Archives for May 8, 2008

BOULDER – Computer analyses of global climate have consistently overstated warming in Antarctica, concludes new research by scientists at the National Center for Atmospheric Research (NCAR) and Ohio State University. The study can help scientists improve computer models and determine if Earth’s southernmost continent will warm significantly this century, a major research question because of Antarctica’s potential impact on global sea-level rise.

The study was published on April 5 in Geophysical Research Letters. It was funded by the National Science Foundation, NCAR’s primary sponsor, and the Department of Energy.

The authors compared recently constructed temperature data sets from Antarctica, based on data from ice cores and ground weather stations, to 20th century simulations from computer models used by scientists to simulate global climate. While the observed Antarctic temperatures rose by about 0.4 degrees Fahrenheit (0.2 degrees Celsius) over the past century, the climate models simulated increases in Antarctic temperatures during the same period of 1.4 degrees F (0.75 degrees C).

The error appeared to be caused by models overestimating the amount of water vapor in the Antarctic atmosphere, the new study concludes. The reason may have to do with the cold Antarctic atmosphere handling moisture differently than the atmosphere over warmer regions.

This map of Antarctica shows the approximate boundaries of areas that have warmed or cooled over the past 35 years. The map is based on temperatures in a recently-constructed data set by NCAR scientist Andrew Monaghan and colleagues. The data combines observations from ground-based weather stations, which are few and far between, with analysis of ice cores used to reveal past temperatures. (Illustration by Steve Deyo, UCAR.)

Read the entire NCAR News Release: Climate Models Overheat Antarctica, New Study Finds
May 07, 2008

Study Title: “Twentieth century Antarctic air temperature and snowfall simulations by IPCC climate models”
Authors: Andrew Monaghan, David Bromwich, and David Schneider

Publication: Geophysical Research Letters, April 5, 2008

Abstract:

We compare new observationally-based data sets of Antarctic near-surface air temperature and snowfall accumulation with 20th century simulations from global climate models (GCMs) that support the Intergovernmental Panel on Climate Change Fourth Assessment Report. Annual Antarctic snowfall accumulation trends in the GCMs agree with observations during 1960–1999, and the sensitivity of snowfall accumulation to near-surface air temperature fluctuations is approximately the same as observed, about 5% K−1. Thus if Antarctic temperatures rise as projected, snowfall increases may partially offset ice sheet mass loss by mitigating an additional 1 mm y−1 of global sea level rise by 2100. However, 20th century (1880–1999) annual Antarctic near-surface air temperature trends in the GCMs are about 2.5-to-5 times larger-than-observed, possibly due to the radiative impact of unrealistic increases in water vapor. Resolving the relative contributions of dynamic and radiative forcing on Antarctic temperature variability in GCMs will lead to more robust 21st century projections.

In part 1 of this series ‘Measuring the Surface Air Temperature’ I wrote that James Hansen of NASA’s Goddard Space Institute explains that it is not easy to measure surface air temperature particularly in the presence of vegetation because the temperature above the vegetation may be very different from the temperature below the vegetation.

So, I thought, maybe it is easier to measure the surface temperature where there is not much vegetation, for example, at the Antarctic.

But apparently knowing the average temperatures on Antarctica has its own challenge including the sparseness of ground-based weather stations particularly in the continent’s high altitude interior and the harsh environment also takes its toll on equipment.

So NASA relies on satellites that measure energy radiated from the ice surface and estimate a level of uncertainty in these measurements between 2-3 degree Celsius (read more here).

Given this level of uncertainty I find it extraordinary that NASA can suggest a warming trend of a fraction of a degree over the last 20 years in the following image.

Bill Kininmonth, former head of Australia’s Bureau of Meteorology’s National Climate Centre, recently emailed me that because it is very difficult to assess surface temperature over ice surfaces using satellite radiometers it is more realistic to consider sea surface temperatures and to also exclude regions of seasonal sea ice.

In the same email he provided the following image of the sea surface temperatures.

Bill also explained that the Larsen B ice shelf at the Antarctic shattered rather than melted earlier this year, with the comment “shattering is not related to melting”.

BOFFINS fear Arctic ice melting could see the rise of a polar bear and grizzly bear hybrid – dubbed the ‘grolar bear.’ The effects of climate change means the hybrid bears could become more common as their habitats increasingly overlap due to global warning. …And he delivered a stark warning of what the future holds. He believes that by THIS summer there could be no ice at the North Pole. …And Dr Divoky had a message for climate change sceptics, saying: “Having a polar bear show up in your front yard is one of the more compelling pieces of evidence that climate change is real.”

The Sun: Grolar bears are global warning

Koalas are threatened by the rising level of carbon dioxide pollution in the atmosphere because it saps nutrients from the eucalyptus leaves they feed on, a researcher said Wednesday.

CNN.com: Koalas under threat from toxic eucalyptus leaves