2019 capped off the world’s hottest decade in recorded history

WASHINGTON - The past decade was the hottest ever recorded on the planet, driven by an acceleration of temperature increases in the past five years, according to new data released Wednesday by the U.S. government.

The findings, released jointly by NASA and the National Oceanic and Atmospheric Administration (NOAA), detail a troubling trajectory: 2019 was the second-hottest year on record, trailing only 2016. The past five years each rank among the five hottest since record-keeping began. And 19 of the hottest 20 years have occurred during the past two decades.

The warming trend also bears the unmistakable fingerprint of humans, who continue to emit tens of billions of tons of carbon dioxide into the atmosphere each year, scientists say.

"No individual hot year - or hot day or hot season, for that matter - is by itself evidence for climate change. But this hot year is just one of many hot years in this decade," said Kate Marvel, a research scientist at NASA and Columbia University. "The planet is statistically, detectably warmer than before the Industrial Revolution. We know why. We know what it means. And we can do something about it."

Leaders from nations around the world have vowed to try to limit the Earth's warming to no more than 1.5 degrees Celsius (2.7 degrees Fahrenheit) above preindustrial levels, in an effort to head off catastrophic sea level rise, ever-deadlier extreme weather events and other climate-related catastrophes. But hitting that ambitious target would require a rapid, transformational shift away from fossil fuels that has yet to materialize.

Instead, global greenhouse gas emissions hit a record high in 2019, even as they fell slightly in the United States, and the amount of carbon dioxide in the atmosphere now sits at the highest level in human history - a level probably not seen on the planet for 3 million years.

The 2019 figures from NASA and NOAA match similar data released by Berkeley Earth, an independent group that analyzes temperature data. The findings also are in line with data released last week by the Copernicus Climate Change Service, a science initiative of the European Union. The World Meteorological Organization confirmed the analysis.

In fact, Berkeley Earth researchers said, no place on Earth experienced a record cold annual average during 2019. But 36 countries - from Belize to Botswana, from Slovakia to South Africa - experienced their hottest year since instrumental records began. Those same researchers estimated that more warming lies ahead, and that a 95% chance exists that 2020 will become one of the five hottest years.

Wednesday's figures offer the latest evidence of the globe's inexorable temperature rise, particularly in recent decades. But the warming over the past century - and the impacts of climate change - have affected different parts of the world in vastly different ways.

A recent Washington Post analysis found numerous locations around the globe that already have warmed by at least 2 degrees Celsius over the past century. That's a number that scientists and policymakers have identified as a red line if the planet is to avoid catastrophic and irreversible consequences.

Some entire countries, including Switzerland and Kazakhstan, have warmed by 2C, and other hot spots exist around the world, particularly in the fast-warming Arctic. Scientists say extreme warming is helping to fuel wildfires from Australia to California, melt permafrost from Alaska to Siberia and fuel more intense storms and floods. It is also altering marine ecosystems from Canada to South America to the African coast, threatening wildlife and the livelihoods of those who depend on the sea.

"The evidence isn't just in surface temperature," Benjamin Santer, a researcher at Lawrence Livermore National Laboratory, said of the human-fueled warming trend. "It's Arctic sea ice. It's atmospheric water vapor increases. It's changes in glaciers in Alaska. It's changes in the Greenland Ice Sheet. It's all of the above."

The past year alone featured a litany of disasters that scientists say were worsened by climate change - disasters they argue are only more likely in the future unless global emissions begin to fall sharply.

During a tragic and terrifying December in Australia, with bush fires proliferating amid heat and drought, the country shattered its record for the hottest-ever day. On Dec. 18, the national average high temperature was a blistering 107.4 degrees (50.6 Celsius). Europe recorded its hottest year ever, and a sizzling heat wave in July saw temperature records crumble. Paris, for example, registered a sweltering 108.7 degrees July 25, shattering a record set in 1947.

Alaska also had its hottest year on record in 2019. It included an alarming lack of ice cover during the winter in the Bering and Chukchi Seas, and in the summer the temperature at Ted Stevens Anchorage International Airport hit 90 degrees for the first time.

Hurricanes such as Dorian devastated the Bahamas and other areas after rapidly intensifying, which some studies show is linked to warming seas and air temperatures. A pair of powerful cyclones hit Mozambique in rapid succession, killing hundreds of people, destroying homes and causing devastating floods.

The year also brought signs that the natural systems that serve to store huge quantities of carbon dioxide and methane, another powerful greenhouse gas, may be faltering as temperatures increase.

In December, a federal report indicated that melting permafrost throughout Arctic may already be a net source of atmospheric carbon, a shift that could accelerate global warming. Raging fires in the Amazon now threaten to turn the world's most productive rainforest into a drier, less carbon-rich savanna.

Widespread reports from the U.N. Intergovernmental Panel on Climate Change (IPCC) last year detailed how climate change is already threatening food and water supplies, increasing the threat of droughts and floods, killing coral reefs, supercharging monster storms, fueling deadly marine heat waves and contributing to record losses of sea ice.

A new study this week also found that 2019 was the warmest on record for the world's oceans, with all of the top five hottest years coming since 2015. The oceans have long absorbed the vast majority - about 93% - of the extra heat humans are adding to the climate through greenhouse gas emissions.

Still, even as millions of protesters have taken to the streets to demand action, world leaders have so far shown little ability to move as fast as scientists say is necessary to cut greenhouse gas emissions.

In a bleak report last fall, the United Nations warned that the world had squandered so much time mustering the willpower to combat climate change that drastic, unprecedented cuts in emissions are now the only way to avoid an ever-intensifying cascade of consequences. The U.N. report said global temperatures are on pace to rise as much as 3.2 degrees Celsius (5.8 degrees Fahrenheit) by the end of the century, and that emissions must begin falling by 7.6% each year beginning 2020 to meet the most ambitious goals of the Paris climate accord.

So far, many countries have failed to live up to the promises they made as part of the 2015 global agreement, including some of the world's largest emitters. More than 100 countries have vowed to submit more ambitious plans to fight climate change the end of 2020, but they collectively represent only about 15% of global emissions. The Trump administration plans to exit the international accord later this year.

Zeke Hausfather, a climate researcher for Berkeley Earth, said that despite the clear warming trend, humans still have an opportunity to shape what lies ahead.

"We don't have any sign yet of global warming slowing down, but we also don't have any sign of global emissions slowing down," he said. "What happens in the future depends a lot on our emissions of greenhouse gases as a society. If we continue emitting at current levels, we will continue warming at about the same rate.

“What happens in the future is really up to us.”