Good news/bad news on global warming record
It appears that climate change deniers may have China to thank for the hiatus in global warming between 1999 and 2008 that has, hitherto, not been fully explained.
New research published in the Proceedings of the the US Academy of Sciences postulates that a huge leap in sulfur emissions - together with the cyclical decline in solar activity and a change from El Nino to La Nina conditions - was the reason behind the levelling out of average temperatures over the decade.
And the main cause of the surge in sulfur emissions? The massive build-up of coal-fired power generating capacity in China.
According International Energy Agency figures Chinese coal consumption more than doubled in just four years form 2003 to 2007 whereas the previous doubling took 22 years. Over this four year period, Chinese coal consumption accounted for 77 percent of the 26 percent rise in global coal consumption.
The researchers say there was no statistically significant effect on surface temperature from either a reduction in water vapour or an increase in black carbon. They say there is a high degree of certainty that the amount of sulfur in the atmosphere, deflecting solar radiation, accounts for the fact that "anthropogenic activities that warm and cool the planet largely cancel after 1998, which allows natural variables to play a more significant role."
The research paper points out that the same phenomena can be observed in an earlier period of stable global temperatures, coinciding with rising coal use in the US and Europe: "In-sample simulations indicate that temperature does not rise between the 1940s and 1970s because the cooling effects of sulfur emissions rise slightly faster than the warming effect of greenhouse gases."
A naïve conclusion to this would be that burning coal is not such a bad thing after all but that would be to ignore the fact that sulfur emissions are the primary cause of acid rain and a significant contributor to human respiratory disease.
The new study's lead researcher, Robert Kaufmann of Boston University, has been quick to point out that China is well aware of these problem and is actively deploying sulfur scrubbers in its coal plants, which has some worrying implications for the climate change if recent history repeats itself.
One of the concisions of the new paper is that: "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."
China claims that it exceeded its target of reducing air pollution by 10 percent during the last Five Year Plan, from 2006-2010. With regard to sulfur dioxide (S02) emissions in particular, this is supported by observations from NASA's Aura satellite. From 2005 to 2007 it detracted substantial increases in SO2 over several areas in northern China where large coal-fired power plants were starting operations. From 2008, however, a dramatic reduction in SO2 was observed, confirming the effectiveness of the flue-gas desulfurization devices in reducing SO2 emissions, which likely became operational between 2007 and 2008.
These findings will, of course, being taken as grist to the mill for those who deny that the climate is changing, or that human activity is driving it.
One issue that will not go away will be the ominous phrase that the study used "statistical models" that were different from the "models traditionally used" to simulate the Earth's climate. The IPCC set the argument on global warming back a couple of years when its modelling and statistical dataset were later found wanting.