific. There is a lag in the response ofclimate to increasing greenhouse gasesbecause the oceans take a long time towarm and cool. The greenhouse gasemissions that have already occurred willcontinue to change the climate for the next30-50 years.

2: Economic. The energy infrastructure(power stations etc.) is typically designed for30-50 years, so it is more cost effective tophase in infrastructure changes than havingto make them much more rapidly later.

3: Political. Countries such as China andIndia are industrializing very rapidly. In orderto provide an example of effective leadershipwe need to start now.

Both the challenges and opportunities for allof us are unmistakable.

THE HUMAN INFLUENCE

“No one made a greater mistake than he who did nothing because hecould do so little”.

Edmund Burke

Box 2

Past and futureatmospheric CO2

concentrations. Allmeasures before 1950 areice core data, 1950-2000are direct measurementsand 200 onwards areprojections.

Graph Credit:IPCC 2001 Synthesis Report.

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The Science of Climate Change

‘greenhouse gases’ absorbing and re-emitting radiation to warm the Earth’s surfaceand lower atmosphere.

Over the last few hundred years, man hascleared forests and has burnt coal, oil andgas in ever greater quantities, so increasingthe amount of CO2 in the atmosphere. Theexpanding human population also produceslarger quantities of methane fromdecomposing rubbish and increased animalproduction. With more of these gases in theatmosphere, more of the Earth’s outgoingradiation is trapped, resulting in increasingtemperatures.

Climate change is not confined to changes inair temperature alone. Oceans contain a vastamount of energy and although temperaturechange in the ocean is very slow even a smallrise in temperature results in a lot more energyin the atmosphere. The result is that theweather system has more energy and as aconsequence, the weather becomes moreextreme. Increased evaporation of watermeans more clouds, heavier rain and strongerwinds.

Research has shown that in the last ice agethe concentration of CO2 in the atmosphere

2.2 WHAT ARE ‘GLOBAL WARMING’ AND THE‘GREENHOUSE EFFECT’? Andrew Casebow

Box 1 Schematic diagram showing the Earth’s energy cycles and the ‘Greenhouse Effect’.

Image Credit: Planet Guernsey and Chris Regan, 2007

What do we mean by the terms ‘climatechange’ and ‘global warming’ and ‘thegreenhouse effect’?

Section 1 showed the Earth’s climate is in avery delicate balance. Climate change iscaused by various naturally occurringcycles, including the Earth’s movementaround the sun and factors such as volcaniceruptions. Some cycles occur over periodsof a few years, others over thousands ofyears and some over hundreds of thousandsof years. The climate change occurringnow, which we refer to as ‘global warming’,is caused by increasing concentrations ofgases and chemicals in the Earth’satmosphere from human sources. Thesegases are accentuating the ‘greenhouse’effect.

We rely on the earth’s ‘greenhouse’ effectto keep us warm, because naturalgreenhouse gases, such as CO2, methaneand water vapour act as a blanket,preventing the escape of heat from theEarth. Without them our climate would bemore like that of Mars, with temperaturesbelow zero; life as we know it could notsurvive. The schematic diagram (Box 1)highlights how the effect works, with

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To investigate the extent towhich global warming maybe natural or man-made, amodel of the climatesystem was developed bythe UK Met Office’s HadleyCentre.

Box 3, graph (a) showsaverage annualtemperature and modelpredictions based on thenatural factors discussed inChapter 1, primarily the sun,volcanoes and internalfeedback influences. Notethe wide differencebetween what actuallyoccurred and what themodel predicted over thepast 30 years.

When the known emissionsof CO2 were incorporatedin the model (b), thesimulation matched theactual temperature veryclosely, suggesting that thetemperature increase wascaused by the higherconcentration of man-made CO2 in theatmosphere.

was between 200 and 220 parts per million(ppm). Man has been cutting down andburning woodland for around 20,000 years,but with social and technological changesin more recent times this has increased.From about 1700 a slow increase in theamount of CO2 in the atmosphere tookplace to reach 280ppm by the early 19thcentury.

By 1960, when more accurate monitoringstarted the figure was 316ppm. Box 2illustrates how CO2 concentrations havebeen rising steadily since monitoring beganin1959. The concentration increases everywinter and reduces each summer due tophotosynthesis converting CO2 into plantgrowth.

THE HUMAN INFLUENCE

Graph Source: Adapted from NOAA/GMD by Planet Guernsey

Image Credit: Met Office Hadley Centre and Planet Guernsey, 2007Image Credit: Planet Guernsey, 2007. Originally, Met Office, Hadley Centre

Graph Source: Adapted from NOAA/GMD by Planet Guernsey

Box 2Monthly average CO2 in the atmospherefrom 1955 to 2005.

Source: National Oceanic and Atmospheric Administration,Climate Monitoring and Diagnostics Laboratory.

