Global Warming Hiatus Research Articles

Mid-2000s North Atlantic shift: Heat budget and circulation changes.

Prior to the 2000s, the North Atlantic was the basin showing the greatest warming. However, since the mid‐2000s during the so‐called global warming hiatus, large amounts of heat were transferred in this basin from upper to deeper levels while the dominance in terms of atmospheric heat capture moved into the Indo‐Pacific. Here we show that a large transformation of modal waters in the eastern North Atlantic (ENA) played a crucial role in such contrasting behavior. First, strong winter mixing in 2005 transformed ENA modal waters into a much saltier, warmer, and denser variety, transferring upper ocean heat and salt gained slowly over time to deeper layers. The new denser waters also altered the zonal dynamic height gradient reversing the southward regional flow and enhancing the access of saltier southern waters to higher latitudes. Then, the excess salinity in northern regions favored additional heat injection through deep convection events in later years.

Making sense of the early-2000s warming slowdown

It has been claimed that the early-2000s global warming slowdown or hiatus, characterized by a reduced rate of global surface warming, has been overstated, lacks sound scientific basis, or is unsupported by observations. The evidence presented here contradicts these claims.

The roles of external forcing and natural variability in global warming hiatuses

Global mean surface temperature (GMST) rising has slowed down since late 1990s, which is referred to as the global warming hiatus. There was another global warming hiatus event during 1940s–1960s. The roles of the external forcing and the natural variability in both global warming hiatuses are explored, using EOF analysis. The first two leading EOF modes of the 5-year running mean global sea surface temperature (SST) reflect the global warming scenario (EOF1) and the interdecadal Pacific oscillation (IPO)-like natural variability (EOF2), respectively. In observation, PC2 was in its positive phase (eastern Pacific cooling) during 1940s–1960s, which contributed to the previous warming hiatus. In addition, GMST trends are found to be negative during late 1950s and 1960s in most of the CMIP5 historical runs, which implies that the external forcing also contributed to the pause in the GMST rising. It is further demonstrated that it is the natural radiative forcing (volcanic forcing) that caused the drop-down of GMST in 1960s. The current global warming hiatus has been attributed to the eastern Pacific cooling/enhanced Pacific trade winds. It is shown that the PC2 switched to its positive phase in late 1990s, and hence the IPO-like natural variability made a contribution to the slowdown of GMST rising in the past decade. It is also found that the EOF1 mode (global warming mode) of the observed SST features a smaller warming in tropical Pacific compared to the Indian Ocean and the tropical Atlantic. Such inter-basin warming contrast, which is attributed to the “ocean thermostat” mechanism, has been suggested to contribute to the intensification of Pacific trade winds since late 1990s as well. Global warming hiatuses are also found in the future projections from CMIP5 models, and the spatial pattern of the SST trends during the warming-hiatus periods exhibits an IPO-like pattern, which resembles the observed SST trends since late 1990s.

Detecting climate signals in precipitation extremes from TRMM (1998–2013)—Increasing contrast between wet and dry extremes during the “global warming hiatus”

AbstractWe investigate changes in daily precipitation extremes using Tropical Rainfall Measuring Mission (TRMM) data (1998–2013), which coincides with the “global warming hiatus.” Results show a change in probability distribution functions of local precipitation events (LPEs) during this period consistent with previous global warming studies, indicating increasing contrast between wet and dry extremes, with more intense LPE, less moderate LPE, and more dry (no rain) days globally. Analyses for land and ocean separately reveal more complex and nuanced changes over land, characterized by a strong positive trend (+12.0% per decade, 99% confidence level (c.l.)) in frequency of extreme LPEs over the Northern Hemisphere extratropics during the wet season but a negative global trend (−6.6% per decade, 95% c.l.) during the dry season. A significant global drying trend (3.2% per decade, 99% c.l.) over land is also found during the dry season. Regions of pronounced increased dry events include western and central U.S., northeastern Asia, and Southern Europe/Mediterranean.

The Footprint of the Inter-decadal Pacific Oscillation in Indian Ocean Sea Surface Temperatures.

