A new look at the “vital signs” of Earth’s climate reveals a stark picture of declining health. As global temperatures rise, so do sea level and the amount of heat trapped in the ocean’s upper layers. Meanwhile, mountain glaciers and Arctic sea ice are melting away beneath an atmosphere where concentrations of three key planet-warming greenhouse gases continue to rise.
“Data show that the climate is changing more rapidly now than it has at any time in the historical record,” says Thomas Karl, director of the National Oceanic and Atmospheric Administration’s (NOAA’s) National Climatic Data Center in Asheville, North Carolina. “The numbers speak for themselves.”
The numbers speak pretty loudly, too. Depending on which data set scientists look at, 2013 falls somewhere between the second warmest and sixth warmest year since record keeping began in 1880. Global sea level reached a new record high last year—about 3.8 centimeters (1.5 inches) above the average measured by satellites between 1993 and 2010. Overall, sea level is rising about 3 millimeters (one-eighth of an inch) each year. And for the 23rd straight year, mountain glaciers on the whole lost more ice than they gained, says Jessica Blunden of ERT Inc., who works with Karl at the climate monitoring agency in Asheville. “Changes in these [glaciers] are visible and obvious signs of climate change,” Blunden says.
The new study, State of the Climate in 2013, was released online today in the Bulletin of the American Meteorological Society. The detailed, peer-reviewed analysis was based on data from environmental monitoring stations on land, sea, and ice and from sensors on satellites and planes. More than 400 scientists from 57 countries contributed to the report. (Previous State of the Climate reports, issued annually since 1991, can be found here.)
Increases in the levels of three key greenhouse gases are likely to be the root of recent warming, scientists suggest. The global average concentration of carbon dioxide reached more than 395 parts per million last year, a 2.8 ppm increase over 2012 levels, according to the new report. Levels of both methane and nitrous oxide (N2O), which on a pound-for-pound basis trap heat more effectively than CO2, rose last year about 0.3%. (Nevertheless, about two-thirds of the atmosphere’s heat-trapping power comes from CO2, which is much more prevalent than the other two gases, the researchers report. Carbon dioxide levels are now in uncharted territory, the scientists say: Ice core records reveal that until the early 20th century, CO2 concentrations hadn’t risen above 300 ppm during the previous 800,000 years.)
From pole to pole, few parts of the globe are being spared warm-up. In the Eurasian Arctic, average temperatures last summer ranged between 1°C and 3°C warmer than the average temperatures there from 2007 through 2012. Fairbanks, Alaska, had a record number of days (36) in which the daily high temperature reached 27°C (80°F) or higher. All that warmth is seeping into the ground, too. Permafrost temperatures measured 20 meters below ground at many sites in Alaska reached record highs last year, the scientists report. And 2013’s Arctic sea ice coverage in September, the month it usually falls to its lowest for the year, was 18% below the average coverage for that month from 1981 through 2010. Although not a record low amount, the scientists note that September sea ice coverage is declining almost 14% per decade since satellites started measuring sea ice extent in 1979.
At the other end of Earth, 2013’s average annual temperature at the South Pole was –47.4°C (–53.3°F): chilly, yes, but nevertheless a record high since scientists started collecting weather data there in 1957.
In between, China, Japan, and South Korea suffered their warmest summer on record, and Australia really suffered: With large swaths of the Land Down Under tallying summertime highs above 45°C (113°F), Australia had its warmest year since record keeping began in 1910.
The amount of heat stored in the upper 700 meters of the world’s oceans, which has increased substantially over the past 2 decades, also reached a record level last year. That increased heat content helps boost the strength of typhoons and hurricanes, Karl suggests. In the next couple of months, he notes, NOAA will release a report that discusses how climate change might be related to several episodes of extreme weather last year.
By Sid Perkins
Sid is a freelance science journalist.
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