There are lots of ways that carbon dioxide (CO2) enters and leaves the Earth's atmosphere. Even though the natural movements of CO2 are enormous, all indications are that the total inputs and outputs to the atmosphere were well-balanced before the Industrial Revolution, because the CO2 concentration was not changing very much.
In the past 150 years or so, the concentration of carbon dioxide has increased in Earth's atmosphere because the emissions from human activities exceed the various processes that humans have induced to remove CO2 from the atmosphere. (See my blog: http://blogs.nicholas.duke.edu/citizenscientist/the-missing-sink/ ).
About 1/3 of the CO2 that we emit accumulates in the atmosphere, leading to climate change. The processes that remove the rest of the CO2 from the Earth's atmosphere are known as "sinks"—think of it as disappearing down the kitchen sink. For instance, the uptake of CO2 by the oceans is now higher than it was a few decades ago because a greater amount of CO2 dissolves in ocean water as its concentration in the atmosphere increases.
Recognizing that there are sinks for CO2, it is logical to ask if we might increase sinks or make them more efficient in the removal of this gas from the atmosphere. Some recent work by a group organized by The Nature Conservancy (TNC) suggests that the answer is yes. It emphasizes how natural climate solutions harnessed to help slow the rise of CO2 in the atmosphere might reduce the changes in Earth's climate.
The TNC group shows that how we manage forests can have huge impact on the removal of CO2 from Earth's atmosphere and its storage in a long-term sink—forest biomass. The options in forestry include reforestation of deforested lands, avoiding forest losses from harvest, and better management of existing forests. Adoption of the low-cost options in forests would provide about 2/3 of the total enhancement of uptake and storage of CO2 that might be achieved in terrestrial ecosystems. Preservation of wetlands, especially peatlands, can also offer a major sink for CO2 that might otherwise accumulate in the atmosphere. Together forest and wetland sinks could provide 37 percent of the mitigation of CO2 stipulated by the Paris Climate Agreement for 2030. Enhancement of these natural carbon sinks would allow a more orderly withdrawal of fossil fuels from our economy during the next several decades.
The TNC study also identifies options that are costly (reforestation and application of biochar to soils) and those that are relatively inexpensive, which could be adopted immediately (avoiding deforestation and more judicious use of fertilizers by farmers). In general, enhancing the storage of carbon in wood is more effective than enhancing the storage of carbon in soils, even though the latter has some ancillary benefits to farmers. If we are to avoid changing our planet's temperature by more than 2 C by 2030, then actions that can be instituted immediately and at low cost should be the highest priority.
Let's hope that our elected officials soon recognize that climate change is real and that forests and wetlands work on behalf of the planet. They should be preserved.
References
Anderson, C.M., C.B. Field and K.J. Mach. 2017. Forest offsets partner climate-change mitigation with conservation. Frontiers in Ecology and Environment 15: 359-365.
Boysen, L.R., and 5 others. 2017. The limits to global-warming mitigation by terrestrial carbon removal. Earth's Future doi: 10.1002/2016EF000469
Boysen, L.R., W. Lucht, and D. Gerten. 2017. Trade-offs for food production, nature conservation and climate limit the terrestrial carbon dioxide removal potential. Global Change Biology 23: 4303-4317.
Griscom, B.W. J. Adams, and 30 others. 2017. Natural pathways to climate mitigation. Proceedings of the National Academy of Sciences
Mackey, B. and 6 others. 2013. Untangling the confusion around land carbon science and climate change mitigation policy. Nature Climate Change doi: 10.1039/NClimate1904
Xu, Y and V. Ramanathan. 2017. Well below 2oC: Mitigation strategies for avoiding dangerous to catastrophic climate changes. Proceedings of the National Academy of Sciences 114: doi: 10.1073/pnas.1618481114