Superimposed on a pronounced warming trend, the Indian Ocean (IO) sea surface temperatures (SSTs) also show considerable decadal variations that can cause regional climate oscillations around the IO. However, the mechanisms of the IO decadal variability remain unclear. Here we perform numerical experiments using a state-of-the-art, fully coupled climate model in which the external forcings with or without the observed SSTs in the tropical eastern Pacific Ocean (TEP) are applied for 1871–2012. Both the observed timing and magnitude of the IO decadal variations are well reproduced in those experiments with the TEP SSTs prescribed to observations. Although the external forcings account for most of the warming trend, the decadal variability in IO SSTs is dominated by internal variability that is induced by the TEP SSTs, especially the Inter-decadal Pacific Oscillation (IPO). The IPO weakens (enhances) the warming of the external forcings by about 50% over the IO during IPO’s cold (warm) phase, which contributes about 10% to the recent global warming hiatus since 1999. The decadal variability in IO SSTs is modulated by the IPO-induced atmospheric adjustment through changing surface heat fluxes, sea surface height and thermocline depth.

入境宁波的热带气旋活动特征的气候统计及其年代际变化

本文利用中国气象局热带气旋(TC)资料中心最佳路径数据集，对入境宁波的TC进行统计，从1949到2014年共有71个TC入境宁波，通过合成分析和显著性检验发现：TC源地强东风引导气流的存在和西风带的南北位置是影响TC路径的重要原因。在1990s中后期以来的全球变暖减缓阶段，入境宁波的TC频数在9~10月份显著增多。1990s中后期之后，整个太平洋海表面温度(SST)呈现出太平洋年代际涛动(PDO)的负位相和赤道太平洋的类拉尼娜型海温分布，Walker环流增强，调制了西太副高的加强和西伸，使得西北太平洋TC移动路径偏西，登陆我国海岸线中段的TC频数增多，造成了在9~10月份入境宁波的TC频数增多。就TC生成而言，1990s年代中期之后西北太平洋TC源地西部垂直风切变的减弱和相对湿度的增加可能造成了TC生成的增加，而较东位置则与之相反。 Based on the Best Track Dataset from China Meteorological Administration during 1949-2014, there were 71 tropical cyclones (TCs) during the period landfall in Ningbo. According to composited analysis and t-test, the area which TC genesis with strong east-wind and the location of westerlies play an important role in TC moving. During the autumn season (September and October) of global warming hiatus epoch after the mid-to-end of 1990s, the TC number of moving to Ningbo was increased significantly. The reason may be associated with the Pacific decadal oscillation became into its negative phase. Since the sea surface temperature showing a La Nina-like pattern, which enhanced Walker Circulation and further modulated western Pacific subtropical high (WPSH), the WPSH extended westward and intensified, causing TC moving favorite to western region and favorite landing at Chinese mainland. The genesis of TC over the western North Pacific also appears interdecadal shift indicated by genesis potential index of TC. The decreasing of vertical wind shear and increasing of relative humidity play a dominant role in TC genesis increasing.

Role of radiatively forced temperature changes in enhanced semi-arid warming in the cold season over east Asia

Abstract. As climate change has occurred over east Asia since the 1950s, intense interest and debate have arisen concerning the contribution of human activities to the observed warming in past decades. In this study, we investigate regional surface temperature change during the boreal cold season using a recently developed methodology that can successfully identify and separate the dynamically induced temperature (DIT) and radiatively forced temperature (RFT) changes in raw surface air temperature (SAT) data. For regional averages, DIT and RFT contribute 44 and 56 % to the SAT over east Asia, respectively. The DIT changes dominate the SAT decadal variability and are mainly determined by internal climate variability, represented by the North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), and Atlantic Multi-decadal Oscillation (AMO). Radiatively forced SAT changes have made a major contribution to the global-scale warming trend and the regional-scale enhanced semi-arid warming (ESAW). Such enhanced warming is also found in radiatively forced daily maximum and minimum SAT. The long-term global-mean SAT warming trend is mainly related to radiative forcing produced by global well-mixed greenhouse gases. The regional anthropogenic radiative forcing, however, caused the enhanced warming in the semi-arid region, which may be closely associated with local human activities. Finally, the relationship between the so-called "global warming hiatus" and regional enhanced warming is discussed.

