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Page 1: Forest Fires: Particulate Effects on Global Climatology

Forest Fires: Particulate Forest Fires: Particulate Effects on Global ClimatologyEffects on Global Climatology

Akua Asa-Awuku, Christos Fountoukis, & Robyn Williams

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Summary• I. Introduction

– What are aerosols?– How are clouds formed? – What is the direct/indirect effect (IPCC) chart

• Tropospheric Effects– Semi-direct effect– Amazon data on cloud coverage– Amazon pictures and article

•  Stratospheric Effects•  Conclusions

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Biomass Burning• Wildfires consume a million or

more square kilometers per year. • Fire is a tool used in agriculture to

clear croplands and help return nutrients to the soil.

• Annually, humans burn anywhere from 750,000 to 8.2 million square km of forest and grassland around the world.

• It is expected that a surface warming trend at high northern latitudes will lead to an increase in boreal fires and their effects, such a trend toward increased burning has already been detected (Stocks et al., 1998)

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Forest Fires emit Aerosols• suspension of a fine solid or liquid particles in

gas. – Primary– Secondary

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J.T. Houghton: “The science of climate change”

• Clouds significantly reflect incoming Solar Radiation

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Not Just Water Vapor

• Many areas of the globe with high water vapor concentrations do not form clouds

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Why are clouds linked to aerosols?

• Clouds form in regions of the atmosphere where water vapor is supersaturated.

• Water vapor supersaturation is generated by cooling (primarily through expansion in updraft regions and radiative cooling).

• Cloud droplets form from pre-existing particles found in the atmosphere (aerosols). This process is known as activation.

• Aerosols that can become droplets are called cloud condensation nuclei (CCN).

CCN that activatesinto a cloud drop

Aerosol particlethat does not activate

Cloud

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More polluted:Smaller drops

Less polluted:Larger drops

Changing Cloud Properties• Direct Effect• Indirect Effect• The radiative properties are highly complex (and poorly

understood).

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The Indirect Effect

The crushed smaller particle ice, reflects more than the larger ice particles

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IPCC, 2001

What is the Impact?

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Forest Fire Effects• Tropospheric• Stratospheric Differences

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“Semi-direct” effect• Reduction in cloud cover• Warming of the surface

– In the morning: heating of the atmosphere, cooling of the surface (increased static stability, supressed convection)

– In the afternoon: less cloud cover, more sunlight in the surface

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Heavy smoke “chokes” clouds

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Decreased cloud cover

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NASA Measurements

• Total amount of light reflected through the top of the atmosphere

• Area covered by clouds and by smoke• “Optical thickness” of smoke• Measurements in meteorologically different

regions

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NASA Results• Much less solar energy reflected back up to the space

with the reduction in cloud cover• Smoke “chokes off” cloud formation rather than being

a reflector of sun light• Similar examples in Africa and Canada• Global cooling influence of aerosols smaller than

previously thought• The semi-direct effect amounts to a reduction in

global annual mean cloud cover and LWP of 0.2% and 0.3g/m2, respectively

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Stratospheric Effect• Long Lifetime and Distance

• Unknown Degree of Prevalence

• Fromm and Servranckx Study

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Smoke Particulate Transport

• Tropopause– Vertical Transport

Inhibitor– Well Mixed

Tropopause vs. Very Stable Stratosphere

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Smoke Particulate Transport• Volcanoes

• “Nuclear Winter”

• Supercell Convection– Boreal Fire - Summer of 1998

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Supercell Convection

• Highly organized thunderstorm

• Extremely strong rotating updraft

• Ability to produce severe weather

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Case Study: Chisholm Fire

• 28/29 May 2001

• 160km North of Edmonton, Alberta

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Pre-Convection

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Early Stage of Convection

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Fully Developed Convection

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Post-Convection

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Case Study: Chisholm Fire• Dynamic Relationship Between Fire and

Convection– Surface Heating – Destabilization of Air– Generation of wind and lightening– Aggravation of existing fires – Supercell Storms– Intense Interfacial Gravity Waves

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Case Study: Chisholm Fire• Transport from planetary boundary layer to

upper troposphere/lower stratosphere

• 1998 Substantial Statospheric Aerosol Increase

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Conclusions: Semi-Direct Effect

• In highly polluted regions: increase of BC causes a reduction of LWP and cloud cover

• However, indirect effect causes the opposite• Therefore, all aerosols radiative effects should

be calculated simultaneously in order to determine the net increase/decrease of cloud cover and LWP

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Conclusions: Stratospheric Effect

• Volcanic Haze Effect

• Material Distribution with a radiative, chemical, and cloud impact

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Where Do We Go From Here?• Unknown Extent Quantify

• Increased Urgency of Increased Fire Prevention Methods

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Questions?


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