Last year, 2016 was the hottest year on record, European climate researchers announced on Friday as global temperatures continued their unstoppable rise caused by the emission of heat-storing greenhouse gases.
The record warmth that triggered deadly heat waves, droughts, violent forest fires and other environmental disasters worldwide in 2020 occurred despite the development of La Niña in the second half of the year, a global climate phenomenon characterized in large part by surface cooling of the equatorial Pacific.
And while 2020 may tie the record, the last six years are among the hottest ever, said Freja Vamborg, a senior scientist at Copernicus Climate Change Service.
“It’s a reminder that if we don’t cut greenhouse gas emissions, temperatures will change and will keep changing,” said Dr. Vamborg.
According to Copernicus, a European Union program, the global average temperature in 2020 was 1.25 degrees Celsius warmer than the average from 1850 to 1900, before emissions from the spread of industrialization increased. The 2020 average was slightly below the 2016 average, too small a difference to be significant.
Some regions experienced exceptional warming. For the second year in a row, Europe had the warmest year ever, suffering from deadly heat waves. The temperature difference between 2020 and 2019 was remarkable, however: 2020 was 0.4 degrees Celsius, or nearly three quarters of a degree Fahrenheit, warmer.
Although not quite as drastic as in Europe, the temperatures in North America were also above average. Warming played a crucial role in the widespread drought that hit most of the western half of the United States and in the violent forest fires that devastated California and Colorado.
The Arctic is warming much faster than anywhere else, a feature that was reflected in the 2020 numbers. Average temperatures in some parts of the Arctic last year were more than 6 degrees Celsius higher than the average between 1981 and 2010. Europe, however, was 1.6 degrees Celsius higher last year than for the same reason.
In the Arctic, and particularly in parts of Siberia, conditions were unusually warm for most of the year. The heat caused the vegetation to dry out, which in Siberia helped fuel one of the most intense forest fire seasons in history.
Parts of the southern hemisphere experienced sub-par temperatures, possibly due to the arrival of conditions in La Niña in the second half of 2020.
Dr. Vamborg said it was difficult to directly attribute temperature differences to La Niña, but the cooling effect of the phenomenon could be why December 2020, when La Niña got stronger, was only the sixth warmest December ever, during most of the other months of the year were in the top three.
Zeke Hausfather, a scientist at Berkeley Earth, an independent research group in California, said that La Niña’s greatest impact on global temperatures typically occurs several months after conditions peak in the Pacific. “While La Niña has certainly had some cooling effect in recent months, it will likely have a bigger impact on temperatures in 2021,” he said.
Dr. Hausfather said it was noteworthy that 2020 coincided with 2016 because that year’s record heat was fueled by El Niño. El Niño is essentially the opposite of La Niña when surface warming in the Pacific tends to increase global temperatures.
So 2020 and 2016 are equally warm, said Dr. Hausfather, which means the past five years of global warming have had a cumulative effect roughly the same as El Niño.
Berkeley Earth will publish its own analysis of global temperatures for 2020 later this month, as will the National Oceanic and Atmospheric Administration and NASA. The three analyzes take a similar approach and essentially produce thousands of temperature measurements worldwide.
Copernicus uses a technique called reanalysis that uses fewer temperature measurements but adds other weather data like barometric pressure and feeds everything into a computer model to get the temperature averages.
Despite the differences, the results of the analyzes tend to be very similar.