Northwestern Pacific typhoon intensity controlled by changes in ocean temperatures

Dominant climatic factors controlling the lifetime peak intensity of typhoons are determined from six decades of Pacific typhoon data. We find that upper ocean temperatures in the low-latitude northwestern Pacific (LLNWP) and sea surface temperatures in the central equatorial Pacific control the seasonal average lifetime peak intensity by setting the rate and duration of typhoon intensification, respectively. An anomalously strong LLNWP upper ocean warming has favored increased intensification rates and led to unprecedentedly high average typhoon intensity during the recent global warming hiatus period, despite a reduction in intensification duration tied to the central equatorial Pacific surface cooling. Continued LLNWP upper ocean warming as predicted under a moderate [that is, Representative Concentration Pathway (RCP) 4.5] climate change scenario is expected to further increase the average typhoon intensity by an additional 14% by 2100.

Extreme North America Winter Storm Season of 2013/14: Roles of Radiative Forcing and the Global Warming Hiatus

Extreme North America Winter Storm Season of 2013/14: Roles of Radiative Forcing and the Global Warming Hiatus

Extreme North America Winter Storm Season of 2013/14: Roles of Radiative Forcing and the Global Warming Hiatus

Extreme North America Winter Storm Season of 2013/14: Roles of Radiative Forcing and the Global Warming Hiatus

Characteristics of the Trends in the Global Tropopause Estimated From COSMIC Radio Occultation Data

This paper discusses the variabilities and trends in the global tropopause based on the gridded monthly mean Global Positioning System radio occultation data from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission during July 2006–February 2014. We find that the tropopause height can reflect El Nino–Southern Oscillation (ENSO) events. The correlation coefficient between global tropopause height anomalies and the Nino 3.4 sea surface temperature index is 0.53, with a maximum correlation coefficient of 0.8 at a lag of three months. We present first the detailed investigations about the spatial distribution of trends in tropopause parameters in each 10° $\times$ 5° longitude–latitude grid cell over the globe and find that the rates of change in the tropopause parameters during this time period are high in some particular regions such as the Southern Indian Ocean, Antarctica, Western Europe, North Pacific, and the east coast of North America. An analysis of global monthly means of the tropopause parameters indicates a global tropopause height increase of 0.03 $\pm$ 2.36 m/year during 2006–2014, with a corresponding temperature increase of 0.020 $\pm$ 0.008 °C/year, and a pressure increase of 0.11 $\pm$ 0.059 hPa/year. The upward trend of tropopause height is significantly weaker than that in the past years, which might be attributed to the expected stratospheric ozone recovery associated with the Montreal Protocol, the global warming slowdown, and the abnormal global climate change in recent years. The trends of the tropopause parameters are the most significant over the Southern Indian Ocean and Antarctica during September/October/November, which could be due to the stratospheric ozone recovery.

The coastal ocean response to the global warming acceleration and hiatus.

Coastlines are fundamental to humans for habitation, commerce, and natural resources. Many coastal ecosystem disasters, caused by extreme sea surface temperature (SST), were reported when the global climate shifted from global warming to global surface warming hiatus after 1998. The task of understanding the coastal SST variations within the global context is an urgent matter. Our study on the global coastal SST from 1982 to 2013 revealed a significant cooling trend in the low and mid latitudes (31.4% of the global coastlines) after 1998, while 17.9% of the global coastlines changed from a cooling trend to a warming trend concurrently. The trend reversals in the Northern Pacific and Atlantic coincided with the phase shift of Pacific Decadal Oscillation and North Atlantic Oscillation, respectively. These coastal SST changes are larger than the changes of the global mean and open ocean, resulting in a fast increase of extremely hot/cold days, and thus extremely hot/cold events. Meanwhile, a continuous increase of SST was detected for a considerable portion of coastlines (46.7%) with a strengthened warming along the coastlines in the high northern latitudes. This suggests the warming still continued and strengthened in some regions after 1998, but with a weaker pattern in the low and mid latitudes.

Distinct energy budgets for anthropogenic and natural changes during global warming hiatus

Closure of the Earth’s energy budget relies on strong aerosol cooling since 1998, if the same feedbacks apply for anthropogenic and natural variability. An analysis of climate model simulations suggests that these feedbacks are instead distinct.

