Global warming slowed, but not for long

Research reports that natural processes have caused warming to slow recently.

Global warming slowed, but not for long

Allison Kronberg

When it comes to global warming discussion, many people think the climate will exclusively rise in temperature and at a consistent rate.

And any time it doesn’t, some want an explanation.

The speed at which the earth has been warming has noticeably slowed since about 1998, scientists say, even though last year was the hottest year on record. Some scientists attributed the slowdown to the natural randomness of global temperature, which paved way for climate change deniers to doubt the science of a warming planet from human activity altogether.

But recent University of Minnesota-Duluth and Pennsylvania State University research shows why the warming paused and emphasizes that human activity will keep warming the
planet regardless.

“Our findings suggest that we may have been ‘lulled’ into a false complacency by this short-term respite from the longer-term pattern of warming,” said Michael Mann, a researcher on the study and meteorology professor at Penn State.

The research, published in the journal Science last month, averaged data from all available climate-temperature models to eliminate randomness.

It confirmed previous studies that said the cause of global temperature slowdown was due to ocean surface temperatures interacting with the earth’s atmospheric temperature, but it also confirmed the role human industry emissions have played in continuing to move global warming along, despite the temporary slowdown.

The research categorized the global temperature models by factors of influence, such as global weather events like El Niño, inland events like volcanic eruptions and unnatural factors like greenhouse gas emissions from humans.

With a new regression-based method, which allows researchers to group patterns, the scientists were able to separate inconsistent factors from those that were consistent or internal.

“This question has been around since climate dynamics has been a field of research: What is the influence of internal variability on earth’s temperature history?” lead researcher and UMD assistant professor Byron Steinman said. “If you can understand that, then you can answer questions about the recent slowdown in warming.”

They found that the internal, natural factors had enough influence to put global warming on pause for a short while.

Surface temperatures of the Atlantic and Pacific oceans are colder in some years and warmer in others, and that has an effect on how warm or cold the planet is as a whole.

The researchers’ analyses of ocean temperature models found that in recent years there was a cooling trend in the northern Pacific Ocean because of increased El Niño events. Atlantic Ocean surface temperature, on the other hand, rose slightly. But the two oceans’ combined effect on the atmosphere is still a cooling one.

Human activity may still be motivating the natural phenomenon, though.

Ocean temperatures vary at different depths. Warmer water sometimes sits on top or sometimes lies deeper. The atmosphere, heated by greenhouse gases, can then heat the surface of the ocean. That warmer water may get redistributed deeper in the ocean, other research has found.

Like most climatological cycles, the process of heating the planet is interconnected, Steinman said.

The cool water at the surface of the Pacific will follow the natural process to reverse and eventually become warm, he said.

If that happens, the global warming slowdown may reverse and head toward an even faster warming climate.

Ben Booth, a government research scientist working in the United Kingdom, said the UMD and Penn State research has international implications because it’s the first work to provide a long-term picture of how ocean temperature operates alongside greenhouse gas emissions to influence global climate.

The research gave more conclusive evidence on the relationship between natural processes, people and the climate than earlier papers, Steinman said, but there’s still plenty of more research to do.

“Our paper is the next step forward,” he said, “and I foresee in a couple months somebody else building off of the research we’ve done.”