Box 3 Mean annual temperatures and modelpredictions

a) Predictions based on natural solar and volcanic cycles

b) Predictions based on natural cycles and human activity

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A Changing World?

2007 was a watershed. Previously, someGovernments had chosen not to accept theoverwhelming evidence that climate change wasoccurring. Many people considered that therewas still a ‘debate’ about whether or not climatechange caused by global warming was a reality.There was still a lot of misinformation anddiscussion about the causes of climate changeand whether it was a naturally occurringphenomenon. Then the 4th Assessment Reportfrom the IPCC was published.

The report shows that it is virtually certain thatclimate change induced by human activity ishappening, and is occurring faster than had beenpreviously anticipated.

The Intergovernmental Panel on Climate Changeis the world’s leading authority on climatechange. It was set up by the WorldMeteorological Organisation (WMO) and theUnited Nations Environment Programme (UNEP) in1988.

“The role of the IPCC is to assess on acomprehensive, objective, open and transparentbasis the scientific, technical and socio-economicinformation relevant to understanding thescientific basis of human induced climatechange, its potential impacts and options foradaptation and mitigation’.

The IPCC provided its first major assessment reportin 1990, a second in 1996, a third report in 2001and its most recent fourth report in 2007.Together, they provide the most comprehensivescientific information available, prepared byteams of the world’s leading climate scientists.

The reports carefully distinguish between what isknown with reasonable certainty, and the areaswhere uncertainties remain. The language used isvery ‘measured’ and conservative, and forfindings to be incorporated into the report theymust have a very wide degree of internationalacceptance that they are correct.

The IPCC 2007 report points out that: “Globalatmospheric concentrations of carbon dioxide,methane and nitrous oxide have increasedmarkedly as a result of human activities since 1750and now far exceed pre-industrial valuesdetermined from ice cores spanning many

2.3 The Intergovernmental Panel on ClimateChange (IPCC) Andrew Casebow

The full reports and summaries are available at http://www.ipcc.ch

Climate CampaignsThe IPCC shared the 2007 NobelPeace Prize with Al Gore for their ef-forts to promote and raise awarenessof climate change globally.

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thousands of years. The global increase inCO2 concentration is due primarily to fossilfuel use and land use change, whilst those ofmethane and nitrous oxide are primarily dueto agriculture”.

CO2 is the most important greenhouse gascaused by human intervention. “The globalatmospheric concentration of CO2 hasincreased from a pre-industrial level of about280 parts per million (ppm ) to 379ppm in2005. The atmospheric concentration of CO2

in 2005 exceeds by far the natural range overthe last 650,000 years”.

“The global atmospheric concentration ofmethane has increased from a pre-industriallevel of about 715ppb to 1732ppb in the early1990’s and was 1774ppb in 2005. It is verylikely that the increase in methane is due tohuman activities, mainly agriculture and fossilfuel use. The concentration of nitrous oxidehas increased from a pre-industrial level ofabout 270ppb to 319ppb in 2005. More thana third of all nitrous oxide emissions come fromhuman activity and are primarily due toagriculture”.

There are still some individuals andorganisations that seek to undermine thescience of climate change and the work ofthe IPCC. The Royal Society of Londonbelieves that “they appear motivated in theirarguments by opposition to the UNFramework Convention on Climate Changeand the Kyoto Protocol, which seek urgentaction to tackle climate change through areduction in greenhouse gas emissions.”

“It has been claimed that the rise inatmospheric concentrations of CO2 is actuallya consequence of climate change, ratherthan a cause. The IPCC report pointed outthat the chemical analyses of the carbondioxide show that the increase in theatmosphere, and an accompanyingdecrease in oxygen concentrations, areprimarily due to the burning of fossil fuels anddeforestation”. However, a number ofclimate change skeptics still continue tobelieve, despite the scientific evidence, thatclimate warming is caused by naturalphenomena, and have been arguing for abusiness-as-usual approach. In response SirMartin Rees, President of the Royal Society,has said:

"Global temperature is increasing. Thiswarming threatens the future health andwellbeing of many millions of peoplethroughout the world. This is especially true ofthose in the developing countries who are theleast able to adapt and who are likely to bethe worst affected. Many factors play a partin global warming but there is significantscientific evidence that greenhouse gasemissions, particularly carbon dioxide, areresponsible for most of the temperature rise. Ifpresent trends continue the projected climatechange will be far greater than that alreadyexperienced. Greenhouse gas emissions aresomething that we can and must take actionon”.

THE HUMAN INFLUENCE

Box 2The IPCC produce individual reports on the science, impacts and mitigation of climatechange as well as a synthesis by assessing the latest scientific, technical and socio-economic literature.

“Those who promote fringe scientific views but ignore the weight of evidence areplaying a dangerous game. They run the risk of diverting attention from what we cando to ensure the world's population has the best possible future." ."

