Investigation of chemistry-climate interactions, with a closer look at the U.S.

warming hole

Loretta J. MickleyEric Leibensperger, Xu Yue, Daniel Jacob, Jennifer Logan

David Rind, GISSJed Kaplan, U Geneva

2009 wildfire in Southern California

Millions of people in US live in areas with unhealthy levels of ozone or particulate matter (PM2.5).

Number of people living in areas that exceed the national ambient air quality standards (NAAQS) in 2010.

Bars on barplot will change with changing emissions.

Climate change could also change the size of these bars, by changing the day-to-day weather.

Ozonedaily maximum 8-hour average

PM2.5

24-hour average or annual average

Particles affect solar radiation directly…and also indirectly by modifying cloud properties.

Pollution off U.S. east coast Black carbonCalifornia fire plumes

Aircraft contrails and cirrus over EuropeLight-colored particles reflect sunlight and cool the earth’s surface.

cooler3

4

Life cycle of particulate matter (PM, aerosols)

nucleation coagulation

condensation

wildfirescombustion

sea salt

..

...

.cycling

ultra-fine(<0.01 mm)

fine(0.01-1 mm)

cloud(1-100 mm)

combustionvolcanoes

agriculturebiosphere

coarse(1-10 mm) scavenging

precursor gases

SO2 -- sulfur dioxideNOx -- nitrogen oxides

Soup of chemical reactions

NOxNOx

NOx

NOxNOx

VOCs

VOCsVOCs

VOCs

Organic carbon

SO2

NH3

SO2

VOCs -- volatile organic compoundsNH3 -- ammonia

Black carbon

dust

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

• Wildfire in the western United States in the mid-21st century

• Consequences for air quality.

Rim fire, Yosemite Natl Park, 2013

Climate change Air Quality

Hayman fire, June 8-22, 2002 56,000 ha burned 30 miles from Denver and Colorado Springs

Colorado Dept. of Public Health and EnvironmentVedal et al., 2006

June 8, 2002 June 9, 2002 PM10 = 372 μg/m3

PM2.5 = 200 μg/m3

Standard = 35 µg/m3

PM10 = 40 μg/m3

PM2.5 = 10 μg/m3

Unhealthy air quality in Denver

Effects of wildfires on air quality in cities in Western US can be very dramatic.

Fire activity had a big impact on California air quality in 2013.

Unhealthy air

Very unhealthy air

Rim Fire

Aug 28

Aug 30

Timeseries of 3-hour average PM2.5 concentrations in Foothills Area

August 20 August 31

PM2.

5 (m

g m

-3)

Hazardous levels > 250 mg m-3

Will fire change in the future climate?

Very unhealthy

Gillett et al., 2004

Area burned in Canada has increased since the 1960s, correlated with temperature increase.

Westerling et al., 2007

Increased fire frequency over the western U.S. since 1970, related to warmer temperatures and earlier snow melt.

Observations suggest that fires are increasing in North America.

1970 2000

5 yr means

area burned

obs temperature

1960 2000

IPCC AR4 models show increasing temperatures across North America by 2100 in A1B scenario.

Models show increases of JJA temperatures of ~ 3K in Western US.

Results for precipitation changes are not so clear.

D Temperature JJA, oC D Precipitation JJA, %

IPCC, 2007

most models

few models

Number of models showing increased precipitation.

How do we predict fires in a future climate?We don’t have a good mechanistic approach for modeling wildfires.

JJA Temperature increase by 2100

Use ensemble of climate models to gain confidence in prediction.

Relationship between observed meteorology + area burned + Future

meteorologyFuture area burned

Start with the past.

2 approaches

Regression approach. Regress meteorological variables and fire indexes onto annual mean area burned in each of six ecoregions with a stepwise approach.

PNW

ERM

NMS

RMF

DSWCCS

Ecoregions are aggregates of those in Bailey et al. (1994)

Identify the meteorological variables and fire indexes that best predict area burned.

Include lagged met variables.

For example,Area burned in Nevada/ semi-desert = f ( + T summer max that year

+ RH and rainfall previous years)

Best predictors: Temp, RH, precip, Build-up Index, Drought code, Duff moisture code.

Predicted fires match observed area burned reasonably well. Least best fit is in Southern California.

Obs Fit

Area burned in many ecoregions depends on previous year’s relative humidity, rainfall, or temp. Yue et al., 2013

CCS

PNW

NMS

DSW

RMF ERM

Relationship between observed meteorology + area burned + Future

meteorologyFuture area burned

Start with the past.

Use of an ensemble of 15 climate models improves confidence in the results.

Changes in 2050s climate in the West.• Temperature increases 2-2.5 K.• Changes in precip and relative humidity

are small and not always robust.

Next step: apply meteorology from climate models to the two fire prediction schemes.

Yue et al., 2013

Wildfire area burned increases across the western United States by the 2050s timeframe.

Relationship between observed meteorology + area burned + Future

meteorologyFuture area burned

Results from regressions approach.Shown are median results.

