The Earth today is warmer than it’s been in 120,000 years, and could be poised to break a 2-million-year temperature record, thanks to current greenhouse gas levels that may have already committed Earth to an eventual total warming of 5 degrees Celsius over the next few millenniums, according to a new study.
But other scientists say it’s too soon to rule that current carbon levels have sealed the Earth’s fate in terms of rising temperatures.
The study, published Monday in the journal Nature, constructs a 2-million-year-long temperature record to predict future rises in heat. Using 61 sea surface temperature proxies taken from ocean sediment cores from around the world, Carolyn Snyder, who conducted the research at Stanford University and now works as a climate policy official at the Environmental Protection Agency, looked at average temperatures over periods of 5,000 years, finding that changes in temperature coincided with carbon dioxide levels.
Using that relationship, Dr. Snyder predicted that a doubling of carbon dioxide levels would create a rise of 9 degrees Celsius over the next few thousand years – a jump high enough to spell serious trouble for coastal cities, coral reefs, and other wildlife.
“This is based on what happened in the past,” Snyder told CBS News. “In the past it wasn’t humans messing with the atmosphere.”
But some prominent experts in the field say the findings aren’t proof of specific temperature increases in the future, and that drawing a line from a past correlation between carbon levels and temperature to make predictions about the future is illogical.
“This is simply wrong,” Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, told Gizmodo. “The actual committed warming is only 0.5 to perhaps 1 [degree Celsius] – and nothing in the study changes that. You have this chicken and egg situation, where ice changes, which causes CO2 to change, which causes ice to change, and so on and so forth.”
When researchers look back far enough, the effects of the relationship become blurry. “You’re mixing the impact of CO2 on climate, and climate on CO2,” he said.
Snyder’s study cautioned that the records, especially those dating further back where fewer proxies were available, are merely rough estimates with high margins of error. Still, others praised the work, highlighting how useful the temperature records could be for future research.
“Snyder’s work is a great contribution and future work should build on it,” Jeremy Shakun, a professor of earth and environmental science at Boston College, told CBS News.
Previously, scientists had only mapped temperature records back 22,000 years.
Snyder said she didn’t intend for the study to make predictions about climate change, but instead to map the past relationship between carbon dioxide levels and temperature and project the possibility of a continued correlation.
“This research cannot and does not provide a forecast or prediction for future climate change,” Snyder told Gizmodo. “All we can say is, if we take the past relationship [between temperature and CO2] and translate it forward, this is what we get.”