A major factor of uncertainty regarding future climate forecasts is the amount of carbon emitted by thawing permafrost, soil that is usually constantly frozen.
Researchers have previously predicted that rapidly rising temperatures will cause emissions of 50 to 100 billion tons of carbon from permafrost by the year 2100.
Now an international team of researchers from Umeå University, Stockholm and France has shown that the priming effect of plant roots can cause emissions of another 40 billion tonnes of carbon.
This means that humanity has much less of its emission budget left than previously thought if it is to be able to keep global warming to a maximum of 1.5 degrees Celsius.
- It is a lot, but it also shows the uncertainty about what we know. The fact that such a small process can contribute so much makes me wonder what more we do not know, how many more such surprises we can get, says Frida Keuper, who is one of those who lead the research group.
Plant roots "feed" bacteria with sugar
Priming is called the mechanism by which plant roots help and stimulate microbial degradation in the soil by "feeding" the microorganisms in the soil with sugar.
- We have known about "priming" since the 1950s, but we did not know if this small-scale ecological interaction had a significant impact on the global carbon dioxide cycle, says Frida Keuper.
By combining maps of plant activity with data on carbon content in the soil and an extensive literature study on the properties of plant roots, the research group was able to show that the priming effect increases microbial respiration by twelve percent.
That increase corresponds to almost a quarter of humanity's remaining emission budget.
- This is of course not good news, says Frida Keuper.
See more in the clip above.