4/8/2009, "Half of recent arctic warming may not be due to greenhouse gases," Houston Chronicle, Eric Berger
"According to a new report, half of the recent Arctic warming is not due to greenhouse gases, but rather clean air policies.
That’s the conclusion of two scientists in a new Nature Geoscience paper (see abstract), which is more deeply outlined in this NASA news release.
Here’s a quote from lead author Drew Shindell of the NASA Goddard Institute for Space Studies:
“There’s a tendency to think of aerosols as small players, but they’re not,” said Shindell. “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.” “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.”.The following graphic [above] shows how clean air regulations passed in the 1970s have likely accelerated warming by diminishing the cooling effect of sulfates.
[Ed. note: PNAS study 7/19/2011 validated the results. Cited global cooling effects of sulfates being lost via air pollution policies: "The post 1970 period of warming...is driven by efforts to reduce air pollution in general and acid deposition in particular, which cause sulfur emissions to decline while the concentration of greenhouse gases continues to rise (7)."...]
(continuing): "the notion that global warming is causing an accelerating, headlong retreat of the Arctic sea ice and driving the polar bear to imminent death…well, these notions just aren’t wholly correct anymore.
The study suggests that as much as half of the recent Arctic melting is not due to global warming, but rather to other factors. This report does not speak to global temperatures, but rather the Northern Hemisphere. And it does not suggest that global warming has played no role in the Arctic warming.
All the same, this is potentially a huge blow to those who advocate immediate action on controlling carbon dioxide.
Finally, for those of you who hate James Hansen: Please note that the author of this study works for Hansen."
Image above from Nasa.gov.
George Bush #1 signs Clean Air Act amendments in 1990, making rules stricter than 1970 and 1977 versions. Top left, clapping, Bush EPA chief William Reilly, plucked from his job as WWF president by Bush.
3/22/2009, "Climate response to regional radiative forcing during the twentieth century," Nature Geoscience, Drew Shindell1 and Greg Faluvegi1
"Regional climate change can arise from three different effects.... The relative importance of these effects is not clear, particularly because neither the response to regional forcings nor the regional forcings themselves are well known for the twentieth century. Here we investigate the sensitivity of regional climate to changes in carbon dioxide, black carbon aerosols, sulphate aerosols and ozone in the tropics, mid-latitudes and polar regions, using a coupled ocean–atmosphere model. We find that mid- and high-latitude climate is quite sensitive to the location of the forcing. Using these relationships between forcing and response along with observations of twentieth century climate change, we reconstruct radiative forcing from aerosols in space and time. Our reconstructions broadly agree with historical emissions estimates, and can explain the differences between observed changes in Arctic temperatures and expectations from non-aerosol forcings plus unforced variability. We conclude that decreasing concentrations of sulphate aerosols and increasing concentrations of black carbon have substantially contributed to rapid Arctic warming during the past three decades." [1979-2009]
- "NASA Goddard Institute for Space Studies (GISS) and Columbia University, New York 10025, USA"
4/8/2009, "Aerosols May Drive a Significant Portion of Arctic Warming," nasa.gov/topics
"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.
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....
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.
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 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)....
Since decreasing amounts of sulfates and increasing amounts of black carbon both encourage warming, temperature increases can be especially rapid. The build-up of aerosols also triggers positive feedback cycles that further accelerate warming as snow and ice cover retreat.
In the Antarctic, in contrast, the impact of sulfates and black carbon is minimized because of the continent’s isolation from major population centers and the emissions they produce.
"There's a tendency to think of aerosols as small players, but they're not," said Shindell. "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."
The growing recognition that aerosols may play a larger climate role can have implications for policymakers.
"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.""...
Clean Air Acts of 1970, 1977 and 1990, epa.gov.
July 19, 2011 PNAS study notes post 1970 warming "is driven by efforts to reduce air pollution in general and acid deposition in particular, which cause sulfur emissions to decline."
7/19/2011, "Reconciling anthropogenic climate change with observed temperature 1998–2008," PNAS.org
"The post 1970 period of warming, which constitutes a significant portion of the increase in global surface temperature since the mid 20th century, is driven by efforts to reduce air pollution in general and acid deposition in particular, which cause sulfur emissions to decline while the concentration of greenhouse gases continues to rise (7)."...
In a section titled "Results" the PNAS study says cooling sulfur emissions rose somewhat after 2002 due to extreme acceleration of China's coal use, which "partly reverses a period of declining sulfur emissions that had a warming effect of 0.19 W/m2 between 1990 and 2002." (Subhead "Results"):
"Increasing emissions and concentrations of carbon dioxide receive considerable attention, but our analyses identify an important change in another pathway for anthropogenic climate change—a rapid rise in anthropogenic sulfur emissions driven by large increases in coal consumption in Asia in general, and China in particular. Chinese coal consumption more than doubles in the 4 y from 2003 to 2007 (the previous doubling takes 22 y, 1980–2002). In this four year period, Chinese coal consumption accounts for 77% of the 26% rise in global coal consumption (8). These increases are large relative to previous growth rates. For example, global coal consumption increases only 27% in the twenty two years between 1980 and 2002 (8). Because of the resultant increase in anthropogenic sulfur emissions, there is a 0.06 W/m2 (absolute) increase in their cooling effect since 2002 (Fig. 1). This increase partly reverses a period of declining sulfur emissions that had a warming effect of 0.19 W/m2 between 1990 and 2002."
For reference, the purpose of this 2011 PNAS study was to address "the lack of a clear increase in global surface temperature between 1998 and 2008:"
"Data for global surface temperature indicate little warming between 1998 and 2008 (1). Furthermore, global surface temperature declines 0.2 °C between 2005 and 2008. Although temperature increases in 2009 and 2010, the lack of a clear increase in global surface temperature between 1998 and 2008 (1), combined with rising concentrations of atmospheric CO2 and other greenhouse gases, prompts some popular commentators (2, 3) to doubt the existing understanding of the relationship among radiative forcing, internal variability, and global surface temperature. This seeming disconnect may be one reason why the public is increasingly sceptical about anthropogenic climate change (4)."...