New study shows no simultaneous warming of northern and southern hemispheres as a result of climate change for 20,000 years

Lund University News (Sweden): A common argument against global warming is that the climate has always varied. Temperatures rise sometimes and this is perfectly natural is the usual line. However, Svante Björck, a climate researcher at Lund University in Sweden, has now shown that global warming, i.e. simultaneous warming events in the northern and southern hemispheres, have not occurred in the past 20,000 years, which is as far back as it is possible to analyse with sufficient precision to compare with modern developments. Svante Björck’s study thus goes 14 000 years further back in time than previous studies have done. “What is happening today is unique from a historical geological perspective”, he says

Svante Björck has gone through the global climate archives, which are presented in a large number of research publications, and looked for evidence that any of the climate events that have occurred since the end of the last Ice Age 20 000 years ago could have generated similar effects on both the northern and southern hemispheres simultaneously. It has not, however, been possible to verify this. Instead, he has found that when, for example, the temperature rises in one hemisphere, it falls or remains unchanged in the other.

“My study shows that, apart from the larger-scale developments, such as the general change into warm periods and ice ages, climate change has previously only produced similar effects on local or regional level”, says Svante Björck.

...“As long as we don’t find any evidence for earlier climate changes leading to similar simultaneous effects on a global scale, we must see today’s global warming as an exception caused by human influence on the earth’s carbon cycle”, says Svante Björck, continuing: “this is a good example of how geological knowledge can be used to understand our world. It offers perspectives on how the earth functions without our direct influence and thus how and to what extent human activity affects the system.”...

Off the Greenland coast, shot by Christine Zenino, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license