(Royal Society press release 9 March 2007)

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A Changing World?

institution employs specialist researchers whorecreate global climate from the availabledata, using sophisticated statistical methodsto make data series compatible or calculateany uncertainty associated with these climatere-constructions.

Any unreliable or unrepresentative data isidentified and discarded during a vigorousstatistical analysis process. Measures ofuncertainty are given with the data and theseprovide an indication of the degree ofconfidence held in the data.

The uncertainty in annual measurements ofthe global average temperature calculatedby the Hadley Centre is ~0.05°C since 1950and ~0.15°C in the early part of theinstrumental record.

Uncertainty in the data can stem fromincomplete records. Climate datasets are notcomprehensive for several reasons:

Can we be confident in records of ‘globalclimate’?

Measuring the climate is not a simple task. Itrequires long series of records over largeareas to establish climate means. Even basicequipment, such as thermometers and raingauges, has only become widely available inthe last 150 years.

Prior to the mid 19th century a goodapproximation of the climate for someregions of the world has been establishedusing methods such as tree ring, lakesediment and ice core analysis as well asqualitative written observations. Suchrecords can be pieced together to analysehow climate has changed during the 20thcentury.

Temperature has proved the most reliableand well-documented of records, with globaldatasets maintained by the UK Met Office’sHadley Centre, NASA and others. Each

2.4 HOW DO WE MEASURE GLOBAL CLIMATECHANGE? James Le Ruez

Box 1The network of observation stations used in the University of East Anglia ClimaticResearch Unit (CRU) dataset. Note the high concentration of long records (red) indeveloped regions (e.g. USA and Europe) in contrast with large areas with scarcemeasurements (e.g. Siberia, central Africa and the Amazon).

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LENGTH OF RECORDS

Box 1 shows that the longest climate recordsare predominately from the developed worldwhere technology and a stable socialenvironment have encouraged recordkeeping. Some parts of the world, such as thepolar regions, South America and Africa havemuch shorter periods of records.

SPATIAL COVERAGE

In many less developed nations, records canbe sparse. Box 1 shows that spatially manyregions have very few records of significantlength.

Records of sea surface temperature, whichare important in recreating past climates, areeven more sparsely distributed. The greaterland area of the northern hemisphere holds afar greater number of measurements than thesouthern hemisphere.

POINT MEASUREMENT

In order to establish regional climate patterns,numerous atmospheric measurements takenat single points over the representative areaare combined. In data - sparse areas onepoint measurement may be required torepresent the climate of an unrealisticallylarge area.

INSTRUMENTS USED

In addition, measurements from differentstations, using different instruments and datacollection methodologies can causeinconsistencies in the data. Thereforecorrections have to be made.

For example, sea temperature historically wassampled by collecting seawater over the sideof the ship in a canvas bucket. Now thetemperature of the engine intake water issampled. This resulted in a ‘blip’ in therecords, which had to be corrected to makethe two sets of records compatible.

SATELLITES

Satellites may provide an answer to many ofthese issues in the future. However, they havebeen operating for a relatively short timeperiod and early measurements havesuffered from instrument problems.

As more sophisticated measurementinstruments are used and data is collectedmore widely around the globe, the climatedatasets will become more complete. Withtime the certainty in which we hold globalclimate change measurements will increase.

THE HUMAN INFLUENCE

Global climate is changing, temperatures increasing, rainfall and atmosphericcirculation patterns varying, oceans warming and sea levels rising. Despite thereservations above, the IPCC states with 90% confidence that these effects are

due to human influences.

Box 2The concentration of CO2 inthe atmosphere is measuredin remote locations to avoidthe influence of local sourcessuch as traffic or industry.The longest record of CO2

concentration is maintainedby the Mauna LoaObservatory, Hawaii, whereits height of 3,397 metresprovides ideal conditions formeasurements free of suchinfluences.

Image Credit: http://mlso.hao.ucar.edu/

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A Changing World?

days in mid-latitude regions, an increase inthe number of warm extremes and areduction in the number of daily coldextremes has been observed in 70 to 75% ofland regions.

PRECIPITATION

From 1900 to 2005, precipitation has generallyincreased in areas north of 30°N butdecreased in the Tropics since the 1970s - Ithas become wetter in eastern parts of theAmericas, in northern Europe and northernand central Asia. Conversely, in the Sahel,Mediterranean, southern Africa and parts ofsouthern Asia it has become drier.Precipitation change is more spatially andseasonally variable than temperaturechange.

Heavy precipitation events are becomingmore frequent - Evidence suggests therehave been increases in the number of heavyprecipitation events, even in regions wherethere has been a reduction in totalprecipitation. Such observations areconsistent with forecasts of climate change.

Droughts have become more common,especially in tropical regions, since the 1970s -In the past 30 years droughts have been moreintense, longer, and affected a wider areadue to decreased land precipitation andincreased temperatures enhancing

The summaries below highlight the mostsignificant conclusions made by the IPCC intheir 4th Assessment Report.

