In a recent paper published by researchers at the National Center for Atmospheric Research, scientists report that computer models of climate change specific to the Antarctic may not be as accurate as they were originally believed. Computer models based on data of Earth’s climate help scientists make predictions of climate change over time. From these mathematical models, scientists run simulations based on data collected in order to assess potential outcomes such as warming or cooling trends around the Earth. While computer models representing climate in the other continents are accurately depicting the phenomenon of increasing temperatures, the models used in Antarctica inaccurately point to larger increases in temperatures than is actually being observed. (The models show an increase of 1.4 degrees Fahrenheit or 0.2 degrees Celsius in the Antarctic versus the actual increase of 0.4 degrees Fahrenheit or 0.75 degrees Celsius).
Why the discrepancy in the Antarctic? Scientists point to a number of reasons, all of which are excellent examples to show students the ongoing investigative nature of scientific study. For starters, the conditions in Antarctica make it difficult to take weather readings (or any kind of readings for that matter) in the first place. This recent report came as a result of improved measurements in the Antarctic region that will provide more accurate data in the future. Using ice core data samples and the increased ability to take actual climate observations and comparing these to the models gives scientists a better idea of how these data compare. That said, scientists still caution that the models used today still may not be as accurate as they are in other parts of the world. NCAR scientist David Schneider states, “The current generation of climate models has improved over previous generations, but still leaves Antarctic surface temperature projections for the 21st century with a high degree of uncertainty.”
Another factor in the discrepancy between models and actual data deals with the ozone hole over Antarctica. Because of the hole, the upper layers of atmosphere over Antarctica are cooler, creating cooler temperatures in the central part of the continent. This is in contrast to warming trends in other continents, as well as the warming trend in the Antarctic Peninsula. This cooler air reduces the amount of water vapor present, something that the computer models point to as a source of increase temperatures in the region that are in contrast to actual readings.
Scientist Andrew Monaghan, a co-author of this recent report, states, “We can now compare computer simulations with observations of actual climate trends in Antarctica. This is showing us that, over the past century, most of Antarctica has not undergone the fairly dramatic warming that has affected the rest of the globe. The challenges of studying climate in this remote environment make it difficult to say what the future holds for Antarctica’s climate.”
Dr. Monaghan is a guest columnist for the upcoming June issue (Weather and Climate: From Home to the Poles) of Beyond Penguins and Polar Bears.
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[…] Atmospheric Research has found that computer analyses of global climate change have consistently overstated warming in Antarctica. By comparing climate records from the past 50 to 100 years with computer-run […]
Photos of antartica are being circulated with the comment that the area is experiencing the ‘coldest weather in decades’. Is the claim true and, if so, how does it affect the prevailing claims about global warming? I don’t understand how the ozone hole would be making the continent cooler; seems like it would make it warmer. Thanks.
Greg: Thanks for your question. I contacted Dr. Monaghan to respond to it, and he provided me with an answer for you. I hope this provides you with more insight.
Robert
Dr. Monaghan’s response:
Not having access to the photos/data of Antarctica, I’m not certain over what time frame the originator of the comment is referring (i.e., ‘this year is the coldest in decades’, ‘this decade is the coldest in decades’, etc…). So, I’ll make a more general statement about Antarctic near-surface temperatures over the past several decades.
Near-surface temperatures have not changed much over most of continental Antarctica over the past 50 years. If one evaluates the trends over the past five decades, there has been a very, very slight warming (averaged over the continent) that is not statistically different from a trend of zero (meaning that there is so much year-to-year variability that the noise in the data prevents any trend from being considered real). If one evaluates the trends only over the past 20-30 years, there is actually a slight cooling (averaged over the continent), but it too is not statistically different from a trend of zero. So, based on the past 20-30 years, some people point out that there has been recent cooling over Antarctica. However, it might be more accurate to say that there hasn’t been much change over most of the continent. In any case, compared to the considerable warming that has been widespread over the rest of the globe during the past 50 years, the lack of warming over most of Antarctica has been a subject of much interest.
