1900 1920 1940 1960 1980 2000

-0.4

0.0

0.4

AM

O (K

) 0.25

-0.24

11-yr mov avg

Observation

NOAA-20CR

ERA-20CM

GISS ModelE

MDA8 ozone

Extreme ozone

24-h PM2.5

MLR (1980-2013)

Local met: T, RH, surface u v, 500-hPa u v

Synoptic pattern

MLR (1999-2013)

Local met: T, RH, surface u v precipitation

Synoptic pattern

Hybrid-EVT with T (2003-2012)

A

B

C

D

(d) Changes in air quality in one-half cycle of AMO

(b) Statistical method (c) Meteorology (a) Pollutant

Midwest Northeast South Central Southeast

0

1

2

3

4

ObsNOAA

ERAGISS

ObsNOAA

ERAGISS

ObsNOAA

ERAGISS

ObsNOAA

ERAGISS

Ozo

ne c

onc

(ppb

v)

(b) Regional MDA8 ozone changes

Midwest Northeast South Central Southeast

0.0

0.5

1.0

1.5

2.0

Obs NOAA

ERAGISS

Obs NOAA

ERAGISS

Obs NOAA

ERAGISS

Obs NOAA

ERAGISS

Ozo

ne e

piso

des

(day

s)

(d) Regional ozone episode changes

Midwest Northeast South Central Southeast

0.0

0.5

1.0

1.5

ObsNOAA

ERAGISS

ObsNOAA

ERAGISS

ObsNOAA

ERAGISS

ObsNOAA

ERAGISS

PM2.5 (

µ g

m−3)

(f) Regional PM2.5 changes

Changes of surface air quality in one-half cycle of AMO

1900 1950 2000 2050 2100

-10

12

34

Tem

pera

ture

Ano

mal

y (K

)

Base climatology(1951-2010)

Observed vs. CMIP5 JJA temperatures in the eastern US

obsCMIP5

East MW NE SC SE

AMO-T

RCP4.5

AMO-T

RCP4.5

AMO-T

RCP4.5

AMO-T

RCP4.5

AMO-T

RCP4.5

0.0

0.5

1.0

1.5

ΔJJ

A T

empe

ratu

re (K

)

JJA T in one-half AMO cycle vs. 2010-2040 warming trend

The Atlantic Multidecadal Oscillation drives multidecadal variability of summertime surface air quality in the eastern United States

Lu Shen1, Loretta J. Mickley1, Eric M. Leibensperger2, Mingwei Li3 1School of Engineering and Applied Sciences, Harvard University. 2 Center for Earth and Environmental Science, Sunny Plattsburgh. 3Department of Earth, Atmospheric and Planetary Sciences, MIT

1. Abstract

2. Introduction

Atlantic sea surface temperatures have a significant influence on the summertime meteorology and air quality in the eastern United States. Here we investigate the effect of the Atlantic Multidecadal Oscillation (AMO) on two key air pollutants, surface ozone and PM2.5, over the eastern United States. The shift of AMO from cold to warm phase increases surface air temperatures by ~0.5-1 K across the East and reduces precipitation, resulting in a warmer and drier summer. By applying observed, present-day relationships between these pollutants and meteorological variables to a variety of observations and historical reanalysis datasets, we calculate the impacts of AMO on U.S. air quality. Our study reveals a multidecadal variability in mean summertime (JJA) maximum daily 8-hour (MDA8) ozone and surface PM2.5 concentrations in the eastern United States. In one-half cycle (~30 years) of the AMO from negative to positive phase with constant anthropogenic emissions, JJA MDA8 ozone concentrations increase by 1-3 ppbv in the Northeast and 2-5 ppbv in the Great Plains; JJA PM2.5 concentrations increase by 0.6-1.0 µg m-3 in the Northeast and Southeast. The resulting impact on mortality rates is ~3000 excess deaths per year at the peak of the positive phase of AMO relative to the negative phase. A complete picture of air quality management in coming decades thus requires consideration of the AMO influence.

3. Summertime air quality is related to SST

References Sutton, R. T., & Hodson, D. L.. Atlantic Ocean forcing of North American and European summer climate. Science, 309(5731), 115-118, 2005. Shen, L., Mickley, L.J. and Gilleland, E.. Impact of increasing heat waves on US ozone episodes in the 2050s: Results from a multimodel analysis using extreme value theory. Geophys. Res. Lett., 43, 2016a. Shen, L., Mickley, L. J., and Murray, L. T.. Strong influence of 2000–2050 climate change on particulate matter in the United States: Results from a new statistical model, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-954, 2016b. McKinnon KA, Rhines A, Tingley MP, Huybers P. Long-lead predictions of eastern United States hot days from Pacific sea surface temperatures. Nat Geosci, 9(5), 2016.