Decadal trends of the upper ocean salinity in the tropical Indo-Pacific since mid-1990s.

A contrasting trend pattern of sea surface salinity (SSS) between the western tropical Pacific (WTP) and the southeastern tropical Indian Ocean (SETIO) is observed during 2004–2013, with significant salinity increase in the WTP and freshening in the SETIO. In this study, we show that increased precipitation around the Maritime Continent (MC), decreased precipitation in the western-central tropical Pacific, and ocean advection processes contribute to the salinity trends in the region. From a longer historical record, these salinity trends started in the mid-1990s, a few years before the Global Warming Hiatus from 1998 to present. The salinity trends are associated a strengthening trend of the Walker Circulation over the tropical Indo-Pacific, which have reversed the long-term salinity changes in the tropical Indo-Pacific as a consequence of global warming. Understanding decadal variations of SSS in the tropical Indo-Pacific will better inform on how the tropical hydrological cycle will be affected by the natural variability and a warming climate.

Principal nonlinear dynamical modes of climate variability.

We suggest a new nonlinear expansion of space-distributed observational time series. The expansion allows constructing principal nonlinear manifolds holding essential part of observed variability. It yields low-dimensional hidden time series interpreted as internal modes driving observed multivariate dynamics as well as their mapping to a geographic grid. Bayesian optimality is used for selecting relevant structure of nonlinear transformation, including both the number of principal modes and degree of nonlinearity. Furthermore, the optimal characteristic time scale of the reconstructed modes is also found. The technique is applied to monthly sea surface temperature (SST) time series having a duration of 33 years and covering the globe. Three dominant nonlinear modes were extracted from the time series: the first efficiently separates the annual cycle, the second is responsible for ENSO variability, and combinations of the second and the third modes explain substantial parts of Pacific and Atlantic dynamics. A relation of the obtained modes to decadal natural climate variability including current hiatus in global warming is exhibited and discussed.

Regime shift in Arabian dust activity, triggered by persistent Fertile Crescent drought

AbstractThe Arabian Peninsula has experienced pronounced interannual to decadal variability in dust activity, including an abrupt regime shift around 2006 from an inactive dust period during 1998–2005 to an active period during 2007–2013. Corresponding in time to the onset of this regime shift, the climate state transitioned into a combined La Niña and negative phase of the Pacific Decadal Oscillation, which incited a hiatus in global warming in the 2000s. Superimposed upon a long‐term regional drying trend, synergistic interactions between these teleconnection modes triggered the establishment of a devastating and prolonged drought, which engulfed the Fertile Crescent, namely, Iraq and Syria, and led to crop failure and civil unrest. Dried soils and diminished vegetation cover in the Fertile Crescent, as evident through remotely sensed enhanced vegetation indices, supported greater dust generation and transport to the Arabian Peninsula in 2007–2013, as identified both in increased dust days observed at weather stations and enhanced remotely sensed aerosol optical depth. According to backward trajectory analysis of dust days on the Arabian Peninsula, increased dust lifting and atmospheric dust concentration in the Fertile Crescent during this recent, prolonged drought episode supported a greater frequency of dust events across the peninsula with associated northerly trajectories and led to the dust regime shift. These findings are particularly concerning, considering projections of warming and drying for the eastern Mediterranean region and potential collapse of the Fertile Crescent during this century.

Rapid warming in the Tibetan Plateau from observations and CMIP5 models in recent decades

ABSTRACTOn the basis of mean temperature, maximum temperature and minimum temperature from the updated China Homogenized Historical Temperature Data Sets, the recent warming in the Tibetan Plateau (TP) during 1961–2005 and global warming hiatus period are examined. During 1961–2005, the mean temperature, maximum temperature and minimum temperature in the whole TP show a statistically increasing trend especially after the 1980s, with the annual rates of 0.27, 0.19 and 0.36 °C decade−1, respectively. The performance of 26 general circulation models (GCMs) available in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) is evaluated in the TP by comparison with the observations during 1961–2005. Most CMIP5 GCMs can capture the decadal variations of the observed mean temperature, maximum temperature and minimum temperature, and have significant positive correlations with observations (R > 0.5), with root mean squared error <1 °C. This suggests that CMIP5 GCMs can reproduce the recent temperature evolution in the TP, but with cold biases. However, most CMIP5 GCMs underestimate the observed warming rates, especially the CNRM‐CM5, GISS‐E2‐H and MRI‐CGCM3 models. There are significant positive correlations between the trend magnitudes and the anomaly of the mean temperature, maximum temperature and minimum temperature, with correlations of 0.85, 0.86 and 0.87, respectively. The warming from the observations and CMIP5 mean in the TP is significant during the global hiatus period, consistent with decreasing snow cover and albedo in the region. This study suggests that positive snow/ice‐albedo feedback processes may account for ongoing surface warming in the TP despite the pause in global mean surface warming.

