Scientists say the Earth is warming up fast, and policy makers have been urged to keep that warming to an increase of 2 degrees Celsius. But a new study suggests that may not be possible. Environmental Protection Agency Director of the Climate Protection Partnerships Division, Carolyn Snyder mapped out Earth’s global temperature over the “past two million years,” and based on what she found, Earth may already be committed to warming by around 5 degrees Celsius.
Snyder set out to reconstruct global temperatures for longer than the 22,000 years that had been mapped out before. She didn’t map out each of the two million years one by one, but rather averaged temperatures over 5,000-year periods. She utilized 61 unique proxies for sea surface temperatures, such as acidity or the ratio between calcium and magnesium. She made it clear these are rough estimates, but that global temperature changes in different periods of time did appear to correspond to levels of carbon dioxide.
Setting our current trends in the two million year context, Synder was able to predict levels of warming in the future, and the answer isn’t pretty. If factors are similar to what can be seen in the past, “stabilization at today’s greenhouse gas levels may already commit Earth to an eventual total warming of 5 degrees Celsius (range 3 to 7 degrees Celsius, 95 per cent credible interval) over the next few millennia,” as she wrote in her study.
Synder said, “This is based on what happened in the past. In the past it wasn’t humans messing with the atmosphere.”
Snyder’s study met with mixed reviews. One scientist said future studies should build on her two-million-year reconstruction. Others said her 5 degrees Celsius estimate seems excessive. Still another called for more research.
The study, published by Nature this week, is part of Snyder’s doctoral dissertation. Snyder obtained her PhD from Stanford University.