Carbon dioxide's impact on global temperatures mapped over 485 million years

Earth’s temperature has varied more over the period than previously thought, researchers find

A wildfire in Aveiro, Portugal. Researchers have published a new paper on how CO2 controls global temperatures. AFP

Earth’s temperature has varied more over the past 485 million years than previously thought and is strongly linked to the amount of carbon dioxide in the atmosphere, a study has found.

The research offers the most detailed picture yet of how global temperatures have changed in the 541 million years since the start of the current Phanerozoic Aeon, which is marked by an abundance of fossils. Over the aeon, the global mean temperature has spanned 11°C to 36°C, with colder temperatures associated with lower levels of carbon dioxide, or CO2, and warmer with higher levels

“This research illustrates clearly that carbon dioxide is the dominant control on global temperatures across geological time,” said Jessica Tierney, a paleoclimatologist at the University of Arizona and a co-author of the new paper. “When CO2 is low, the temperature is cold; when CO2 is high, the temperature is warm.”

The study also dismisses the idea that the Earth has a “tropical thermostat”, with a maximum temperature that the tropics can reach, Emily Judd, the lead author of the paper and a former postdoctoral researcher at the National Museum of Natural History and the University of Arizona, told The National. “In the 1990s and early 2000s, several studies generated data, based on the shells from foraminifera – or little calcified “sea bugs”, from warm intervals in Earth’s past with elevation CO2 concentrations that suggested tropical temperatures weren’t that much warmer than today,” she said. “This sparked some controversy over whether there was an upper limit for tropical warmth.”

However, researchers have since shown the data had been altered by processes that occurred after the organisms had died. “In our study, we carefully screen all the data that went into our analysis to make sure that any data that were potentially altered by processes occurring after the death of the organism were excluded,” she said. “Both those subsequent studies that carefully examined each specimen and our work dispel the idea of a tropical thermostat, and demonstrate that under elevated CO2 concentrations, Earth’s tropics experience significant warming above their current temperature.”

The findings indicate that Earth’s current global mean temperature of 15°C is cooler than it has been over much of the aeon. But greenhouse gases are warming the planet at a substantially quicker rate than even the fastest warming events of the Phanerozoic. That puts species and ecosystems around the world at risk and is causing a rapid rise in sea levels, the researchers said. Other episodes of rapid climate change during the Phanerozoic have sparked mass extinctions, they added.

Using an approach called data assimilation, researchers combined data from the geologic record and climate models to create a more complete understanding of ancient climates. But while the new paper is the most robust study of temperature change to date, it is far from a finished project, Brian Huber from the Smithsonian’s National Museum of Natural History, said.

“We all agree that this isn’t the final curve,” he added. “Researchers will continue to uncover additional clues about the deep past, which will help revise this curve down the road.”

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