Northeast Forestry University, China (People's Republic)
Abstract: Climate warming is steadily enhancing drought risk in most regions of the Earth, which considerably affects terrestrial ecosystem respiration (ER), the largest land to air CO2 flux. However, it remains uncertain to what extent temperature and water availability control ER variations across spatial and temporal scales. Here, we provide a data-driven estimate of global ER product from 1989 to 2018 using a modified CO2 flux partitioning model based on eddy covariance, a Random Forest model, meteorological and remote-sensing observations. Our results showed that global ER decreased at a rate of -0.050 Pg C yr-2 in 1989-2018, especially during 1998-2018 (-0.090 ± 0.017 Pg C yr-2), which differs from the existing view with an increasing trend as well as from 1989-1998 in this study. This declining trend in the global terrestrial ER was primarily driven by increasing moisture limitation, especially in a majority of tropical and temperate regions, while the increasing trend of ER was generally considered due to climate warming in boreal zone. Unfortunately, current Earth system models fail to adequately capture this apparent decreased trend in ER over 1989-2018 due to the strong positive correlations between ER and rising temperature in most land regions, implying the overthinking of rising temperature on global ER and the underestimation of the importance of soil moisture. Our findings pose new scientific challenges and opportunities for model benchmarking, hypothesis generation and testing, and ecological forecasting.
