Global Temperature Variations Research Articles

Multi‐model assessment of global temperature variability on different time scales

AbstractThis study explores the near‐surface air temperature (TAS) prediction skills at different time scales via coupled climate models that were involved in the Coupled Model Intercomparison Project phase 5 (CMIP5). The simulation skills of the global mean TAS are first assessed between the observations and models; then, the temporal variability is separated into three parts (the linear trend, decadal variability and inter‐annual variability), and each part is compared with the observations. It is found that the global mean TAS anomaly and the decadal variability are well captured by the model, while the inter‐annual variability is poorly presented. In all the three parts of different time scales, there are larger differences among the 18 models, and the ensemble mean of CMIP5 is the closest to the observations. Besides, the TAS decadal variability is better presented for global ocean than for global land. In the assessment of climate oscillation, it is found that the models can well reproduce the TAS decadal variation patterns correlated with the Pacific Decadal Oscillation (PDO) and the inter‐annual variation patterns correlated with El Niño–Southern Oscillation (ENSO) but poor for the decadal variation patterns related to the Atlantic Multidecadal Oscillation (AMO). This study provides a reference assessing the simulation skills of climate models and an indicator evaluating the advantage of CMIP6 in comparison with CMIP5.

Calibration Uncertainties of Tropical Pacific Climate Reconstructions over the Last Millennium

AbstractSeveral climate field reconstruction methods assume stationarity between the leading patterns of variability identified during the instrumental calibration period and the reconstruction period. We examine how and to what extent this restrictive assumption may generate uncertainties in reconstructing past tropical Pacific climate variability. Based on the Last Millennium (850–2005 CE) ensemble simulations conducted with the Community Earth System Model and by developing a series of pseudoproxy reconstructions for different calibration periods, we find that the overall reconstruction skill for global and more regional-scale climate indices depends significantly on the magnitude of externally forced global mean temperature variability during the chosen calibration period. This effect strongly reduces the fidelity of reconstructions of decadal to centennial-scale tropical climate variability, associated with the interdecadal Pacific oscillation (IPO) and centennial-scale temperature shifts between the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). In contrast, our pseudoproxy-based analysis demonstrates that reconstructions of interannual El Niño–Southern Oscillation (ENSO) variability are more robust and less affected by changes in calibration period.

Dominant Modes of China Summer Heat Waves Driven by Global Sea Surface Temperature and Atmospheric Internal Variability

AbstractThis study applies the maximum temperatures at more than 2000 Chinese stations to investigate the dominant modes of China summer heat waves (HWs). The first empirical orthogonal function (EOF) mode of the HW days reflects an increased frequency of HWs in northern China (NC), while the second and third modes represent two distinct interannual modes, with key regions over the Yangtze River valley (YRV) and southern China (SC), respectively. The NC HWs are possibly associated with the Atlantic–Eurasian teleconnection, showing zonally propagating wave trains over the North Atlantic and Eurasian continent. The YRV HWs are proposed to be linked to the North Atlantic Oscillation, which may trigger a southeastward-propagating wave train over northern Russia and East Asia that results in a high pressure anomaly over the YRV. The SC HWs are obviously dominated by the Indian Ocean and northwest Pacific warm SSTs owing to the transition from the preceding El Niño to La Niña, which excites above-normal highs over SC. The anomalously high pressures over NC, the YRV, and SC are usually accompanied by descending air motions, clear skies, decreased precipitation, and increased solar radiation, which jointly cause a drier and hotter soil condition that favors the emergence of HWs. The GFDL HiRAM experiments are able to reproduce the historical evolution of NC and SC HWs, but fail to capture the YRV HWs. The correlation coefficient between model PC1 (PC2) and observed PC1 (PC3) for the period of 1979–2008 is 0.65 (0.38), which significantly exceeds the 95% (90%) confidence level, indicating that this model has a more faithful representation for the SST-forced HWs.

Manifestation and possible reasons of ∼60-year oscillations in solar-atmospheric links

In this work we continue studying possible reasons for temporal variability observed in correlation links between characteristics of the lower atmosphere and solar activity phenomena at the multidecadal time scale. Temporal variations of correlation coefficients between troposphere pressure at extratropical latitudes and sunspot numbers are compared with the evolution of the large-scale circulation forms according to the Vangengeim-Girs classification, as well as the characteristics of the stratospheric polar vortex and global temperature anomalies. The results obtained show that temporal variability of solar activity/galactic cosmic ray (SA/GCR) effects on troposphere pressure (the development of extratropical baric systems) is characterized by a roughly 60-year periodicity and closely related to changes in the regime of large-scale circulation which accompany transitions between the different states of the polar vortex. It was suggested that the character of SA/GCR effects depends on the polar vortex strength influencing the troposphere-stratosphere coupling. It was shown that the evolution of the polar vortex may be associated with global temperature variations, with a possible reason for these variations being long-term changes of total solar irradiance.

