Carbon dioxide levels in the atmosphere are steadily rising because of human activities, which is wreaking havoc on the environment. Some of that excess carbon can also be stored in the so-called carbon sinks of nature, like the ocean or rainforest, for example. Trees are also well known for absorbing carbon. But new research reported in Science has shown that on land, most of the carbon actually seems to be held in water, sediments, or soil.
Scientists are still learning about the carbon sinks of the terrestrial world, like boreal or rainforests and other vegetation, organic matter in soil, or sediments of lakes or rivers, for example. Carbon in some of these places doesn't only derive from burning fossil fuels, it also comes from natural sources like dead animals and plants or excrement. Researchers are also still learning about the accumulation and exchange of carbon in these environments. These processes are not like plant photosynthesis, which is a well-described phenomenon; they are still difficult to understand and measure.
Scientists have attempted to gauge the fluctuations in carbon sinks on land, using data gathered with various remote sensors, or in the field. They assessed data that was collected from 1992 to 2019. These measurements were considered along with carbon exchanges between the atmosphere, oceans, and land to try to determine where carbon was accumulating on land.
This effort indicated that around 35 gigatons of carbon were stored on Earth's surface from 1992 to 2019, and the amount of stored terrestrial carbon has increased by about 30% in the past decade, from 0.5 gigatons per year to 1.7 gigatons per year.
But vegetation, including forests, is only holding about 6% of that increased carbon, however. This is contrary to recent assumptions.
A large portion of the organic carbon that is stored in land-based environments, however, is kept at the bottoms of natural and constructed bodies of water and other oxygen-free environments like soils.
Another big part of the carbon that is stored in terrestrial environments were, surprisingly, linked to human activities such as built dams, artificial ponds, and timber operations.
This study has suggested that even though forests are crucial and should be protected, particularly from wildfires that emit massive amounts of carbon, they do not appear to be the major carbon repositories that they are considered to be. Models should also do more to include these terrestrial carbon sinks, and how they may influence climate change, the research indicated.
Sources: INRAE - National Research Institute for Agriculture, Food and Environment, Science
