Usually when we think of global warming, we are led to believe that it is caused primarily by increasing greenhouse gases. After all, that is what all the fuss is about in Washington DC these days. But is that entirely true?

After all there are lots of other things going on all the while. For instance, to what degree has the global temperature record in recent decades been influenced by the variability in aerosol emissions?

This question has been the subject of a series of articles in recent years by Martin Wild and colleagues which look at the impacts of (primarily sulfate) aerosols on the earth’s climate. They typically conclude that sulfate aerosols play a larger role in multi-decadal climate fluctuations than the climate models generally give them credit for. And that models’ inability to properly handle the climate aspects of aerosols “may hamper the predictive skills of these models to project near future climate evolution.”

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For another look at how the results of the latest work by Kyle Swanson and Anastasios Tsonis—which show, among other things, that the earth’s climate most likely shifted into a state which could result in a slowed rate of global warming lasting for another decade or so—are impacting the processes (both scientific and political) of climate change, see this piece over at MasterResource.org.

“Has the climate recently shifted?” is the title of a just-published paper in Geophysical Research Letters by researchers Kyle Swanson and Anastasios Tsonis from the University of Wisconsin-Milwaukee. Their examination of this topic was undoubtedly prompted by the recent behavior of global temperature which shows that the rate of warming has dramatically slowed during the past 7-12 years.

Updating a methodology that they had previously developed and used to identify several changes in the climate state that occurred during the 20th century, Swanson and Tsonis examined the temperature data from recent years to see if another state change had taken place:

Here, a new and improved means to quantify the coupling between climate modes confirms that another synchronization of these modes, followed by an increase in coupling occurred in 2001/02. This suggests that a break in the global mean temperature trend from the consistent warming over the 1976/77–2001/02 period may have occurred.

In other words, the authors think that they have identified another in a string of break points that signal a change in the general state of the earth’s climate.

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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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