Scientists Warn We May Be on Track for 'Hothouse Earth'
In two recent studies, scientists have looked into the future and into the past to see what might happen to the global climate if we fail to curb greenhouse gas emissions in time. The results are frightening.
A study published Monday in Proceedings of the National Academy of Sciences examined how, once a certain threshold was crossed, feedback loops could push the planet's climate towards a "Hothouse Earth."
The researchers expressed uncertainty as to whether limiting warming to the Paris agreement's upper limit of 2 degrees Celsius above pre-industrial levels would be enough to halt the impacts of climate change, or if feedback loops already in motion would accelerate the process regardless.
"We note that the Earth has never in its history had a quasi-stable state that is around 2C warmer than the preindustrial and suggest that there is substantial risk that the system, itself, will 'want' to continue warming because of all of these other processes—even if we stop emissions," study author Katherine Richardson from the University of Copenhagen told The Guardian.
Some of those other processes include the release of methane from the thawing of the permafrost and the dieback of carbon sinks like the Amazon Rainforest.
When it comes to sea level rise, the scientists outlined how the melting of Greenland's ice could disrupt the Gulf Stream current, lifting sea levels and warming the Southern Ocean, which would in turn melt more ice in Antarctica.
A "Hothouse Earth" would be four degrees warmer than pre-industrial levels, and the path towards reaching it would most likely flood deltas, increase the intensity of coastal storms, and kill off coral reefs by the end of this century or sooner.
Currently, the Earth is around one degree Celsius warmer than pre-industrial levels, and that is already leading to more extreme impacts than would have been predicted, study author and executive director of the Stockholm Resilience Centre Johan Rockström told The Guardian.
"The heatwave we now have in Europe is not something that was expected with just 1C of warming," Rockström said. "Several positive feedback loops are already in operation, but they are still weak. We need studies to show when they might cause a runaway effect."
The paper concluded that to safely avoid a hothouse scenario, humans would have to change their relationship to the Earth.
"Collective human action is required to steer the Earth System away from a potential threshold and stabilize it in a habitable interglacial-like state. Such action entails stewardship of the entire Earth System—biosphere, climate and societies—and could include decarbonization of the global economy, enhancement of biosphere carbon sinks, behavioral changes, technological innovations, new governance arrangements, and transformed social values," the paper said.
Another paper published July 30 in Nature Geoscience looked millions of years into the past to see how hot an Earth with a carbon-dioxide-heavy atmosphere would really be.
The study used peat fossils to assess mid-level temperatures in the early Paleogene, 56 to 48 million years ago.
This was the period after the extinction of the dinosaurs that saw the rise of mammals, as well as atmospheric carbon dioxide levels of 1,000 parts per million, which is what they are predicted to reach by the end of this century if no action is taken, The Atlantic reported.
The study found that during that time, average temperatures in what are now the UK, Germany and New Zealand averaged 23 to 39 degrees Celsius, 10 to 15 degrees warmer than now.
"Europe would look like the Everglades and a heat wave like we're currently experiencing in Europe would be completely normal. That is, it would be the everyday climate," study author and University of Bristol geochemist David Naafs told The Atlantic.
Naafs and his colleagues tried to assess temperatures in the tropics as well, but the ancient lignite samples from India they found turned up temperatures too hot for their method to accurately measure.
"Some climate models suggest that the tropics just became a dead zone with temperatures over 50 degrees Celsius like in Africa and South America," Naafs told The Atlantic. "But we have no data so we don't know."
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By Jeff Masters, Ph.D.
Earth had its second-warmest year on record in 2020, just 0.02 degrees Celsius (0.04°F) behind the record set in 2016, and 0.98 degrees Celsius (1.76°F) above the 20th-century average, NOAA reported January 14.
Figure 1. Departure of temperature from average for 2020, the second-warmest year the globe has seen since record-keeping began in 1880, according to NOAA. Record-high annual temperatures over land and ocean surfaces were measured across parts of Europe, Asia, southern North America, South America, and across parts of the Atlantic, Indian, and Pacific oceans. No land or ocean areas were record cold for the year. NOAA National Centers for Environmental Information
Figure 2. Total ocean heat content (OHC) in the top 2000 meters from 1958-2020. Cheng et al., Upper Ocean Temperatures Hit Record High in 2020, Advances in Atmospheric Sciences
Figure 3. Departure of sea surface temperature from average in the benchmark Niño 3.4 region of the eastern tropical Pacific (5°N-5°S, 170°W-120°W). Sea surface temperature were approximately one degree Celsius below average over the past month, characteristic of moderate La Niña conditions. Tropical Tidbits
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