Climate responsibility in extreme events

From October 29 to 31, 2012, Hurricane Sandy affects New York City and neighboring New Jersey. Thousands of homes were destroyed, the subway was flooded, shops and businesses had to close, electricity was cut off, oil terminals were completely devastated. In New York State alone, 53 people are dying. The total loss is 50 billion euros. A team of American climatologists is returning to disaster today. They were able to calculate the share of damage attributable to global warming. That represents more than 6.5 billion euros, or 13% of the final bill, as their article just appeared Communications of nature.

How did these researchers assess climate responsibility so accurately? Hurricane Sandy was certainly an exceptional event, “Storm Frankenstein,” as the American media called it. But its devastating effect is amplified by the fact that it “landed” at the time of the tide of strong coefficient. In addition, reports Intergovernmental Panel on Climate Experts (IPCC) have not yet concluded on the impact of rising temperatures on the frequency and intensity of tropical storms affecting the Pacific, Indian, and Atlantic Oceans. The study therefore does not rely on these data, but considers a well-known physical phenomenon: sea level rise since the beginning of the industrial era.

Comparison of models with and without temperature rise

The researchers first tried to eliminate all physical factors except sea level rise caused by the pole by melting Arctic and Antarctic sea ice and glaciers, and the other half by spreading surface waters hot.

Thus, the effects of subsidence (lowering of the earth’s surface) caused, for example, by pumping groundwater and storing water in dams are excluded. In this way, they were able to estimate that between 1900 and 2012, the level of the sea region in which bathing north of the United States increased by 8.9 centimeters only by increasing the level of greenhouse gases of human origin in the atmosphere.

To simulate the impact of this increase, the researchers built a hydrodynamic model that allowed them to reconstruct flooding of urban areas with water, according to different hypotheses. “The authors constructed a “factual” world in which they take into account the rise in sea level caused by anthropogenic emissions and a “counterfeit” world (which therefore does not exist) without emissions and with a constant sea level, Explain Davide Faranda, researcher at Climate and Environment Laboratory (LSCE, CNRS / CEA). Statistical results show that there is a difference in sinking that directly affects a population with fairly large economic losses. ” U.S. researchers estimate that 36,000 homes would not be flooded without contributing to climate change, which is causing 71,000 additional casualties.

The loss and damage caused by climate change is already here

The study of Sandy clearly shows the direction of this new area of ​​research that is Extreme attribution of events, attributed to the increase in global temperatures of the fiercest and most severe events. One of the fathers of this new scientific field, Myles Allen, researcher at Oxford University (United Kingdom), he came up with the idea in 2005 considering the damage caused by the extreme floods in his city of Oxford. “It was necessary to be able to determine the share of responsibility for climate change so that victims would have the opportunity to file a lawsuit against the authorities and companies that do not combat the identified risk, recalls Aglaë Jezequel, a researcher at the Dynamic Metrology Laboratory (LMD / Pierre-Simon Laplace Institute). The interest is therefore as social as it is scientific. “

It is actually a question of establishing a connection between inaction and its consequences. This area of ​​study has developed specifically since 2014. In November 2013, indeed, during COP19 in Poland, the member states of the Climate Convention decided to create “The Warsaw Mechanism“Compensation for damage and damage already caused by climate change. Negotiators recognize that impacts are already being felt everywhere on the planet, especially in the 48 most affected countries, all tropical and all poor united in Vulnerable twenty groups. Two figures are given. The current damage was already $ 50 billion a year in 2010, and could reach $ 400 billion a year in two decades.

Attribution makes it possible to seek justice in the courts

The Warsaw Mechanism is one of the most discussed topics in the Communities of Practice. How to really separate the meteorological danger from the extreme climate? “Attribution” is a good way to shorten controversy in a way that provides a scientific basis for assessing the damage done. Davide Faranda is one of those researchers who have invested in this new field of knowledge. He graduated in 2013 on extreme events. “This research area was then dominated by mathematics, remembers Davide Faranda. It was determined using statistics and probabilities whether the investigated event deviated in frequency and intensity from anything previously observed. A new generation is coming that integrates physics into this work. “ The physical interpretation of extreme events now consists in separating what is the consequence of an increase in temperature from the natural properties of the atmospheric circulation that produces a temporal event. That’s exactly what American researchers are doing with Storm Sandy.

Therefore, this more solid attribution opens up a large legal domain. The 71,000 people Sandy hit when their homes could be spared, that the U.S. state and economy had indeed begun to act on greenhouse gas emissions, have to blame themselves unlike those victims of a natural disaster. Insurers could also find a new remedy. The poorest countries will finally have enough to provide scientific evidence that the damage caused to their territory is due to the inactivity of the countries that emit the most greenhouse gases. And that they have to pay.

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