Detecting Warming Hiatus Periods in CMIP5 Climate Model Projections

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.

Robustness of CMIP6 Historical Global Mean Temperature Simulations: Trends, Long‐Term Persistence, Autocorrelation, and Distributional Shape

“…Examples of accelerated warming periods include the early twentieth century and late twentieth century. Examples of slowed warming periods, or “hiatus” periods, include the mid‐twentieth century and the 2000s (Li & Baker, 2016; Medhaug et al, 2017; Trenberth & Fasullo, 2013). We evaluate whether models reproduce the warming rates during these periods.…”

Predicting Slowdowns in Decadal Climate Warming Trends With Explainable Neural Networks

“…While there have been numerous definitions and data sets used for identifying warming slowdown (or so‐called hiatus/pause) events (e.g., Risbey et al., 2018; Wei et al., 2021), they are often classified as a near‐zero or negative 10–20 yr linear trend of the GMST. Recent studies show that the frequency of slowdown events in CMIP5 models decreases substantially by the end of the 21st century using a negative 10 yr linear trend definition (e.g., Li & Baker, 2016; Maher et al., 2014; Sévellec et al., 2016). Their frequency could also decrease due to increasing climate sensitivity (Modak & Mauritsen, 2021).…”

“…Their frequency could also decrease due to increasing climate sensitivity (Modak & Mauritsen, 2021). Yet, internal variability is still projected to affect regional and global climate trends even under higher future emission scenarios (Cassou et al., 2018; Easterling & Wehner, 2009; Li & Baker, 2016; Maher et al., 2020). Here, we take a GMST slowdown threshold using decadal (10 yr) trends (e.g., Maher et al., 2014; Meehl et al., 2011), which is on the shorter end of previously used timescales and focus on the influence of oceanic internal variability.…”