Until the Industrial Revolution in the 19th century, the surface layer of Earth’s oceans had been steadily cooling for 1,800 years. For a thousand of those years, between 801 and 1800 AD, that trend was probably driven by large and frequent volcanic eruptions. The cooling was sufficient to produce the “Little Ice Age” from the 16th to 18th centuries with lower than average temperatures on land.
Then came the Anthropocene, and man-made factors began to overwhelm the long term trend. Volcanic activity just wasn’t enough to counter human activity and subsequent global warming.
Could we tame volcanos to beat warming?
So how does volcanic activity cool the oceans? Could volcanos ever be “harnessed” to work against damaging climate change?
When volcanos erupt they inject debris and “aerosols” into the stratosphere, and as this material spreads rapidly around the planet, it reflects solar radiation to space. This produces a cooling effect which continues as long as the aerosols remain in the stratosphere. There is an immediate short term effect and a more significant long term cooling of the oceans.
Compared to the atmosphere, the oceans can absorb much more heat and trap it for longer periods of time. When volcanic eruptions cluster together in a relatively short period of time, the temperature changes can become prolonged.
“Volcanic eruptions have a short-term cooling effect on the atmosphere, but our results showed that when volcanic eruptions occurred more frequently, there was long-term ocean cooling,” said lead author Helen McGregor, an Australian Research Council (ARC) Future Fellow at the University of Wollongong in Australia.
“With this research, we now have new insight into the century-scale global sea-surface temperature variations that came before man-made greenhouse gas forcing.”
“Today, the Earth is warming about 20 times faster than it cooled during the past 1,800 years,” said Michael Evans, second author of the study.
If those massive explosions that occasionally ground aircraft and strand passengers around the world are so good at countering global warming, would it ever be feasible to trigger volcanic eruptions in an attempt to slow down the damage? The team behind the study don’t think so. In their FAQ response to this suggestion they reply: “This is well beyond our expertise, and not only likely to be unfeasible, but also unpredictable and uncontrollable.”
Data points to the effects of volcanos
The research combined 57 previously published marine surface temperature reconstructions. The team compiled the data within 200-year brackets to observe long-term trends, and then compared the findings to land-based reconstructions, which revealed similar cooling trends.
“No matter how we divided the data set, the cooling trend stands out as a robust signal,” said McGregor.
The researchers used climate models to investigate the cause of the cooling trend. They examined how sea-surface temperatures reacted to various “forcing” factors, such as changes in solar output, Earth’s orbit, land use, volcanic activity, and greenhouse gases. Only volcanic events resulted in a cooling trend that matched the team’s real-world observations.
“We are still learning how the oceans mediate climate variations,” said Evans. “Further work combining both observations and simulations of ocean climate will refine our understanding of the ocean’s role in climate change.”
These findings are part of an international study just published in the journal Nature Geoscience.
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