TEMPERATURE

Increasing global temperature ‘anomalies’since 1850 (Box 1) - A linear trend line drawnthrough the global mean surface temperaturesover the last 100 years (1906–2005) indicates atemperature rise of 0.74°C (± 0.18°C). The rateof warming over the last 50 years is almostdouble that over the last 100 years.

2005 was one of the two warmest years onrecord - The warmest years in the instrumentalrecord were 1998 and 2005. 1998 ranks first inone estimate (Box 1) but 2005 is slightly higher inthe other two estimates. 2002 to 2004 were the3rd, 4th and 5th warmest years in the seriessince 1850. 11 of the last 12 years rank amongthe 12 warmest years on record.

Land regions have warmed at a faster ratethan the oceans - Surface air temperaturesover land have risen at about double theocean surface rate since 1979 (more than0.27°C vs. 0.13°C per decade). This is becausesome heat is absorbed by the ocean andmixed to greater depths.

Changes in extremes of temperature areconsistent with warming of the climate - Awidespread reduction in the number of frost

2.5 HOW HAS GLOBAL CLIMATE CHANGED INRECENT TIMES?

Box 1This graph represents the climate ‘anomalies’ using the 1961-1990 average temperatureas the reference period. This reveals how global temperatures have increased since1980. Graph Source: University of East Anglia, Climatic Research Unit, http://cru.uea.ac.uk

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evaporation. The extreme nature of droughts inAustralia and Europe, suggest links to climatechange.

ICE REGIONS (THE CRYOSPHERE )

Temperature increases are consistent withobserved changes in the cryosphere - Consistentwith higher surface temperatures there has beena global reduction in glacier and small ice capmass and extent in the 20th century (excludingAntarctica and Greenland). Snow cover hasdecreased in many regions of the northernhemisphere and the extent of sea ice hasdecreased in the Arctic (Box 2), particularly inspring and summer. In addition the oceans arewarming and sea level is increasing.

Average Arctic temperatures increased at almosttwice the global average rate in the past 100years. Mean Arctic sea ice extent continues todecline by 2.7 ± 0.6% per decade since 1978 -Submarine-derived data for the central Arctic,supported by model-based reconstructions,indicate that the average sea ice thickness in thecentral Arctic has very likely decreased by up to 1metre from 1987 to 1997.

Mass loss of glaciers and ice caps is estimated tobe 0.50 ± 0.18 mm/yr in sea level equivalent (SLE)between 1961 and 2004, and 0.77 ± 0.22 mm/yrSLE between 1991 and 2004 - The biggestcontributions to sea level rise came from Alaska,the Arctic and the Asian high mountains.Thickening in central regions of Greenland hasbeen more than offset by increased melting nearthe coast. Flow speed has increased for someGreenland and Antarctic outlet glaciers, whichdrain ice from the interior.

Temperature at the top of the permafrost layerhas increased by up to 3°C since the 1980s in theArctic - The permafrost base has been thawing ata rate ranging from up to 0.04 metres per year inAlaska since 1992 and 0.02 metres per year on theTibetan Plateau since the 1960s.

MARINE CLIMATE

The oceans are warming - Over the period 1961 to2003, global ocean temperature has risen by 0.10°C from the surface to a depth of 700 metres.

The chemistry of our oceans is changing - Thetotal inorganic carbon content of the oceansincreased by approximately 118 gigatonnes ofcarbon between the end of the pre-industrial

period (about 1750) and 1994 and continues toincrease. It is more likely than not that thefraction of emitted CO2 that was taken up bythe oceans has decreased. NB 1 Giga tonne =1,000,000,000 tonnes

Global mean sea level has been increasing -From 1961 to 2003, the average rate of sealevel increase was approximately 1.8 mm peryear. There is high confidence that the rate ofsea level increase has risen between the mid-19th and 20th centuries. Sea level change isextremely varied and in some regions rates areup to several times the global mean rise, whilein other regions sea level is decreasing. There isevidence of an increase in the occurrence ofextreme high water world-wide related tostorm surges and variations in extremes.

THE HUMAN INFLUENCE

Box 2The evidence shows that the poles arewarming at a higher rate in comparisonto other areas of the planet. Thereduction in sea ice between 1979 and2003 is evident in these satellite images.In recent years the rate of ice melt hasincreased to unprecedented rates.

Image Source: NASA Press Release,‘Recent Warming of Arctic may affect worldwide climate’

REFERENCESSourced from the IPCC 4th Assessment Re-port. For the full report go to http://www.ipcc.ch/

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Jersey’s climate through the 20th Century2.6 HAVE WE OBSERVED CHANGES TO THEISLAND’S CLIMATE?

Jersey Meteorological Department

Box 1The weather station at the Maison StLouis observatory.

