A decade of ice, ocean and atmospheric studies found systems nearing dangerous tipping points. As the evidence mounted, countries worldwide began to see the risk.

BY BOB BERWYN, INSIDECLIMATE NEWS

DEC 28, 2019

The 2010s may go down in environmental history as the decade when the fingerprints of climate change became evident in extreme weather events, from heat waves to destructive storms, and climate tipping points once thought to be far off were found to be much closer.

It was the decade when governments worldwide woke up to the risk and signed the Paris climate agreement, yet still failed to reduce the greenhouse gas emissions at the pace and scale needed. And when climate scientists, seeing the evidence before them, cast away their reluctance to publicly advocate for action.

The sum of the decade’s climate science research, compiled in a series of reports by the Intergovernmental Panel on Climate Change (IPCC), suggests global warming is pushing many planetary systems toward a breakdown.

New studies showed polar ice caps melting and sea level rising much faster than just 10 years ago. Ocean researchers showed how marine heat waves kill corals and force fish to move northward, affecting food supplies for millions of people in developing countries. They tracked changes to crucial ocean currents and concluded that hurricanes will intensify faster in a warming world.

Together, the research showed how important it will be to cap the global temperature rise as far below 2 degrees Celsius—the Paris Agreement goal—as possible.

Feedback Loops on the Greenland Ice Sheet

At the start of the decade, it was unclear how fast the Greenland and West Antarctic Ice Sheets would melt. As recently as the 1990s, melting of the Greenland Ice Sheet was balanced by the buildup of new snow and ice, offering some hope that sea-level rise would be slow, allowing coastal communities time to adapt.

By the end of 2019, a study published in the scientific journal Nature showed the Greenland Ice Sheet was melting seven times faster than it had been in the 1990s. That’s on pace with the IPCC’s worst-case climate scenario, with Greenland alone contributing 2 to 5 inches of sea level rise by 2100. Another study, looking at evidence in fossilized shells, showed temperatures are very near a threshold that will melt most of the ice sheet.

Scientists discovered feedback loops and new ways earth’s systems interact to melt the ice. Global warming is expanding ice slabs beneath Greenland’s snowy areas, hastening runoff and sea level rise. In Antarctica, they showed how global warming is shifting winds and pushing warmer water under floating ice shelves—both of which could contribute to rapid disintegration of ice shelves with a subsequent surge of sea level rise.

“The rate and magnitude of Greenland Ice Sheet mass loss, and of ice loss globally, has been dramatic,” said Twila Moon, a climate researcher with the National Snow and Ice Data Center.

How Sea Ice Loss Influences the Atmosphere

Many studies in the second half of the decade showed how important it is to keep the global temperature rise as far below 2 degrees Celsius as possible to avoid triggering tipping points that would have cascading consequences. Arctic sea ice is one of the big concerns. 

Even now, in its diminished state, the summer Arctic sea ice is a 1.6 million square-mile shield that reflects incoming solar radiation back to space. The more it melts, the more darker-colored ocean can absorb heat, speeding up the planet’s overall warming.

At 2 degrees Celsius warming, Arctic Ocean sea ice will probably melt completely, said National Snow and Ice Data Center climate researcher Walt Meier. “Some ice probably will persist if warming is limited to 1.5 degrees Celsius,” Meier said. He noted that research has suggested the ice could recover fairly quickly—if greenhouse gas concentrations are reduced enough to drop the temperature.

One intriguing question has been how the loss of Arctic sea ice will affect weather patterns in North America, Europe and Asia.

Melting that much of Earth’s icebox could alter wind patterns that shunt weather systems around the Northern Hemisphere, scientists reasoned early in the decade. A study in 2012 suggested a mechanism: Sea ice melt alters the jet stream by reducing the temperature contrast between the Arctic and the mid-latitudes. As the jet stream weakens, it enables areas of rainy weather or hot, dry conditions to linger longer over a given area, leading to extreme rainfall or heat waves and drought.

As the decade ended, studies seemed to support that early conclusion. Research published by Michael Mann, Stefan Rahmstorf and others showed how heat waves, floods and wildfires are linked with a jet stream pattern that, in turn, is related to an over-heated Arctic. In a climate warmed by greenhouse gases, the jet stream is more likely to set up in a pattern that causes extremes to linger longer over Europe and North America.

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