Researchers from Northeastern University with collaborators from Oak Ridge National Laboratory, examined the impacts of sustained climate warming and land use and land cover changes (LULCC) on the terrestrial carbon cycle extremes following the Representative Concentration Pathway 8.5 (RCP8.5) and its extension to the year 2300, in an Earth system model simulation. Increasing climate extremes due to fossil fuel emissions have a net negative impact on carbon uptake during extremes. Despite a reduction of total GPP due to LULCC, the increased interannual variability (IAV) in GPP as a result of the altered biogeochemical and biogeophysical impact causes an intensification of carbon cycle extremes.
Our analysis suggests that sustained multi-century climate warming could cause the growth rate in the magnitude of negative carbon extremes to grow faster (1.8×) than positive extremes. We estimate that the LULCC will further cause large losses (−10%) during extremes. With climate change, the number of extremes driven by temperature and fire is expected to increase, though precipitation declines are likely to be the dominant trigger for GPP extremes, while reduced soil moisture leads to persistent extremes.
Carbon dioxide fertilization, improved water use efficiency, and longer growing seasons cause GPP to increase globally. Global warming will cause increasing climate extremes and increasing IAV of GPP. We found that the negative extremes in GPP, which are associated with higher losses in carbon uptake than expected, increase at a higher rate than positive GPP extremes; and this rate rises with LULCC forcing. The most dominant climate driver causing GPP extremes is soil moisture anomalies, which are triggered by extremes in precipitation and temperature. The lagged responses of climate drivers on GPP extremes vary with specific drivers and spatial location. Half of all negative GPP extremes are driven by the compound effect of water, temperature, and fire drivers.