There is a new paper which has appeared that demonstrates that geoengineering, although inadvertent, is already occurring (thanks to Kiminori Itoh for alerting us to it!).
The paper is
Hofmann, D., J. Barnes, M. O’Neill, M. Trudeau, and R. Neely (2009), Increase in background stratospheric aerosol observed with lidar at Mauna Loa Observatory and Boulder, Colorado, Geophys. Res. Lett., 36, L15808, doi:10.1029/2009GL039008.
The abstract reads
“The stratospheric aerosol layer has been monitored with lidars at Mauna Loa Observatory in Hawaii and Boulder in Colorado since 1975 and 2000, respectively. Following the Pinatubo volcanic eruption in June 1991, the global stratosphere has not been perturbed by a major volcanic eruption providing an unprecedented opportunity to study the background aerosol. Since about 2000, an increase of 4–7% per year in the aerosol backscatter in the altitude range 20–30 km has been detected at both Mauna Loa and Boulder. This increase is superimposed on a seasonal cycle with a winter maximum that is modulated by the quasi-biennial oscillation (QBO) in tropical winds. Of the three major causes for a stratospheric aerosol increase: volcanic emissions to the stratosphere, increased tropical upwelling, and an increase in anthropogenic sulfur gas emissions in the troposphere, it appears that a large increase in coal burning since 2002, mainly in China, is the likely source of sulfur dioxide that ultimately ends up as the sulfate aerosol responsible for the increased backscatter from the stratospheric aerosol layer. The results are consistent with 0.6–0.8% of tropospheric sulfur entering the stratosphere.”
Among the conclusions in the paper are
- “Background stratospheric aerosol conditions have existed since about 1996 (12 years).
- There is an increasing average trend in aerosol backscatter above 20 km after 2000 of about 4–7% per year (0.015–0.02 TgS per yr).
- China’s estimates of future coal use without removal of SO2 could result in a doubling of the ‘‘normal’’ 2000 level of background stratospheric aerosol by about 2022, resulting in a small perturbation to tropospheric temperatures and stratospheric ozone with a stratospheric background aerosol level comparable to about 5% of the Pinatubo volcanic aerosol maximum.”
This study further highlights the diverse ways that humans are altering the climate, as was summarized in NRC (2005). Proposals to deliberately geoengineer the climate system could learn from these inadvertent climate modifications. Predicting the consequences of the human alteration of the climate is much more complicated, and has a wider range of consequences, than has been claimed in the existing ideas to influence the global climate heating and cooling.