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Thursday, April 02, 2020

2019 was hot. The 2010s were even hotter 

Since the 1960s, each decade has been warmer than the previous one, by significant amounts. While the 2010s continued this trend, the second half of the decade was especially warm — the five hottest years ever have occurred during that span.

By: New York Times | Updated: January 16, 2020 9:09:19 am
2019 was hot. The 2010s were even hotter  On an unusually warm morning in Anchorage, Alaska, July 3, 2019. Last year was Alaska’s warmest on record, NOAA reported in a January 2020 analysis. (The New York Times: Joshua Corbett)

Written by Henry Fountain

The past decade was the hottest on record, government researchers announced Wednesday, the latest sign of global warming’s grip on the planet. And 2019 was the second warmest year ever, they said, just shy of 2016.

Analyses by the National Aeronautics and Space Administration and the National Oceanic and Atmospheric Administration showed that global average surface temperatures last year were nearly 1 degree Celsius (1.8 degrees Fahrenheit) higher than the average from the middle of last century, driven in large part by emissions of carbon dioxide and other heat-trapping gases from the burning of fossil fuels. That much warming means the world is far from meeting goals set to combat climate change.

“These trends are the footprints of human activity stomping on the atmosphere,” said Gavin A. Schmidt, director of the Goddard Institute for Space Studies, which conducted the NASA analysis.

The average for 2019 was only a small fraction of a degree lower than in 2016, a year with a strong El Niño, when changes in the ocean and air in the equatorial Pacific Ocean led to shifting weather patterns worldwide — and pumped a lot of heat from the Pacific into the atmosphere.

Since the 1960s, each decade has been warmer than the previous one, by significant amounts. While the 2010s continued this trend, the second half of the decade was especially warm — the five hottest years ever have occurred during that span.

“We’ve entered a new neighborhood in the last five years,” said Deke Arndt, chief of the monitoring branch of the National Centers for Environmental information, which conducted the NOAA research.

NASA and NOAA do independent analyses but use most of the same temperature data, which is gathered at sea from ships and buoys and on land from tens of thousands of observing stations coordinated by government meteorological agencies. This exhaustive data set is then combed for errors and less obvious factors — like the moving of a weather station from one year to the next — that might bias the analysis.

Also read | 2019 was second hottest year ever, more extreme weather coming, says UN

The studies take into account the contribution of natural influences, or forcings, on climate, like volcanic eruptions that can temporarily cool the atmosphere or regular changes in Earth’s orbital cycle.

“We end up with a massive discrepancy,” Schmidt said. ‘That tells us the natural forcings are not capable of explaining the trends we’ve seen since the 19th century.”

The two studies differ only slightly; their overall findings are the same. And their results closely match those from analyses by agencies overseas and private groups, including one released last week by a European climate agency that was based more on computer modeling than on observational data from 2019.

Only a few parts of the world — most notably central Canada and the Northern Plains in the United States — had cooler-than-average conditions last year. Some regions showed extreme warming, with devastating effects in some cases.

In Australia, known for its summer heat, 2019 was exceptionally warm, with temperatures 1.5 degrees Celsius (2.7 Fahrenheit) higher than the mid-20th century average, according to the Australian government’s Bureau of Meteorology. Combined with low rainfall totals — in December the country had the least rainfall on record — the heat has contributed to a severe drought that has gripped most of the country since 2017.

The heat has also helped fuel wildfires that began in September and have continued burning across much of eastern Australia. Prolonged heat sucks more moisture from vegetation, making it more susceptible to burning. “A warmer atmosphere is a thirstier atmosphere,” Arndt said.

As in Australia, extreme heat in southern Africa has contributed to the region’s worst drought in decades. Zambia and Zimbabwe are most affected, with millions of people suffering food shortages as production of maize and other grains declined by 30% or more.

The countries’ electricity supply is also at risk, as water levels along the Zambezi, one of Africa’s major rivers, are exceptionally low. Under normal conditions Zambia and Zimbabwe each get about halt of their electricity from separate hydroelectric plants at a dam on the Zambezi. The reservoir behind the dam is currently at less than 20% of capacity, meaning the plants cannot generate as much power.

In North America, record high temperatures were set across Alaska, including in Anchorage, the largest city. On a weekend in early July, there were back-to-back days of record-high average temperatures statewide.

But 2019 only continued a long-term warming trend, one that has led to increased melting of the state’s thousands of glaciers, thawing of permanently frozen ground, or permafrost, and a lack of sea-ice coverage in some of the Arctic waters surrounding the state.

The Bering Sea, off Alaska’s northwest coast, was ice-free for much of last year. Satellite images taken in late March showed largely open water at a time when the sea is normally completely covered in ice. The lack of ice is thought to have contributed to the increased warming across the state — a positive feedback loop in which warming creates conditions that lead to more warming.

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