by Staff Writers
Zurich, Switzerland (SPX) Jan 25, 2016
At the recent COP21 climate conference in Paris, delegates reached an agreement that plans to limit global warming to "well below" two degrees Celsius. This stems from the fact that scientists and politicians now agree: the global average temperature must rise by no more than two degrees if we are to prevent serious, irreversible damage to humans and the environment.
"However, this climate target is abstract and invites misunderstanding," says Sonia Seneviratne, Professor of Land-Climate Dynamics at ETH Zurich. According to Seneviratne, many people will interpret two degrees globally as two degrees of warming in their region and, accordingly, will not be proactive enough about reducing CO2 emissions in their countries.
The problem is that, according to various climate models, the temperature will rise more sharply over land than over oceans. The big question is therefore how a maximum of two degrees global warming will affect individual regions of the world.
First quantitative treatment
Recently published in Nature as a "Perspective", this study constitutes one of the first quantitative treatments of this issue. Several qualitative examinations have already been carried out on the relationships. This study was supported by Seneviratne's ERC Consolidator Grant project "DROUGHT-HEAT".
The research team based their calculations on several existing climate scenarios, as well as on the assumed and effective development in atmospheric CO2 concentration.
New graphical depictions were a key result of the calculations. They show at a glance how average temperatures respond to the overall quantity of CO2 emitted and in relation to average global warming in major geographical regions.
Four model regions tested
The scientists tested their new model using four examples: the Mediterranean, the USA, Brazil and the Arctic. For each of these regions, the researchers computed a separate graphical representation.
For the Mediterranean, the results reveal the following: if the global average temperature increases by 2C, the region will see mean temperatures increase by 3.4C on average. If, however, our aim is to limit warming in the Mediterranean to 2C, then the global temperature must rise by no more than 1.4C. The most extreme changes could be seen in the Arctic: with global warming of 2C, the average temperatures in the far north increased by 6C. The 2C target for the Arctic had already been exceeded when global warming reached 0.6C on average (this figure is now approximately 1C).
For the ETH climate researcher, the study is a practical aid - "a communications measure," as she puts it - for defining regional emissions targets. "The regional impacts of global warming are far more important," she says. The study could be helpful during negotiations, as it would quickly show the significance of climate change for the various parties, adds Seneviratne. This could also help citizens and decision-makers of individual countries to understand why it is important to rapidly reduce CO2 emissions and, specifically, to below the global 2C target if possible.
Valuable tool for everyone
However, the scientists also point out that the calculations have their limitations. For example, they only provide statements on climate evolution for major regions. "The diagrams cannot be used to deduce what temperatures will be like in the city of Zurich if we reach two-degrees of warming on a global scale," says the ETH professor.
Seneviratne SI, Donat MG, Pitman AJ, Knutti R, Wilby RL. Allowable CO2 emissions based on regional and impact-related climate targets. Nature, Advance Online Publication, 20 January 2016. DOI: 10.1038/nature16542
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