Carbon dioxide levels could reach their highest point in 50 million years by the end of the century

Continuing to burn fossil fuels at the current rate could bring atmospheric carbon dioxide to its highest concentration in 50 million years, jumping from about 400 parts per million now to more than 900 parts per million by the end of this century, a new study warns.

And if greenhouse gas emissions continue unabated beyond that point, the climate could reach a warming state that hasn’t been seen in the past 420 million years.

Some research suggests that, if humans burned through all fossil fuels on Earth, atmospheric carbon dioxide concentrations could hit 5,000 parts per million by the year 2400.
The new study speaks to the power of human influence over the climate. It suggests that after millions of years of relative stability in the absence of human activity, just a few hundred years of anthropogenic greenhouse gas emissions are on track to cause unprecedented warming.

To come to these grim conclusions, which were published Tuesday in the journal Nature Communications, the researchers constructed a continuous record of atmospheric carbon dioxide concentrations spanning the last 420 million years. They created the record by compiling more than 1,500 estimates of atmospheric carbon dioxide concentrations drawn from 112 published studies.
According to lead author Gavin Foster, a geochemistry professor at the University of Southampton, those estimates were constructed mainly using the carbon isotope composition of ancient soil samples or examining the abundance of pores on the leaves of fossilized plants, an indicator of how much carbon dioxide was available for them to draw from the air while they were alive.

The findings suggest that, until humans started rapidly burning fossil fuels with the advent of the Industrial Revolution, Earth’s climate had been relatively stable for millions of years, and carbon dioxide concentrations were declining. Thanks to the human emission of greenhouse gases, though, that’s all changing at record-breaking pace.

Current concentrations of CO2 emissions are at their highest in human history, currently hovering around 400 parts per million and continuing to rise. Before the Industrial Revolution, carbon dioxide concentrations had settled into an average of about 280 parts per million.

On a business-as-usual pathway — a trajectory in which greenhouse gas emissions would continue at their current rate — carbon dioxide concentrations will hit a level that hasn’t been seen in 50 million years, according to the research.