A mountain of evidence shows that humans are causing global warming, and it may change the world irrevocably. But new evidence suggests that things might be even worse than previously thought. A new report published in the Proceedings of the National Academy of Sciences shows that scientists may have been comparing current temperatures to the wrong periods in the earth’s history.

Throughout the planet’s lifetime, there have been “icehouse phases” with large reserves of ice, and “greenhouse phases,” during which these ice reserves melted. Until now, researchers have been comparing global temperatures to those of “greenhouse phases,” which tend to be much warmer. But the study argues that the large ice sheets in the Antarctic and Arctic suggest the earth is in an “icehouse phase.” That means it's possible global warming has been even more rapid and severe than previously thought.

Why This Matters

The new research means that the already-sounding alarm on climate change is ringing harder and louder than before. Icehouse phases are much more affected by warming than greenhouse phases. “If you raised CO2 by the same amount in a greenhouse world, there isn’t much effect, but icehouses seem to be much more sensitive to change and marine anoxia,” explains Isabel Montañez, one of the new study’s researchers and a professor at the UC Davis Department of Earth and Planetary Sciences.

Despite evidence that fossil fuels must be completely phased out to prevent the world from warming to catastrophic levels, levels of greenhouse gases like methane and carbon dioxide keep rising. According to the World Meteorological Organization, there is a 50-50 chance of the earth surpassing the 1.5-degree Celsius mark in the next five years.

Learning From The Last Icehouse

The Kasimovian-Gzhelian Boundary (KGB) was another icehouse period that occurred approximately 305 million years ago, over a period of 300,000 year, CO2 levels doubled in the atmosphere, oxygen levels in the ocean went down, and many species went extinct. Scientists think that this carbon release could’ve been caused by volcanic eruptions that ended up melting permafrost.

Terry Isson, one of the study’s researchers from the University of Waikato, New Zealand, states, “This research indicates that this process may be more rapid and more severe in our current climate, and we may be seriously underestimating the rate and effect of global warming if we continue to rely on greenhouse comparisons.”