(CN) — Many estimates on atmospheric carbon dioxide levels focus on decades and centuries, but a study published Thursday in Science analyzes it over millions of years.
Today, Earth’s air contains 420 parts per million of carbon dioxide (CO2), and the consortium of more than 80 researchers from 16 nations who contributed to the study examined published research and geologic records to confirm that the last time Earth’s air had that level of CO2 was 14 million years ago.
“In only the last 150 years, humans have rolled back the CO2 clock by some 14 million years,” said study co-author Gabriel Bowen, a professor at the University of Utah. In an email, he described three different climate regimes of the planet: The first was a global greenhouse with very little snow and ice and an Antarctica that was home to palm trees. The second was an intermediate state with mild climate and an icy Antarctic continent, while the third is a cold icehouse climate that encompasses all of human history.
“The levels in the atmosphere today are similar to those occurring during the second, mild climate regime, during which climate conditions, sea levels, etc. were unlike anything our species has ever experienced,” said Bowen. “The climate system has not yet caught up with this change in CO2, but if we continue to emit carbon and keep atmospheric CO2 levels this high (or higher) it eventually will.”
The consortium said that long-term climate is highly sensitive to greenhouse gas with effects that may evolve over thousands of years.
All estimates say the planet is dangerously close to a more than 2 degree Celsius warming by the end of the century. Bärbel Hönisch, a geochemist at Columbia University’s Lamont-Doherty Earth Observatory who coordinated the consortium, hopes that Earth avoids that level of warming, saying long-lasting environmental damage is likely to begin if it does.
“Global temperatures two degrees warmer than today have not yet been experienced by our species, so we will be entering uncharted territory by the time we reach this level,” said Hönisch via email. “Two degrees warming is also considered dangerous, because warming is causing cascading effects through the climate system. We already see the severity and frequency of storms and droughts increasing, the sea level is rising, and models project that there is a lot more of this to come.”
Bowen said that while this study cannot precisely predict what will happen next, climate modelers can still use it to make more accurate projections.
“At this point, every year CO2 levels are higher than we (humans) have ever seen before. That means that our models are always being forced to extrapolate. We are using them to guess how the climate system will respond outside of the range of conditions in which the models were developed and tested," said Bowen. "One way to address this is to test how well the models predict climate conditions at points in the geological past when CO2 levels were higher than today (and similar to what they are likely to be in future decades). By refining the record of paleo-CO2, our study helps modelers understand what periods of geologic time are good candidates for this work, and what the CO2 levels during those periods were.”
Currently, the consortium is working on a larger project charting how CO2 and climate evolved over the entire Phanerozoic eon, from 540 million years ago to now.
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