Frequent volcanic eruptions cause an actual gear shift in the global climate system, ”says Stefan Brönnimann, head of the international research team on the effects of a series of eruptions on oceans and thus on atmospheric circulation.
Less rain in Africa and India, more rain and snow in Europe
For their investigations, the researchers analyzed new climate reconstructions that include atmospheric circulation and comparison of results to observation-based data. Model simulations have finally helped pinpoint the role of the oceans in climate change in the early 19th century and showed that they could not recover from the effects of a series of eruptions. The results: The Atlantic-European sector of the persistent weakening of the African and Indian monsoon systems and a shift in atmospheric circulation. This led to an increase in low-pressure systems crossing central Europe.
The last glacier advance in the Alps from the 1820s to the 1850s, depicted in paintings and even old photographs, is a result of increased precipitation combined with altered circulation in low temperatures. However, global warming has increased since the late 19th century onward. The Little Ice Age was eventually superseded by a first phase of global warming, culminating in the 1940s and a significant humanmade contribution.
Definition of “pre-industrial climate”
The New Bern study is not the only global early 19th century climate, but it is also relevant for the present. “Given the great climatic changes in the early 19th century, it is difficult to define a pre-industrial climate,” says lead author Stefan Brönnimann, “a notion to which all our climate goals refer.” And for policymakers, who want to limit global temperatures to between 1.5 and 2 degrees at Celsius. Depending on the reference period, the climate has already been warmed up much more than assumed in climate negotiations. The Reason: Today’s climate is more than usual with an 1850-1900 reference period to quantify current warming. The average global temperature has increased by 1 degree. “1850 to 1900 is a good choice but compared to the first half of the 19th century, when it was a cooler due to frequent volcanic eruptions, the temperature increase is already around 1.2 degrees,” Stefan Brönnimann points out.
Reference-
daily science