A key greenhouse gas responsible for warming the planet, carbon dioxide, isn't just hanging around in the air. It's also locked up deep under the ground.

In the soil, stocks of carbon have built up over thousands of years, and levels have been kept relatively stable by the slow activity of bacteria which use carbon for energy. Scientists have long speculated over whether global warming could be affecting this process. A new study by Yale University suggests that it is.

The research paper, published this week in the journal Nature, states that climate change is ramping up the activity of all these bacteria, meaning that more carbon is starting to get released into the atmosphere.

That's bad news for the planet, because as extensive research has shown, increasing levels of greenhouse gases are contributing to the Earth warming up.

It also says that the extra emissions from underground could be massive - totalling the amount that's already released by the US, the second largest emitter of greenhouse gases on the planet.

In fact, the paper states that around 17 percent more emissions will be released into the atmosphere by 2050 than was previously predicted.

The majority of carbon emissions from soil come from the ground in colder places and at high latitudes, as well as places that are missing from previous research.

This is because carbon stores are greatest in places like the Arctic and sub-Arctic where soil is cold and often frozen. Microbes are less active when it's cold, so carbon can build up and up under the surface over many centuries.

As things warm up, the activities of microbes increase, and that's when more carbon dioxide escapes.

"The scary thing is, these cold regions are the places that are expected to warm the most under climate change," Thomas Crowther, a postdoctoral fellow at the Yale School of Forestry and Environmental Studies and at the Netherlands Institute of Ecology, said in a statement.

The results are based on an analysis of 20 years worth of data on stored soil carbon in different regions.

The team predicted that for every single-degree Celsius of warming, about 30 petagrams - that's around 30,000,000,000,000 kilograms - of carbon will be released from the soil. That's the same weight as about 190,000,000 blue whales.

The Paris Climate Agreement has the goal of not allowing the earth to warm over 2 degrees Celsius, but even that increase would emit a colossal amount of carbon dioxide.

Soil carbon losses are not the only response to global warming. Several other biological processes such as accelerated plant growth could have a positive or negative effect on the amount of carbon released.

"Getting a handle on these kinds of feedbacks is essential if we're going to make meaningful projections about future climate conditions," said Crowther.

"Only then can we generate realistic greenhouse gas emission targets that are effective at limiting climate change."

This article was originally published by Business Insider.

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