4. AMO leads to a warmer summer in the eastern US

Positive AMO and its spatial pattern in the sea surface temperatures (SSTs)

•  AMO is the leading mode of variability in North Atlantic SSTs with a timescale of 50-70 years.

•  We define the AMO index as the SST averaged over the extra-tropical North Atlantic minus the regression on global mean temperature.

6. Changes in air quality in one-half AMO cycle

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Acknowledgments. This work was supported by NASA AQAST, NASA MAP, and NIH.

Name Description

Observations (1895-2015)

•  Temperature: NCDC1, GHCN2, Delaware3, MLOST4 and HADCRUT5

•  Precipitation: NCDC1, GPCC6, GHCN2, Delaware3

•  Sea level pressure: HadSLP27

•  Ozone/PM2.5: EPA-AQS (1980-2015)

NOAA-20th Century Reanalysis (56 runs,1861-2014)

•  Boundary conditions: observed SST and sea ice data •  Assimilation: observed sea level pressure

ERA-20CM (10 runs, 1900-2010)

•  Boundary conditions: observed SST and sea ice data •  Assimilation: none

GISS ModelE •  Boundary conditions: prescribed SST and sea ice data in warm and cold

AMO phases. •  Assimilation: none

1900 1950 2000 2050 2100

-10

12

34

Tem

pera

ture

Ano

mal

y (K

)

Base climatology(1951-2010)

Observed vs. CMIP5 JJA temperatures in the eastern US

obsCMIP5

East MW NE SC SE

AMO-T

RCP4.5

AMO-T

RCP4.5

AMO-T

RCP4.5

AMO-T

RCP4.5

AMO-T

RCP4.5

0.0

0.5

1.0

1.5

ΔJJ

A T

empe

ratu

re (K

)

JJA T in one-half AMO cycle vs. 2010-2040 warming trend

Data and climate model simulations

1 Historical temperature, precipitation and drought indices for U.S. climate divisions from National Climatic Data Center [Vose et al., 2014]. 2 Gridded Historical Climatology Network (GHCN, v2 for precipitation and v3 for temperature) provided by the NOAA/OAR/ESRL PSD. 3 University of Delaware air temperature and precipitation [Willmott and Matsuura, 2001]. 4 Merged Land-Ocean Surface Temperature Analysis (MLOST) [Smith et al., 2008; Vose et al., 2012]. 5 Jones (CRU) Air Temperature Anomalies Version 4 (CRUTEM4) [Jones et al., 2012]. 6 Global Precipitation Climatology Centre (GPCC) [Schneider et al., 2011]. 7 Hadley Centre Sea Level Pressure data (HadSLP2) [Allan et al., 2006].

•  JJA temperature and air quality in the East are highly related to large-scale climate patterns. •  Could the multidecadal variability in Atlantic SSTs influence US air quality?

Significant at 0.05 level

Similar to the correlation pattern between SLP and AMO in Sutton et al. [2005]

Pacific extreme pattern, McKinnon et al. [2016]

Observations and modeling studies confirm that a warm AMO leads to a warmer and drier summer in the eastern United States.

5. Calculate the influence of AMO on air quality

The details of Hybrid extreme value theory (Hybrid-EVT) model can be found in Shen et al. [2016a] and the method to characterize synoptic pattern is from Shen et al. [2016b].

Greater temperature change here

PM2.5 is more sensitive to temperature here

7. Implications for future air quality management

Ensemble mean of 22 IPCC models under RCP45. scenario

Observed JJA temperatures

•  Climate models have difficulty in modeling AMO variability. •  If AMO continues its periodicity of 50-90 years, it is very likely to shift into a cold phase in

the next few decades. This shift will partly compensate the climate penalty on air quality in the eastern United States brought on by global warming.

•  A complete picture of air quality management in coming decades thus requires consideration of the AMO influence.

•  We identify a multidecadal variability in both ozone and PM2.5 air quality in the eastern United States driven by AMO.

•  AMO-driven changes in ozone and PM2.5 concentrations can result in ~3,000 excess deaths per year at the peak of positive phase AMO relative to the peak negative phase in the eastern United States.

AMO (11-yr running mean)

JJA temperature in the eastern US (11-yr running mean)

* Midwest (MW), Northeast (NE), South Central (SC) and Southeast (SE) * Midwest (MW), Northeast (NE), South Central (SC) and Southeast (SE)

AMO index

Observations