The report, written by 104 authors from 36 countries and approved by government representatives on Sept. 24, increases sea level rise projections by the end of the century by about 4 inches when compared to the last IPCC report, which was released in 2014. It also explicitly mentions the possibility that the West Antarctic Ice Sheet could collapse entirely in the next few centuries or less, which would set into motion multiple meters of sea level rise.
“For the first time ever, the IPCC has produced an in-depth report exploring the furthest corners of the world,” said Ko Barrett, an IPCC vice chair and an official at the National Oceanic and Atmospheric Administration.
“We’ve found that even and especially in these places, global warming is evident,” she said during a call with reporters on Monday.
‘Unprecedented’ changes in the oceans
The report paints a dire picture of the planet’s oceans under assault from increased carbon dioxide levels in the atmosphere, which are heating waters, disrupting ecosystems, raising sea levels and causing the oceans to become more acidic and less productive.
“Over the 21st century, the ocean is projected to transition to unprecedented conditions with increasing temperatures, greater upper ocean stratification, further acidification, oxygen decline, and altered net primary production,” the report states.
In other words, the oceans of our future will be starkly different from what we grew up with, and societies dependent on marine ecosystems for sustenance and livelihoods could be buffeted by food shortages and loss of income.
Marine ecosystems are forecast to undergo massive shifts, with plant and animal communities moving long distances to find the water temperatures and nutrients that best sustain them. Coastal wetlands are particularly threatened by rising sea levels, the report found.
In addition, “extreme” El Niño and La Niña events are likely to occur, along with a sharp increase in the frequency, duration, spatial extent and maximum temperature of marine heat waves. The report projects a 20- to 50-fold increase in marine heat waves, depending on the level of greenhouse gas emissions. Marine heat waves, such as the developing “Blob” in the Northeast Pacific Ocean, can significantly alter the weather over land.
A Pacific marine heat wave in the northeast Pacific during the 2014-2016 period was tied to the severe California drought, for example.
The oceans have been taking in more than 90 percent of the extra heat from greenhouse gases, which is warming waters worldwide, the report shows. Since 1993, the rate of ocean warming has likely doubled, the report found.
By 2100, the IPCC report says, the top 6,500 feet of the ocean are projected to absorb five to seven times more heat under a high-emissions scenario, compared with two to four times more heat if the world enacts swift and strict limits on planet-warming greenhouse gas emissions.
“The ocean has been acting like a sponge, absorbing carbon dioxide and heat … but it can’t keep up,” Barrett said. “The consequences for nature and humanity are sweeping and severe.”
Sea level rise: 100-year floods to become annual events
The era of accelerating sea level rise is already upon us. Mass loss from the Antarctic ice sheet during the 2007-2016 period tripled when compared with 1997 to 2006, and the loss rate for the Greenland Ice Sheet doubled during the same period as well.
While sea level has risen globally by around six inches during the 20th century, it is currently rising more than twice as fast, the report found. This is leading to an uptick in “extreme sea level events” in coastal areas.
The report shows increased continued mass losses from the Greenland and Antarctic ice sheets throughout the 21st century and beyond, but notes that the rate of ice loss can still be reduced by cutting emissions before 2050.
The sea level rise projections in the new report are more in line with recent studies than with the IPCC’s Fifth Assessment Report that came out in 2014, in that the new report has about four additional inches of sea level rise by 2100 under a high-emissions scenario, for a total of more than three feet. The report mentions the possibility of multiple meters of sea level rise during the next few centuries if, as some studies show, the West Antarctic Ice Sheet collapses. Recent studies have shown increasing signs of fragility in East Antarctica, too.
Due to sea level rise, the report finds that sea level rise would cause floods that had occurred about once in 100 years to take place annually by 2050 in many coastal megacities and small island developing states.
Permafrost is melting — quickly
In recent years, scientists have observed increased levels of permafrost melt in the Arctic, which has the potential to release large amounts of stored carbon, methane and other greenhouse gases that had been trapped in the frozen ground. The IPCC report does not offer good news on this front, either.
By 2100, a high-emissions scenario would yield “the cumulative release of tens to hundreds of billions of tons of permafrost carbon,” thereby accelerating global warming further. Lower-emissions scenarios would cut down on the amount of permafrost lost, however, and limit a positive feedback that can exacerbate global warming.
The report comes two days after a major U.N. climate summit that failed to deliver major new emissions reduction pledges from the world’s biggest emitters, including China and the United States.