An Arctic free of ice and stocked with swamp-loving reptiles. Temperate forests covering Antarctica, thriving on heat that kept them alive through the dark months. Average temperatures along the equator of about 100 degrees Fahrenheit.

High carbon dioxide levels kept the planet warm enough to sustain that life 50 million years ago during the Eocene Epoch. As the CO2 levels dropped, the planet tilted toward a cooling, and the ice caps were formed, choking off the life that once thrived at the poles.

Now, humanity’s consumption of fossil fuels is pushing the planet toward the CO2 levels of the period when dinosaurs roamed the Earth. And that’s the rosier scenario for 200 years from now, a new study has found.

By 2300, there would be little precedent for the transformation of the Earth. That’s because humanity’s billowing of CO2 into the atmosphere, chiefly through the consumption of fossil fuels, may be on track in a few centuries to hit a level not seen in 420 million years, according to the findings published yesterday in Nature Communications.

Researchers are still trying to figure out what that might mean for life on Earth.

“As far as we can tell, the Earth hasn’t experienced that in the last 420 million years. How the Earth will respond, there is no precedent in the geological record,” said Gavin Foster, lead author of the study and a professor of isotope geochemistry at the University of Southampton in England.

The amount of atmospheric CO2 has already increased in the last two centuries at a rate not seen in the geologic record, Foster said. Scientists believe the CO2 levels now in the atmosphere haven’t been seen in 3 million years. And the planet is warming as a result of the boom in CO2 from industrialization, almost 2 degrees Fahrenheit in the last 150 years.

What’s more, the Earth has set high temperature records for each of the last three years and triggered a melting of the Arctic that scientists fear is already past the tipping point.

30% CO2 growth since 1960

Foster and other researchers used the geologic record to determine previous levels of atmospheric CO2 and to project possible scenarios for future warming if CO2 levels hit 2,000 parts per million (ppm) in the next 200 years. They examined plant fossils, soil and ocean carbons and the composition of fossil shells. In total, they examined 1,200 estimates of ancient atmospheric CO2 concentrations.

The amount of atmospheric CO2 is set to top 410 ppm this year, researchers have found. Last month, the National Oceanic and Atmospheric Administration announced that global carbon emissions have been measured at an all-time high. The CO2 measured at the Mauna Loa Baseline Atmospheric Observatory in Hawaii hit 405.1 ppm last year. That’s an increase of 3 ppm and makes five consecutive years of CO2 increases of at least 2 ppm, an unprecedented rate of growth, according to NOAA.

Since 1960, CO2 has increased more than 30 percent, or 100 ppm. Before the age of industrialization, or about 150 years ago, the amount of atmospheric CO2 was 280 ppm. The amount of atmospheric CO2 had remained at 280 ppm since about 10,000 years ago.

Even if CO2 levels reach the same rate they hit millions of years ago, there is no clear way to determine how the planet would react, said Dan Lunt, a professor of climate science at the University of Bristol in England and a co-author of the study. For one thing, since the sun is brighter now, it would be more of a contributor to warming, Lunt said.

“Due to nuclear reactions in stars, like our sun, over time they become brighter,” he said. “This means that, although carbon dioxide concentrations were high hundreds of millions of years ago, the net warming effect of CO2 and sunlight was less.”

The study examines a possible scenario based on current emissions levels and the geologic record but still contains a lot of uncertainty, Foster cautioned. He said the record-high levels of CO2 are based on the assumption that humanity will eventually burn its way through all of the available fossil fuels. In addition, the geologic record doesn’t always capture rapid changes that occur over a few hundred years, so it’s impossible to be entirely certain that there was a sudden spike in CO2 levels at some point in geologic history that was not in the record, Foster said.

Still, researchers are more certain that the spike in CO2 levels means life would have to adapt to a more extreme heat than anything humanity has ever experienced, he said.

“It’s a level of forcing that has not been experienced by the Earth, as far as we can tell,” he said, adding, “It puts the enormity of what we’re doing in context.”

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at