Investigation of the U.S. warming hole and other adventures in chemistry-climate

interactions

Loretta J. MickleyPattanun Achakulwisut, Becky Alexander, Tom Breider, Bryan Duncan, Rynda Hudman, Daniel Jacob, Jennifer Logan, Shannon Koplitz, Eric Leibensperger, Lee Murray, Justin Parrella, David Rind, Lulu Shen, Dominick Spracklen, Amos Tai, Shiliang Wu, Xu Yue, and Lei Zhu

Running head for JAL’s first atmos chem paper.

2009 wildfire in Southern California

2013 ~1:1 ratio

1977 1 in 50

OzonePM2.5

Millions of people in US living in areas in violation of the EPA standards.

What is climate penalty on air quality? How will size of bars change with changing climate?

How do trends in short-lived species affect global and regional climate? Regional forcings are as large as global forcings from well-mixed GHGs.Short-lived species can affect methane lifetime.

1990 2001

Calculated trend in surface sulfate concentrations

Observations in circles

-2 Wm-2

Leibensperger et al., 2012

Atmospheric Chemistry

Assimilated meteorologyGEOS-4GEOS-5

GEOS-Chem

Atmospheric ChemistryLand cover model

GEOS-Chem

Meteorology from freely running climate model

Fire prediction model

Chemical feedbacks

Model frameworks1. Standard

2. Chemistry-climate

1. Examine observed sensitivities of short-lived species or other variables to meteorology.

E.g. Area burned = f(meteorology)

2. Apply sensitivities to archived meteorology from an ensemble of models.

Some methods to overcome uncertainties in model apparatus.

Yue et al., in review

Area

bur

ned

(105 h

a)

R2 ~ 0.5

Area burned over Southwest

model

observed

Area

bur

ned

(105 h

a) Timeseries of area burned

observed model3. Benchmark chemistry-climate interactions in the recent + distant past with observations.• Arctic 1980-2010• Last Glacial Maximum • Equatorial Asia 2000sArea burned in Southwest US may double by 2050.

Observed US surface temperature trend

GISTEMP 2010

Is the U.S. “warming hole” a signature of cooling due to anthropogenic aerosols?

Observed spatial trend in temperatures, 1930-1990

No trend between 1930 and 1980.

Warming trend after 1980

Contiguous US-1

1

0

o C1-1

We applied decadal trends in anthropogenic aerosol to the GISS climate model.

Increasing sulfate from 1950-1990s.

Decreasing sulfate beginning in 1990s.

1950 1960

1970 1980

1990 2001

Leibensperger et al., 2012a

Calculated trend in surface sulfate concentrations

Clearing trend in particles over United States since 1980s suggests possible recent warming.

Circles show observations.

Leibensperger et al., 2012a.

Direct radiative forcing

Indirect radiative forcing

Forcing from US anthropogenic aerosols peaks in 1980 -1990s.

Forcings over Eastern US

Peak forcings -2 W m-2, mainly from sulfate.

Warming from black carbon offsets the cooling early in the record.

Results suggest little climate benefit to reducing black carbon sources in US.

CLeibensperger et al., 2012b

Cooling from U.S. anthropogenic aerosols during 1970-1990.

Results are from two 5-member ensembles, with and without US anthropogenic aerosols.

Cooling is greatest over the Eastern US and North Atlantic.

1 oC cooling at surface over East

D Model Temperature 1970-1990

C

D Soil moisture availabilityD Cloud Cover

%%

Cooling over U.S. is not co-located with aerosol burden.

Cooling over North Atlantic strengthens Bermuda High, increasing onshore flow of moisture from Gulf of Mexico.

Local changes in cloud cover and soil moisture amplify the cooling effect.

Results are controversial.

Inclusion of US anthropogenic aerosols improves match with observed trends in surface temperatures over the East.

Most of the warming from reducing aerosol sources has already been realized.

• Results suggest that US anthropogenic aerosols can explain the “warming hole.”

• Warming since 1990s can be attributed to reductions in aerosol sources.

Leibensperger et al., 2012b

Observations

Model without US aerosols

Standard model

Eastern US

U.S. BC emissions (Tg

C)

1850

U.S.

SO

2 em

issio

ns (T

g S)

1900 1950 2000

BC

SO2

Timeseries of US emissionsHow have competing trends in BC and SO2 over 20th century affected regional climate across mid-latitudes?

Ongoing work.

BC aerosol• warms mid- to upper

troposphere• cools surface• stabilizes atmosphere

SO2 cools surface, may augment stabilization.

We will compare model BC with lake core sediments from Adirondacks (Husain et al., 2008)

BC d

epos

ition

(g m

-2 a

-1)

1860 1940

obstobservations

model

Deposition in Adirondacks

Leibensperger