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This study analyzes the temporal patterns of rainfed cereal phenology extracted from the GIMMS NDVI3g dataset in the main cereal-growing regions under a Mediterranean climate in Spain, Portugal, France and Italy during the period 1982–2022. The series before and after the beginning of the 21st century were analyzed separately. Phenological parameters were extracted using the modified dynamic threshold method, and their trends were analyzed. Correlation analyses were performed to study the relationships among these parameters and to analyze the influence of hydroclimatic variables on the start (SOS) and end (EOS) of the growing season. Results showed a temporal reversal in phenological trends between both study periods, coinciding with the global warming hiatus. In the first period (1982–2002), SOS and EOS advanced (−7.5 and −3.1 days, respectively), and the length of growing season (LOS) increased. However, during the second stage (2003–2022), SOS and EOS were delayed (7.5 and 1.7 days, respectively), and LOS decreased. Similar dynamics were observed for the influence of the hydroclimatic variables on SOS and EOS, stronger in the first period and weaker in the second. This study provides valuable information on the phenological dynamics of rainfed cereals that may be useful for their management and planning in climate change scenarios. [ABSTRACT FROM AUTHOR]

Study region: The Issyk-Kul Basin, Central Asia. Study focus: Currently, there is a scarcity of in-depth evaluations of the progression and factors that affect the intensification of the water cycle at the basin level, given the increased fluctuations in the global hydrological cycle. In this study, a water cycle intensity (WCI) indicator based on the terrestrial water balance equation was used to assess basin-scale water cycle characteristics from 1982 to 2017, and the Bayesian estimator algorithm (BEAST) and wavelet transform coherence (WTC) were used to analyse the temporal evolution characteristics and factors influencing the intensity of the water cycle. New hydrological insights for the region: The WCI of the Issyk-Kul Basin (ISKB) undergoes an abrupt change and displays an intensified trend with a clear time-scale effect in the trend change following the global warming hiatus. In terms of forcing factors, the interannual variability in the WCI was driven by the Tibetan Plateau Index_B (TPI) and the North Atlantic Oscillation (NAO) until 1998, while afterwards it was driven by the Antarctic Oscillation (AAO). The alteration in the forcing relationship was a significant contributor to the sudden shift observed in the WCI in 1998. This study improves the comprehension of basin-scale alterations in the intensity of the water cycle and their driving mechanisms under climate change, with practical implications for the management of water resources in arid Central Asia.

Gaining a deep understanding of how climate change affects the carbon cycle in dryland vegetation is of utmost importance, as it plays a pivotal role in shaping the overall carbon cycle in global ecosystems. It is currently not clear how plant communities at varying elevations in arid mountainous regions will respond to climate change in terms of their productivity. The aim of this study was to investigate the effect of climate change on vegetation productivity in different altitudinal vegetation belts of the Tianshan Mountains between 2000 and 2021, utilizing satellite-derived vegetation productivity and climate data. The findings suggest a notable increase in vegetation productivity across diverse altitudinal vegetation belts. The productivity of vegetation in the coniferous forest and alpine meadow belts displayed a notably higher interannual trend compared to other vegetation belts. Notably, an increase in vegetation productivity was accompanied by warming and drying. The productivity of altitudinal vegetation belts, however, appears to be resilient to current climate trends and was not significantly impacted by the severity of atmospheric drought. The trend of increased vegetation productivity was primarily driven by CO2 fertilization. Our results highlight that the extent of climate change may need to reach a threshold to noticeably affect variations in vegetation productivity in arid mountainous. [ABSTRACT FROM AUTHOR]

This study analyzes the temporal patterns of rainfed cereal phenology extracted from the GIMMS NDVI3g dataset in the main cereal-growing regions under a Mediterranean climate in Spain, Portugal, France and Italy during the period 1982–2022. The series before and after the beginning of the 21st century were analyzed separately. Phenological parameters were extracted using the modified dynamic threshold method, and their trends were analyzed. Correlation analyses were performed to study the relationships among these parameters and to analyze the influence of hydroclimatic variables on the start (SOS) and end (EOS) of the growing season. Results showed a temporal reversal in phenological trends between both study periods, coinciding with the global warming hiatus. In the first period (1982–2002), SOS and EOS advanced (−7.5 and −3.1 days, respectively), and the length of growing season (LOS) increased. However, during the second stage (2003–2022), SOS and EOS were delayed (7.5 and 1.7 days, respectively), and LOS decreased. Similar dynamics were observed for the influence of the hydroclimatic variables on SOS and EOS, stronger in the first period and weaker in the second. This study provides valuable information on the phenological dynamics of rainfed cereals that may be useful for their management and planning in climate change scenarios.

