• Energy Research

AbstractUnder the Paris Agreement, signatories aim to limit the global mean temperature increase to well below 2°C above pre‐industrial levels. To achieve this, many countries have made net zero greenhouse gas emissions targets, with the aim of halting global warming and stabilizing the climate. Here, we analyze the stability of global and local temperatures in an ensemble of simulations from the zero‐emissions commitment Model Intercomparison Project, where CO2 emissions are abruptly ceased. Our findings show that at both the global and local level stabilization does not occur immediately after net zero CO2 emissions. The multi‐model median (mean) global average temperature stabilizes after approximately 90 (124) years, with an inter‐model range of 64–330 years. However, for some models, this may underestimate the actual time to become stable, as this is the end of the simulation. Seven models exhibited cooling post‐emission cessation, with two of the models then warming after the initial cooling. One model gradually warmed through the entire simulation, while another had alternating cooling and warming. At the local level, responses varied significantly, with many models simulating the reversal of trends in some areas. Changes at the local level, at many locations, continue beyond the stabilization of global temperature and are not stable by the end of the simulations.

AbstractRecent climate change is characterized by rapid global warming, but the goal of the Paris Agreement is to achieve a stable climate where global temperatures remain well below 2°C above pre‐industrial levels. Inferences about conditions at or below 2°C are usually made based on transient climate projections. To better understand climate change impacts on natural and human systems under the Paris Agreement, we must understand how a stable climate may differ from transient conditions at the same warming level. Here we examine differences between transient and quasi‐equilibrium climates using a statistical framework applied to greenhouse gas‐only model simulations. This allows us to infer climate change patterns at 1.5°C and 2°C global warming in both transient and quasi‐equilibrium climate states. We find substantial local differences between seasonal‐average temperatures dependent on the rate of global warming, with mid‐latitude land regions in boreal summer considerably warmer in a transient climate than a quasi‐equilibrium state at both 1.5°C and 2°C global warming. In a rapidly warming world, such locations may experience a temporary emergence of a local climate change signal that weakens if the global climate stabilizes and the Paris Agreement goals are met. Our research demonstrates that the rate of global warming must be considered in regional projections.

AbstractAs more countries make net zero greenhouse gas emissions pledges, it is crucial to understand the effects on global climate after achieving net zero emissions. The climate has been found to continue to evolve even after the abrupt cessation of CO2 emissions, with some models simulating a small warming and others simulating a small cooling. In this study, we analyze if the temperature and precipitation changes post abrupt cessation of CO2 emissions are significantly different compared to natural climate variations. We find that the temperature changes are outside of natural variability for most models, whilst the precipitation changes are mostly non‐significant. We also demonstrate that post‐net zero temperature changes have implications for the remaining carbon budget. The possibility of further global warming post‐net zero adds to the evidence supporting more rapid emissions reductions in the near‐term.

AbstractAnthropogenic emissions of greenhouse gases have warmed the planet by around 1.3°C and have contributed to the intensification of heat extremes. To stop continued global warming, we understand that we must reach and sustain net‐zero global CO2 emissions, however, there is limited knowledge on how heat extremes might change in net‐zero futures. In this study, we explore possible changes in temperature extreme intensity over the century after net‐zero CO2 emissions using projections from Earth System Models in the Zero Emissions Commitment Model Intercomparison Project (ZECMIP). Specifically, we investigate how regional single‐day temperature extreme intensities scale with global mean surface temperatures changes before and after net‐zero CO2 emissions. We also explore potential hydrological drivers of changes in temperature extreme scaling by performing focused investigations over the Mediterranean and Southern African regions. Our results show substantial reductions in scaling of temperature extreme intensity after reaching net‐zero CO2 emissions over nearly all land regions, however, scaling changes are dependent on the cumulative emissions prior to reaching net‐zero CO2. Temperature extreme scaling reductions after net‐zero CO2 are also regionally dependent, and the regional magnitudes of scaling reductions tend to favor mid‐latitude land in the Northern Hemisphere relative to tropical and Southern Hemispheric land masses. From focused investigations over the Mediterranean and Southern African regions, we find that changes in atmospheric circulation and local precipitation may play a major role in determining the sign and magnitude of changes in temperature extremes after net‐zero CO2 emissions.