Record High Temperatures, Record Low Arctic Sea Ice
Two key climate change indicators - global surface temperatures and Arctic sea ice extent - have broken numerous records through the first half of 2016, according to NASA analyses of ground-based observations and satellite data.
Each of the first six months of 2016 set a record as the warmest respective month globally in the modern temperature record, which dates to 1880, according to scientists at NASA's Goddard Institute for Space Studies in New York. The six-month period from January to June was also the planet's warmest half-year on record, with an average temperature 1.3 degrees Celsius (2.4 degrees Fahrenheit) warmer than the late nineteenth century.
Five of the first six months of 2016 also set records for the smallest respective monthly Arctic sea ice extent since consistent satellite records began in 1979, according to analyses developed by scientists at NASA's Goddard Space Flight Center, in Greenbelt, Maryland. The one exception, March, recorded the second smallest extent for that month.
While these two key climate indicators have broken records in 2016, NASA scientists said it is more significant that global temperature and Arctic sea ice are continuing their decades-long trends of change. Both trends are ultimately driven by rising concentrations of heat-trapping carbon dioxide and other greenhouse gases in the atmosphere.
The extent of Arctic sea ice at the peak of the summer melt season now typically covers 40 percent less area than it did in the late 1970s and early 1980s. Arctic sea ice extent in September, the seasonal low point in the annual cycle, has been declining at a rate of 13.4 percent per decade.
Polar ice loss increased in the first two weeks of August, according to NASA's latest images released on Friday.
This year’s melt season in the Arctic Ocean and surrounding seas started with a record low maximum extent in March and relatively rapid ice loss through May. The melt slowed down in June, however, making it highly unlikely that this year’s summertime sea ice minimum extent will set a new record.
“Even when it’s likely that we won’t have a record low, the sea ice is not showing any kind of recovery. It’s still in a continued decline over the long term,” said Walt Meier, a sea ice scientist at NASA’s Goddard Space Flight Center in Maryland. “It’s just not going to be as extreme as other years because the weather conditions in the Arctic were not as extreme as in other years.
“A decade ago, this year’s sea ice extent would have set a new record low and by a fair amount. Now, we’re kind of used to these low levels of sea ice – it’s the new normal.”
This year’s sea ice cover of the Barents and Kara seas north of Russia opened up early, in April, exposing the surface ocean waters to the energy from the sun weeks ahead of schedule. By May 31, the extent of the Arctic sea ice cover was comparable to end-of-June average levels.
But the Arctic weather changed in June and slowed the sea ice loss. A persistent area of low atmospheric pressure, accompanied by cloudiness, winds that dispersed ice and lower-than-average temperatures, didn’t favor melt.
The rate of ice loss picked up again during the first two weeks of August, and is now greater than average for this time of the year. A strong cyclone is moving through the Arctic, similar to one that occurred in early August 2012. Four years ago, the storm caused an accelerated loss of ice during a period when the decline in sea ice is normally slowing because the sun is setting in the Arctic. However, the current storm doesn’t appear to be as strong as the 2012 cyclone, and ice conditions are less vulnerable than four years ago, Meier said.
“This year is a great case study in showing how important the weather conditions are during the summer, especially in June and July, when you have 24 hours of sunlight and the sun is high in the sky in the Arctic,” Meier said. “If you get the right atmospheric conditions during those two months, they can really accelerate the ice loss. If you don’t, they can slow down any melting momentum you had. So our predictive ability in May of the September minimum is limited, because the sea ice cover is so sensitive to the early-to-mid-summer atmospheric conditions, and you can’t foresee summer weather.”