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Despite the rapid increase of greenhouse gases (GHGs) in the atmosphere during the past 50 years, observed global mean surface temperature (GMST) showed a pause in the warming trend during the first decade of the twenty-first century. This is referred to as the global warming "hiatus". A dominant hypothesis emphasizes that the superimposition of the cold phase of the Pacific decadal variability and the global warming trend can lead to the hiatus. Using simply energy balance models, we explore two potential mechanisms that may supress the GMST warming trend: enhanced negative climate feedback and downward heat mixing. Forced by linearly increasing heating, a stronger negative climate feedback can reduce the GMST warming rate, but cannot result in a warming hiatus. Downward mixing of heat can cause a short-lived hiatus of surface warming rate due to enhanced nonlinear ocean heat uptake by the lower ocean, but the surface warming would be accelerated in the long run due to the decline of downward heat mixing rate. This study provides further evidence, both theoretically and numerically, that in the long run, the only route to contain the global warming effectively is to reduce GHG emissions. [ABSTRACT FROM AUTHOR]

Marine heatwaves (MHWs) have been reported often throughout the world, producing severe effects on marine ecosystems. However, the spatial pattern and trend of MHWs in the Gulf of Thailand (GOT) is still unknown. Based on high-resolution daily satellite data over a 40-year period from 1982 to 2021, changes in annual mean SST and MHW occurrences across the GOT are explored here. The results demonstrate that during a warming hiatus (1998–2009), annual mean SST in the GOT encountered a dropping trend, followed by an increasing trend during a warming reacceleration period (2010–2021). Although a warming hiatus and a warming reacceleration occurred in the annual mean SST after 1998, regional averaged SSTs were still 0.18 °C–0.42 °C higher than that for 1982–1997. Statistical distributions reveal that there was a significant shift in both annual mean SSTs and annual extreme hot SSTs. These changes have the potential to increase the frequency of MHWs. Further analysis reveals that MHW frequency has increased at a rate of 1.11 events per decade from 1982 to 2021, which is 2.5 times the global mean rate. For the period 2010–2021, the frequency and intensity of MHWs in the GOT have never dropped, but have instead been more frequent, longer lasting and extreme than those metrics of MHWs between 1982 and 2009. Furthermore, the findings highlight significant changes in the SST over the GOT that may lead us to change or modify the reference period of the MHW definition. The findings also suggest that heat transport and redistribution mechanisms in the GOT sea are changing. This study contributes to our understanding of MHW features in the GOT and the implications for marine ecosystems. • A warming hiatus exhibited in the GOT during 1998-2009. • Annual mean and extreme hot SSTs are found a significant increase. • More frequent and longer lasting MHW over the GOT occurred after the warming hiatus. • Significant changes in sea surface temperature over the GOT suggest modifying the reference period of the MHW definition. [ABSTRACT FROM AUTHOR]

During 1998–2013, global surface air temperature increased more slowly than greenhouse gas concentrations, and therefore this period was defined as a "global warming hiatus." The characteristics of climate extremes in China during this period are still not clear. In this study, based on 2,841 meteorological station observations in China, the trends of precipitation and temperature extremes during the global warming hiatus were investigated relative to the reference period (RF) (1982–1997) and the whole historical period (HIS) (1982–2017). Machine learning was used to capture the nonlinear regression of climate extremes, and the Theil–Sen method with the Mann–Kendall significant test was used to calculate the slopes of their linear trends. During the global warming hiatus, annual and summer (JJA) warmest days TXx and the number of summer days SU over the whole of China and most of its four subregions were found to decrease relative to the HIS and RF periods. Annual and winter (DJF) coldest nights TNn over China and its four subregions were found to decrease moderately relative to the HIS and RF periods, whereas the number of frost days FD increased consistently. Precipitation extremes showed more temporal and spatial variability than temperature extremes. Trends of annual and JJA wet extremes during the hiatus were found to decrease relative to the HIS and RF periods, whereas the dry extreme index during the hiatus was found to increase generally over China and in most subregions. Lighter winds and lower relative humidity over most areas of China might have contributed to less pronounced trends of wet extremes during the hiatus period. [ABSTRACT FROM AUTHOR]

A flattening trend of global surface temperature from 1998 to 2013 is generally referred to global warming hiatus. In this review, its basics and controlling mechanisms are the focuses with the latter receiving more attention. The mechanisms for the hiatus are largely derived from internal climate variabilities which could be divided into sea surface temperature (SST) and energy variabilities. The major SST variabilities are Interdecadal Pacific Oscillation (IPO) and Atlantic Multi-decadal Oscillation (AMO). The negative phase of IPO during the hiatus is associated with strengthened Pacific trade winds that enhance subsurface heat uptake, which is generally thought to be the predominant mechanism for the hiatus. Furthermore, AMO influences the global surface temperature at decadal time scales, or even the IPO, which are considered to be the main drivers of hiatus. As for the energy variabilities, vertical uptake and interbasin redistribution of heat are also suggested to be capable of leading to a hiatus period. There was significant warming of global ocean below 700 m during the hiatus as an evidence for the storage of excessive heat in deep ocean. And various heat redistribution patterns like those through ITF or AMOC could also play a significant role in regulating the hiatus.

