May 18, 2012

CO2 Not to Blame for Southwest Droughts?

Filed under: Floods, Precipitation

In our last WCR, we discussed a series of articles that found that higher resolution climate models—models which include a better representation of the complex terrain features of the Southwest—produce less drought stress on the Southwestern U.S. in their projections of future climate change from greenhouse gas emissions than do coarser resolution general circulation models.

Now comes along a new paper published in Nature magazine by Robert Allen and colleagues which suggests that the drying trend which remains is being caused more by black carbon aerosols and tropospheric ozone than by greenhouse gas emissions.


May 14, 2012

Future Southwest Drought in Doubt?

Filed under: Droughts, Precipitation

One of the most “robust” signals from global climate models run under scenarios of increasing human greenhouse gas emissions is an even drier climate in the Southwestern U.S. than exists there currently.

The 2009 report “Global Climate Change Impacts in the United States” from the U.S. Global Change Research Program (a report which the EPA relied upon in making its “Endangerment Finding” from carbon dioxide and other greenhouse gases) has this to say about the prospects of future drought in the U.S. (p. 33):

“In the future, droughts are likely to become more frequent and severe in some regions. The Southwest, in particular, is expected to experience increasing drought as changes in atmospheric circulation patterns cause the dry zone just outside the tropics to expand farther northward in the United States.”

The 2007 Fourth Assessment Report of the IPCC (another report which the EPA relied heavily upon in making its “Endangerment Finding”) had this to say (p. 890):

“Annual mean precipitation is very likely to increase in Canada and the northeast USA, and likely to decrease in the southwest USA.”

Not surprisingly, the EPA included this statement about projected changes in precipitation in the Executive Summary of its Technical Support Document for its “Endangerment and Cause or Contribute Findings for Greenhouse Gases under Section 202(a) of the Clean Air Act”:

“Increases in the amount of precipitation are very likely in higher latitudes, while decreases are likely in most subtropical latitudes and the southwestern U.S., continuing observed patterns.”

But new research published in Geophysical Research Letters suggests that the USGCRP, the IPCC, and consequently, the EPA may be overdoing things a bit.


May 9, 2012

No sea level rise catastrophe?

Filed under: Climate History

As one of the central tenets of climate change catastrophe involves inundation by rapidly rising seas, we like to visit the issue from time to time here at World Climate Report. Interestingly, or perhaps some may prefer predictably, we usually are able to uncover plenty of science that indicates that the situation is not nearly so dire.

More evidence of this was published this week in Science magazine.

A paper by Twila Moon, Ian Joughin, Ben Smith, and Ian Howat titled “21st Century Evolution of Greenland Outlet Glacier Velocities” examined the flow characteristics from nearly 200 glaciers across Greenland for the period 2000-2010 as analyzed using synthetic aperture radar data collected from various satellites. Moon and colleagues assessed changes in the flow rate of each of the glaciers.

And what they found—much like what is found whenever the climate system is examined in detail rather than painted with a broad brush—was that the patterns of flow rate changes across Greenland were complex, both in space and time. Glaciers that were accelerating during a few years were found to be decelerating in others. Some accelerating glaciers were found in close proximity to other glaciers that were decelerating. The authors hypothesize that a variety of local factors are important in controlling the flow rate of individual glaciers including “fjord, glacier, and bed geometry,” “local climate” and “small-scale ocean water flow and terminus sea ice conditions.”


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