The phrase “tipping point” is not a good one when it comes to climate change. We reached one recently when atmospheric concentrations of carbon dioxide reached 400ppm, a historic high that shows how quickly humanity has transformed the atmosphere.

As revealed in a new study in the journal Nature, we are poised to tip over another. According to the Yale University-led research, the current rate of warming will unleash around 55 billion tonnes (60.6 billion tons) of carbon trapped in soil into the atmosphere.

Specifically, an extra 1°C (1.8°F) of warming – something many experts, including those in this instance, think will happen by around 2050 – will have the effect of placing another United States’ worth of emissions into the sky.

These striking conclusions were reached using predictive models based on 20 years of soil samples. The team primarily focused on the under-investigated Arctic region, whose soils have millennia’s worth of trapped carbon within them.

“Carbon stores are greatest in places like the Arctic and the sub-Arctic, where the soil is cold and often frozen,” lead author Thomas Crowther, a former postdoctoral researcher at Yale, said in a statement. “In those conditions, microbes are less active and so carbon has been allowed to build up over many centuries.

“But as you start to warm, the activities of those microbes increase, and that’s when the losses start to happen,” he added, before noting that “the scary thing is, these cold regions are the places that are expected to warm the most under climate change.”

Such a sudden carbon release could trigger runaway climate change, wherein the warming accelerates the carbon release, which in turn further accelerates warming. This is known as a “positive feedback cycle,” and it’s potentially irreversible. Although it's not clear how likely such a scenario actually is, it's certainly a possibility.

^{Explaining the new study's results. NIOO KNAW via YouTube}

One of the most underreported aspects of climate change, these cycles describe any process that is self-amplifying, and the soil’s release of carbon– in the form of carbon dioxide– is just one of many.

Imagine you have a bonfire going – that represents climate change. Now, imagine you have individual cans of fuel. These fuel cans are positive feedback cycles, like carbon trapped in soil. We do not want to throw them onto an already raging bonfire, but we’re about to.

Positive feedback cycles can be found all over the planet.

Take the Arctic, for example. When there’s less sea ice, there’s more water, and water absorbs a lot more heat and stores it for long periods of time. This means that more ice melts, and so on and so forth. This is one of the reasons the Arctic is warming twice as fast as the rest of the world.

The Arctic’s permafrost could also trigger another positive feedback cycle. This potent greenhouse gas – shorter lived in our atmosphere than carbon dioxide, but magnitudes more effective at trapping heat – appears when microbes, under low-oxygen conditions, break down organic matter and release it as a biproduct.

If this escapes into the sky in vast enough quantities, this could induce a sudden warming. This will then potentially unleash more methane, and the new positive feedback cycle could possibly begin. Again, it's good to be clear, however, that a lot of uncertainty exists as to how plausible this particular scenario actually is too.

In any case, the problem with positive feedback cycles is that, by their nature, they are incredibly difficult to stop. Just to give a rather extreme example of this, a lack of water, accumulating carbon dioxide and a runaway greenhouse effect is the reason that Venus is now an incredible hot world. Once it began in earnest, it was inexorable.

Thanks to our oceans absorbing an unfathomable amount of greenhouse gases, Earth has not, and will not, turn into Venus. However, warmer waters hold less carbon dioxide than colder waters, and the oceans are definitely getting warmer.

Another positive feedback cycle could be about to begin. Another can of fuel on the bonfire.

^{The Arctic contains a lot of locked-up carbon. Gregory A. Pozhvanov/Shutterstock}