Global mean surface temperatures (GMST) exhibited a smaller rate of warming during 1998-2013, compared to the warming in the latter half of the 20th Century. Although, not a "true" hiatus in the strict definition of the word, this has been termed the "global warming hiatus" by IPCC (2013). There have been other periods that have also been defined as the "hiatus" depending on the analysis. There are a number of uncertainties and knowledge gaps regarding the "hiatus." This report reviews these issues and also posits insights from a collective set of diverse information that helps us understand what we do and do not know. One salient insight is that the GMST phenomenon is a surface characteristic that does not represent a slowdown in warming of the climate system but rather is an energy redistribution within the oceans. Improved understanding of the ocean distribution and redistribution of heat will help better monitor Earth's energy budget and its consequences. A review of recent scientific publications on the "hiatus" shows the difficulty and complexities in pinpointing the oceanic sink of the "missing heat" from the atmosphere and the upper layer of the oceans, which defines the "hiatus." Advances in "hiatus" research and outlooks (recommendations) are given in this report.

Spring phenology is the most sensitive indicator of climate change and exploring its response to climate change has important implications for ecosystem processes in the study area. The temperature changes before and after the global warming hiatus may affect the spatiotemporal pattern of land surface phenology. In this paper, taking the China–DPRK (Democratic People’s Republic of Korea)–Russia cross-border region as an example, based on GIMMS NDVI data, the Polyfit-Maximum method was used to extract the start date of the vegetation growing season (SOS). The variation trend of SOS and its response to climate change were analyzed in the early (1982–1998) and late (1998–2015) periods of the warming hiatus. At the regional scale, the spatial distribution of the SOS in the China–DPRK–Russia (CDR) cross-border area presents an elevation gradient, which is earlier in high-elevation areas and later in low-elevation areas. The temporal and spatial trend of SOS is mainly correlated by daytime maximum temperature (Tmax). The significant increase in Tmax in the early period promoted the advance of SOS (0.47 days/year), and the decrease in Tmax in the later period caused the delay of SOS (0.51 days/year). While the main influencing factor of the SOS changes in the region in the early and late periods was Tmax, the response of the SOS changes in China, DPRK and Russia to climate change also changed with the dramatic temperature changes during the warming hiatus. The Chinese side is increasingly responding to Tmax, while the North Korean side is becoming less responsive to climatic factors, and precipitation and radiation on the Russian side are driving the advance of the SOS.

This study examines extended boreal summer (May–October) tropical cyclogenesis events (TCGEs) associated with large-scale flow patterns (LFPs) over the western North Pacific (WNP) between 1979–1997 and 1998–2012. WNP TCGEs are objectively identified to be associated with five LFPs [e.g., monsoon shear line (SL), monsoon confluence region (CR), monsoon gyre (GY), Pacific easterly wave (EW) and preexisting tropical cyclone (PTC)]. Results show that an apparent decrease in TCGEs from 1998–2012 was due to the significant decrease in TCGEs associated with the PTC pattern and to a somewhat lesser degree, TCGEs associated with the GY pattern. In contrast, TCGEs associated with the SL pattern show a small increase, which seems to contradict the weakened monsoon circulation since 1998 but corresponds well to cyclonic anomalies over the Philippines region. Decreased TCGEs associated with the GY pattern and increased TCGEs associated with the EW pattern are closely related to the strengthening of Pacific easterly waves in response to the Mega La Niña-like pattern that predominated during 1998–2012. Weakened easterly shear over the eastern WNP is not conducive to the development and propagation into the southeastern WNP of Rossby wave trains induced by preexisting TC energy dispersion. Consequently, there is a significant reduction of TCGEs associated with the PTC pattern and a weakening in the contribution of TCGEs associated with the PTC pattern to TCGEs associated with the EW pattern. An increased correlation between TCs associated with the SL/GY/EW patterns and central Pacific (CP)-type ENSO during 1998–2012 is observed. A stable and robust association between TCGEs associated with the CR pattern and tropical North Atlantic sea surface temperature is observed regardless of decadal climate regime shifts. However, there is no significant link between TCGEs associated with the PTC pattern and more CP ENSO events during 1998–2012, but there is a strong association between the Pacific meridional mode and TCGEs associated with the PTC pattern during 1979–1997. More observational analyses and numerical simulations are needed to further investigate the underlying physical mechanism. [ABSTRACT FROM AUTHOR]

