We occasionally highlight articles from the scientific literature showing that the cooling impact of aerosol emissions from human activities has been overestimated. Such findings are important because they mean that warming from greenhouse gases has been similarly overestimated.

Climate models rely on aerosol cooling to keep warming in check—otherwise they predict far more warming to occur than has been observed. So, if aerosols produce less cooling, then this means that the climate models must compensate by producing less warming from greenhouse gases than they do presently. If they don’t, they will fail to replicate the observed temperature history.

In a paper soon to appear in Geophysical Research Letters, an M.I.T. research team led by Jason Cohen finds that by including in climate models aerosol-influencing processes that take place in urban environments, the total global-average negative forcing (i.e., cooling pressure) from aerosols is significantly less than when these urban processes are not considered—as is currently the case with all climate models.

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A few weeks back, in our article Biggest Drop in U.S. Greenhouse Gas Emissions, we promised to take a look at the implications of a new study that calculated the impact on the earth’s greenhouse effect from the extraction and use of natural gas produced from deep underground shale beds (through a process known as hydraulic fracturing, or “fracking”). The study was conducted by a research team from Cornell University led by Dr. Robert Howarth, and its conclusions were quite surprising:

“Compared to coal, the [greenhouse gas] footprint of shale gas is at least 20% greater and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years.”

The reason that this is surprising (and has a lot of people talking) is that natural gas has long been considered the most “climate friendly” of all the fossil fuels and a potential “bridge” to a low carbon future. The Howarth et al. study now threatens natural gas’s most favored status (at least among climate change-fearing types).

Over at the free market energy blog Master Resource, WCR’s Chip Knappenberger takes a look at the Howarth et al. study, as well as its many criticisms.

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In 2009, greenhouse gas emissions in the U.S. experienced their biggest drop since the U.S. Energy Information Administration began tracking them during the 1990-2009 timeframe.

The EIA’s latest numbers on greenhouse gas emissions can be found in their just released report “Emissions of Greenhouse Gases in the United States 2009.”

The EIA starts out with this summary:

Total U.S. anthropogenic (human-caused) greenhouse gas emissions in 2009 were 5.8 percent below the 2008 total. The decline in total emissions—from 6,983 million metric tons carbon dioxide equivalent (MMTCO2e) in 2008 to 6,576 MMTCO2e in 2009—was the largest since emissions have been tracked over the 1990-2009 time frame. It was largely the result of a 419-MMTCO2e drop in carbon dioxide (CO2) emissions (7.1 percent).

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We see many articles like the following two that show more evidence of a solar control on climate even at the regional scale.

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We have written about the solar control on climate many times in the past, and to say the least, the debate continues to rage regarding the solar influence of Earth’s climate. IPCC has been luke warm on the subject, stating in the Technical Summary that “Solar irradiance contributions to global average radiative forcing are considerably smaller than the contribution of increases in greenhouse gases over the industrial period.” Two articles have appeared recently that provide even more evidence that variations in solar output have a profound impact on regional, hemispheric, and global climatic variations.

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One of the enduring pillars of the climate change issue is that the temperature of the Earth is increasing at an unprecedented rate … we’ve heard it a million times over the past few decades. However, it is well known that the temperature of the Earth has not increased over the past decade, and the lack of recent warming is now receiving serious consideration in the leading scientific journals. Two recent articles are of particular interest to us at World Climate Report.

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Nicola Scafetta is an atmospheric scientist with Duke University’s highly regarded Department of Physics, and in a recent article in the Journal of Atmospheric and Solar-Terrestrial Physics, he provides an excellent introduction for us stating “Estimating the solar contribution to global mean air surface temperature change is fundamental for evaluating the anthropogenic contribution to climate change. This is regarded as one of the most important issues of our time. While some theoretical climate model studies indicate that the solar variability has little effect on climate (these studies estimate that less than 10% of the global warming observed since 1900 is due to the sun), several empirical studies suggest that large climatic variations are well synchronized with solar variations and, therefore, climate is quite sensitive to solar changes.”

No doubt about it – a considerable debate rages in the climate community about the role of the sun in controlling the temperature of the earth. There are many leading climate scientists who believe that the sun’s impact is negligible while others believe the sun’s control on earth’s temperature is substantial. Both groups publish regularly, and there is no end of empirical and theoretical evidence to support both camps. If you think the debate is over in the world of climate change, look at the literature on solar control of climate, and you will immediately conclude the debate is as lively as ever.

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A couple of months back, there was a discussion taking place over at Joe Romm’s ClimateProgress blog concerning a report that the earth’s ability to take-up atmospheric carbon dioxide was declining. A declining CO2 sink, of course, meant that things climatological were going to be even worse than expected, because a growing proportion of anthropogenic CO2 emissions were going to remain in the atmosphere, thus pushing the rise of CO2 concentrations and the degree of climate change higher.

At the time, an alert reader pointed out to Joe Romm that there was in fact, no indication from data and observations that a larger percentage of human CO2 emissions were ending up in the atmosphere. In fact, the data showed that the fraction of CO2 emitted into the atmospheric by human activities has remained constant for the past 40 years.

This fact runs directly counter to the idea that the earth’s natural CO2 sinks are weakening—instead it indicates that natural sinks have been expanding as anthropogenic CO2 emissions have increased. After all, in order to keep the airborne fraction of CO2 emissions constant over time, increasing anthropogenic CO2 emissions must be countered by an increasing CO2 sink.

Joe Romm was a bit dismissive (to say the least) of this line of argument.

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One of the indisputable facts in the field of global climate change is that the atmospheric build-up of methane (CH4) has been, over the past few decades, occurring much more slowly than all predictions as to its behavior (Figure 1). Since methane is a particularly potent greenhouse gas (thought to have about 25 times the warming power of CO2), emissions scenarios which fail to track methane will struggle to well-replicate the total climate forcing, likely erring on the high side—and feeding too much forcing into climate models leads to too much global warming coming out of them.

Figure 1. Atmospheric methane concentrations, 1985-2008, with the IPCC methane projections overlaid (adapted from: Dlugokencky et al., 2009)

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Over at MasterResource.org is an article looking at EPA’s Proposed Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Sections 202(a) of the Clean Air Act, and wonders whether or not the EPA has set its sight on the correct gas. The EPA’s focus seems to be on carbon dioxide, but a very strong case can be made that the net effect of increasing atmospheric carbon dioxide concentrations may not be so bad (in fact, it may be quite good). So instead of risking the possibility that if they consider the climate impacts of CO2 alone they very well may not be able to build a case for an “endangerment to public health or welfare,” the EPA has lumped CO2 together with five other greenhouse gases thus watering down the positive aspects of CO2 with the potential negative ones from the other gases.

The MasterResource piece argues that to make a fair assessment of its effect on climate, CO2 should be unlumped and considered on its own.