LONDON (TIP): Molten lava spit out from the depths of the earth’s crust has caused destruction for centuries. But scientists now say volcanic eruptions have actually benefited the planet. Such eruptions in the early part of the 21st century cooled the planet, according to a study led by Lawrence Livermore National Laboratory in California. This cooling partly offset the warming produced by greenhouse gases.

Despite continuing increases in atmospheric levels of greenhouse gases and in the total heat content of the ocean, global mean temperatures at the surface of the planet and in the troposphere (the lowest portion of the Earth’s atmosphere) have shown relatively little warming since 1998. This socalled slowdown or hiatus has received considerable scientific, political and popular attention. Volcanic eruptions inject sulphur dioxide into the atmosphere.

If the eruptions are large enough to add sulphur dioxide to the stratosphere (the atmospheric layer above the troposphere), the gas forms tiny droplets of sulphuric acid, also known as volcanic aerosols. These droplets reflect some portion of the incoming sunlight back into space, cooling the Earth’s surface and the lower atmosphere. “In the last decade, the amount of volcanic aerosol in the stratosphere has increased, so more sunlight is being reflected back into space,” said Lawrence Livermore climate scientist Benjamin Santer.

“This has created a natural cooling of the planet and has partly offset the increase in surface and atmospheric temperatures due to human influence.” The researchers performed two different statistical tests to determine whether recent volcanic eruptions have cooling effects that can be distinguished from the intrinsic variability of the climate.

The team found evidence for significant correlations between volcanic aerosol observations and satellite-based estimates of lower tropospheric temperatures as well as the sunlight reflected back to space by the aerosol particles. “This is the most comprehensive observational evaluation of the role of volcanic activity on climate in the early part of the 21st century,” said co-author Susan Solomon from MIT. “We assess the contributions of volcanoes on temperatures in the troposphere — the lowest layer of the atmosphere — and find they’ve certainly played some role in keeping the Earth cooler.”