Friday, March 2, 2007

Climate Change: Smoke & Mirrors?

Smoke & Mirrors

New studies show that aerosol particles have a far greater impact on global climate than was originally believed. This is due to how aerosols change the pattern of heating and cooling regionally.

Aerosols impact on surface heating depends largely on the type of aerosol. Some are very effective reflectors leading to localized cooling. These type of aerosols were the more widely known and studied until recently. The most common reflective aerosol is derived from sulfur emissions from power plants which were greatly reduced by the late 1990s by sulfur reduction regulations.

The other type of aerosol absorbs heat and can lead to warming over a region. These types, called black carbon, are more typical of fossil fuel (and other fire) emissions. A lot less is know about the hows and wheres of this aerosol with respect to localized warming.

What the latest round of studies show is that these aerosols, by altering the regional pattern of heating and cooling, have a larger (zonal and global) impact by altering the patterns of winds and ocean circulation.

What does this mean for anthropogenic climate change?

Well it potentially complicates attribution to the source of climate change in that more seems to be attributable to changes in circulation stemming from these aerosols but not necessarily. But this complication does not necessarily reduce the impact on climate of greenhouse gases, only complicates the picture. That said these studies only add fuel to the fire since humans are likely overwhelmingly responsible for the increase in aerosol load due to fossil fuel and other burning.

What does this mean for alternative fuels?

Another complication since alternative fuels are no less likely to produce the aerosols when burned than are fossil fuels. This speaks to increasing solar and wind power and centralizing burning fuel use so as to reduce emissions of particulates.

Excepts from :


New studies show aerosols from burning fuels altering everything from rainfall to great ocean currents, with effects that can girdle the globe

Figure 1

The microscopic aerosol particle has long been recognized as a mighty agent of climate change. At a micrometer or less in size, this bit of combustion crud from power plant, tailpipe, or farmer's fire can reflect sunlight back to space and cool the polluted eastern United States. Or it could suppress rainfall over smoggy Houston, Texas. But for years, atmospheric scientists generally assumed that pollutant aerosols worked locally or regionally. Most dramatically, the brown haze over Asia weakens both the Indian and Asian monsoons that bring essential rains to the continent.

So far, the expanding reach of aerosols is being documented primarily in global climate models, with tantalizing parallels with what's been happening in the real world in recent decades. In the case of Australia, Rotstayn and colleagues ran a global climate model to simulate the changing climate of the 20th century. In the past decade or two, production of aerosols over Asia has soared as developing economies cranked up, especially those of India and China. When Rotstayn and colleagues plugged increasing Asian aerosols into their model along with increasing greenhouse gases, rainfall and cloud cover increased over Australia, especially in the northwest. Yet when they omitted the distant aerosols, rainfall and cloudiness decreased, contrary to observations.

North American aerosols seem to hold sway over a far more massive moisture flow: the great "conveyor belt" of currents that carries heat from the Southern Hemisphere into the far North Atlantic, called the meridional overturning circulation (MOC). That's according to modeling reported in a January 2006 paper in Geophysical Research Letters (GRL) by Thomas Delworth and Keith Dixon of the Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey. Increasing greenhouse gases should be slowing the MOC, according to a raft of models, but in their model, Delworth and Dixon found that aerosols counter the effect of the strengthening greenhouse on the MOC. By counteracting the greenhouse's warming and its enhancement of precipitation at high latitudes, the aerosols have delayed the MOC's slowing by roughly 40 years, they find. Modeler Wenju Cai of CSIRO Aspendale and colleagues found a similar aerosol-induced MOC slowing in their model, as they reported last No vember in GRL.

Untangling the web of aerosol effects will take a while. In the meantime, aerosol emissions are changing. North American and western European hazes have faded as developed countries reduced their emissions for health reasons. When will the developing nations of Asia follow suit? What will be the effects? Researchers will likely still be playing catch-up as the air clears.