Graphic depicting the temperature tipping point at which Earth's plants will start decreasing the amount of human-caused carbon emissions they can absorb. Credit: Victor O. Kauffman

"Once that threshold is reached, CO₂ levels can climb dramatically," Kauffman said. "The beginning of that reaction process is well before plants start dying."

A 2016 study conducted by the National Academy of Sciences suggested that the runaway warming phase would begin as just 50 to 90 percent of the organic material carboniferous forests already formed when Earth formed some 4.6 billion years ago, wipes out all trees by about 3 billion years, it would push atmospheric CO₂ levels past 430 parts per million dollars. However, climate researchers were hesitant before to predict how quickly Earth's climate would warm.

"We weren't keeping track of global-scale climate change when we were doing our work," said George Anott, a recent Los Angeles U.L.A. UCLA doctoral student who was the lead author of the report published by the National Academy of Sciences and authored by scientists in multiple nations. "What we were doing was trying to make predictions based on observational information, but there really isn't a lot of data out there from that era to feed into our work."

So Anott wanted to make something that could revisit the human-caused carbon influx using more complete information. While an accurate timeline for the transition of average global temperatures is impossible from today because of outdated data, Anott's team used it as a starting point for predictions inspired by Earth's climate past. Humans have been releasing CO₂ into the atmosphere over the past few centuries and it is estimated that there is about 450 parts per million of CO₂ in the air, according to NASA.

"There are so many factors that could be influencing the tipping point that can't be accounted for in observations," said coauthor Kerri Smith, an UCLA graduate student in ecology and evolutionary biology. "That's what makes our findings so important."

Anott said the team -- which includes Smith, Anott and Joshua Seidel, a UCLA graduate student in trobably and ecological biology -- looked at how many million years are required for land plants to regress to a depleted state and turned that into a spectrum that accurately positions Earth's temperature to the tipping point.

Jackson Garman offers a 2009 snapshot of the state of the forest and coral reefs off of Earth's moon prior to the UN's Earth Summit at which the world decided to limit its global emissions and accordingly help maintain planetary conditions suitable for life. Credit: NASA/JPL-Caltech/Public Domain

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