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 CO 2 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

A team of climate researchers from Switzerland, Australia and the UK led by Seneviratne has now addressed this question. For the first time, the scientists have calculated the levels of extreme and average temperatures, as well as of heavy precipitation, that will occur in individual regions if the average global rise in temperature is taken as a reference.

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 CO 2 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 CO 2 emitted and in relation to average global warming in major geographical regions.

Four model regions tested

The depictions are easy to interpret: the graphical representation is like a type of ruler on which the envisaged target value – such as the global two-degree target – can be set; a linked warming value can then be identified in the corresponding region.

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.