Volcanoes behind global warming 'pause'

Cooling caused by volcanic eruptions during last 15 years is partly responsible for the recent global warming 'pause', a new study has found.
This hiatus, a mismatch between actual warming and climate-model predictions, started in 1998, when Earth's average surface temperatures halted their feverish rise.
Researchers said the average rate of warming was 0.17 degrees Celsius per decade between 1970 and 1998, but decreased to 0.04 C per decade between 1998 and 2012.
As many as 17 small volcanic eruptions since 2000 spewed enough aerosols into the atmosphere to explain a significant portion of the slowdown, researchers said.
Aerosols are fine, airborne particles - such as sulfate - that scatter the Sun's energy, cooling the Earth.

This cooling has offset the ongoing warming caused by greenhouse gases such as carbon dioxide by 15 per cent, 'LiveScience' reported.

"Part of the lack of the increase in warming for the last 15 years may be due to the cooling effect of volcanoes," said Celine Bonfils, a study co-author from Lawrence Livermore National Laboratory (LNNL) in Livermore.
Scientists correlated 17 volcanic eruptions since 2000 with shifts in troposphere temperatures, for which there is a global satellite record of temperature trends.
Making use of computer models and statistical tests, the researchers calculated that aerosols from the volcanoes reduced global troposphere temperatures. The aerosols also cooled the troposphere by reflecting sunlight.

"We see a statistically significant correlation with not only temperature, but reflected sunlight - which are both independent measures," researchers said.
The findings show that the slowdown in global warming can't be blamed on a single factor, the researchers said.
The study was published in the journal Nature Geoscience.