Investigating the path dependence of climate changes in a 200-member ensemble of overshoot scenarios

Current policies have global mean temperature (GMT) on track to surpass the temperature thresholds agreed upon in the Paris Agreement. Therefore, if the goals of the Paris Agreement are to be met, there is an increasing likelihood of temporarily overshooting the 1.5°C or well-below 2.0°C thresholds. Using an intermediate complexity global Earth system model, we explore the climate implications of temperature overshoot using ≈100 pairs of multi-gas emissions scenarios from the ENGAGE project, with peak temperatures from ≈1.5°C to ≈2.2°C. For each pair of scenarios, the first is constrained by the remaining carbon budget (RCB) in 2100, which allows for the possibility of overshoot, while the second is constrained by the same RCB irrespective of a time horizon and acts as a baseline scenario. The comparisons of the pairs of scenarios demonstrate that the climate changes that occur at a given GMT are path dependent. In this presentation, we show how the impacts of overshoot vary depending on: 1) peak temperature, 2) the degree of overshoot, 3) the duration of overshoot, and 4) the amount of warming caused by CO2 vs. non-CO2 emissions. Our study expands on the literature by investigating the climate implications of temperature overshoot in an ensemble of ≈200 multi-gas scenarios with a range of temperature targets using a spatially explicit Earth system model.