Based on the disproportionate amount of attention paid by climate scientists to the supposed global warming hiatus, it has recently been argued that contrarian discourse has "seeped into" climate science. While I agree that seepage has occurred, its effects remain unclear. This lack of clarity may give the impression that climate science has been compromised in a way that it hasn't—such a conclusion should be defended against. To do this I argue that the effects of seepage should be analyzed in terms of objectivity. I use seven meanings of objectivity to analyze contrarian discourse's impact on climate science. The resulting account supports the important point that climate science has not been compromised in a way that invalidates the conclusions its scientists have drawn, despite the reality of seepage having occurred. • ·Objectivity is a useful concept for assessing the impact of climate contrarianism on the climate science community • Knowledge about climate processes gained from studying the "hiatus" is legitimate, despite seepage having occurred • The global warming "hiatus" case involves successes and partial failures of objectivity in the climate science community • The disproportionate amount of focus on the "hiatus" time period may partially be a product of "hobby-horse" riding [ABSTRACT FROM AUTHOR]

Global mean surface air temperature (SAT) has remained relative stagnant since the late 1990s, a phenomenon known as global warming hiatus. Despite widespread concern and discussion, there is still an open question about whether this hiatus exists, partly due to the biases in observations. The stable isotopic composition of precipitation in mid- and high-latitude continents closely tracks change of the air temperature, providing an alternative to evaluate global warming hiatus. Here we use the long-term precipitation δ18O records available to investigate changes in SAT over the period 1970–2016. The results reveal slight decline in δ18O anomaly from 1998 to 2012, with a slope of −0.000 4‰ decade−1 which is significantly different from that of pre-1998 interval This downward δ18O anomaly trend suggests a slight cooling for about −0.001 oC decade−1, corroborating the recent hiatus in global warming. Our work provides new evidence for recent global warming hiatus and highlights the potential of utilizing precipitation isotope for tracking climate changes. [ABSTRACT FROM AUTHOR]

The 1998-2012 global warming hiatus has aroused great public interest over the past several years. Based on the air temperature measurements from 622 meteorological stations in China, the temperature response to the global warming hiatus was analyzed at national and regional scales. We found that air temperature changed −0.221°C/10a during 1998-2012, which was lower than the long-term trend for 1960-1998 by 0.427°C/10a. Therefore, the warming hiatus in China was more pronounced than the global mean. Winter played a dominant role in the nationwide warming hiatus, contributing 74.13%, while summer contributed the least among the four seasons. Furthermore, the warming hiatus was spatial heterogeneous across different climate conditions in China. Comparing the three geographic zones, the monsoon region of eastern China, arid region of northwestern China, and high frigid region of the Tibetan Plateau, there was significant cooling in eastern and northwestern China. In eastern China, which contributed 53.79%, the trend magnitudes were 0.896°C/10a in winter and 0.134°C/10a in summer. In the Tibetan Plateau, air temperature increased by 0.204°C/10a, indicating a lack of a significant warming hiatus. More broadly, the warming hiatus in China may have been associated with the negative phase of PDO and reduction in sunspot numbers and total solar radiation. Finally, although a warming hiatus occurred in China from 1998 to 2012, air temperature rapidly increased after 2012 and will likely to continuously warm in the next few years. [ABSTRACT FROM AUTHOR]

Abstract The slowdown in global warming since 1998, often termed the global warming hiatus. Reconciling the "hiatus" is a main focus in the 2013 climate change conference. Accurately characterizing the spatiotemporal trends in surface air temperature (SAT) is helps to better understand the "hiatus" during the period. This article presents a satellite-based regional warming simulation to diagnose the "hiatus" for 2001–2015 in China. Results show that the rapid warming is mainly in western and southern China, such as Yunnan (mean ± standard deviation: 0.39 ± 0.26 °C (10 yr)−1), Tibet (0.22 ± 0.25 °C (10 yr)−1), Taiwan (0.21 ± 0.25 °C (10 yr)−1), and Sichuan (0.19 ± 0.25 °C (10 yr)−1). On the contrary, there is a cooling trend by 0.29 ± 0.26 °C (10 yr)−1 in northern China during the recent 15 yr, where a warming rate about 0.38 ± 0.11 °C (10 yr)−1 happened for 1960–2000. Overall, satellite simulation shows that the warming rate is reduced to −0.02 °C (10 yr)−1. The changes in underlying surface, Earth's orbit, solar radiation and atmospheric counter radiation (USEOSRACR) cause China's temperature rise about 0.02 °C (10 yr)−1. A combination of greenhouse gases (GHGs) and other natural forcing (ONAT, predominately volcanic activity, and atmosphere and ocean circulation) explain another part of temperature trend by approximately −0.04 °C (10 yr)−1. We conclude that there is a regional warming hiatus, a pause or a slowdown in China, and imply that GHGs-induced warming is suppressed by ONAT in the early 21st century. Graphical abstract Unlabelled Image Highlights • The satellite data is used to investigate regional climate warming. • Characterizing the spatiotemporal trends in near-surface air temperature in China. • A regional warming hiatus is diagnosed for the period 2001–2015 in China. • We estimate the land surface temperature-induced warming during the period. • Greenhouse gases-induced warming is suppressed by natural variability. [ABSTRACT FROM AUTHOR]