This index shows the maximum temperature recorded in Jersey for each year since 1894. Note alarge degree of year to year variation. The straight line regression shows a steady increasethrough the period with the annual maximum temperature below 29°C in 1894 but now above30°C. The trend is not constant as shown by the blue line which is the 20 year moving average(each point represents the average maximum temperature in the previous twenty years). Wesee that in the 1920s and the 1970s annual maximum temperatures were not so high, but from1980 onwards the tendency towards higher maximum temperatures. The highest temperaturerecorded in Jersey so far was 36.0°C in August 2003. There has been a similar rise of about 1°Cin the annual minimum temperature, where the annual minimum temperature was about -4°Cin 1900 compared to -3°C in 2000.

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As we have seen, climate can be regarded to someextent as an average of the weather observed in alocation. To establish that climate a long record isneeded. In Jersey we are fortunate to have therecords from the Maison St Louis Observatory (Box 1),currently run by the Jersey MeteorologicalDepartment, where daily observations stretch back to1894.

To establish whether there has been change in ourlocal climate, one method recommended by theWorld Meteorological Organisation and World ClimateResearch Programme and adopted here is to convertsome of the readings into ‘indices’.

This analysis uses examples from the recommended setof 27 indices, each intended to give a recognisablemeasure of the climatic conditions of a location fromwhich changes can be assessed. A seasonalapproach has been adopted for rainfall as thismethod proved more revealing. The summaries belowassess how several indices of interest have changedover the last 100 years.

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THE HUMAN INFLUENCE

Warm and Cool Days

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The upper and lower plots show thepercentage of warm and cool dayseach year. The averagetemperature for each day iscalculated to determine whether itfalls into the 10% of warmest orcoldest days for the entire 1894-2007period.

The index reveals a significantupward trend in the number ofwarm days across the observationperiod. As with maximumtemperatures above, there hasbeen a distinct rise in the number ofwarm days observed recently,particularly since about 1970.

In contrast, the lower plot reveals avery steep decline in the number ofcool days recorded. These analysesstrong suggest that summer days arebecoming increasingly warmer andwinter days increasingly milder.

A warm spell is defined as a period of at least 6 consecutive days when the maximumtemperature is higher than the 90th percentile (in Jersey’s case 21.3°C). If no 6 day warmperiod is observed in a year, the index is zero otherwise it returns the combined number ofdays from the warm periods recorded. For instance, a warm period of 11 consecutive dayswould have an index of 11, while two periods of 6 days each or one period of 12 dayswould show an index of 12. Although the most common result in this dataset is zero, therange extends up to an aggregated 44 days over five warm spells in 1990. The long termtrend shown by the black line indicates warm spells have become more likely and nowaverage 10 days each year, compared with the early period when there were very fewwarm spells. The running mean (blue line) shows a slight increase in the frequency of warmperiods in the middle of the 20th century.

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2.6 CONTINUED…

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Warm and Cool Nights

Summer Days

Jersey’s climate through the 20th Century

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A ‘summer day’ is defined as having a maximum temperature above 25°C. Again wesee a large year to year variation but the linear trend in black highlights a steadyincrease in the number of summer days in recent times. The running mean reveals aperiod of fewer summer days in the 1960s and early 1970s, but a noticeable increase hasoccurred in the last thirty years. This is highlighted by the fact that of 12 years with morethan 20 summer days, 8 have occurred since 1975.

Changes in the night time climateare similar to those in the day. Asan indicator of night time climatewe use here the minimumtemperature, which typicallyoccurs just after dawn.

In the upper graph warm nightsare plotted showing thepercentage of days each yearwhen the minimum temperatureexceeded the 90th percentile(14.4°C).

Cool nights are plotted in thelower graph, where thepercentage of days each yearwhen the minimum temperaturewas below the 10th percentile(2.0°C). The running mean forwarm nights reveals a relativelyconstant climate.

Jersey Meteorological Department

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THE HUMAN INFLUENCE

From the analysis above, it seems reasonably clearthat the Jersey climate has been changing over theperiod of the Maison St. Louis record, with an increasein warmth and winter rainfall. Variability isconsiderable for year to year, but it is the long termchange which may have important consequences forthe environment, planning and society in general.

The long-term changes are highlighted in theregression lines and running means on the graphs.They show trends in line with the global pattern ofclimate change, particularly the marked warmingtrend over the last 30 years. Scientific consensus is thatmuch of this warming is the result of human activity -the main debate has moved on and now concernswhat proportion is due to human activity and whatshould be done about it.

Seasonal Precipitation

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mmSummer

Rainfall

Local rainfall shows an increase in winter rainfall through the 20th century, while summerrainfall has decreased. The variability of the running mean since 1894 compared with thelinear trend is relatively small, without the large variation since the 1970s we noted in thetemperature record. Of interest, is that winter precipitation has increased more thansummer precipitation has decreased. However, as water is in greatest demand in thesummer this does not necessarily mean there is more ‘useful’ water on the Island althoughwinter rainfall can charge the water table for the summer ( see also Article 4.19).

