A pause in the growth rate of atmospheric carbon dioxide (CO2) has been observed in recent years, despite increasing emissions of CO2from human activity, reports a study published in Nature Communications this week. These findings suggest that enhanced carbon uptake from land-based vegetation has decreased the proportion of human-induced CO2 emissions that remain in the atmosphere.
While absolute atmospheric CO2 levels have been increasing since the Industrial Revolution, there is significant year-to-year variability in the rate at which this increase occurs, largely driven by annual differences in plant growth. Quantifying the changes in the rate of CO2 emissions is essential due to the role CO2 plays in driving climate change. However, these changes are difficult to assess because of the different processes that govern plant growth, especially the balance between the uptake and release of CO2.
Trevor Keenan and colleagues use observations and vegetation models to determine the balance of these driving forces. They show that increasing atmospheric CO2 has enhanced photosynthesis (a CO2 uptake process), but that a slowdown in the rise of global temperatures has also reduced respiration (which releases CO2). Both factors mean more CO2 has been taken up by plants, thereby slowing the rate of CO2accumulation in the atmosphere between 2002 and 2014 by approximately 2.2%/year.
The authors caution that the slowdown in the growth rate of atmospheric CO2 may be temporary, and that increased carbon storage by plants will not resolve the issue of climate change in light of continued increases in absolute CO2 concentrations.