Recent Global Warming Hiatus Research Articles

Full‐depth temperature trends in the northeastern Atlantic through the early 21st century

AbstractThe vertical structure of temperature trends in the northeastern Atlantic (NEA) is investigated using a blend of Argo and hydrography data. The representativeness of sparse hydrography sampling in the basin mean is assessed using a numerical model. Between 2003 and 2013, the NEA underwent a strong surface cooling (0–450 m) and a significant warming at intermediate and deep levels (1000 m to 3000 m) that followed a strong cooling trend observed between 1988 and 2003. During 2003–2013, gyre‐specific changes are found in the upper 1000 m (warming and cooling of the subtropical and subpolar gyres, respectively), while the intermediate and deep warming primarily occurred in the subpolar gyre, with important contributions from isopycnal heave and water mass property changes. The full‐depth temperature change requires a local downward heat flux of 0.53 ± 0.06 W m−2 through the sea surface, and its vertical distribution highlights the likely important role of the NEA in the recent global warming hiatus.

한반도 극한 기온의 선형 및 비선형 변화 경향

This study explores the long-term trends of surface air temperatures in 11 KMA stations over the period of 1960~2012. Both linear and nonlinear trends are examined for the <TEX>$95^{th}$</TEX>, <TEX>$50^{th}$</TEX>, and <TEX>$5^{th}$</TEX> percentiles of daily maximum (<TEX>$T_{max}$</TEX>) and minimum temperatures (<TEX>$T_{min}$</TEX>) by using quantile regression method. It is found that in most stations linear trends of <TEX>$T_{max}$</TEX> and <TEX>$T_{min}$</TEX> are generally stronger in winter than in summer, and warming trend of the <TEX>$5^{th}$</TEX> percentile temperature (cold extreme) is stronger than that of the <TEX>$95^{th}$</TEX> percentile temperature (warm extreme) in both seasons. The nonlinear trends, which are evaluated by the second order polynomial fitting, show a strong nonlinearity in winter. Specifically, winter temperatures have increased until 2000s but slightly decreased afterward in all percentiles. This contrasts with the <TEX>$95^{th}$</TEX> and <TEX>$50^{th}$</TEX> percentiles of summer <TEX>$T_{min}$</TEX> that show a decreasing trend until 1980s then an increasing trend. While this result is consistent with a seasonal dependence of the recent global warming hiatus, most of the nonlinear trends are statistically insignificant, making a quantitative attribution of nonlinear temperature trends challenging.

Observed and simulated temperature extremes during the recent warming hiatus

The discrepancy between recent observed and simulated trends in global mean surface temperature has provoked a debate about possible causes and implications for future climate change projections. However, little has been said in this discussion about observed and simulated trends in global temperature extremes. Here we assess trend patterns in temperature extremes and evaluate the consistency between observed and simulated temperature extremes over the past four decades (1971–2010) in comparison to the recent 15 years (1996–2010). We consider the coldest night and warmest day in a year in the observational dataset HadEX2 and in the current generation of global climate models (CMIP5). In general, the observed trends fall within the simulated range of trends, with better consistency for the longer period. Spatial trend patterns differ for the warm and cold extremes, with the warm extremes showing continuous positive trends across the globe and the cold extremes exhibiting a coherent cooling pattern across the Northern Hemisphere mid-latitudes that has emerged in the recent 15 years and is not reproduced by the models. This regional inconsistency between models and observations might be a key to understanding the recent hiatus in global mean temperature warming.

The cause of the pause

A global climate model that factors in the observed temperature of the surface ocean in the eastern equatorial Pacific offers an explanation for the recent hiatus in global warming. See Letter p.403 Global warming has largely stalled since the late 1990s, raising concerns regarding our understanding of climate sensitivity, the underlying mechanisms influencing climate variability and the ability of climate models to represent decadal variability. Yu Kosaka and Shang-Ping Xie show that the warming hiatus, including most of its seasonal and spatial aspects, can be resolved when observations of recently observed cooling in the eastern equatorial Pacific are directly incorporated into a climate model. The results suggest that the current hiatus is a normal instance of internal climate variability, and that long-term warming is likely to resume as greenhouse gas concentrations continue to increase.

Recent global-warming hiatus tied to equatorial Pacific surface cooling

Despite the continued increase in atmospheric greenhouse gas concentrations, the annual-mean global temperature has not risen in the twenty-first century, challenging the prevailing view that anthropogenic forcing causes climate warming. Various mechanisms have been proposed for this hiatus in global warming, but their relative importance has not been quantified, hampering observational estimates of climate sensitivity. Here we show that accounting for recent cooling in the eastern equatorial Pacific reconciles climate simulations and observations. We present a novel method of uncovering mechanisms for global temperature change by prescribing, in addition to radiative forcing, the observed history of sea surface temperature over the central to eastern tropical Pacific in a climate model. Although the surface temperature prescription is limited to only 8.2% of the global surface, our model reproduces the annual-mean global temperature remarkably well with correlation coefficient r = 0.97 for 1970-2012 (which includes the current hiatus and a period of accelerated global warming). Moreover, our simulation captures major seasonal and regional characteristics of the hiatus, including the intensified Walker circulation, the winter cooling in northwestern North America and the prolonged drought in the southern USA. Our results show that the current hiatus is part of natural climate variability, tied specifically to a La-Niña-like decadal cooling. Although similar decadal hiatus events may occur in the future, the multi-decadal warming trend is very likely to continue with greenhouse gas increase.