Previous studies demonstrate that recent global warming hiatuses are associated with an ongoing cooling in the eastern Pacific. However, the possible driver for this cooling remains vigorously debated. Present theories can be generally categorized into three different frameworks, the most prevailing theory considering the increased heat uptake in ocean interior as a direct trigger in cooling the eastern equatorial Pacific, the next regarding the prolonged solar minimum as a potential driver in producing weak radiative forcing over the Pacific, while another suggesting that changes in atmospheric water vapour and aerosols play an unnegligible role in absorbing and reflecting solar radiation. Most recently, some studies argue that the ongoing cooling in the eastern Pacific is induced by a strengthening of the easterly trade winds. Nevertheless, observational records coming from the monitoring buoys deployed along the equator by NOAA since 1992 indicate that an intensification of the trade winds is only confined to the central tropical Pacific (around 170° E–170° W) during hiatus decades, elsewhere along the equatorial Pacific the trade winds exhibit a stable condition even a slight weakening in the eastern equatorial Pacific, rendering it as a trigger of this cooling in the eastern Pacific unlikely. Here we use a model and long-term observational data to demonstrate that a persistent cooling in the eastern Pacific is directly linked to an eastward displacement of the Southeast Pacific Subtropical Anticyclone (SPSA). Interactions between the Andes and an eastward shift of the SPSA generate greater pressure gradients in the eastern flank, in turn, stronger alongshore winds and more intense upwelling, ultimately contributing to hiatus decades.

The poleward branches of the Hadley Cells and the edge of the tropics show a robust poleward shift during the satellite era, leading to concerns over the possible encroachment of the globe’s subtropical dry zones into currently temperate climates. The extent to which this trend is caused by anthropogenic forcing versus internal variability remains the subject of considerable debate. In this study, we use a Joint EOF method to identify two distinct modes of tropical width variability: (1) an anthropogenically-forced mode, which we identify using a 20-member simulation of the historical climate, and (2) an internal mode, which we identify using a 1000-year pre-industrial control simulation. The forced mode is found to be closely related to the top of the atmosphere radiative imbalance and exhibits a long-term trend since 1860, while the internal mode is essentially indistinguishable from the El Niño Southern Oscillation. Together these two modes explain an average of 70% of the interannual variability seen in model “edge indices” over the historical period. Since 1980, the superposition of forced and internal modes has resulted in a period of accelerated Hadley Cell expansion and decelerated global warming (i.e., the “hiatus”). A comparison of the change in these modes since 1980 indicates that by 2013 the signal has emerged above the noise of internal variability in the Southern Hemisphere, but not in the Northern Hemisphere, with the latter also exhibiting strong zonal asymmetry, particularly in the North Atlantic. Our results highlight the important interplay of internal and forced modes of tropical width change and improve our understanding of the interannual variability and long-term trend seen in observations. [ABSTRACT FROM AUTHOR]

In this study, the possible effects of subduction rate on global warming hiatus were investigated using Simple Ocean Data Assimilation (SODA) data. This study first analyzed the characteristics of the temporal and spatial distribution of global subduction rate, which revealed that the North Atlantic meridional overturning circulation region and the Antarctic Circumpolar Current region are the two main sea areas with great subduction variations. On this basis, four key areas were selected to explore the relationship between the local subduction rate and the global mean sea surface temperature. In addition, the reason for the variations in subduction rate was preliminarily explored. The results show good correspondence of the subduction of the key areas in the North Atlantic meridional overturning the circulation region and the Antarctic Circumpolar Current region to the global warming hiatus, with the former leading by about 10 years. The subduction process may be a physical mechanism by which the North Atlantic overturning circulation and the Antarctic Circumpolar Current act on the stagnation of global warming. Advection effect plays an important role in the variations in subduction in the key regions. In the Antarctic Circumpolar Current region, the magnitude of sea surface wind stress is closely related to the local changes in subduction. [ABSTRACT FROM AUTHOR]

