Tuesday, March 15, 2016

How 2 degrees may turn into 4

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Public Release: 20-Jan-2016
How 2 degrees may turn into 4
ETH Zurich

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.


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 2°C (3.6°F), the region will see mean temperatures increase by 3.4°C (6.12°F) on average. If, however, our aim is to limit warming in the Mediterranean to 2°C, then the global temperature must rise by no more than 1.4°C. The most extreme changes could be seen in the Arctic: with global warming of 2°C, the average temperatures in the far north increased by 6°C (10.8°F). The 2°C target for the Arctic had already been exceeded when global warming reached 0.6°C on average (this figure is now approximately 1°C).


According to Seneviratne, anyone can use these calculations to see how 2°C of warming would affect their region; this makes them a valuable tool for politicians and decisions-makers, as well as for civilians, agriculture and the tourism industry.

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.

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