Forest Fires: Particulate Effects on Global Climatology Akua Asa-Awuku, Christos Fountoukis, & Robyn Williams

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

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)

Forest Fires emit Aerosols suspension of a fine solid or liquid particles in gas. – Primary – Secondary

J.T. Houghton: “The science of climate change” Clouds significantly reflect incoming Solar Radiation

Not Just Water Vapor Many areas of the globe with high water vapor concentrations do not form clouds

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 activates into a cloud drop Aerosol particle that does not activate Cloud

More polluted: Smaller drops Less polluted: Larger drops Changing Cloud Properties Direct Effect Indirect Effect The radiative properties are highly complex (and poorly understood).

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

IPCC, 2001 What is the Impact?

Forest Fire Effects Tropospheric Stratospheric Differences

“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

Heavy smoke “chokes” clouds

Decreased cloud cover

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

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/m 2, respectively

Stratospheric Effect Long Lifetime and Distance Unknown Degree of Prevalence Fromm and Servranckx Study

Smoke Particulate Transport Tropopause – Vertical Transport Inhibitor – Well Mixed Tropopause vs. Very Stable Stratosphere

Smoke Particulate Transport Volcanoes “Nuclear Winter” Supercell Convection – Boreal Fire - Summer of 1998

Supercell Convection Highly organized thunderstorm Extremely strong rotating updraft Ability to produce severe weather

Case Study: Chisholm Fire 28/29 May km North of Edmonton, Alberta

Pre-Convection

Early Stage of Convection

Fully Developed Convection

Post-Convection

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

Case Study: Chisholm Fire Transport from planetary boundary layer to upper troposphere/lower stratosphere 1998 Substantial Statospheric Aerosol Increase

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

Conclusions: Stratospheric Effect Volcanic Haze Effect Material Distribution with a radiative, chemical, and cloud impact

Where Do We Go From Here? Unknown Extent Quantify Increased Urgency of Increased Fire Prevention Methods

Questions?