By Patricia Reaney
LONDON — Sea levels would have risen higher and ocean temperatures would have been warmer in the 20th century if the Krakatoa volcano in Indonesia had not erupted in 1883, scientists said on Wednesday.
The impact of the eruption that spewed molten rock and sulfate aerosols into the atmosphere was felt for decades — much longer than previously thought.
“It appears as though with a very large eruption the effect can last for many decades and possibly as long as a century,” said Peter Gleckler, a climatologist at the Lawrence Livermore National Laboratory in California.
Sea levels rise when ocean temperatures are warmer and recede when they cool. Volcanoes release aerosols and dust that block sunlight and cause the ocean surface to cool which can offset, at least temporarily, sea level rises caused by increased greenhouse gases in the atmosphere.
In recent decades, the average ocean temperature has warmed by about .037 degrees Celsius, according to the scientists.
Gleckler and researchers in the United States and Britain were studying models of climate simulations when they noticed the impact of volcanic eruptions.
Some of the climate models included the impact of such eruptions while others did not.
“As we looked at the first picture of all these models together, we saw that just at the time of Krakatoa there was this very clean separation of those that included the eruption and those that did not,” Gleckler told Reuters.
“Volcanoes have a big impact. The ocean warming and sea level would have risen much more if it weren’t for volcanoes,” said Gleckler, who reported the findings in the journal Nature.
The study also included more recent eruptions including Pinatubo in the Philippines in 1991, which was on a similar scale to Krakatoa.
But the effect of Pinatubo on ocean temperatures was much smaller because of the impact of greenhouse gases which were much higher in 1991 than in 1883.
“The Pinatubo eruption influence on sea level and heat content was dampened by this background warming,” said Gleckler.
He added that scientists must think more carefully about how they include the effects of volcanic eruptions such as Krakatoa and even earlier ones, in climate modeling.
“We can’t rely on future volcanic eruptions slowing ocean warming and sea level rises,” Gleckler added.