Arctic and boreal ecosystems in the northern high latitudes such as forests and wetlands are responsible for soaking up large amounts of carbon dioxide (CO₂) released by burning fossil fuels through photosynthesis. Plants absorb CO₂ out of the atmosphere and return oxygen. This process is called carbon sinks which help to combat climate change as CO₂ traps more sun’s heat. 

Since high-latitude ecosystems are generally limited by cold temperature, climate warming contributes to stronger carbon sinks in the early growing season through promoting earlier thawing, earlier onset of vegetation productivity, and longer growing seasons, and thus benefits photosynthesis more than respiration. However, seasonal dynamics of net CO₂ uptake in response to temperature anomalies remain uncertain. 

In a study published in Global Change Biology, Dr. LIU Zhihua from the Institute of Applied Ecology of the Chinese Academy of Sciences (CAS) and Dr. WANG Wenjuan from the Northeast Institute of Geography and Agroecology of CAS assessed how temperature anomalies affect seasonal CO₂ exchange. 

Based on in situ observations, model simulations (TRENDY, Atmospheric CO₂ inversions), and atmospheric CO₂ inversions, the researchers investigated the net CO₂ seasonal cycle and climatic and environmental controls across Alaska and northwestern Canada during the anomalously warm winter to spring conditions in 2015 and 2016. 

The results showed that photosynthesis was enhanced more than respiration in the warming spring, leading to greater CO₂ uptake. However, photosynthetic enhancement from spring warming was partially offset by greater respiration during the preceding anomalously warm winter, resulting in nearly neutral effects on the annual net CO₂ balance. 

Besides, they found that air temperature was a primary influence on net CO₂ exchange in winter and spring, while soil moisture was a primary control on net CO₂ exchange in the fall. 

This study suggested that seasonal compensation in the carbon cycle is widespread during a warm winter to spring transition, and under warmer climates, the carbon cycle in the high-latitude ecosystems may be increasingly controlled by hydrologic conditions and subject to much larger uncertainty due to poor understanding of future moisture conditions and their large spatial heterogeneity.