Of course a period of cooling from an increase in aerosols is possible; the IPCC site discusses this in some detail, and there was at least one Science or Nature paper on a very relevant case study. This happened when Mt Pinatubo erupted in the Phillipines, throwing many tons of fine ash in the atmosphere. Global mean temperatures did briefly cool (for two or three years). The interesting result, however, was that the ash essentially fell out of atmospheric solution with time. Moreover, the trend of global mean temperature increases shot right back up. The trendline didn't have a different trajectory, just a small blip. Thus, the cooling effect was masked of the warming trend. To pick an arbitrary date such as 2030 and say that year will be cooler doesn't invalidate the volanic aerosols might have a brief interruptive impact on global mean temperature. Any "trend" would be extremely brief and unimportant over a decadal or century timescale.
The second big aerosol negative forcing comes from burning dirty fuel (eg, coal, diesel, countries that allow cars without efficient emissions systems). This effect is like a small constantly rumbling Pinatubo. However, countries like the US and Canada are very interested in making cities like Los Angeles and Houston have cleaner air quality to reduce health problems, and particulate pollution is part of these localized air quality problems. By gradually removing aerosols generated by combustion processes, we are indeed cleaning the atmosphere, but we're also adding fewer aerosols and effectively reducing the opacity of the aerosol mask -- and allowing the atmosphere to get warmer faster. I'm not suggesting that we continue to distribute aerosols from combustion. But this second effect would not realistically generate a "cooling trend." On Jun 28, 2006, at 5:36 PM, Wil Burns wrote: > My suggestion, Paul, is that you go to the library and check out a > book on > climatology and do some bedtime reading about the impacts of > aerosols and > volcanic phenomena on temperature trends; unfortunately, the fairly > effective job that the Clean Air Act in the U.S. and equivalent > legislation > in other countries, is doing to reduce concentrations of aerosols > means that > we won't have this buffer in the future (and, as Hansen, etc. have > pointed > out; the GCMs that incorporate volcanic activity and aerosols > pretty closely > approximate temperatures over the past century). You might also > consult > realclimate.org's excellent critique of the egregious flaws in > Lindzen's > interpretation of the data. > > * > http://www.realclimate.org/index.php/archives/2006/04/open-thread- > on-lindzen > -op-ed-in-wsj/ > * > http://www.realclimate.org/index.php/archives/2006/04/lindzen-point- > by-point > / > > Hell, Hansen's drubbing of Lindzen's screeds in 1999 are also > germane on > this: http://www.giss.nasa.gov/edu/gwdebate/ > > > Dr. Wil Burns, Co-Chair > American Society of International Law - International Environmental > Law > Group > 1702 Arlington Blvd. > El Cerrito, CA 94530 USA > Ph: 650.281.9126 > Fax: 214.580.9415 > [EMAIL PROTECTED] > > > -----Original Message----- > From: Ecological Society of America: grants, jobs, news > [mailto:[EMAIL PROTECTED] On Behalf Of Paul Cherubini > Sent: Wednesday, June 28, 2006 3:01 PM > To: ECOLOG-L@LISTSERV.UMD.EDU > Subject: Re: Wall Street Journal op-ed on "An Inconvenient Truth" > > Richard Lindzen pointed out that "global mean temperatures decreased > between 1940 and the early '70s, despite increases in the levels of > carbon dioxide in the atmosphere. Lindzen suggests this period > of global cooling was due to "a natural fluctuation in the climate > system." > > NOAA climate data http://lwf.ncdc.noaa.gov/oa/climate/research/cag3/ > na.html > indicates mean temperatures in the USA also declined between > 1939-1972: > http://i5.photobucket.com/albums/y189/mastertech/ustemp.jpg > > Thus, thanks to the balanced information provided by Lindzen, > Wall Street Journal readers realize that another decades long period > of global cooling might be just around the corner. > > Paul Cherubini > El Dorado, Calif.