38

SEA TEMPERATURE

Sea temperature has been recorded at St HelierHarbour since 1933, with a gap during theOccupation. Despite the linear trend lineshowing a clear warming (Box 1) it is noticeablethat the 20 year running mean (blue Line) showsrelatively little change in sea temperature until1989. Indeed, the 1970’s and early 1980’sappear to be slightly cooler than the 1950’s.

If the last 10 to 15 years are considered alone,there is a clear warming trend with 8 of the 10warmest years on record occurring since 1989.This is highlighted in Box 2, as well as the clearincrease in the running mean plotted below.Taking two respective averages highlights howmuch the mean sea temperature has increasedover the observation period.

Considering the short time series available, itappears reasonable to take a twenty yearaverage, which shows the St Helier mean seatemperature has increased from an average of12.2°C between 1946 and 1965 to an average of13°C between 1988 and 2007.

Jersey’s climate through the 20th Century

2.7 IS THE LOCAL MARINE CLIMATECHANGING?

10

11

12

13

14

1930 1940 1950 1960 1970 1980 1990 2000

Max

imum

Tem

pera

ture

/ ºC

Box 1There has been a clear increase in the long term sea temperature measured at St Helier.Temperatures appear to have risen sharply since the late 1980s.

No. Year Mean Temp

1 2007 13.9

2 2003 13.8

3 1989 13.7

4 1990 13.3

5 2002 13.36 1959 13.2

7 1999 13.2

8 1995 13.2

9 1950 13.2

10 2005 13.111 1961 13.0

12 1997 13.0

13 2001 12.914 2004 12.9

15 2006 12.9

16 2000 12.9

17 1991 12.818 1994 12.8

19 1998 12.8

20 1957 12.8

Box 2The twenty warmest sea temperaturesrecorded show a high proportion ofresults from recent years.

Jersey Meteorological Department

39

SEA LEVEL INCREASE

Tide heights were recorded at the St HelierHarbour from 1966 to 1988 and although notcomplete this time series gives a goodindication of the change in sea level in thatperiod. After a gap of several years a digitalgauge was installed in 1993, with theProudman Oceanographic Laboratory takingresponsibility for the measurements, but usinga different point of reference.

Around the world an increase in sea level ofabout 170mm has been measured since 1870.This increase has not been constant, with anoticeable upward trend in yearly rate ofincrease since about 1930.

In Jersey the 1966 to 1988 period (Box 3a)shows year to year variation without anyobvious rise over the 23 years. A line of best fitillustrates a 0.6mm increase each year,equating to an increase of 14mm in the 23years. In the 14 years between 1993 and 2007(Box 3b) a sea level increase of 2.9 mm eachyear is indicated by the linear trend. Despitethe more recent period being 9 years shorter,sea level rose by 4mm, or nearly three timesmore quickly than the previous period,highlighting the increase in the rate of sealevel rise.

The measured increase in sea level cannot bepurely attributed to rising water levels as landmasses also rise and fall (known as isostaticrebound). However, Jersey is considered tobe geologically stable, so most of the

THE HUMAN INFLUENCE

697069806990700070107020703070407050

1993 1995 1997 1999 2001 2003 2005

Sea

leve

l (m

m a

bove

dat

um)

6000

6050

6100

6150

6200

6250

1965 1970 1975 1980 1985 1990Sea

leve

l (m

m a

bove

dat

um)

Box 3Despite inconsistencies in the record thereis a clear upward trend in sea level sincerecords began in the mid-1960s.

Sources: Proudman Oceanographic Laboratory.

Storm Surges

A storm surge is producedwhen the movement of astorm, barometric pressureand strong winds combine toproduce an increase in sealevel above the predictedastronomical tide.

In the North Sea surges frequently exceed 1 m but are rarely of this magnitude in the EnglishChannel. Typically two or three surges of 60 cm or more occur each year in the ChannelIslands. The largest measured surge in Jersey was 1.67 meters in the October 1987 storm, but itoccurred on a neap tide so no flooding resulted. With such a large tidal range, only surgescoinciding with a high spring tide are likely to cause flooding in Jersey. By the 2080s the BritishIrish Council Hadley Report predicts the 1 in 50 year storm surges around the Channel Islandsmay be 0.5m higher than at present. Such events, particularly when combined with anincrease in sea level, could result in flooding and potentially serious damage to property andthe environment as witnessed in the severe weather of 10th March 2008 when a surge of 1.15meters was recorded at the time of high tide.

(a)

(b)

observed sea level rise is likely to becaused by thermal expansion of seawaterdue to warmer temperatures, rather thanisostatic rebound.

