
The phrase “considerably larger than expectations” seems to occur with depressing regularity in climate observations.
Image above shows current Arctic sea ice extent compared to the record low 2011/2012 ice season, dotted line, and the average of 1981 – 2010.
Climate models have consistently been unable to capture the speed with which arctic sea ice has declined, especially over the last half decade.
Below, new research on what may be one reason the models have fallen short.
AP:
The Arctic isn’t nearly as bright and white as it used to be because of more ice melting in the ocean, and that’s turning out to be a global problem, a new study says.
With more dark, open water in the summer, less of the sun’s heat is reflected back into space. So the entire Earth is absorbing more heat than expected, according to a study published Monday in the Proceedings of the National Academy of Sciences.
That extra absorbed energy is so big that it measures about one-quarter of the entire heat-trapping effect of carbon dioxide, said the study’s lead author, Ian Eisenman, a climate scientist at the Scripps Institution of Oceanography in California.
The Arctic grew 8 percent darker between 1979 and 2011, Eisenman found, measuring how much sunlight is reflected back into space.
“Basically, it means more warming,” Eisenman said in an interview.
Eisenman et al:
The decline of Arctic sea ice has been documented in over 30 y of satellite passive microwave observations. The resulting darkening of the Arctic and its amplification of global warming was hypothesized almost 50 y ago but has yet to be verified with direct observations. This study uses satellite radiation budget measure- ments along with satellite microwave sea ice data to document the Arctic-wide decrease in planetary albedo and its amplifying effect on the warming. The analysis reveals a striking relationship between planetary albedo and sea ice cover, quantities inferred from two independent satellite instruments. We find that the Arctic planetary albedo has decreased from 0.52 to 0.48 between 1979 and 2011, corresponding to an additional 6.4 ± 0.9 W/m2 of solar energy input into the Arctic Ocean region since 1979. Averaged over the globe, this albedo decrease corresponds to a forcing that is 25% as large as that due to the change in CO2 during this period,considerably larger than expectations from models and other less direct recent estimates. Changes in cloudiness appear to play a negligible role in observed Arctic darkening, thus reducing the possibility of Arctic cloud albedo feedbacks mitigating future Arctic warming.