Guest Commentary

Joel Schwartz
Visiting Fellow
American Enterprise Institute

What happens to future air pollution if the climate warms? Efthimios Tagaris and colleagues (Tagaris et al., 2007) have come closer than anyone before them in providing a realistic answer to this question. They predict that between 2001 and 2050, mean summer 8-hour ozone levels over the U.S. will decline by 11% to 28%, depending on the region, with an average decline of 20%. Fine particulate matter (PM2.5) will decline by 9% to 32%, with an average decline of 23%.

Tagaris et al.’s results stand in marked contrast to previous studies, nearly all of which predict higher air pollution levels over the U.S. in the future (e.g., Knowlton et al. (2004), Mickley et al. (2004), and Sitch et al. (2007)).

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In 1998, Balling et al. published an article in Climate Research dealing with summer and winter warming rates in several widely-used gridded temperature time series. As seen in Figure 1 below, the Balling crew (which includes several World Climate Report team members) found that winters were warming far more than summers, based on near-surface thermometer records, for a large part of northern and central Asia over the period 1946-1995. We repeated the analyses for the satellite-based lower-tropospheric temperature measurements over the period 1979-1995 and found the same red blob (wamer temperatures) over northern and central Asia. We suggested in the article that the build-up of greenhouse gases would most impact the coldest and driest air masses of the world, which just happen to be the air masses that cover northern and central Asia in the winter. Elevated greenhouse gas concentrations in warm and moist air masses would have less of an effect given the overwhelming greenhouse effect of naturally occurring water vapor. We had produced what appeared to be a smoking gun – the greenhouse “fingerprint” looked rather obvious in our analyses. Of course, finding that the coldest and driest air masses of the planet were warming slightly is seen by some as a blessing and not a great cause for concern – are residents of northern Siberia really worried about their winters being a bit warmer?

Figure 1. Seasonal difference (winter minus summer) in temperature trends (°C per decade) for the thermometer-based near-surface data over the period 1946-1995 (from Balling et al., 1998).

Well, the smoking gun has become a bit cloudier given a recent article in Nature entitled “Warming trends in Asia amplified by brown cloud solar absorption.”

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That appears to be what is happening, judging from three papers in the May 6 issue of Science.

These three papers argue that the amount of incoming solar radiation reaching the surface of the earth has increased dramatically in the last two decades. While the values vary from paper to paper, in toto the new studies suggest that the increase in solar radiation absorbed at the earth’s surface had almost 10 times as much warming power during that time as the concurrent increases in carbon dioxide, the main global warming gas. Therefore, the warming observed over the past 20 years must have little to do with changes in greenhouse gases.

Before you kill the greenhouse effect, please note that we think this is a lot of hooey. But if you accept these results, that’s where you have to go.
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There are three primary tools that global warming alarmists use in their arguments that anthropogenic enhancements to the world’s naturally occurring greenhouse effect are causing the climate to behave as it never has before and this will ultimately be catastrophic. They are 1) the “hockey stick” temperature reconstruction for the past 1,000 years, which purports to show that left to its own devices, the global average temperature changes very little, yet it jumps at the slightest provocation from mankind; 2) the IPCC 21st century temperature projections which show a range of possible warming by century’s end that spans 1.4 to 5.8ºC (of course, the alarmist attention is given to the high end projection); and 3) the sea ice in the Arctic Ocean has been steadily declining for the past several decades and will be entirely gone in the summertime in the next 50 years as a result of rising levels of atmospheric greenhouse gases. With the latest publication by NASA scientists Dorothy Koch and James Hansen, the final of these arguments now joins the first two in being soundly repudiated.
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