Yue et al., 2013

Predicted area burned shows large increases in 2050s during peak months.

future

present-day

X4 increase X2 increase

Yue et al., 2013

Units = 104 hectares

GEOS-CHEM Global chemistry model

Ensemble of climate models

Median area burned

Emissions = area burned x fuel consumption x emission factors

How will changing area burned affect air quality?

Future air quality

Future meteorology

Yue et al., 2013

Organic particles increase in future atmosphere over the western U.S. in summer, especially during extreme events.

Change in summertime mean organic PM2.5 in ~2050s, relative to present-day.

Wildfires may swamp efforts to regulate air quality in future.

D Organic Carbon, OC

Ma 2050s

Present-day

doubling

May-Oct

JJA

Cumulative probability of daily mean concentrations of OC, Rocky Mountains

What do these increases in wildfire aerosol mean for human health?

Ongoing project with Yale will look at health impacts of these increases.

Yue et al., 2013

% area burned

% OC particles

Ratio of 2050s area burned to present-day

Ecoregions West to East

Alaska Boreal Cordillera

How will wildfire change in a changing climate in Canada?

Ratio of 2050s area burned to present-day

Area burned increases in the West due to:• Higher temperatures• More frequent blocking

high pressure systems.

Increased rainfall in Central and eastern Canada blunt these effects.

Yue, in progress

Pittsburgh, 1973

• Regional climate effects of 1950-2050 trends in US anthropogenic aerosols.

Aerosols Climate change

Observed US surface temperature trend

GISTEMP 2010

What caused the U.S. warming hole of the 20th century?

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

Increasing sulfate from 1950-1990s.

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.

Decreasing sulfate by 2001.

Spin-up Constant aerosols everywhere

Zeroed US aerosols, constant elsewhere

2010 2050

We first perform a pilot study:Constant aerosols vs. zeroed US aerosols

A1B scenario of greenhouse gases

Forcing due to aerosol removal over US

Model setup causes large warming over East.

By comparison, global DF from CO2 is +1.8 Wm-2.

GISS climate model

Results from pilot study: Removal of aerosol sources over US increases annual mean surface temperatures by 0.5 o C.

Warming due to 2010-2050 trend in greenhouse gases.

Additional warming due to zeroing of US aerosols

Mickley et al., 2012white areas = insignificant differences

Summertime temperatures increase as much as 1.5 oC.Only direct aerosol effect included.

Warming begins immediately and persists through the decades.

Mickley et al., 2012

Warming due to aerosol removal is strongest in late summer / early fall

Heatwaves show 1-2 K increase.

D Temperature, 2050s

Daily max T

Daily mean T

A1B

Change in surface temperatures due to aerosol removal, Northeast US

Climate response of Northeast to aerosol removal

28

Shift from increased latent flux to increased sensible and LW flux in late summer.

Increased diurnal temperature range, higher Tmax

Increased solar flux in July-October

Warming, especially in late summer, early fall.

Increased sunlight depletes soil moisture by late summer.

Reduced cloud cover and relative humidity

Daily max T

Daily mean T

LW

Latent heatSensible heat

Low cloud cover

Rel humidity

D D

D D

D D

LW

Latent heat

Sensible heat

DSoil moisture depletes through summer.

Cloud cover diminishes in response.

Shift from increased latent flux to increased sensible and LW flux in late summer.

Feedbacks involving soil moisture and low cloud cover amplify local temperature response in Aug-Oct period.

Diffuse warming

Local warming

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

Next, we perform a more realistic set of simulations, with changing emissions, 1950-2050.

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.

Indirect radiative forcing from clouds is about the same magnitude as direct effect.

Net DF

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.

Indirect + direct effects included.

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.

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

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

Results are controversial.

Westward extent of Bermuda High

200019801950

NCEP

ERA

Reference longitude

East

West

Li et al., 2011

Observations show intensification of the Bermuda High during the 1980s and early 1990s, apparently consistent with aerosol loading.

Variation of western edge of Bermuda High during JJA, 1948-2007.

Edge = 1560-gpm contour line at 850 hPa.

Period of greatest aerosol loading

1948-1977 1978-2007

Shift westward

What about effect of Pacific Decadal Oscillation?

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 em

issions (Tg C)

1850

U.S

. SO

2 em

issi

ons

(Tg

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

Sulfate cools surface, may augment stabilization.

We will compare model BC with lake core sediments from Adirondacks (Husain et al., 2008) and with ice cores from J. McConnell.

BC d

epos

ition

(g m

-2 a

-1)

1860 1940

obstobservations

model

Deposition in Adirondacks

Leibensperger, Cusworth, and Mickley

Take home messages.

• Area burned by wildfires may increase significantly across western North America by 2050s, depending on the ecosystem.

• Increased smoke from wildfires may thwart efforts to regulate air quality in coming decades. This is a climate penalty.

• Decreases in aerosol loading may have unintended consequences for regional climate, leading to warming.

Wildfires in Quebec the same day.Haze over Boston on May 31, 2010