Arctic Aerosols Indicate Melting Ice Not Caused By CO2

NASA researchers report that much of the atmospheric warming observed in the Arctic since 1976 may be due to changes in tiny airborne particles called aerosols. Though greenhouse gases are invariably blamed for global climate change, and the shrinking Arctic ice cover in particular, this new research indicates that as much as half the warming in the Arctic can be attributed to sort lived particulate pollution—basically soot. Unlike the dreaded gas, CO2, aerosols do not stay in the atmosphere very long, suggesting that the effects of any warming caused by aerosols would quickly be reversed if their emissions ceased.

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. In a report published in the April issue of Nature Geoscience, 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 Arctic is especially subject to aerosol effects because the planet's main industrialized areas are all in the northern hemisphere and because there's not much precipitation to cleanse the air clean. “Right now, in the mid-latitudes of the Northern Hemisphere and in the Arctic, the impact of aerosols is just as strong as that of the greenhouse gases,”said Shindell.

“We will have very little leverage over climate in the next couple of decades if we're just looking at carbon dioxide,” Shindell said. “If we want to try to stop the Arctic summer sea ice from melting completely over the next few decades, we're much better off looking at aerosols and ozone.”

“This is an important model study, raising lots of great questions that will need to be investigated with field research,” said Loretta Mickley, an atmospheric chemist from Harvard University, Cambridge, Mass. who was not directly involved in the NASA research. Understanding how aerosols behave in the atmosphere is still very much a work-in-progress, she noted, and every model needs to be compared rigorously to real life observations. But the science behind Shindell’s results should be taken seriously.

It is noteworthy that aerosols were one of the categories of contributing factors that the IPCC's 2007 report cited as poorly understood. It looks like they were right about that, and will have to significantly rework their climate models in the face of this new evidence. Of course, climate researchers are constantly trying to improve their models, as the recent spate of climate prediction updates indicate. Scientists from the EU and around the world have stated that we are now in for several decades of global cooling, not warming.

There are several varieties of aerosols. Previous research has shown that two types, sulfates and black carbon, are intimately involved in regulating climate change. While both of these particulates are produced by nature, they can also be produced by human activity. Sulfates, which are emitted from burning of coal and oil, scatter incoming solar radiation and have a net cooling effect on climate. Black carbon, on the other hand—which is emitted from burning diesel oil and biofuels—absorbs incoming radiation and warms the atmosphere.

An electron microscope was used to capture these images of black carbon attached to sulfate particles. The spherical structures in image A are sulfates; the arrows point to smaller chains of black carbon. Black carbon is shown in detail in image B. Image C shows fly ash, a product of coal-combustion, that's often found in association with black carbon. Images by Peter Buseck, Arizona State University.

This particulate driven component of global warming is not new—the brown clouds of Asia have been a know problem for more than a decade, and have been reported by the UNEP. Reports have indicated that much of the warming climate in China is being caused by clouds of dark particulates produced by dirty industry and rural burning of biomass.

The image above shows a satellite view of the Asian Brown Cloud. The three photographs on the right show images of (a) dense haze in the Arabian Sea, (b) trade cumuli embedded in the haze and (c) the pristine southern Indian Ocean (click on the image for a larger view). Source N. Kuring, NASA.

In a demonstration of the law of unexpected consequences, the success of anti-pollution laws may actually be responsible for part of global temperature rise over the past three decades. The United States and European countries passed a series of laws that reduced sulfate emissions by 50% since the 1970s. While improving air quality, curbing acid rain and generally improving public health, an inadvertent result has been less atmospheric cooling from sulfates.

Other scientists have recently suggested that it's not just the Arctic that is subject to aerosol effects. Scientists from the US National Oceanic and Atmospheric Administration have said, in a paper in Science, that aerosol levels from dust storms and volcanoes alone would account for much of the temperature rise seen in the Atlantic ocean during the past three decades. Using 26 years of satellite data to drive a simple physical model for estimating ocean temperature response, their results suggest that 69% of the recent upward trend in northern tropical Atlantic Ocean temperatures is a response to regional variability in aerosols, leaving almost no part for carbon to play.

John Holdren, President Obama's new science adviser, has just suggested that the subject of "geoengineering"—intentionally trying to modifying Earth's climate on a gigantic scale—must be considered as a countermeasure to global warming. One measure put forward by geoengineering advocates is the deliberate injection of sulfur particulates into the atmosphere. Others have suggested we should simply let China and India continue to belch sulfur into the atmosphere.

Anyone who watched last year's Olympic games will recall the choking smog that filled Beijing's air on several occasions, causing many athletes to worry about the effects of competing in such a polluted atmosphere. Now imaging living in a city with similar environmental problems, breathing air that will most certainly shorten your life. The truly good news here is that we have effective technology for filtering particulates from industrial and automotive sources. Widespread adoption of this technology by Asian nations could not only put a damper on global warming concerns but greatly improve their citizen's quality of life.

Meanwhile, the UK's The Register speculates that Dr Shindell's position at NASA's Goddard Institute must now be a potentially stressful one. “His boss, Dr James Hansen, is more or less the father of the carbon-driven global warming menace,” the online edition reported, “[h]e won't be pleased at the suggestion that carbon emissions may not be such an overriding concern after all.” Politics and personal prejudice interfering with government sponsored research? Sadly, there is nothing new in that.

Be safe, enjoy the interglacial and stay skeptical.