The oceans are warming faster than climate reports have suggested, according to a new synthesis of temperature observations published this week. The most recent report from the United Nations Intergovernmental Panel on Climate Change made what turned out to be a very conservative estimate of rise in ocean temperature, and scientists are advising us to adjust our expectations.
“The numbers are coming in 40 to 50 percent [warmer] than the last IPCC report,” said Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research and an author on the report, published in Science Magazine on Thursday.
Furthermore, Trenberth said, “2018 will be the warmest year on record in the oceans" as 2017 was and 2016 before that.
Oceans cover 70 percent of the globe and absorb 93 percent of the planet’s extra heat from climate change. They are responsible for spawning disasters like hurricanes Florence and Maria and generating torrential rainfall via meteorological processes with names like “atmospheric river” and “Pineapple Express.”
Sea level is rising with observable consequences along the East Coast and around the world, both physically and financially. Trenberth and his colleagues say if society continues to emit greenhouse gas at its current rate, oceans will rise one foot by the end of the century on top of the rise expected from melting land ice on Greenland and Antarctica.
Scientists have started to pin down how climate change is loading the dice on extreme weather. After Hurricane Harvey, researchers found the storm’s deadly and costly effects were probably made worse by warmer oceans. And, as The Washington Post reported in December, “a drought in East Africa that left 6 million people in Somalia facing food shortages was caused by dramatic ocean warming that could not have occurred without humans' impact on the environment.”
After several studies published over the past couple of years, some of which included errors that needed to be corrected and published for the record, “we felt the need to do a more general assessment," said Trenberth.
The scientists combined four data sets to paint a picture of what has been happening in the oceans since 1991. Trenberth and his co-authors say ocean heat content, which is a measure of the warmth of the water down to about 2,000 meters, is a “great metric for measuring global warming” because the data isn’t as erratic as the temperature on land, and it captures much more of the planet.
In the process, they discovered something interesting: Their data agrees with what the climate models were predicting. “Oh, maybe the models have more credibility than we thought,” Trenberth said, tongue firmly in cheek.
As the planet warms, models have proven an invaluable tool. It’s not enough to say the climate is changing — scientists want to know how it is going to change in the future. Yet these models are one of the preferred targets of climate change skeptics. They appeared to miss the so-called global warming hiatus between 1998 and 2013. At the time, scientists posited there wasn’t really a hiatus, but that the heat was simply building up in the oceans, or that there was a data collection issue. They were right, but that didn’t save the models from criticism.
This synthesis suggests the models are doing just fine. In fact, in the oceans, they are performing even better than expected, and have marched in lockstep with the extreme ocean heating observed by thousands of temperature-collecting floats all over the world. If climate models have actually performed well in the past, it gives scientists more confidence in their predictions for the future.
Trenberth said their comparatively concise article published Thursday “highlights some of the developments that have occurred since the last IPCC report," which came out in 2014. The previous one came out in 2007.
Articles like the one in Science are helpful to remind people of the advances that happen in science between the big, sweeping reports, said Tom Di Liberto, a climatologist at the National Oceanic and Atmospheric Administration. The IPCC reports have research deadlines at least a year before they are published; science in the most recent report may have been done six to eight years ago and “there’s a whole lot of stuff that has happened since then,” Di Liberto said.
“It speaks to the broader issue of science communication,” he continued. “Science works slower than the way we communicate now.”
Looking forward, there are two scenarios scientists are working with. The low-emissions scenario that the Paris climate change agreement was built around is no longer realistic, Trenberth said. The high-emissions, business-as-usual scenario will probably continue until about 2040, in his opinion, but eventually society will figure out how to manage the crisis.
“Yes, we need to try and stop emitting greenhouse gas. But the inertia is large,” Trenberth said. “Therefore the climate is going to continue to change.” He believes adaptation is the way forward, rather than geoengineering, which is “not thought out well at all and problematic.”
Di Liberto agrees that we’re already feeling the effects, but he sees things changing in society, too.
“We’ve spent too much time and effort on people who may not be convinced” that climate change is real and important, he said. “But now there seems to be this grass-roots movement of young people who care. I don’t remember a time like this.”