Based on the satellite-derived global daily sea surface temperature (SST) data set with high resolution (0.25° by 0.25°), we analyzed changes in annual mean SST and extreme SSTs over the China Seas since 1982. Results show that the annual mean SST in the China Seas has experienced a remarkable declining trend during the global warming hiatus (1998–2013), which was dominated by the striking cooling of SST in boreal winter. Despite annual mean SST experienced warming hiatus after 1998, the regional averaged SST for 1998–2013 was still 0.5 °C above that for 1982–1997. The statistical distributions show that there are not only significant warmer climate shift in annual mean SSTs but also in annual extreme hot SSTs and cold SSTs. These changes can increase the likelihood of extreme oceanic warming events, known as marine heatwaves (MHWs). Further analyses reveal that, from 1982 to present, the MHW frequency increases at a rate of 1.13 events per decade, 2.5 times the global mean rate. For the period 1998–2013, the MHWs in the China Sea has never decreased in both of the frequency and intensity but has already become more frequent, longer duration and more intense than those metrics of MHWs during 1982–1997.

Based on regular surface meteorological observations and NCEP/DOE reanalysis data, this study investigates the evolution of surface sensible heat (SH) over the central and eastern Tibetan Plateau (CE-TP) under the recent global warming hiatus. The results reveal that the SH over the CE-TP presents a recovery since the slowdown of the global warming. The restored surface wind speed together with increased difference in ground-air temperature contribute to the recovery in SH. During the global warming hiatus, the persistent weakening wind speed is alleviated due to the variation of the meridional temperature gradient. Meanwhile, the ground surface temperature and the difference in ground-air temperature show a significant increasing trend in that period caused by the increased total cloud amount, especially at night. At nighttime, the increased total cloud cover reduces the surface effective radiation via a strengthening of atmospheric counter radiation and subsequently brings about a clear upward trend in ground surface temperature and the difference in ground-air temperature. Cloud-radiation feedback plays a significant role in the evolution of the surface temperature and even SH during the global warming hiatus. Consequently, besides the surface wind speed, the difference in ground-air temperature becomes another significant factor for the variation in SH since the slowdown of global warming, particularly at night. [ABSTRACT FROM AUTHOR]

A surface cooling pattern in the equatorial Pacific associated with a negative phase of the Interdecadal Pacific Oscillation is the leading hypothesis to explain the smaller rate of global warming during 1998-2012, with these cooler than normal conditions thought to have accelerated the oceanic heat uptake. Here using a 30-member ensemble simulation of a global Earth system model, we show that in 10% of all simulated decades with a global cooling trend, the eastern equatorial Pacific actually warms. This implies that there is a 1 in 10 chance that decadal hiatus periods may occur without the equatorial Pacific being the dominant pacemaker. In addition, the global ocean heat uptake tends to slow down during hiatus decades implying a fundamentally different global climate feedback factor on decadal time scales than on centennial time scales and calling for caution inferring climate sensitivity from decadal-scale variability. [ABSTRACT FROM AUTHOR]

The recent slowdown in global mean surface temperature (GMST) warming during boreal winter is examined from a regional perspective using 10-member initial-condition ensembles with two global coupled climate models in which observed tropical Pacific sea surface temperature anomalies (TPAC SSTAs) and radiative forcings are specified. Both models show considerable diversity in their surface air temperature (SAT) trend patterns across the members, attesting to the importance of internal variability beyond the tropical Pacific that is superimposed upon the response to TPAC SSTA and radiative forcing. Only one model shows a close relationship between the realism of its simulated GMST trends and SAT trend patterns. In this model, Eurasian cooling plays a dominant role in determining the GMST trend amplitude, just as in nature. In the most realistic member, intrinsic atmospheric dynamics and teleconnections forced by TPAC SSTA cause cooling over Eurasia (and North America), and contribute equally to its GMST trend. [ABSTRACT FROM AUTHOR]

Over the past decade, anomalously hot summers and persistent droughts frequented over the western United States (wUS), the condition similar to the 1950s and 1960s. While atmospheric internal variability is important for mid-latitude interannual climate variability, it has been suggested that anthropogenic external forcing and multidecadal modes of variability in sea surface temperature, namely, the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO), also affect the occurrence of droughts and hot summers. In this study, 100-member ensemble simulations for 1951-2010 by an atmospheric general circulation model were used to explore relative contributions of anthropogenic warming, atmospheric internal variability, and atmospheric response to PDO and AMO to the decadal anomalies over the wUS. By comparing historical and sensitivity simulations driven by observed sea surface temperature, sea ice, historical forcing agents, and non-warming counterfactual climate forcing, we found that large portions of recent increases in mean temperature and frequency of hot summers (66 and 82 %) over the wUS can be attributed to the anthropogenic global warming. In contrast, multidecadal change in the wUS precipitation is explained by a combination of the negative PDO and the positive AMO after the 2000s. Diagnostics using a linear baroclinic model indicate that AMO- and PDO-related diabatic heating anomalies over the tropics contribute to the anomalous atmospheric circulation associated with the droughts and hot summers over wUS on multidecadal timescale. Those anomalies are not robust during the periods when PDO and AMO are in phase. The prolonged PDO-AMO antiphase period since the late twentieth century resulted in the substantial component of multidecadal anomalies in temperature and precipitation over the wUS. [ABSTRACT FROM AUTHOR]

