In very simple terms, attribution scientists compare the probability of a weather event—say, a storm, heat wave, or flood from a melting ice—of occurring or reaching a certain severity with the probability or severity of that same event in a simulation. A world in which greenhouse gas emissions have been eliminated from human activities. The difference between the two results is the ‘attribution value’ by which the direct impact of climate change can be expressed. These types of models are now so accurate that they can even predict the impact of slow effects of climate change, such as sea level rise and crop loss due to warm weather.
“The clarity with which we can determine how climate change affects the environment has improved dramatically,” said Robert Stewart Smith, an expert in climate law at the University of Oxford. For example, scientists were able to determine that the hottest days during a heatwave in the Pacific Northwest of the United States in 2021 were 2 degrees Celsius warmer than the same heatwave in an emissions-free world, and that Hurricane Harvey dumped 15 percent of the precipitation. on the city. Then Houston plunged into a virtual world without climate change.
But these models of attribution have their limitations, and those limitations are often determined by historical disparities. This is because the technology requires local and regional weather and climate data, and that data is based on solid historical measurements. According to Maryam Zakaria, a climate scientist with the World Weather Referral Program, who conducted this year’s analysis for Pakistan, this data has traditionally been collected primarily in the Northern Hemisphere, often making it difficult to do attribution science for areas where it is unreliable. weather data. .
However, this “knowledge can certainly start a conversation” about injustice, for example in the case of Pakistan. In the aftermath of the floods there, the UN Secretary-General called for “massive financial support to tackle this crisis,” adding that it was “not only about generosity but also about justice.”
Although much progress has been made in attribution science, the use of this method is controversial. Simply put, the contributions can show that the rainfall in Pakistan last summer was 75 percent higher than it should have been and that the damage from all that excess water should be borne by the responsible nations, i.e., the developed countries. For example, since the beginning of the Industrial Revolution in the mid-19th century, the United States has emitted about a quarter of the world’s greenhouse gases and is therefore responsible for about 25 percent of the costs. Major US oil companies, including Chevron and Exxon, are said to be responsible for three percent of historic global emissions.
But in practice, attributing the difference between the actual situation and the situation in a world without climate change is a very complex matter. Countries or companies that have a lot of carbon dioxide2 emits it, we believe that its contribution to climate change does not mean that it is also responsible for solving the problem. And according to Rachel James, a climate expert at the University of Bristol in the UK, social science research shows that these countries and companies do not agree to equate debt and attribution, so they are likely to be reluctant to talk about such a solution.
Moreover, many countries and companies responsible for large emissions believe that it is impossible to establish a direct link between the emissions for which they are responsible and the specific consequences of climate change, because greenhouse gases such as carbon dioxide2 They quickly spread throughout the atmosphere and their source can no longer be traced.
But recent analyzes increasingly contradict this argument. In August, a team at Dartmouth University was able to link historical emissions from one country to economic damage done elsewhere. They calculated that from 1990 onwards, US emissions—two years after climatologist James Hansen testified before the US Congress that human-induced climate change had already occurred—the rest of the world amounted to about $1,800 billion in damages. This may be a low estimate.
“Large emitters can no longer hide behind a veil of irresponsibility,” said Christopher Callahan, a climate researcher at Dartmouth University and lead author of the study. Individual emitters can be held liable for the damage they cause.
According to Thomas of the University of the Bahamas, “We have had the scientific evidence for decades to show that it is about the consequences of human actions. The main culprits are well known. The question now is whether it is a moral, social or political problem and how we deal with it.”
This article was originally published in English on nationalgeographic.com
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