Why is it difficult to predict climate? Understanding current scientific challenges Akua Asa-Awuku October 22, 2009 Global Climate Change (GCC) Workshop University of California - Riverside Bourns College of Engineering Center for Environmental Research and Technology (CE-CERT)
Aerosol-indirect-effect forcing: important and elusive IPCC (2001)
Natural Sources Volcanoes Sea-Salt Spray Marine Animals Trees Anthropogenic Pandora s Box of Answers Power Plants Vehicular Emissions Ship stack Emissions
Biomass Burning Borneo Fires, Southeast Asia, 1997 Haze from automobile combustion and biomass burning, like this huge smoke plume over Borneo, may blot out the sun for a short while, causing local cooling. But aerosols in the atmosphere rival carbon dioxide as an agent of warming, exacerbating humanity's effect on climate. Photo credit: NASA
Dust China, dust storm 2001 The role of Dust Large increases in water consumption, intensive farming practices and deforestation in China have led to more frequent dust storms, Dust blowing off the Sahara Desert each winter makes its way across the Atlantic Ocean. It takes less than two weeks for a dust plume to lift off in Africa, cross the Atlantic, and settle in the Caribbean, the United States, or South America. Photo credit: NASA
Dust & the Ecosystem Rich in iron, the dust is a vital nutrient that helps sustain marine ecosystems, but can also trigger toxic blooms of algae, like red tides, that kill fish and damage corals. As dust settles into the ocean, algae respond with huge blooms, not all of them toxic. The collective activity of trillions of single-celled critters could play a major role in Earth's climate by sucking carbon dioxide out of the atmosphere. Photo credit: NASA/GeoEye
IPCC, 2007
Understanding climate change J.T. Houghton: The science of climate change Clouds cool climate Facts: Clouds account for 50% of planetary albedo. Small changes in clouds yield large changes in global energy balance. 1% increase in global cloud cover can counteract warming from doubling atmospheric CO 2 concentrations. Consequence: Understanding cloud formation is necessary for reliable climate change predictions.
Every cloud has a filthy lining Aerosols provide nuclei for cloud droplets to condense. If not the sky would always be clear and the air around us, thick and humid
Droplet Size Matters The crushed smaller particle ice, reflects more than the larger ice particles The smaller droplets reflects more than the larger droplets
CLOUD FORMATION 101: CONDENSATION OF WATER VAPOR ON AEROSOL Aerosols that activate and become droplets are called Cloud Condensation Nuclei (CCN) Lower Al bedo Higher Al bedo CCN Clean Environment (few CCN) CCN Polluted Environment (more CCN) Aerosols impact clouds and hence climate. This phenomenon is known as aerosol indirect climatic effect. Humans increase global aerosol by alot! So, in addition to greenhouse gases (that warm), humans also cool the planet via the indirect effect (potentially alot). Where do CCN (or particles) come from? Climate models are the only tools for assessing the anthropogenic indirect effect, but predictions are subject to very large uncertainty.
Observational evidence of indirect effect Ship tracks : linear features of high cloud reflectivity embedded in marine stratus clouds, resulting from aerosols emitted by ships. M.Kulmala: Nucleation and Atmospheric Aerosols, 1996
Current Treatment of Aerosol Indirect Effect Aerosol Properties (e.g., Number Concentration, Size, Composition)? Cloud Droplet Number and Size Cloud Reflective Properties
Known: Plants emit gases that can form aerosols (solid phase particles) in the atmosphere But Why?
Hypothesis: Plants emit these gases when they are hot! The aerosols that form in the atmosphere can be used to form cloud droplets and clouds which will then provide cloud coverage and potentially rain to cool them off!
e.g. Phytoplankton emit Dimethylsulfide (DMS). Do they influence cloud formation over the ocean?!!
Spatial Variation Global Climate Models resolve Aerosol-cloud interactions on large scales (100 x 100 km) Cirrus or Ice clouds, at high altitude clouds, can trap in energy (long wave radiation)
What Next? Improve knowledge of the Earth's past and present climate and environment, including its natural variability, and improve understanding of the causes of observed variability and change. Improve quantification of the radiative forces bringing about changes in the Earth's climate and related systems. Reduce uncertainty in projections of how the Earth's climate and related systems may change in the future. Understand the sensitivity and adaptability of different natural and managed ecosystems and human systems to climate and related global changes.
Why is it difficult to predict climate? Understanding current scientific challenges Akua Asa-Awuku Email: akua@engr.ucr.edu Global Climate Change (GCC) Workshop University of California - Riverside Bourns College of Engineering Center for Environmental Research and Technology (CE-CERT)