NASA’s former climate chief has issued a stark new study that finds that the world’s current climate goal could be inadequate and may not prevent catastrophic losses from rising seas, ocean temperatures and changes in global weather. But the extreme nature of his projections has some scientists questioning the methods he used and the results he reached.
Global leaders and scientists have agreed that keeping global warming to within 2°C (3.6°F) of pre-industrial temperatures represents a safe level of climate change. The new findings, published as a discussion paper in the European Geophysical Union’s Atmospheric Chemistry and Physics journal, indicate something else. They show that 2°C (3.6°F) of warming could lead to runaway ice melt at the poles, causing sea level rise and ocean circulation changes by 2100 that are much more extreme than most current projections.
The new study says that limiting warming to 2°C (3.6°F) “does not provide safety, as such warming would likely yield sea level rise of several meters along with numerous other severely disruptive consequences for human society and ecosystems.”
The research was lead by James Hansen, the former head of NASA Goddard Institute for Space Studies and current Columbia University faculty. Hansen rose to prominence for his research and Congressional testimony in 1988 about the role of carbon dioxide and other human greenhouse gas emissions in causing the global temperature to rise. He has advocated for keeping atmospheric carbon dioxide around 350 parts per million (ppm) to avoid dangerous climate change. They recently passed the 400 ppm milestone globally.
The paper uses paleoclimate data and modeling to show that if ice sheets in Greenland and West Antarctica continue to double their melt rates every 10 years as they currently are, sea levels could rise up to 16 ft as soon as 2100.
A sudden influx of fresh, cold water to oceans around Antarctica and Greenland could have other notable impacts. The study argues that it could slow down ocean conveyor belts that shuttle water around the world’s oceans and alter air temperatures and storm tracks. Most provocatively, the study indicates it could cause cooling over the southern third of the globe as well as parts of the northern Atlantic and Europe and slow warming in other parts of the globe.
The changes the study outlines are dramatic and much more alarming than the upper limits most scientists have outlined as possible if human greenhouse gas emissions continue on their current trends. The upper level of sea level rise projections from the most recent Intergovernmental Panel on Climate Change report indicates a rise of four ft by 2100 is possible. There is some evidence the West Antarctic Ice Sheet—which contains enough ice to raise seas by 13 ft—has entered collapse, but it’s unlikely to completely melt away by century’s end.
“I agree with the overall magnitude of sea level rise that they are interpreting for the last interglacial,” Andrea Dutton, a geochemist at the University of Florida, said. “What does not come across in this paper is that there is still debate regarding the timing of ice-sheet collapse during this warm period.”
Dutton led research published last week in Science showing that sea levels rose by 20 to 30 ft about 125,000 years ago, the same period analyzed in the new Hansen study. She is working with a group of scientists to get a better handle on how fast ice melted then as well as during other periods of rapid sea level rise in the past three million years.
“Setting the rates can be a challenge, but we’re starting to develop tools and techniques to understand them,” she said.