By Joshua S Hill | 25 October 2011, 12:34 BST
One of the common arguments to dismiss those supporting the idea that the climate is warming as a result of manmade carbon dioxide emissions is that global warming is a natural thing; that it has always varied and that sometimes temperatures rise and that this is a perfectly natural occurrence. However in a new study it has been shown that a simultaneous warming of both the Southern and Northern Hemispheres has never happened in the past 20,000 years.
The study, conducted by Svante Björck, a climate researcher at Lund University in Sweden, steps back as far as it is possible to step to analyse with sufficient precision to compare modern developments. As a result, Björck's study has gone back a whole 14,000 years further than any other study ever conducted.
"What is happening today is unique from a historical geological perspective," he says.
Björck's study looked at the global climate archives - compiled from core samples taken from marine and lake sediments and glacier ice that provide a record of temperatures, precipitation and concentration of atmospheric gases - that have been made available in research publications over the years and looked for any evidence that suggests dramatic climate events have happened simultaneously in both hemispheres, and found none.
"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 Björck.
Björck provides the Little Ice Age, which saw Europe experience some of its coldest centuries during the years 1600 to 1900, as an example of his study. While there were massive and dramatic effects throughout Europe, affecting agriculture, state economics and transport, there is no evidence in the Southern Hemisphere that anything similar took place.
In fact, the only times that the researchers saw the Northern and Southern Hemispheres corresponding to one another was during 'calmer' climatic periods when the climate system was influenced by external processes.
"This could be, for example, at the time of a meteorite crash, when an asteroid hits the earth or after a violent volcanic eruption when ash is spread across the globe. In these cases we can see similar effects around the world simultaneously", says Svante Björck.
Professor Björck links this finding to today's situation with manmade greenhouse gasses spreading through the atmosphere taking place at the same time as a global warming.
"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 Björck. "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."
Source: Lund University
Source: Planet Save