World map showing trends of gross primary productivity, increasing in the northern latitudes and decreasing in the tropics
Trends in gross primary productivity (GPP in gC m-2 yr-1) 1982-2016. Green and blue tones indicate positive trends. Red tones at low latitudes (10°N–10°S) show strong negative trends and delineate the world’s major rainforests. These trends accelerated with higher vapor pressure deficit (VPD) in tropical and arid regions in the last two decades and were amplified by drought. This map illustrates the spatial distribution of water stress controls on atmospheric fertilization. Credit: Madani et al., 2020, Figure 1
Source: AGU Advances

Satellite observations over the last nearly four decades have now captured changes in plant photosynthetic activity tied to the increased greenness, concurrent with increasing atmospheric CO2. Using an improved light use efficiency model and hydrometeorological data (e.g., air temperature, vapor pressure deficit, and root zone soil moisture), Madani et al. [2020] estimated the evolution of spatially varying gross primary productivity (GPP) globally. The results show higher GPP in the mid and high latitudes, counterbalanced by accelerated decreases at lower latitudes (10°N–10°S), including the Amazon, Congo, and Southeast Asia rainforests.

The increases in GPP at higher latitudes result from warmer temperatures and longer growing seasons, a negative climate feedback. The decreases in the tropics’ GPP result from increased atmospheric water stress, further enhanced by reductions in soil moisture during episodic drought, a positive climate feedback. The potential emergence of water stress at higher latitudes could potentially switch regions of negative climate feedback to positive feedback, accelerating the global downward trend in carbon uptake by plants in the future. This study demonstrates the strong coupling between the water and carbon cycles and highlights water stress controls of the terrestrial carbon sink.

Citation: Madani, N., Parazoo, N. C., Kimball, J. S., Ballantyne, A. P., Reichle, R. H., Maneta, M., et al. [2020]. Recent amplified global gross primary productivity due to temperature increase is offset by reduced productivity due to water constraints. AGU Advances, 1, e2020AV000180.

—Ana Barros, Editor, AGU Advances

Text © 2020. The authors. CC BY-NC-ND 3.0
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