Over the past 100 years, global temperatures have risen by an average amount of 0.8° C (1.4° F), which according to the Intergovernmental Panel on Climate Change (IPCC), is due largely to humanity's release of pollutants into the atmosphere. Now an international team of researchers has analyzed almost 40 years worth of data in order to quantify exactly what fraction of the change can be attributed to mankind based on events and trends in different regions.

The study was undertaken by researchers at Germany's Potsdam Institute for Climate Impact Research and Lawrence Berkeley National Laboratory in California, working together to develop a novel way of assessing humanity's impact on the planet's climate.

The team focused on individual regional impact events identified by the IPCC, such as melting glaciers or Alaskan wildfires, taking place between 1971 and 2010. Using a specially-developed algorithm, the researchers worked through each event, judging whether the gathered data on the local climate was sufficiently detailed to allow conclusions to be drawn, and whether the models used to analyze said data were sufficiently detailed and appropriately tailored to the region.

Once those criteria were met, the algorithm compared the observed results with numerous model simulations of what would have occurred with and without the presence of harmful emissions resulting from human activities. Each event was then given a score to describe the measure of confidence in human-generated emissions having affected the change in climate, and those results combined to provide an overall conclusion.

While the link between the harmful emissions and changes in rainfall were weak, when it came to cases of warming over land or in coastal areas, a strong correlation – almost two thirds of the recorded impacts – were found to be the result of human activity. Furthermore, in cases where the connection between the emissions and local warming was found to be weak, this was usually due to insufficient data rather than evidence of other causes.

According to the researchers, the new study is a big step forward. Previous work looked more at the big picture, without studying individual events in detail.

"Our analysis is the first to bridge these gaps for a large range of impacts, by assessing the role of human-related emissions in each impact individually, including impacts related to trends in precipitation and sea ice," said the Potsdam Institute's Dr. Gerrit Hansen.

The findings are published in the journal Nature Climate Change.

Source: Lawrence Berkeley National Laboratory