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A world tour of a record year

2020 was effectively tied with 2016 for the warmest year on record, with global warming linked to greenhouse gas emissions showing no signs of slowing down.

Siberia and the Arctic were among the warmest regions. The heat fueled forest fires that pumped more carbon dioxide into the atmosphere.

Temperatures in the Siberian city of Verkhoyansk reached a record high of 100 degrees Fahrenheit in June, more than 30 degrees above average.

The heat was also felt in Europe, which experienced the hottest year in its history and experienced searing heatwaves until September.

The surface cooling of the tropical Pacific Ocean, which began in the second half of the year, has hardly offset the heat elsewhere.

In central South America, warming and drought triggered forest fires that burned a quarter of the vast Pantanal wetland.

In the United States, the warming has been greatest in the northeast and southwest. The drought has spread to half of the country.

This analysis of global temperatures, carried out by the Goddard Institute for Space Studies at NASA and released on Thursday, found that 2020 was slightly warmer than 2016. But the difference was insignificant, said institute director Gavin Schmidt, in an interview.

“In fact, it’s a statistical equality,” he says.

Other analyzes released Thursday, one by the National Oceanic and Atmospheric Administration and another by Berkeley Earth, an independent research group in California, found that 2020 was slightly colder than 2016, just like the one released last week by the Copernicus Climate Change Service in Europe. But the difference was small enough that it was not statistically significant.

With the 2020 results, the past seven years have been the warmest since modern archiving began almost a century and a half ago, Dr Schmidt said.

“We’re now very, very clear on the underlying long-term trends,” he said. “We understand where they come from. This is because of the greenhouse gases pumped into the atmosphere.

The planet has warmed by more than 1 degree Celsius (about 2 degrees Fahrenheit) since the late 1800s, when the spread of industrialization resulted in increased emissions of carbon dioxide and other greenhouse gases. greenhouse, and the pace has accelerated in recent decades. Since 1980, warming has averaged about 0.18 degrees Celsius (about 0.32 degrees Fahrenheit) per decade.

But the numbers are only a small part of the story. As climatologists predicted, the world is seeing an increase in heat waves, storms and other extreme weather conditions as the planet warms, and disasters such as droughts, floods and wildfires. that result. The past year has offered no respite, with record fires in Australia and California, and severe drought in central South America and the American Southwest.

Some climatologists had thought that the arrival of cooler sea surface temperatures in the Pacific Ocean – part of the recurring global climate phenomenon called La Niña – would squeeze temperatures this year. It is difficult to quantify the influence of La Niña, but it is clear that any effect has been overshadowed by the rise in temperature linked to emissions.

La Niña only appeared in September and grew stronger a few months later. La Niña’s climate impact tends to peak several months after the waters of the Pacific have reached their coldest point, so it may have more cooling effect in 2021.

When La Niña is factored in, “you don’t expect a banner year” in 2021, Dr Schmidt said. “But another year in the top five, and one that is clearly part of a series of very hot years that we have had,” he added.

Dr Schmidt said his team and others have studied the effects of the coronavirus pandemic on temperatures in 2020. Lockdown orders and the economic downturn have reduced greenhouse gas emissions by about 10% in the United States only, according to a recent report.

Such a reduction does not have an immediate effect on temperatures, Dr Schmidt said, and emissions will likely rise again as the pandemic subsides and the global economy returns to normal.

The biggest short-term effect, he said, could be the reduction of some transport-related pollution, including exhaust emissions of nitrogen oxides, as driving has declined during the pandemic.

Nitrogen oxides form aerosols in the atmosphere that reflect some of the sun’s rays, which would otherwise strike the surface and be re-emitted as heat. Even a slight reduction in these aerosols would allow more sunlight to reach the surface, generating more heat that would be trapped in the atmosphere by greenhouse gases.

Dr Schmidt said efforts were underway to quantify the effect over the past year. “The numbers aren’t important,” he said, but they may have played a role in making 2020 a banner year.

“The warming associated with aerosol reduction can be history,” he said.

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