Scientists have been investigating the potential effects of climate change for years. Though many of the predicted changes are now occurring, such as loss of sea ice, accelerated sea level rise, and more extreme heat waves, not all effects are well understood.

Most of us are aware that the global temperatures are creeping upward as a result of heat trapped in the atmosphere due to greenhouse gas emissions. But we may not know the full extent of changes this rise in temperature could have on our world. In a recent investigation published in the scientific journal Nature, scientists have explored the influence of global warming on soil carbon stocks located in the earth’s soil, which is still unclear to the scientific community.

Soil carbon stocks have a role to play in climate change because of the many biological processes of organisms living in the soil. Plants, microbes, and animals that live in the soil require exchange of carbon with the atmosphere, resulting in either sequestration of carbon through processes such as photosynthesis or liberation of carbon through processes such as decay. Scientists believe that the rate of these processes could be accelerated by global warming.

In the most recent investigation, scientists compiled a global database of soil carbon stock responses to global warming using worldwide climate change experiments. The soil samples used in the analysis were collected from 49 climate change experiments spanning six biomes in North America, Europe, and Asia. The team focused on soil samples collected within the top 10 cm of soil, which contains the greatest proportion of biologically active soil carbon.

Soil carbon stocks were compared with warmed and ambient control plots to understand the influence of temperature on carbon liberation. From these experiments, the team was able to understand the net result of long-term change in soil carbon exchange due to climate warming. It was also able to spatially map the temperature sensitivity of soil carbon stocks at a global scale.

The researchers found that the impact of warming on soil carbon stocks varied across sites. But they were able to predict the direction and magnitude of the changes, which were related to the size of the standing soil carbon stocks and the extent and duration of warming. They found that substantial losses occurred in high latitude areas.

The team took its analysis a step further by extrapolating the carbon stocks' empirical relationship to the global scale. In doing so, the scientists were able to provide estimates of the sensitivity of soil carbon exchange to global warming that can inform top climate change modeling, such as the earth system model projections.

According to their empirical relationship, global soil carbon stocks are going to fall with warming. Meaning, more carbon is going to be liberated into the atmosphere. For one degree of warming, the team predicts a fall by 30 ± 30 petagrams of carbon to 203 ± 161 petagrams of carbon in upper soil horizons. These values are dependent on the rate at which the effects of warming occur.

Assuming the response of soil carbon to warming will occur within a year and no mitigating actions against climate change occur (business as usual climate scenario), upper soil horizons would liberate 55 ± 50 petagrams of carbon into the atmosphere by 2050. This amount of carbon liberation is roughly 12-17 percent of the already expected anthropogenic emissions over the period. Regardless of the scenario, the global soil carbon response consistently exhibits increased liberation.

Together, this analysis strongly supports the assertion that global warming will stimulate liberation of soil carbon stocks into the atmosphere, creating a positive-feedback mechanism that could further accelerate climate change. This analysis should be taken into consideration when developing future climate change models to best predict the outcomes and to develop the most effective mitigation plans.

Nature, 2016. DOI: 10.1038/nature20150 (About DOIs).