The Coupled Model Inter-comparison Project Phase 5 (CMIP5) contains a group of state-of-the-art climate models and represents the highest level of climate simulation thus far. However, these models significantly overestimated global mean surface temperature (GMST) during 2006-2014. Based on the ensemble empirical mode decomposition (EEMD) method, the long term change of the observed GMST time series of HadCRUT4 records during 1850-2014 was analyzed, then the simulated GMST by 33 CMIP5 climate models was assessed. The possible reason that climate models failed to project the recent global warming hiatus was revealed. Results show that during 1850-2014 the GMST on a centennial timescale rose with fluctuation, dominated by the secular trend and the multi-decadal variability (MDV). The secular trend was relatively steady beginning in the early 20th century, with an average warming rate of 0.0883°C/decade over the last 50 years. While the MDV (with a ~65-year cycle) showed 2.5 multi-decadal waves during 1850-2014, which deepened and steepened with time, the alarming warming over the last quarter of the 20th century was a result of the concurrence of the secular warming trend and the warming phase of the MDV, both of which accounted one third of the temperature increase during 1975-1998. Recently the slowdown of global warming emerged as the MDV approached its third peak, leading to a reduction in the warming rate. A comparative analysis between the GMST time series derived from HadCRUT4 records and 33 CMIP5 model outputs reveals that the GMSTs during the historical simulation period of 1850-2005 can be reproduced well by models, especially on the accelerated global warming over the last quarter of 20th century. However, the projected GMSTs and their linear trends during 2006-2014 under the RCP4.5 scenario were significantly higher than observed. This is because the CMIP5 models confused the MDV with secular trend underlying the GMST time series, which results in a fast secular trend and an improper MDV with irregular phases and small amplitudes. This implies that the role of atmospheric CO in global warming may be overestimated, while the MDV which is an interior oscillation of the climate system may be underestimated, which should be related to insufficient understanding of key climatic internal dynamic processes. Our study puts forward an important criterion for the new generation of climate models: they should be able to simulate both the secular trend and the MDV of GMST. [ABSTRACT FROM AUTHOR]

Uneven patterns in the rate of climate change have profound implications for adaptation. Assuming a linear or monotonic increase in global or regional temperatures can lead to inefficient planning processes that underestimate the magnitude, pattern, and timing of the risks faced by human and natural systems, which could exaggerate future impacts and the costs of managing them. Adaptation planning needs to move beyond imposing linear thinking and analysis onto nonlinear systems. Doing so would improve research into adaptive management processes that learn from and adapt to new knowledge at a pace that reflects non-linearity. Specifically, the pace of adaptation must consider the potential consequences of uneven increases in weather and climate variables as a means to reduce system vulnerability. Projections simulating periods of relative stability with those of rapid change would lead to more complex and more accurate expectations of future risks and associated consequences for human and natural systems. Adaptation planning based on such projections could then consider the implications of non-linear climate change on the extent of any adaptation effort, including quantified (or qualitative) risks and associated costs and benefits. Adaptation planning could be improved by projections that incorporate more nuanced understandings of how development processes could interact with climate change to alter future risks and vulnerabilities. Two examples are highlighted to illustrate the complexity and dynamic nature of non-monotonic climate-development-response scenarios: vector borne diseases and agricultural productivity. [ABSTRACT FROM AUTHOR]

In recent decades, global warming hiatus/slowdown has attracted considerable attention and has been strongly debated. Many studies suggested that the Arctic is undergoing rapid warming and significantly contributes to a continual global warming trend rather than a hiatus. In this study, we evaluated the climate changes of Ny-Ålesund, Svalbard, a representative location of the northern North Atlantic sector of the Arctic, based on observational records from 1975–2014. The results showed that the annual warming rate was four times higher than the global mean (+0.76 °C·decade−1) and was also much greater than Arctic average. Additionally, the warming trend of Ny-Ålesund started to slow down since 2005–2006, and our estimates showed that there is a 8–9 years-lagged, but significant, correlation between records of Ny-Ålesund and global HadCRUT4 datasets. This finding indicates that the Arctic was likely experiencing a hiatus pattern, which just appeared later than the low-mid latitudes due to transport processes of atmospheric circulations and ocean currents, heat storage effect of cryospheric components, multidecadal variability of Arctic cyclone activities, etc. This case study provides a new perspective on the global warming hiatus/slowdown debate.

