Human-caused sulfur aerosols cause cooling. Human-caused black carbon emissions absorb more sunlight and cause heating. Picture the carbon settling on ice and absorbing sunlight rather than letting the ice reflect sunlight back into space. Well, regulations in Western countries reduced sulfur aerosol emissions and therefore reduced the amount of human-caused cooling. Sulfur aerosols emissions and carbon particulate emissions play big roles in temperature changes. Global warming isn't just about carbon dioxide.
Though greenhouse gases are invariably at the center of discussions about global climate change, new NASA research suggests that much of the atmospheric warming observed in the Arctic since 1976 may be due to changes in tiny airborne particles called aerosols.
It matters where the pollution occurs since the particulates do not stay airborne for long.
Emitted by natural and human sources, aerosols can directly influence climate by reflecting or absorbing the sun's radiation. The small particles also affect climate indirectly by seeding clouds and changing cloud properties, such as reflectivity.
A new study, led by climate scientist Drew Shindell of the NASA Goddard Institute for Space Studies, New York, used a coupled ocean-atmosphere model to investigate how sensitive different regional climates are to changes in levels of carbon dioxide, ozone, and aerosols.
The researchers found that the mid and high latitudes are especially responsive to changes in the level of aerosols. Indeed, the model suggests aerosols likely account for 45 percent or more of the warming that has occurred in the Arctic during the last three decades. The results were published in the April issue of Nature Geoscience.
Carbon particulates cause cancer, respiratory disease, and heart disease. So efforts to cut carbon particulates pollution from coal electric plants, diesel engines, and other industrial activity would improve our health as well as keep more water bound up as ice.
Though there are several varieties of aerosols, previous research has shown that two types -- sulfates and black carbon -- play an especially critical role in regulating climate change. Both are products of human activity.
Sulfates, which come primarily from the burning of coal and oil, scatter incoming solar radiation and have a net cooling effect on climate. Over the past three decades, the United States and European countries have passed a series of laws that have reduced sulfate emissions by 50 percent. While improving air quality and aiding public health, the result has been less atmospheric cooling from sulfates.
One problem is that much of the carbon particulate pollution is coming from countries (most notably China) which place little importance on improving air quality. Parenthetically, Western countries have fed this process by exporting a lot of their manufacturing to a China that allows far more pollution from the same amount of manufacturing activity.
Increased black carbon particulate emissions from Asia have increased absorption of solar radiation while decreased sulfur aerosols from Western countries has cut the cooling effect of Western pollution.
At the same time, black carbon emissions have steadily risen, largely because of increasing emissions from Asia. Black carbon -- small, soot-like particles produced by industrial processes and the combustion of diesel and biofuels -- absorb incoming solar radiation and have a strong warming influence on the atmosphere.
The Northern Hemisphere has far more industrial activity. So the Arctic's temperature has risen more than the Antarctic's temperature.
The regions of Earth that showed the strongest responses to aerosols in the model are the same regions that have witnessed the greatest real-world temperature increases since 1976. The Arctic region has seen its surface air temperatures increase by 1.5 C (2.7 F) since the mid-1970s. In the Antarctic, where aerosols play less of a role, the surface air temperature has increased about 0.35 C (0.6 F).
China's pollution is on a massive scale. I see little chance we can convince the Chinese to cut their particulate pollution any time soon. But Western countries could at least cut their own particulate pollution and gain health advantages in the process.
Gregory Benford suggests we could cool the planet with silicon dioxide rather than sulfur as the cooling aerosol. Combine the silicon dioxide with a huge reduction in carbon particulates and we could stop the ice melt plus improve our health.
|Share |||Randall Parker, 2009 April 11 06:11 PM Climate Trends|