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The emergence of a climate change signal relative to background variability is a useful metric for understanding local changes and their consequences. Studies have identified emergent signals of climate change, particularly in temperature-based indices with weaker signals found for precipitation metrics. In this study, we adapt climate analogue methods to examine multivariate climate change emergence over the historical period. We use seasonal temperature and precipitation observations and apply a sigma dissimilarity method to demonstrate that large local climate changes may already be identified, particularly in low-latitude regions. The multivariate methodology brings forward the time of emergence by several decades in many areas relative to analysing temperature in isolation. We observed particularly large departures from an early-20th century climate in years when the global warming signal is compounded by an El Niño-influence. The latitudinal dependence in the emergent climate change signal means that lower-income nations have experienced earlier and stronger emergent climate change signals than the wealthiest regions. Analysis based on temperature and precipitation extreme indices finds weaker signals and less evidence of emergence but is hampered by lack of long-running observations in equatorial areas. The framework developed here may be extended to attribution and projections analyses.

There is growing interest in how the climate would change under net zero carbon dioxide emissions pathways as many nations aim to reach net zero in coming decades. In today's rapidly warming world, many changes in the climate are detectable, even in the presence of internal variability, but whether climate changes under net zero are expected to be detectable is less well understood. Here, we use a set of 1000‐year‐long net zero carbon dioxide emissions simulations branching from different points in the 21st century to examine detectability of large‐scale, regional and local climate changes as time passes under net zero emissions. We find that even after net zero, there are continued detectable changes to climate for centuries. While local changes and changes in extremes are more challenging to detect, Southern Hemisphere warming and Northern Hemisphere cooling become detectable at many locations within a few centuries under net zero emissions. We also study how detectable delays in achieving emissions cessation are across climate indices. We find that for global mean surface temperature and other large‐scale indices, such as Antarctic and Arctic sea ice extent, the effects of an additional 5 years of high greenhouse gas emissions are detectable. Such delays in emissions cessation result in significantly different local temperatures for most of the planet, and most of the global population. The long simulations used here help with identifying local climate change signals. Multi‐model frameworks will be useful to examine confidence in these changes and improve understanding of post‐net zero climate changes. Plain Language Summary The rapid pace of climate change is observed in many aspects of the Earth system including local warming and rainfall changes, increases in some extremes, and decreasing ice in polar regions. These observable climate change effects have been part of the motivation for the Paris Agreement and the push to achieve net zero emissions. There is a growing understanding that we should expect some aspects of the climate to continue changing under net zero and that there are benefits to getting to net zero sooner, but it has been unclear to date whether these changes will be obvious or masked by noise in the climate. Here we use simulations to examine how apparent climate changes may be under net zero and the effects of delays in achieving net zero. We find that over time, detectable changes in the climate system still occur under net zero. Many people live in places where we identify detectable local climate changes under net zero emissions. Delays in getting to net zero have identifiable effects across many aspects of the climate system. Achieving net zero should not be expected to halt all climate changes, but it is a necessary step in reducing climate change impacts. Key Points We examine detectability of global, regional and local climate change measures using millennial‐scale net zero CO2 emissions simulations Detectable changes under net zero are found in temperature and precipitation means and extremes, Atlantic Meridional Overturning Circulation recovery, and sea ice extent Delays to emissions cessation have widespread consequences for many centuries

Recent 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. Plain Language Summary The world has warmed quickly since around 1970, prompting efforts to mitigate climate change and to stabilize global temperatures between 1.5°C and 2°C above pre‐industrial levels. We explore the differences between a rapidly warming climate and one with little change in global temperature over time. We find that a fast‐warming climate is characterized by warmer temperatures over Northern Hemisphere mid‐latitude land regions than a stable climate at the same level of global warming. The opposite is true in the Southern Ocean where slower warming occurs because of the lag in warming of the deep ocean, so as the global climate stabilizes that region continues to warm. As the world continues to warm, some land locations, such as the interior of North America and Eurasia, may experience a temporary emergence of a climate change signal that weakens if the climate stabilizes and the Paris Agreement goals are met. The difference between fast‐warming and stable climates can be very large locally, so they must be considered in planning for adapting to future climate change. Key Points Warming patterns at Paris Agreement limits differ substantially between transient and quasi‐equilibrium climates Summer climate changes over northern land are clearer in a transient climate than a stabilized climate at the same global warming level Projections of regional climate designed for the Paris Agreement limits are only useful if the rate of global warming is explicit

