Guest author Kenneth Richard examines the impacts of past volcanoes on climate. The findings will surely be controversial.
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Volcanic activity explains long-term climate change better than CO2
By Kenneth Richard
Long-term (decadal and even centennial-scale) volcanic influence on climate has recently gained more and more attention in the scientific literature. Previously thought to influence surface temperatures for only a few years at a time, there is now a growing body of evidence suggesting volcanic aerosols may significantly affect both short and long-term climate changes by blocking solar radiation from heating the oceans’ surface waters.
When specifying the factors contributing to decadal and centennial-scale temperature changes, solar activity and greenhouse gases are usually thought to top the list. And since 93{154653b9ea5f83bbbf00f55de12e21cba2da5b4b158a426ee0e27ae0c1b44117} of the heat from global warming ends up in the oceans (IPCC, 2013), the focus necessarily should be on what mechanisms contribute most to variations in ocean heat content (OHC) and sea surface temperatures (SST).
Back in 2013, Rosenthal et al. published a paper in Science on millennial-scale ocean heat content variations (Pacific). As the graph (Fig. 4B from the paper) below illustrates, the authors document a dramatic cooling of the 0-700 m layer between the Medieval Warm Period (~1000 CE) and Little Ice Age (1600-1800 CE). While OHC has risen since the depths of the Little Ice Age, modern ocean temperatures are still significantly cooler (-0.65°C) than what they were just 1,000 years ago, or during the Medieval Warm Period.
