Aerosols and Climate
Aerosols refer to fine solid or liquid particles suspended in the atmosphere, where they reside typically for days to weeks before falling to the ground or being washed out by rain or snow. They arise both from human activities involving burning of fossil fuels, biofuels and veg and from natural sources (such as desert dust, sea spray and volcanic eruptions). Aerosol particles are tiny, but numerous, and often comprise of a number of inorganic and organic substances. Visible forms of atmospheric aerosol plumes include smoke, smog, haze and dust.
How do aerosols affect climate?
Aerosols can influence the Earth’s climate in two ways. When the sky is clear (devoid of clouds), aerosols can reflect incoming sunlight back to outer space – the direct effect. This blocks part of the energy that would have reached the surface, thus having a cool effect on the climate. Absorbing aerosols, black carbon in particular, can trap solar energy within the atmosphere. Although absorption, like reflection, tends to reduce sunlight at the ground level, the enhanced atmospheric heating eventually warms up the surface, and counteracts the cooling caused by reflection.
As illustrated vividly by “ship tracks”, cloud reflectance or albedo goes up with the number of aerosol particles that provide nucleating sites for forming cloud droplets. The resulting brightening of clouds renders them more potent at shielding the surface from sunlight, causing the first indirect effect (or cloud albedo effect). More aerosols may also enable clouds to last longer by suppressing rainfall – the second indirect effect (or cloud lifetime effect).
Despite many years of active research, aerosols are still the least certain of all known climate forcings. This seriously hinders our ability to separate the roles of aerosols and greenhouse gases in driving the past climate change, thereby precluding one from reliably projecting the future climate.
Scientists at GFDL tackle the problem, by creatively bridging the several-orders-of-magnitude gaps in temporal and spatial scales between aerosol/cloud microphysics and climate models, We design and implement first principles-based parameterizations of the microphysical processes central to simulating the aerosol-cloud-radiation interactions (e.g., cloud droplet activation and meteorological evolution, internal mixing of absorbing and non-absorbing aerosol species, and hygroscopic growth of water-soluble aerosols) in order to improve their model representation. The enhanced model physics allows one to simulate the climate impacts of aerosols and clouds with unprecedented realism.
- Cloud tuning in a coupled climate model: impact on 20th century warming
- Have Aerosols Caused the Observed Atlantic Multi-decadal Variability?
- Nonlinear climate response to regional brightening of tropical marine stratocumulus
- Anthropogenic Aerosols and the Weakening of the South Asian Summer Monsoon
- Two opposing effects of absorbing aerosols on global-mean precipitation
- Levy II, Hiram, Larry W Horowitz, M Daniel Schwarzkopf, Yi Ming, J-C Golaz, Vaishali Naik, and V Ramaswamy, May 2013: The Roles of Aerosol Direct and Indirect Effects in Past and Future Climate Change. Journal of Geophysical Research, 118, DOI:10.1002/jgrd.50192.
- Bollasina, Massimo, Yi Ming, V Ramaswamy, M Daniel Schwarzkopf, and Vaishali Naik, in press: Contribution of Local and Remote Anthropogenic Aerosols to the 20th century Weakening of the South Asian Monsoon. Geophysical Research Letters. DOI:10.1002/2013GL058183. 1/14.
- Bollasina, Massimo, and Yi Ming, February 2013: The general circulation model precipitation bias over the southwestern equatorial Indian Ocean and its implications for simulating the South Asian monsoon. Climate Dynamics, 40(3-4), DOI:10.1007/s00382-012-1347-7.
- Bollasina, Massimo, and Yi Ming, November 2013: The role of land-surface processes in modulating the Indian monsoon annual cycle.Climate Dynamics, 41(9-10), DOI:10.1007/s00382-012-1634-3.
- Bollasina, Massimo, Yi Ming, and V Ramaswamy, July 2013: Earlier onset of the Indian Monsoon in the late 20th century: The role of anthropogenic aerosols. Geophysical Research Letters, 40(14), DOI:10.1002/grl.50719.
- Hill, S A., and Yi Ming, August 2012: Nonlinear climate response to regional brightening of tropical marine stratocumulus. Geophysical Research Letters, 39, L15707, DOI:10.1029/2012GL052064.
- Ming, Yi, and V Ramaswamy, November 2012: Nonlocal component of radiative flux perturbation. Geophysical Research Letters, 39, L22706, DOI:10.1029/2012GL054050.
- Ocko, I B., V Ramaswamy, Paul Ginoux, Yi Ming, and Larry W Horowitz, October 2012: Sensitivity of scattering and absorbing aerosol direct radiative forcing to physical climate factors. Journal of Geophysical Research, 117, D20203, DOI:10.1029/2012JD018019.
- Persad, Geeta, Yi Ming, and V Ramaswamy, April 2012: Tropical tropospheric-only responses to absorbing aerosols. Journal of Climate,25(7), DOI:10.1175/JCLI-D-11-00122.1.
- Bollasina, Massimo, Yi Ming, and V Ramaswamy, October 2011: Anthropogenic aerosols and the weakening of the South Asian summer monsoon. Science, 334(6055), DOI:10.1126/science.1204994.