40

Alternative Climate Change Theories

been regional changes such as the'Medieval Warm Period' and the 'Little IceAge' (Box 1). However, in contrast to theseregional climate phases, the increase ofthree-quarters of a degree centigrade inaverage global temperatures that we haveseen over the last century is larger than canbe accounted for by natural factors alone.Natural effects do not explain the changesin temperature recently observed.

We know from gases trapped in polar icethat the levels of CO2 in the atmosphere arenow 35% greater than they have been for atleast the last 650,000 years. Tests of the gasshow that this is mainly due to the burning offossil fuels. The increase in globaltemperature is consistent with what sciencetells us we should expect when the levels ofCO2 and other greenhouse gases in theatmosphere increase in the way that theyhave.

ARGUMENT 2:

CO2 only makes up a small part of theatmosphere and so cannot be responsiblefor global warming.

The properties of greenhouse gases such asCO2 mean that they strongly absorb heat, afact that can be easily demonstrated in asimple laboratory experiment. The effect ofa greenhouse gases is quantified by their‘radiative forcing’ as explained in Box 2.While there are larger concentrations of

The Royal Society is one of the mostrespected scientific institutions and electsonly the most eminent scientists as members.In April 2007 the Society published a responseto eight of the most popular arguments putforward by ‘climate sceptics’.Accompanying this guide was the followingauthoritative statement:

‘Our scientific understanding of climatechange is sufficiently sound to make us highlyconfident that greenhouse gas emissions arecausing global warming. Science movesforward by challenge and debate and thiswill continue. However, none of the currentcriticisms of climate science, nor thealternative explanations of global warmingare well enough founded to make not takingany action the wise choice.’

The following sections summarise theresponse of the Royal Society to the eightmain arguments:

ARGUMENT 1

The Earth's climate is always changing andthis is nothing to do with humans. Evenbefore the industrial revolution, when humansbegan pumping CO2 into the atmosphere ona large scale, the earth experienced warmperiods i.e. the medieval warm period.

The Earth’s climate has experienced warmerand cooler periods in the past. As well as theglobal effects of ice ages there have also

2.8 ARE GREENHOUSE GASES REALLY TOBLAME?

Graphic adapted from: http://www.spirasolaris.ca/liav3l3s2.gif

Box 1The Medieval Warm period and Little Ice Age existed but both phenomena wereregionally limited to within the North Atlantic region. This does not prevent scepticsfrom suggesting that these were periods of ‘global’ warming and cooling.

James Le Ruez

41

other gases in the atmosphere, (e.g. nitrogen)they do not have these heat trappingqualities and therefore have no effect onwarming the climate.

Water vapour is the most significantgreenhouse gas. Although it occurs naturally,global warming will indirectly affect howmuch is in the atmosphere through, e.g.increased evaporation from oceans andrivers. This will, in turn, cause either cooling orwarming depending on what form the watervapour takes such as different types ofclouds.

ARGUMENT 3:

Rises in the levels of CO2 in the atmosphereare the result of increased temperatures, notthe other way round.

The fluctuations in temperatures that causedthe ice ages were initiated by changes in theEarth's orbit around the Sun which, in turn,drove changes in levels of CO2 in theatmosphere. Data from ice cores shows thatincreases in temperature came first and werefollowed by increases in CO2 levels up toseveral hundred years later. The reasons forthis are not yet fully understood. They can bepartly explained by the fact that oceans emit

CO2 as they warm up and absorb it whenthey cool down. In addition soil andpermafrost release greenhouse gas whenthey warm up. These increased levels ofgreenhouse gases in the atmosphere thenfurther enhanced warming, creating a‘positive feedback'.

In contrast to this natural process chemicalanalysis tells us that the majority of the recentsteep increase in the level of CO2 - some 30per cent in the last 100 years - has come fromthe burning of fossil fuels not naturalprocesses.

CO2 from anthropogenic sources isresponsible for most of the temperatureincrease over the last 50 years. There is muchevidence to back up this explanation - butnone that conflicts it.

THE HUMAN INFLUENCE

REFERENCESThis article is sourced from a documentcompleted by the Royal Society ‘ClimateChange Controversies, A Simple Guide’.http://royalsociety.org/

Box 2Increased radiative forcing is the change in the rate at which additional energy is madeavailable to the earth-atmosphere system due to increased concentration of a "greenhouse"gas. This graph reveals how the increasing concentrations of greenhouse gases havechanged the global radiative forcing since 1979. The largest contribution is clearly made bycarbon dioxide (CO2) followed by methane (CH4) and nitrous oxide (N2O).

Graph Credit: National Oceanic and Atmospheric Administration: http://www.noaa.gov/

42

The Science of Global Warming

ARGUMENT 5:

Computer models which predict the futureclimate are unreliable and based on a seriesof assumptions.

Modern climate models have becomeincreasingly accurate in reproducing howthe real climate 'works'. They are based onour understanding of basic scientificprinciples, observations of the climate andour understanding of how it functions, asdetailed in Chapter 3.