Understanding temporal variability in lake warming rates over decadal scales is important for understanding observed change in aquatic systems. We analyzed a global dataset of lake surface water temperature observations (1985−2009) to examine how lake temperatures responded to a recent global air temperature warming hiatus (1998−2012). Prior to the hiatus (1985−1998), surface water temperatures significantly increased at an average rate of 0.532 °C decade ^−1 (±0.214). In contrast, water temperatures did not change significantly during the hiatus (average rate −0.087 °C decade ^−1 ±0.223). Overall, 83% of lakes in our dataset (129 of 155) had faster warming rates during the pre-hiatus period than during the hiatus period. These results demonstrate that lakes have exhibited decadal-scale variability in warming rates coherent with global air temperatures and represent an independent line of evidence for the recent warming hiatus. Our analyses provide evidence that lakes are sentinels of broader climatological processes and indicate that warming rates based on datasets where a large proportion of observations were collected during the hiatus period may underestimate longer-term trends.

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. [ABSTRACT FROM AUTHOR]

A dramatic increase in winter (December-February) temperature by 7.2 K (1.1 K per decade) since 1950 has occurred in the Ulan Bator basin, Mongolia. This increase in temperature strongly exceeds the global average of late twentieth century warming and even exceeds warming in most of the polar regions with pronounced increases in temperature. The exceptional warming is restricted to Ulan Bator within the Mongolian forest-steppe region and to wintertime. This suggests that the observed warming could result from radiative forcing by black carbon aerosols. In winter, Ulan Bator's air is heavily polluted by particulate matter, including black carbon, originating from the combustion of low-quality fuel at low temperature. Winter smog has strongly increased in recent decades, concomitant to the increase in winter temperature, as the result of a strong increase in the city's population. Exponential growth of Ulan Bator's population started in the mid-twentieth century, but since 1990, altered socioeconomic frame conditions and a warming climate have driven more than 700,000 pastoralists from rural Mongolia to Ulan Bator where people live in provisional dwellings and cause Ulan Bator's heavy air pollution. Tree-ring analysis from larch trees growing at the edge of the Ulan Bator basin shows negative correlation of stem increment with December temperature. This result suggests that milder winters promote herbivores and, thus, reduce the tree's productivity. The negative impact of winter warming on the larch forests adds to adverse effects of summer drought and the impact of high sulfur dioxide emissions. Winter warming putatively associated with high atmospheric concentrations of black carbon aerosols in the Ulan Bator basin is an interesting example of a case where greenhouse gas-mediated climate warming in an area where people themselves hardly contribute to global greenhouse gas emissions affects both humans and ecosystems and causes additional local climate warming. [ABSTRACT FROM AUTHOR]

The dominant modes of variability in the temperature and ocean heat content (OHC; 0–1000 m) of the central Labrador Sea were investigated using the Hilbert–Huang Transform (HHT) based on Argo profiles collected during 2003–2012. Warming trends of approximately 0.03 ° C yr − 1 were observed in the upper 2000 m of the water column. A strong annual temperature cycle exists and dominates at the 500 m depth, while signals at the interannual timescales can explain most of the temperature variability at the 1000 m and 1500 m depths. These interannual signals are closely correlated to the variability of deep convection in the Labrador Sea, which has intermittent enhancement of mixed layer depth (MLD)>1500 m. The Hilbert spectrum from the OHC in the Labrador Sea interior reveals two important components at frequencies of 0.8 − 1.2 cycle yr − 1 ( T =0.8–1.25 years) and 0.1 − 0.3 cycle yr − 1 ( T =3.3–10 years), respectively, superimposed on the warming trends. The former corresponds to the dominant seasonal cycle due to surface heating, while the latter is concomitant with the timing of the reoccurrence of convective events. We also found that the cumulative North Atlantic Oscillation (NAO) index significantly correlates to the low-frequency OHC variations. Therefore, the interannual signals in the Labrador Sea at especially the intermediate layers are attributed to changes in the deep convective processes and the atmospheric conditions. By comparing with an extended OHC record (1945–2010), it was further shown that the warming trends obtained from the 10-year Argo record are part of multi-decadal variations that presumably reflect the Atlantic Multi-decadal Oscillation (AMO). In addition, the recent OHC changes in the Labrador Sea (i.e., increased heat in the deeper layers) may be related to the current global warming hiatus, suggesting the potential contributions from the Atlantic Meridional Overturning Circulation (AMOC) to the low-frequency OHC in the Labrador Sea. [ABSTRACT FROM AUTHOR]