Many nations and organizations around the world have emphasized lowering greenhouse gas emissions with the aim of keeping the global temperature from rising more than 2 degrees Celsius above pre-industrial levels. Past studies have pegged this as a critical tipping point for Earth’s long-term climate, but that may be harder to achieve than we thought. A new analysis suggests that even limiting emissions won’t be able to stop the planet from warming considerably more than the 2-degree cutoff.
Researchers at the Stockholm Resilience Centre note that Earth’s own feedback mechanisms could mean we’ve already crossed the point of no return. At present, the climate has warmed more than a degree above pre-industrial levels, and it’s going up about 0.17 degrees C every decade. Carbon sinks that currently limit the damage of greenhouse gasses could tip the other way and become sources of carbon past 2 degrees of warming.
The feedbacks cited in the study include permafrost, which could thaw as temperatures increase. Warming oceans could also cause the release of carbon dioxide and methane from the ocean floor. Forests that currently soak up atmospheric carbon could also die in many regions, causing the release of all that captured carbon as they decompose. The team likens it to a row of dominoes that could topple one after another once we cross the 2-degree barrier.
If the scenario laid out in the new study is accurate, we could be headed for a so-called Hothouse Earth, where the global temperature stabilizes at 4-5 degrees above pre-industrial averages. At that point, global climate would experience radical shifts, and the oceans would be 10-60 meters higher than today. That would render many currently habitable areas inhospitable to human life.
It might take a century or more for the full effects of Hothouse Earth to be realized, but the study suggests that is inevitable if we don’t make big changes. We’re not talking about the end of the world itself, but it might well be the end of the world for humans.
It’s still unclear if global temperatures can be “parked” at or near 2 degrees C. The Stockholm Resilience Centre study says that simply lowering emissions won’t be enough — we should be working toward ending the use of fossil fuels by the middle of this century. The world may need to exert considerable effort to take carbon out of the atmosphere through the use of new biological carbon stores and as-yet undiscovered technologies that can remove and sequester carbon.