Data starts to confirm climate feedback loop
FRISCO — NASA scientists say that, during the summer, Arctic is absorbing 5 percent more of the sun’s incoming energy than just 15 years ago. The trend coincides with the steady decrease in Arctic sea ice during the same period.
The extra energy is equal to an additional 10-watt light bulb shining continuously over every 10.76 square feet of Arctic Ocean for the entire summer.
The change in the region’s energy balance is happening because ocean water is darker than sea ice and absorbs the sun’s energy at a higher rate. The decline in the region’s reflectivity has been a key concern among scientists since the summer Arctic sea ice cover began shrinking in recent decades.
As more of the sun’s energy is absorbed by the climate system, it enhances ongoing warming in the region, which is more pronounced than anywhere else on the planet.
While a five percent increase may not seem like much, the global rate has remained essentially flat during that same time. No other region on Earth shows a trend of potential long-term change,” said Norman Loeb, of NASA’s Langley Research Center, Hampton, Virginia.
Regionally, the increase is even greater, Loeb said. Areas such as the Beaufort Sea, which has experienced the some of the most pronounced decreases in sea-ice coverage, show a 50 watts per square meter increase in the rate of absorbed solar radiation.
As a region, the Arctic is showing more dramatic signs of climate change than any other spot on the planet. These include a warming of air temperatures at a rate two to three times greater than the rest of the planet and the loss of September sea ice extent at a rate of 13 percent per decade.
While the new measurements could ultimately become another of those signs of dramatic climate change, right now scientists say they have obtained the bare minimum of a data record needed to discern what’s happening over the long term.
Getting data beyond 15 years will allow scientists to better assess if recent trend falls outside the realm of natural variability, said Jennifer Kay, an atmospheric scientist at the Cooperative Institute for Research and Environmental Science at the University of Colorado.
“We need long time series to detect climate change signals over the internal variability. For example, observed sea ice loss over the last 30 years cannot be explained by natural variability alone.” Kay said. “Fifteen years is long, but climate is often defined as the average over 30 years – so we are only half-way there with the CERES observations.”
Increasing absorbed solar radiation is causing multiple changes in the sea ice cover, said Walt Meier, a sea ice scientist from NASA’s Goddard Space Flight Center, Greenbelt, Maryland. Two of those changes include the timing of the beginning of the melt season each year and the loss of older, thicker sea ice.
The onset of the melt season in the high Arctic is now on average seven days earlier than it was in 1982, Meier said. Earlier melting can lead to increased solar radiation absorption. This is one step in a potential feedback cycle of warming leading to melting, melting leading to increased solar radiation absorption, and increased absorption leading to enhanced warming.
Since 2000, the Arctic has lost 1.4 million square kilometers (541,000 square miles) of older ice that is more than 3 meters thick, which during winter has essentially been replaced by ice that is less than 2 meters thick, according to data provided by Mark Tschudi at the University of Colorado. Once again, Meier said, this trend is a step in a feedback cycle.
“Having younger and thus thinner ice during winter makes the system more vulnerable to ice loss during the summer melt season,” Meier said.