Fabrice Lacroix

and 4 more

As the likelihood of temporarily exceeding 1.5 °C of global warming rises, understanding the response of the ocean-climate system to overshooting this warming level is of increasing importance. Here, we apply the Adaptive Emissions Reduction Approach to the Earth System Model GFDL-ESM2M to conduct novel overshoot scenarios which temporarily exceed 1.5 °C of global warming to 2.0, 2.5 and 3.0 °C, alongside a complementary scenario that stabilizes global temperature at 1.5 °C. The simulation framework allows to isolate impacts attributable to the temperature overshoots alone, both during their peaks and after their reversals, in simulation timeframes spanning from 1861 to 2500. Our results reveal that, while global sea surface temperatures eventually retrace to 1.5 °C stabilization levels, substantial residual ocean surface warming persists regionally, particularly in the North Atlantic (regional average of up to +3.1 °C in the 3°C overshoot scenario) and the Southern Ocean (+1.2 °C). The residual warming is primarily attributed to the recoveries of the Atlantic and Southern Ocean meridional overturning circulation, resulting in a reversed pattern of disproportionate surface warming in low-latitude oceans found during the transient peak of the overshoot. Excess subsurface heat storage in low and mid-latitudes furthermore prevents steric sea level rise from reverting to 1.5 °C stabilization levels in any overshoot scenario, with sea level remaining up to 32 % higher in the 3 °C overshoot scenario. Both peak overshoot impacts and persistent changes following overshoot reversal bear significant implications for future assessments of coastlines, regional climates, marine ecosystems, and ice sheets.

Yolandi Ernst

and 30 more

As part of the REgional Carbon Cycle Assessment and Processes Phase 2 (RECCAP2) project, we developed a comprehensive African Greenhouse gases (GHG) budget for the period 2010-2019 and compared it to the budget over the 1985-2009 (RECCAP1) period. We considered bottom-up process-based models, data-driven remotely sensed products, and national GHG inventories in comparison with top-down atmospheric inversions, accounting also for lateral fluxes. We incorporated emission estimates derived from novel methodologies for termites, herbivores, and fire, which are particularly important in Africa. We further constrained global woody biomass change products with high-quality regional observations. During the RECCAP2 period, Africa’s carbon sink capacity is decreasing, with net ecosystem exchange switching from a small sink of −0.61 ± 0.58 PgCyr−1 in RECCAP1 to a small source in RECCAP2 at 0.162 (-1.793/2.633) PgCyr-1. Net CO2 emissions estimated from bottom-up approaches were 1.588 (-6.461/11.439) PgCO2yr-1, net CH4 were 78.453 (36.665/59.677) TgCH4yr-1) and net N2O were 1.81 (1.716/2.239) TgN2Oyr-1. Top-down atmospheric inversions showed similar trends. LUC emissions increased, representing one of the largest contributions at 1.746 (0.841/2.651) PgCO2eq yr-1 to the African GHG budget and almost similar to emissions from fossil fuels at 1.743 (1.531/1.956) PgCO2eq yr-1, which also increased from RECCAP1. Additionally, wildfire emissions decreased, while fuelwood burning increased. For most component fluxes, uncertainty is large, highlighting the need for increased efforts to address Africa-specific data gaps. However, for RECCAP2, we improved our overall understanding of many of the important components of the African GHG budget that will assist to inform climate policy and action.