• Energy Research

Abstract: A key statistic describing climate change impacts is the ‘social cost of carbon dioxide’ (SCCO2), the projected cost to society of releasing an additional tonne of CO2. Cost-benefit integrated assessment models that estimate the SCCO2 lack robust representations of climate feedbacks, economy feedbacks, and climate extremes. We compare the PAGE-ICE model with the decade older PAGE09 and find that PAGE-ICE yields SCCO2 values about two times higher, because of its climate and economic updates. Climate feedbacks only account for a relatively minor increase compared to other updates. Extending PAGE-ICE with economy feedbacks demonstrates a manifold increase in the SCCO2 resulting from an empirically derived estimate of partially persistent economic damages. Both the economy feedbacks and other increases since PAGE09 are almost entirely due to higher damages in the Global South. Including an estimate of interannual temperature variability increases the width of the SCCO2 distribution, with particularly strong effects in the tails and a slight increase in the mean SCCO2. Our results highlight the large impacts of climate change if future adaptation does not exceed historical trends. Robust quantification of climate-economy feedbacks and climate extremes are demonstrated to be essential for estimating the SCCO2 and its uncertainty.

AbstractTo investigate the extent to which differences in regional model projections can be explained by differences in the warming rates of their driving models, we compare projections of temperature and precipitation over the UK from two regional climate ensembles—the EuroCORDEX multi‐model ensemble and UKCP18 perturbed parameter ensemble—along with projections produced by the “parent” GCMs from which boundary conditions were taken. We evaluate the ensembles in terms of their representation of recent climate, then compare the changes simulated between 1981–2010 and 2050–2079. While both ensembles exhibit seasonal biases with similar magnitudes and spatial patterns during the evaluation period, the UKCP18 ensemble exhibits a somewhat stronger change signal in future simulations, due to a combination of higher climate sensitivity of the driving models, variations in the forcings applied, and—in the regional simulations—the inclusion of time‐varying aerosols. In order to reconcile the two sets of projections, we compare two periods corresponding to fixed global warming levels in the driving models, to constrain the variability within and between the ensembles which can be ascribed to differing rates of global warming: the discrepancy between the ensembles is greatly reduced, although some differences in the local response remain, with the UKCP18 runs slightly warmer and drier than the EuroCORDEX runs, particularly in summer. We also highlight potential pitfalls of comparing warming levels with a reference time period, due to uncertainty about the warming that has already occurred in the driving models prior to the reference period.

The oscillatory behaviour of the climate system on decadal timescales before the instrumental record is hard to quantify. However, knowledge of this variability is important for putting current changes in context and for supporting reliable future predictions. Here we investigate the recurrent component of Holocene climate variability in the North Atlantic sector from 10,500 to 2,000 years ago by conducting a frequency analysis of both an annually laminated climate record from a lake in England and outputs from a long transient simulation of the Atlantic meridional overturning circulation. We find consistent decadal variability over the past 6,700 years and before 8,500 years before present, probably reflecting predominance of solar and ocean forcings. Between these dates, climate variability was dampened on decadal timescales. Our results suggest that meltwater discharge into the North Atlantic and the subsequent hydrographic changes, from the opening of the Hudson Bay until the final collapse of the Laurentide Ice Sheet, disrupted the decadal cyclic signals for more than a millennium. Given the current acceleration of the Greenland Ice Sheet melting in response to global warming, this study provides long-term evidence of potential challenges predicting future patterns of the climate system. This study was funded by the Royal Society. C.M.-P. is supported by a Royal Society Dorothy Hodgkin Fellowship (ref: DH150185) and a UKRI Future Leaders Fellowship (MR/W009641/1). A.H. is supported by the Spanish Ministry of Science and Innovation through the Ramón y Cajal Scheme (RYC2020-029253-I). We thank P. Ortega and E. Moreno-Chamarro for valuable discussions. We also thank A. Walsh and G. Biddulph for varve counting in some sections of the record, A. Zhao for plotting complementary climate datasets that helped with the interpretation of the proxy record, A. Brauer and his team for lake coring, and the Diss Council for support during fieldwork. Peer reviewed

Abstract A key statistic describing climate change impacts is the ‘social cost of carbon dioxide’ (SCCO2), the projected cost to society of releasing an additional tonne of CO2. Cost-benefit integrated assessment models that estimate the SCCO2 lack robust representations of climate feedbacks, economy feedbacks, and climate extremes. We compare the PAGE-ICE model with the decade older PAGE09 and find that PAGE-ICE yields SCCO2 values about two times higher, because of its climate and economic updates. Climate feedbacks only account for a relatively minor increase compared to other updates. Extending PAGE-ICE with economy feedbacks demonstrates a manifold increase in the SCCO2 resulting from an empirically derived estimate of partially persistent economic damages. Both the economy feedbacks and other increases since PAGE09 are almost entirely due to higher damages in the Global South. Including an estimate of interannual temperature variability increases the width of the SCCO2 distribution, with particularly strong effects in the tails and a slight increase in the mean SCCO2. Our results highlight the large impacts of climate change if future adaptation does not exceed historical trends. Robust quantification of climate-economy feedbacks and climate extremes are demonstrated to be essential for estimating the SCCO2 and its uncertainty.