Seasonality of tropical Pacific decadal trends associated with the 21st century global warming hiatus

AbstractEquatorial Pacific changes during the transition from a nonhiatus period (pre‐1999) to the present global warming hiatus period (post‐1999) are identified using a combination of reanalysis and observed data sets. Results show increased surface wind forcing has excited significant changes in wind‐driven circulation. Over the last two decades, the core of the Equatorial Undercurrent intensified at a rate of 6.9 cm s−1 decade−1. Similarly, equatorial upwelling associated with the shallow meridional overturning circulation increased at a rate of 2.0 × 10−4 cm s−1 decade−1 in the central Pacific. Further, a seasonal dependence is identified in the sea surface temperature trends and in subsurface dynamics. Seasonal variations are evident in reversals of equatorial surface flow trends, changes in subsurface circulation, and seasonal deepening/shoaling of the thermocline. Anomalous westward surface flow drives cold‐water zonal advection from November to February, leading to surface cooling from December through May. Conversely, eastward surface current anomalies in June–July drive warm‐water zonal advection producing surface warming from July to November. An improved dynamical understanding of how the tropical Pacific Ocean responds during transitions into hiatus events, including its seasonal structure, may help to improve future predictability of decadal climate variations.

The Pause in Global Warming: A Numerical Approach

A Monte Carlo simulation of monthly mean surface temperatures is used to construct a time series of 156 moving decadal temperature trends in a 165-year sample period from 1850 to 2014. We define the current pause in global warming as five consecutive moving decades without a statistically significant decadal temperature trend and find that although such pauses are prevalent in the dataset, the prevalence is mostly a feature of the non-warming first half of the period 1850-1932. The current pause of 2001-2014 is the sole such occurrence in the warming latter half of the sample period 1933-2014. We conclude that the 2001-2014 pause in warming is unlikely to be a manifestation of random natural variability in the context of an overall warming trend.

Investigating the recent apparent hiatus in surface temperature increases: 1. Construction of two 30‐member Earth System Model ensembles

AbstractThe recent Intergovernmental Panel on Climate Change report, along with numerous studies since, has suggested that the apparent global warming hiatus results from some combination of natural variability and changes to external forcings. Herein the external forcings for greenhouse gases (GHGs), long‐lived trace gases, volcanic and tropospheric aerosols, and solar irradiance have been replaced in the Norwegian Earth System Model using recent observational estimates. The potential impact of these alternative forcings, and by residual the internally generated variability, is examined through two 30‐member ensembles covering the period 1980 to 2012. The Reference ensemble uses the Coupled Model Intercomparison Project phase 5 historical forcings extended with the Representative Concentration Pathway 8.5 (RCP8.5) scenario, while the Sensitivity ensemble uses the alternative forcings. Over the hiatus period defined herein as 1998–2012, all of the forcings show some change between the Sensitivity and Reference experiments and have a combined net forcing change of −0.03 W m−2. The GHG forcing is 0.012 W m−2 higher in the Sensitivity forcings. The alternative solar forcing differs from the Reference forcing by −0.08 W m−2, the same as the alternative volcanic forcing that was based on the latest estimates from NASA Goddard Institute for Space Studies. Anthropogenic aerosol emissions were replaced using the EU‐EclipseV4a data set and produce a mean forcing change of 0.11 W m−2 over the period. Part 1 details the creation of the two 30‐member ensembles and their characterization for parameters of particular relevance to the explanation of the hiatus. A detailed investigation of the two resulting ensembles global surface temperature behavior is given in Part 2, along with comparisons to observational data sets.