Abstract
The observed slow-down in the global-mean surface temperature (GST) warming from 1998 to 2012 has been called a “warming hiatus.” Certain climate models, operating under experiments which simulate warming by increasing radiative forcing, have been shown to reproduce periods which resemble the observed hiatus. The present study provides a comprehensive analysis of 38 CMIP5 climate models to provide further evidence that models produce warming hiatus periods during warming experiments. GST rates are simulated in each model for the 21st century using two experiments: a moderate warming scenario (RCP4.5) and high-end scenario (RCP8.5). Warming hiatus periods are identified in model simulations by detecting (1) ≥15-year periods lacking a statistically meaningful trend and (2) rapid changes in the GST rate which resemble the observed 1998–2012 hiatus. Under the RCP4.5 experiment, all tested models produce warming hiatus periods. However, once radiative forcing exceeds 5 W/m2—about 2°C GST increase—as simulated in the RCP8.5 experiment after 2050, nearly all models produce only positive warming trends. All models show evidence of rapid changes in the GST rate resembling the observed hiatus, showing that the climate variations associated with warming hiatus periods are still evident in the models, even under accelerated warming conditions.
Highlights
The global-mean surface temperature rate increase during recent years has slowed down relative to the rates for the second half of the 20th century; according to the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5; [1]), the GST trend between the years 1998–2012 is only about one-third to one-half of the trend from 1951 to 2012, with a GST rate decline from about .13∘C/decade to .07∘C/decade during the warming hiatus period.Previous papers examining the recent hiatus period have proposed a variety of causes for the decline in the GST rate, no consensus has been reached
The results of this study indicate that most models are unable to simulate warming hiatus periods when operating under accelerated warming conditions resulting from radiative forcing of 5 Watts per meters2 (W/m2) and higher
This study provides further evidence that the recent hiatus in GST warming can be reproduced using CMIP5 model simulation data operating under accelerated warming experiments
Summary
The global-mean surface temperature (hereafter GST) rate increase during recent years has slowed down relative to the rates for the second half of the 20th century; according to the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5; [1]), the GST trend between the years 1998–2012 is only about one-third to one-half of the trend from 1951 to 2012, with a GST rate decline from about .13∘C/decade to .07∘C/decade during the warming hiatus period. Roberts et al [11] quantified the probability of 10year warming hiatus periods occurring in 21 models of the CMIP Phase 5 (CMIP5, [12]) model ensemble using presentday and RCP4.5 experiments These studies determined that models are able to produce hiatus periods under present-day conditions as well as under accelerated warming conditions. Previous studies often define hiatus periods as those with a zero or negative GST trend or as periods of 10 or more years; in contrast, the present analysis looks for 15-year or longer periods with no statistically meaningful positive trend. By identifying periods which more closely resemble the observed hiatus through both a lack of a statistically meaningful trend and associated GST rate changes, performed on output from two different warming experiments, the present study provides an updated comprehensive analysis to better characterize model ability to simulate hiatus periods
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