“The whims of foreign nations, not to mention Mother Nature, can completely offset any climate changes induced by U.S. greenhouse gas emissions reductions…. So, what’s the point of forcing Americans into different energy choices?”
A new study provides evidence that air pollution emanating from Asia will warm the U.S. as much or more than warming from U.S. greenhouse gas (GHG) emissions. The implication? Efforts by the U.S. Environmental Protection Agency (and otherwise) to mitigate anthropogenic climate change is moot.
If the future temperature rise in the U.S. is subject to the whims of Asian environmental and energy policy, then what sense does it make for Americans to have their energy choices regulated by efforts aimed at mitigating future temperature increases across the country—efforts which will have less of an impact on temperatures than the policies enacted across Asia?
Maybe the EPA should reconsider the perceived effectiveness of its greenhouse gas emission regulations—at least when it comes to impacting temperatures across the U.S.
A new study just published in the scientific journal Geophysical Research Letters is authored by a team led by Haiyan Teng from the National Center for Atmospheric Research, in Boulder, Colorado. The paper is titled “Potential Impacts of Asian Carbon Aerosols on Future US Warming.”
Skipping the details of this climate modeling study and cutting to the chase, here is the abstract of the paper:
This study uses an atmosphere-ocean fully coupled climate model to investigate possible remote impacts of Asian carbonaceous aerosols on US climate change. We took a 21st century mitigation scenario as a reference, and carried out three sets of sensitivity experiments in which the prescribed carbonaceous aerosol concentrations over a selected Asian domain are increased by a factor of two, six, and ten respectively during the period of 2005–2024.
The resulting enhancement of atmospheric solar absorption (only the direct effect of aerosols is included) over Asia induces tropospheric heating anomalies that force large-scale circulation changes which, averaged over the twenty-year period, add as much as an additional 0.4°C warming over the eastern US during winter and over most of the US during summer. Such remote impacts are confirmed by an atmosphere stand-alone experiment with specified heating anomalies over Asia that represent the direct effect of the carbon aerosols.
Usually, when considering the climate impact from carbon aerosol emissions (primarily in the form of black carbon, or soot), the effect is thought to be largely contained to the local or regional scale because the atmospheric lifetime of these particulates is only on the order of a week (before they are rained out). Since Asia lies on the far side of the Pacific Ocean—a distance which requires about a week for air masses to navigate—we usually aren’t overly concerned about the quality of Asian air or the quantity of junk that they emit into it. By the time it gets here, it has largely been naturally scrubbed clean.
But in the Teng et al. study, the authors find that, according to their climate model, the local heating of the atmosphere by the Asian carbon aerosols (which are quite good at absorbing sunlight) can impart changes to the character of the larger-scale atmospheric circulation patterns. And these changes to the broader atmospheric flow produce an effect on the weather patterns in the U.S. and thus induce a change in the climate here characterized by “0.4°C [surface air temperature] warming on average over the eastern US during winter and over almost the entire US during summer” averaged over the 2005–2024 period.
While most of the summer warming doesn’t start to kick in until Asian carbonaceous aerosol emissions are upped in the model to 10 times what they are today, the winter warming over the eastern half of the country is large (several tenths of a °C) even at twice the current rate of Asian emissions.
Now let’s revisit just how much “global warming” that stringent U.S. greenhouse gas emissions reductions may avoid averaged across the country.
In my Master Resource post “Climate Impacts of Waxman-Markey (the IPCC-based arithmetic of no gain)” I calculated that a more than 80% reduction of greenhouse gas emissions in the U.S. by the year 2050 would result in a reduction of global temperatures (from where they otherwise would be) of about 0.05°C. Since the U.S. is projected to warm slightly more than the global average (land warms faster than the oceans), a 0.05°C of global temperature reduction probably amounts to about 0.075°C of temperature “savings” averaged across the U.S., by the year 2050.
Comparing the amount of warming in the U.S. saved by reducing our greenhouse gas emissions by some 80% to the amount of warming added in the U.S. by increases in Asian black carbon (soot) aerosol emissions (at least according to Teng et al.) and there is no clear winner. Which points out the anemic effect that U.S. greenhouse gas reductions will have on the climate of the U.S. and just how easily the whims of foreign nations, not to mention Mother Nature, can completely offset any climate changes induced by our greenhouse gas emissions reductions.
And even if the traditional form of air pollution (e.g., soot) does not increase across Asia (a slim chance of that), greenhouse gases emitted there certainly will. For example, at the current growth rate, new greenhouse gas emissions from China will completely subsume an 80% reduction in U.S. greenhouse gas emission in just over a decade. Once again, pointing out that a reduction in domestic greenhouse gases is for naught, at least when it comes to mitigating climate change.
So, what’s the point, really, of forcing Americans into different energy choices? As I have repeatedly pointed out, nothing we do here (when it comes to greenhouse gas emissions) will make any difference either domestically, or globally, when it comes to influences on the climate. What the powers-that-be behind emissions reduction schemes in the U.S. are hoping for is that 1) it doesn’t hurt us too much, and 2) that China and other large developing nations will follow our lead.
Both outcomes seem dubious at time scales that make a difference.
Teng, H., W. M. M. Washington, G. Branstator, G. A. Meehl, and J.-F. Lamarque, 2012. Potential impact of Asian carbon aerosols on future US warming. Geophysical Research Letters, doi:10.1029/2012GL051723, in press.