Volcanoes partly responsible for global warming slowdown, says climate study

A new study has added volcanoes to the list of culprits responsible for the supposed 'global warming hiatus,' as eruptions release reflective particles into the atmosphere that have cooled the planet and offset some of the expected warming.

When the rate of increase in global surface temperatures slowed down starting in 1998 — from about 0.17 degrees per decade to around 0.04 degrees per decade, despite the continued and increasing release of carbon dioxide into the atmosphere — climate change deniers immediately grabbed hold of this as 'proof' that anthropogenic global warming and climate change were scams, myths or hoaxes. However, as scientists studied the phenomenon, they've found a few natural factors that reduced the rate of heating between 1998 and 2012: deep ocean heating, increases in the Pacific trade winds, changes in solar output, and volcanic eruptions. Even the man-made effect of more sulfur dioxide emissions from China and India have had an effect. This latest study, lead by scientists from the Lawrence Livermore National Laboratory in California, concentrated on the contribution from volcanic ash and gas.

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"In the last decade, the amount of volcanic aerosol in the stratosphere has increased, so more sunlight is being reflected back into space," said Benjamin Santer, climate scientist and lead author of the study, according to a press release. "This has created a natural cooling of the planet and has partly offset the increase in surface and atmospheric temperatures due to human influence."

This new study shows that even numerous smaller eruptions can cause enough of a buildup of sulfur in the atmosphere to produce the same cooling effect as a large eruption. The researchers point to at least 17 different eruptions since the year 2000, and their simulations show that without accounting for these eruptions, temperature estimates made by climate models for are around 15% too high.

"This is the most comprehensive observational evaluation of the role of volcanic activity on climate in the early part of the 21st century," co-author Susan Solomon, a professor of atmospheric chemistry and climate science at MIT, said in the statement. "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."

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It's long been known that sulfur particles released into the stratosphere reduce surface temperatures, as it's been seen time and time again that there is a brief cooling period after particularly large volcanic eruptions. These particles are highly reflective and thus reflect sunlight back into space before it can reach the surface. Pumping sulfur particles into the atmosphere has even been proposed as a potential 'geoengineering' project, should the effects of climate change become so bad that we need to take direct action to halt them. The problem with this is that once you've used this method, you have to continue to use it, or the temperatures will simply shoot up again once the concentration of sulfur particles drops back down to zero (not to mention the potential catastrophic damage to the ozone layer).

Herein lies the danger in seeing the past 15 years or so as any kind of 'haitus' or even 'pause' for global warming. Once these reflective aerosol particles settle to Earth and we have a relatively calm period with fewer volcanic eruptions, temperatures will being to skyrocket again. At best, this can be seen as a reprieve — merely a temporary delay of the worst effects of global warming and climate change.

(Photo courtesy: Reuters)

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