Under the Paris Agreement, signatory nations aim to keep global warming well below 2 °C above pre-industrial levels and preferably below 1.5 °C. This implicitly requires achieving net-zero or net-negative greenhouse gas emissions to ensure long-term global temperature stabilisation or reduction. Despite this requirement, there have been few analyses of stabilised climates, and there is a lack of model experiments to address our need for understanding the implications of the Paris Agreement. Here, we describe a new set of experiments using the Australian Community Climate and Earth System Simulator Earth system model (ACCESS-ESM-1.5) that enables the analysis of climate evolution under net-zero emissions, and we present initial results. Seven 1000-year-long simulations were run with global temperatures stabilising at levels in line with the Paris Agreement and at a range of higher global warming levels (GWLs). We provide an overview of the experimental design and use these simulations to demonstrate the consequences of delayed attainment of global net-zero carbon dioxide emissions. We show that there are substantial differences between transient and stabilising climate states and differences in stabilisation between GWLs. As the climate stabilises under net-zero emissions, we identify significant and robust changes in temperature and precipitation patterns including continued Southern Ocean warming and changes in regional precipitation trends. Changes under net-zero emissions differ greatly between regions, including contrasting trajectories of sea ice extent between the Arctic and Antarctic. We also examine the El Niño–Southern Oscillation (ENSO) and find evidence of reduced amplitude and frequency of ENSO events under climate stabilisation relative to projections under transient warming. An analysis at specific GWLs shows that significant regional changes continue for centuries after emission cessation and that these changes are stronger at higher GWLs. Our findings suggest substantial long-term climate changes are possible even under net-zero emission pathways. These simulations are available for use in the community and will hopefully motivate further experiments and analyses based on other Earth system models.

Recent climate change is characterised 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 based on greenhouse gas-only model simulations at 1.5°C and 2°C global warming. We find substantial local differences between seasonal-average temperatures, 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. Our research demonstrates that the rate of global warming must be considered in regional projections.

Under 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. Plain Language Summary Under the Paris Agreement, countries pledge to limit global warming to below 2°C above pre‐industrial levels by achieving net zero greenhouse gas emissions. Our study examines how local and global temperatures continue to evolve after the abrupt cessation of CO2 emissions in nine earth system models. On the global scale, models, on average, continue to evolve for 124 years after emissions are ceased. There is a large difference between models, with some stabilizing after several decades, whilst others continue to change for centuries. Most models show a cooling trend after emissions cease. In two models, this cooling is then followed by a warming. Many regions are not stable by the end of the simulation, highlighting the ongoing impact of climate change even after emissions stop. Key Points Temperature stabilization does not occur immediately after net zero CO2 emissions at both the global and local levels The global mean temperature stabilizes 124 years after the cessation of emissions, with a model spread of 64–282 years At both local and global scales, the initial temperature response following net zero emissions may exhibit a reversal

Under 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 CO 2 emissions are abruptly ceased. Our findings show that at both the global and local level stabilization does not occur immediately after net zero CO 2 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. Under the Paris Agreement, countries pledge to limit global warming to below 2°C above pre‐industrial levels by achieving net zero greenhouse gas emissions. Our study examines how local and global temperatures continue to evolve after the abrupt cessation of CO 2 emissions in nine earth system models. On the global scale, models, on average, continue to evolve for 124 years after emissions are ceased. There is a large difference between models, with some stabilizing after several decades, whilst others continue to change for centuries. Most models show a cooling trend after emissions cease. In two models, this cooling is then followed by a warming. Many regions are not stable by the end of the simulation, highlighting the ongoing impact of climate change even after emissions stop. Temperature stabilization does not occur immediately after net zero CO 2 emissions at both the global and local levels The global mean temperature stabilizes 124 years after the cessation of emissions, with a model spread of 64–282 years At both local and global scales, the initial temperature response following net zero emissions may exhibit a reversal