As you might expect, the picture is more complicated than generalizing that Antarctica is warming or cooling. This isn’t surprising, since Antarctica is quite large — about 1-1/2 times the size of the United States. Just as there has not been uniform climate change over the U.S., there has not been uniform climate change over Antarctica. For example, despite little change overall, the Antarctic Peninsula — a California-sized thumb that juts out into the Southern Ocean toward the tip of South America - has been one of the most rapidly warming regions on earth (and the positive temperature trends there are statistically different from zero for the most part). The breakup of several large ice shelves on the Peninsula has coincided with this warming and is thought to be unprecedented in recent history (the Larsen B ice shelf existed for at least 10,000 years prior to its breakup). In turn, the land-based glaciers on the Antarctic Peninsula that were buttressed by these former ice shelves have now sped up, in some cases by a factor of 8 (and, unlike the ice shelves, these contribute to sea level rise). Therefore, though the Antarctic Peninsula only comprises about 4-5% of Antarctica (and there has not been much change over the other 95% of the continent), the changes occurring there seem to be disproportionately important, and perhaps foreshadow the types of (rapid) changes that might occur further south on the coastal margins of the Antarctic mainland if the region of warming becomes larger.
In addition to near-surface atmospheric temperatures, there is another twist when considering Antarctic climate change: the ocean. Regional ocean warming (we still don’t know the cause) is driving the acceleration of the large glaciers in West Antarctica (Pine Island and Thwaites glaciers) that are in turn the largest contributors to contemporary sea level rise coming from Antarctica. The West Antarctic Ice Sheet (WAIS) is a marine-based ice sheet (meaning its base sits on the ocean floor, below sea level, instead of resting on land above sea level). So, this exposure of the lower portion of WAIS to ocean waters and the potential consequences if ocean temperatures continue to warm is currently a major concern of climate scientists (more so than the prospect of atmospheric warming, for now). In summary, the changes to the Antarctic ice sheet (which affect sea level rise - the main consequence of climate change in Antarctica) are driven from the ocean in addition to the atmosphere, so both must be considered.
Finally, its important to note that the cooling (or lack of warming)
in recent decades over continental Antarctica has mainly been
attributed to a strengthening of the belt of westerly winds that
encircles Antarctica (called the “Southern Hemisphere Annular Mode”).
In turn, it appears that a combination of natural climatic
variability, stratospheric ozone depletion (the ‘ozone hole’), and
greenhouse gas increases are the cause of these strengthening winds.
The natural variability and the ozone depletion are the two
‘wildcards’ in this equation (since we know that greenhouse gases will
continue to increase). If the ozone hole becomes smaller as projected
(via the limits on CFC emissions put in place by the Montreal
Protocol), several recent studies suggest that the strengthening of
westerlies will taper off. In this case, our understanding of how the
Southern Hemisphere Annular Mode affects Antarctic temperatures
suggests that temperatures over most of Antarctica may begin to
increase.
The contribution to cooling near the surface of Antarctica due to the stratospheric ozone hole is complex, but it can be explained roughly as follows: the stratospheric ozone layer, situated about 15 km above the surface, absorbs ultraviolet radiation from the sun, which in turn keeps that layer warmer than it would be in the absence of ozone. So, when the ozone hole forms in the austral springtime, the temperatures are colder than normal in the stratosphere over Antarctica, which in turn strengthens the gradient of temperature between Antarctica and equatorial regions of earth. A stronger temperature (energy) gradient between the equator and Antarctica causes the belt of westerly winds that encircles Antarctica to strengthen. In turn, this stronger ‘tube’ of westerly winds that encircles Antarctica and extends from the stratosphere all the way down to the surface counteracts the direction of the prevailing winds near the surface of the Antarctic ice sheet, causing them to weaken. This then causes changes to the near surface temperature inversion over Antarctica. The temperature inversion over Antarctica is a layer of very, very cold temperatures near the surface of the ice sheet caused by the constant radiative cooling of the ice. Its strength is modulated by the near-surface winds. If they are strong, they mix warmer air aloft down to the surface and weaken the inversion. If they are weak, the warmer air aloft is not mixed down toward the surface and the inversion remains strong. So, when the near-surface winds become weaker due to the chain of events set off by the ozone hole, it has the effect of cooling the surface by allowing the cold temperature inversion to strengthen. It is important to note, however (as noted in the previous paragraph), that ozone is only one factor affecting the overall change in temperature near the surface. Warming due to greenhouse gases, and natural variability of the climate — which is very large in Antarctica — also play a role.
(The models show an increase of 1.4 degrees Fahrenheit or 0.2 degrees Celsius in the Antarctic versus the actual increase of 0.4 degrees Fahrenheit or 0.75 degrees Celsius).
Should it read .75 Fahrenheit or .4 Celsius? Thanks