NEW YORK – Over the past decade, scientists learned a great deal about the climate, much of it concerning the connection between global warming and extreme events — heat waves, hurricanes, floods, droughts and wildfires.
There has been, for many years, an understanding that a warmer world would be a more temperamental one, and measurements upon measurements show the average temperature is rising in step with those predictions. But until recently it was hard to prove that our changed atmosphere was having an influence on extreme events, which, after all, have been drowning and parching and starving people long before anyone started burning fossil fuels.
Asking whether climate change caused a particular wildfire or hurricane is the wrong question, said Benjamin Cook, a climate researcher with the Lamont-Doherty Earth Observatory. But in the last decade, the ability to model the climate has advanced so much, he said, that people can determine whether human-generated global warming made a storm wetter or a drought longer than it otherwise would have been. Such attribution, he said, is the biggest advance of the 2010s.
“This is important because extreme events are really where the impacts of climate change are being felt,” he said. It’s not necessarily alarming to hear that global temperatures will creep up another couple of degrees, but it’s another thing to realize that human actvity contributed to a string of deadly heat waves in Europe — with temperatures climbing well above 42 degrees in Paris — as well as the apocalyptic fires that destroyed what had been some of the most beautiful parts of California. “There’s a clear climate change signal,” he said.
If there’s any controversy now among scientists, it’s over whether they were too reluctant to sound the alarm about extreme events in the past. There was a reluctance to make recommendations based on probabilities and reasonable assumptions. Now there’s evidence to back them.
Over the past decade, climate researchers have been filling in gaps in their data on past temperatures, and improved models that are calibrated against the past to predict the future. That’s led to better predictions for weather as well, thanks to more complete data, better science and more computer power.
There’s more data on cloud formation, on precipitation, on ground water and on what’s happening underneath ice shelves, said Gavin Schmidt, director of NASA-Goddard, Institute for Space Sciences. All that basic knowledge has come about from a very productive decade of remote sensing.
The Arctic is warming faster than lower latitudes, and this is affecting the wind patterns — especially the jet stream. Researchers say that a weakening of those winds is part of the reason storms such as Hurricane Harvey stall, and dry air lingers in other places for weeks.
Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research in Boulder, Colorado, said that he’s been arguing since 2010 that extreme events are now happening in a different environment.
Because we’ve increased the Earth’s atmospheric carbon by more than 40 percent, the oceans are warmer, and the air above the ocean is warmer and wetter, and the sea level is already a little higher. That contributes to making storms more intense, with heavier, prolonged rainfall, as people witnessed with Harvey in Houston and Florence in the Carolinas. The planet’s dry climates are getting drier, and the wet, wetter.
Global warming is also heating the world’s oceans, and this, too, is not uniform, Trenberth said. And they can now track marine heat waves, which are killing coral and sea life from the Gulf of Maine to the Great Barrier Reef. A decade ago they could measure the ocean’s temperature down to 700 meters, he said; now they can track it to 2,000 meters. “We can actually see that heat penetrating down into the oceans.” The oceans have absorbed most of the energy that’s been trapped on Earth by added greenhouse gases. Some are worried they’re losing their capacity to buffer global warming.
A decade ago, there was already more than enough evidence to justify an effort to cut emissions. Scientists had reached a consensus that it was time to act. But a disinformation campaign was creating a different picture to general public, with hackers stealing scientists’ personal emails, and various bloggers and media outlets launching personal attacks against them.
Adding fuel to the situation was a loss of trust in all of science following the so-called replication crisis, in which social science was exposed as contaminated with flimsy and erroneous results. Much of established nutrition research was overturned, and many medical findings were deemed impossible to reproduce. But this had nothing to do with basic, well-established physics and Earth science. The periodic table didn’t get torn up, electricity still works as predicted, and Einstein’s pedestal has only been elevated.
It was way back in the 1800s that French mathematician Joseph Fourier realized that our planet should be frozen down to the equator, considering it orbits at a distance of 150 million kilometers from the sun. It didn’t take long to realize that the small fraction of our atmosphere made up of carbon dioxide was keeping our planet warm, and that adding substantially to that will make it a lot warmer.
“What’s notable is what hasn’t changed” over the last 10 years, said Penn State University climate scientist Richard Alley. “Carbon dioxide goes up, the temperature goes up, ice melts, and there’s a migration of plants and animals.”
Thus the climate forecast for the 2020s is warmer and more eventful.
Science writer Faye Flam is a Bloomberg Opinion columnist.
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