While climate models are now able toreproduce past and present changes in theglobal climate rather well, they are not yetsufficiently well-developed to projectaccurately detailed impacts at regional orlocal levels. They do give us a reliable guideto the direction of future climate change.The reliability also continues to improvethrough the use of new techniques andtechnologies.

ARGUMENT 6:

It's all to do with the Sun - for example thereis a strong link between increasedtemperatures on Earth with the number ofsunspots on the Sun.

As we saw in Section 1, solar activitycontributes to climate change together withvolcanic and anthropogenic emissions tothe atmosphere. Change in solar activitycannot on its own account for all thechanges in global average temperaturethat we have seen in the 20th Century.

Changes in the Sun's activity influence theEarth's climate through small but significantvariations in its intensity. When it is in a ‘moreactive' phase as indicated by more sunspotson its surface, it emits more light and heat.While there is evidence of a link betweensolar activity and some of the warming inthe early 20th Century, satellitemeasurements show that there has beenvery little change in underlying solar activityin the last 30 years. There is even evidenceof a detectable decline and so this cannotaccount for the recent increases we haveseen in global temperatures.

ARGUMENT 4:

Observations of temperatures taken byweather balloons and satellites do notsupport the theory of global warming.

Some have argued that climate change, asa result of human activities, isn't happeningbecause early measurements taken fromsatellites and weather balloons indicatedthat little warming was happening in thelower atmosphere.

Errors have since been found in the data. Forexample, satellites were found to be slowingand slightly dropping in orbit, leading toinconsistencies in their measurements.Variations between the instruments ondifferent satellites and weather balloon alsoled to discrepancies. Furthermore, amathematical error was found to haveoccurred in one of the original analyses ofsatellite data.

Once adjustments are made to takeaccount of these and other issues, thewarming in the troposphere was shown to bebroadly consistent with the temperaturetrends we see on the Earth's surface.

2.8 CONTINUED...

Box 1There is no doubt the Medieval Warmperiod and Little Ice Age existed butboth were limited to the North Atlanticregion. This does not prevent scepticsfrom suggesting they were periods of‘global’ warming and cooling.

43

ARGUMENT 7:

The climate is affected by cosmic rays.

The potential effect of cosmic rays on theclimate is not yet well understood. If there isan effect it is likely to be small. Cosmic raysare fast moving particles which come fromspace, and release an electric charge in theatmosphere.

Laboratory experiments hint that cosmic rayscould influence the development of tinyparticles that may in turn play a part in theformation of clouds. This process mayenhance the influences of the Sun on theclimate. When the Sun is more active itsmagnetic field is stronger and thereforedeflects cosmic rays away from the Earth.

The argument follows that a more active Sunwould lead to fewer cosmic rays reachingthe Earth, resulting in fewer clouds andtherefore a warmer Earth.

However, observations of clouds and cosmicrays show that any link between them atmost has a small effect. Even if cosmic rayswere shown to have a more substantialimpact, the level of solar activity haschanged so little over the last few decadesthat the process could not explain the recentobserved increases in temperature.

ARGUMENT 8:

The scale of the negative effects of climatechange is often overstated and there is noneed for urgent action.

As previously discussed, the IPCC is the world'sleading authority on climate change. Underone of its mid-range estimates, it projected aglobal average temperature increase of 2 to3ºC this century - a larger climate changethan the world has experienced for at least10,000 years. The impact and pace of thischange would make adaptation by peopleand ecosystems difficult.

In the short term, some parts of the worldcould initially benefit from climate change.For example, more northerly regions of theworld may experience longer growingseasons and yields may increase as higherlevels of carbon dioxide have a fertilisingeffect on plants.

The IPCC has pointed out that as climatechange progresses negative effects are likelyto dominate almost everywhere. Increasingtemperatures are likely to increase thefrequency and severity of weather eventssuch as heat waves, storms and flooding.

There are real concerns that in the long termrising levels of greenhouse gases in theatmosphere could set in motion large-scaleand potentially abrupt changes in ourplanet's natural systems. Some of these couldbe irreversible. Increasing temperatures couldlead to the melting of large ice sheets withmajor consequences for low lying areasworldwide.

Finally, it is predicted that the impacts ofclimate change will fall disproportionately ondeveloping countries and the poor, thosewho can least afford to adapt. Thus achanging climate will exacerbate inequalitiesin health and access to adequate food andclean water.

THE HUMAN INFLUENCE

Box 2As highlighted in Chapter 1, the Sun is themajor force that governs how the climatebehaves. In the last 100 years thevariation in the Sun’s activity is not nearlylarge great enough to account for thechange in observed temperatures.

Image Credit: NASA

REFERENCESThis article is sourced from a documentcompleted by the Royal Society ‘ClimateChange Controversies, A Simple Guide’.http://royalsociety.org/