Scientists are increasingly confident that both the startling melting seen in the Arctic and the predominant cooling pattern in the Antarctic are being driven by human activity.
In a conference call with reporters Friday, scientists from the National Oceanographic and Atmospheric Administration, Rutgers University and the British Antarctic Survey described new research to be published in Eos, a publication of the American Geophysical Union. In a nutshell:
Natural variability everything from unusual winds and heat waves to the effects of El Niño, La Niña and other influential global phenomenon always plays a role in the seasonal melting of sea ice. But the melting seen in the Arctic would not have occurred with natural variability alone; it was the year-on-year erosion of thick, multiyear ice and the gradual warming of the region that has caused a trend in declining sea ice, rather than year-by-year fluctuation.
On Antarctica, the ozone hole is masking the effect of global warming, which otherwise would be causing widespread melting there, said Gareth Marshall, a climatologist with the British Antarctic Survey. The slight but consistent buildup of ice over 30 years was possible because of the way the ozone hole has increased predominantly westerly winds, on average 15%, across the Southern Ocean and Antarctica, effectively blocking warmer air from reaching the continent. The exception is the Antarctic peninsula, which points toward South America, and which has been the site of several high-profile ice shelf collapses.
"At a regional scale, climate change is much more complicated," Marshall said.
Jennifer Francis, a Rutgers atmospheric scientist, called ice "a key vital sign a visual diagnosis of the climate system."
"All the evidence points to human-made effects playing a role in changes at both poles; evidence to the contrary is very hard to find," Francis said. "This further depletes the arsenal that human-caused climate change is nothing to worry about."
James Overland, a NOAA oceanographer, counted himself a global warming skeptic only a few years ago, but now describes himself as "startled" by the changes occurring in the Arctic, and the strong evidence he sees in climate models.
The scientists arrived at their conclusions by running computer models that variously eliminated natural variables or human-caused variables, to see which set of conditions produced the results seen on the ground.
Looking out into the future, the models show an ice-free Arctic by 2030 about two decades ahead of the predictions in the United Nations' Intergovernmental Panel on Climate Change reports.
There's also a good chance that the Arctic will witness another record or near-record melt this summer, with 40% more ice lost than was typical 20 years ago. The melting is predicted despite more favorable weather conditions, Overland said, because the loss of thick sea ice over time leaves the thin, one-year-old ice more vulnerable to smaller changes in the weather.
Vulnerability is the key to understanding the scientists' message. Global warming makes sea ice vulnerable, and then naturally varying weather conditions can easily exploit the vulnerability. The same type of scenario is likely with other global warming impacts, but the effects are much more clear and early in the Arctic.
Over fall and winter and up to today, the amount of ice floating around on the Arctic has been below normal every single day. It has never gone to the other side where there was more than normal," Francis said, noting that April saw a stretch of days several degrees warmer than average. "So all arrows are pointing, certainly, to not a recovery...and probably worse."
Because of worldwide efforts to rein in chlorofluorocarbon emissions, the ozone hole is on a long-term trend toward closing. Given trends in greenhouse gas buildup, that points to increased melting in Antarctica in the coming decades as well.
Enter your city or zip code to get your local temperature and air quality and find local green food and recycling resources near you.