Underestimating global warming: gaps in Arctic temperature data lead scientists and public astray

Jeremy Hance
mongabay.com
January 15, 2014



Thickly packed sea ice in the Arctic from a photo taken in 1949. One day thick, stable sea ice in the Arctic will likely be a thing of the past as the Arctic is warming around eight times faster than the rest of world according to a new analysis. Photo by: Rear Admiral Harley D. Nygren.
Thickly packed sea ice in the Arctic from a photo taken in 1949. One day thick, stable sea ice in the Arctic will likely be a thing of the past as the Arctic is warming around eight times faster than the rest of world according to a new analysis. Photo by: Rear Admiral Harley D. Nygren.

No place on Earth is heating up faster than the Arctic, but just how fast has remained an open question due to large gaps in temperature data across the vast region. Now, a recent study in the Quarterly Journal of the Royal Meteorological Society finds that not only is the Arctic warming eight times faster than the rest of the planet, but failure to account for temperature gaps has led global datasets to underestimate the rise of temperatures worldwide. Recently, some scientists have noted that the pace of global warming appears to have slowed—while many climate change deniers and media groups have erroneously claimed it has stopped altogether. But by adding in new temperature data from satellites over the rapidly-warming Arctic, scientists report that the world's climate is warming as rapidly as predicted, only the Arctic is currently facing the brunt of it.

Lead author, Kevin Cowtan with York University, says that it's quite easy to see how leaving out Arctic temperatures has made global temperatures datasets inaccurate.

"If you take an average but miss out part of the data which behave differently from the population as a whole, then you get the wrong answer," he told mongabay.com. "So for example if you were to estimate how tall people are on average based on a sample group consisting only of women you would underestimate the result—because men are taller on average. In the same way if you take an average of the rate of warming of the earth based only on places which aren't warming very quickly, then you will underestimate the rate of global warming."

Melting Arctic sea ice in 2000. The light blue areas are melt ponds lying on the sea ice; the dark blue areas are open water. Both Arctic sea ice extent and volume have plunged in the recent years. Photo by: NASA.
Melting Arctic sea ice in 2000. The light blue areas are melt ponds lying on the sea ice; the dark blue areas are open water. Both Arctic sea ice extent and volume have plunged in the recent years. Photo by: NASA.

This is exactly what has occurred in the oft-cited Hadley Center and Climatic Research Unit, or CRU, temperature dataset, which covers 84 percent of the planet but leaves out most of the Arctic. The same issue undercuts data by NOAA's National Climatic Data Center (NCDC). In contrast, the NASA GISS dataset has taken into account warming in the Arctic by filling in the gaps with nearby weather stations, however, even their accounts still underestimate the total warming compiled by Cowtan and his partner, Robert Way with the University of Ottawa.

In their new study, Cowtan and Way looked at two possible solutions to the gap in Arctic data.

"One was to simply extrapolate from the nearest weather stations using the CRU data. NASA have done something similar for a long time, but CRU have worked hard to get a lot of high latitude stations," says Cowtan. The other method was more novel: the pair turned to satellites that take temperatures of the lower atmosphere with microwave sensors.

"This isn't the same as the surface temperature, but is quite a good predictor of surface temperature over land, and as far as we can tell over sea ice too," says Cowtan. The researchers then used a tried-and-tested statistical method, known to scientists as "kriging," to reconstruct surface-level temps based on the satellite data.

Climate change is imperiling many Arctic species, including walrus who depend on thick sea ice for giving birth. Photo by: USFWS/Joel Garlich-Miller.
Climate change is imperiling many Arctic species, including walrus who depend on thick sea ice for giving birth. Photo by: USFWS/Joel Garlich-Miller.

Satellites have only been monitoring the Arctic since 1979, meaning they are only able to fill in the gaps beginning with that year. However what the scientists found was shocking: the results show that in the last 15 years warming rates have skyrocketed in the Arctic with the region currently currently heating up around eight times faster than the rest of the world. Moreover, when this warming spike in the region is added into the global total, the much-purported climate change slowdown vanishes.

For example, HadCRUT data shows overall warming of 0.05 Celsius over the last fifteen years, but adding in the new Arctic data more than doubles the rise, to 0.12 Celsius. Cowtan told mongabay.com that while the change isn't "very much" and doesn't add a whole lot to the longterm picture—which is what climate scientists are concerned with—but it shows that global warming is still rising apace.

"The science says exactly what it always did. All we've really done is cleared away a little of the uncertainty concerning short term trends which was being used to obscure the science," notes Cowtan, adding that "scientists have mostly been cautious about drawing conclusions from such short term trends, but they have figured significantly in the public discourse."

Indeed the public discourse—and many climate change deniers—have been obsessed at times over the past year about the much-ballyhooed "pause" in climate change. Even the most recent Intergovernmental Panel on Climate Change (IPCC) makes note of the slowdown in the current rate of climate change versus the past. A slowdown, according to Cowtan and Way, that is based on poor data.

Mendenhall glacier in 2007. The glacier has receded nearly two miles since the 1950s due to global warming, creating a lake at the bottom of the glacier. Vanishing glaciers leads to rising sea levels and water issues. Photo by: Rhett A. Butler.
Mendenhall glacier in 2007. The glacier has receded nearly two miles since the 1950s due to global warming, creating a lake at the bottom of the glacier. Vanishing glaciers leads to rising sea levels and water issues. Photo by: Rhett A. Butler.

"HadCRUT and NCDC need to address the problem. Ideally they should find different approaches to address the issue—the more ways this problem is tackled, the clearer the picture will become," says Cowtan, who notes that the NASA dataset is the closest to their findings, but still underestimates warming a little though the researchers are as yet uncertain why.

The rapid warming in the Arctic has wreaked havoc on the ecosystem already. In 2012, Arctic sea ice extent fell 50 percent below the 1979-2000 averages and hit its lowest point on record, alarming scientists. In total, the Arctic has lost about 40 percent of its sea ice since 1980. Researchers have predicted that the Arctic ocean will be ice free sometime between 2020 and 2100. Recently, some scientists have theorized that the loss of Arctic sea ice may be responsible for extreme weather in places like the U.S. and Europe, such as unusual jet stream blocking patterns and even bitter cold like the most recent polar vortex that hit the U.S.

Arctic sea ice volume (not extent) from 1979 to Spring 2013. Note: the graph does not show this year's low.
Arctic sea ice volume (not extent) from 1979 to Spring 2013. Note: the graph does not show last year's low.

MODIS satellite image of the Arctic. Photo by: NASA.
MODIS satellite image of the Arctic. Photo by: NASA.

Citations:
  • Kevin Cowtanand Robert G. Way. (2013) Coverage bias in the HadCRUT4 temperature series and its impact on recent temperature trends. Quarterly Journal of the Royal Meteorological Society. doi:10.1002/qj.2297














AUTHOR: Jeremy Hance joined Mongabay full-time in 2009. He currently serves as senior writer and editor. He has also authored a book.




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CITATION:
Jeremy Hance
mongabay.com (January 15, 2014).

Underestimating global warming: gaps in Arctic temperature data lead scientists and public astray.

http://news.mongabay.com/2014/0115-hance-gap-arctic-temps.html