Global environmental consequences of twenty-first-century ice-sheet melt.

Government policies currently commit us to surface warming of three to four degrees Celsius above pre-industrial levels by 2100, which will lead to enhanced ice-sheet melt. Ice-sheet discharge was not explicitly included in Coupled Model Intercomparison Project phase 5, so effects on climate from this melt are not currently captured in the simulations most commonly used to inform governmental policy. Here we show, using simulations of the Greenland and Antarctic ice sheets constrained by satellite-based measurements of recent changes in ice mass, that increasing meltwater from Greenland will lead to substantial slowing of the Atlantic overturning circulation, and that meltwater from Antarctica will trap warm water below the sea surface, creating a positive feedback that increases Antarctic ice loss. In our simulations, future ice-sheet melt enhances global temperature variability and contributes up to 25 centimetres to sea level by 2100. However, uncertainties in the way in which future changes in ice dynamics are modelled remain, underlining the need for continued observations and comprehensive multi-model assessments.

Variations of the global annual mean surface temperature during the past 2000 years: results from the CESM1

The influence of external forcings on surface temperature is not fully understood at decadal to multi-centennial timescales. This study uses simulation results from the Community Earth System Model (CESM) forced by total solar irradiation (TSI), greenhouse gases (GHGs) concentrations, volcanic eruptions (VOL), and land use and land covers (LULC) to investigate the possible impacts of external forcing on decadal to multi-centennial timescales over the past 2000 years. The simulated global annual mean surface temperature (GMST) variations show a good coherence with observations over the past 150 years and proxy-based reconstructions over the past 2000 years. Ensemble empirical mode decomposition (EEMD) is used to isolate the GMST variations on decadal to multi-centennial timescales. We found that the VOL forcing has a significant effect on GMST at decadal to multi-decadal timescales, but its effect weakens gradually as the timescale lengthens. The TSI forcing is a major factor of GMST on multi-decadal to sub-millennial timescales, and its effect strengthens as the timescale lengthens. The GHGs is the dominant driver of recent warming, but its effect is weak in the pre-industrial times. The LULC could lead to a slight cooling trend over the past 2000 years but has no large impact on GMST at decadal to multi-centennial timescales. This study reports a 2000-year length climate simulation and may contribute to better understanding external drivers of GMST at different timescales.

Diurnal temperature range and mortality in Tabriz (the northwest of Iran)

Recently there has been a lot of interest in global warming and temperature variation's effect on health. This study evaluates the impact of Diurnal Temperature Range (DTR) on mortality in Tabriz, northwest of Iran. Distributed Lag Non-linear Models combined with a quasi-Poisson regression were used to assess the impact of DTR on cause, age and gender specific mortality, controlled for potential confounders such as long-term trend of daily mortality, day of week effect, holidays, mean temperature, humidity, wind speed and air pollutants. As the effect of DTR may vary between the hot season (from May to October) and cold season (from November to April of the next year), we conducted analyses separately for these two seasons. In high DTR values (all percentiles), the Cumulative Relative Risk (CRR) of Non-Accidental Death, Respiratory Death and Cardiovascular Death increased in the cold season. In full year and high DTR value (percentile 90), the CRR of respiratory deaths increased as well (CRR, Lag 0-6:1.32(1.006, 1.75). Although there was no clear significant effect in low DTR values, high values of DTR increase the risk of mortality in the cold season, in Tabriz, Iran.

Diurnal Temperature Range and Mortality in Tabriz (the Northwest of Iran)

Introduction: Recently there has been a lot of interest in global warming and temperature variation's effect on health. This study evaluates the impact of Diurnal Temperature Range (DTR) on mortality in Tabriz, northwest of Iran.Methods: Distributed Lag Non-linear Models combined with a quasi-Poisson regression were used to assess the impact of DTR on cause, age and gender specific mortality, controlled for potential confounders such as long-term trend of daily mortality, day of week effect, holidays, mean temperature, humidity, wind speed and air pollutants. As the effect of DTR may vary between the hot season (from May to October) and cold season (from November to April of the next year), we conducted analyses separately for these two seasons.Results: In high DTR values (all percentiles), the Cumulative Relative Risk (CRR) of Non-Accidental Death, Respiratory Death and Cardiovascular Death increased in the cold season. In all seasons and high DTR value (percentile 90), the CRR (lag 0-6) of respiratory deaths increased as well.Conclusion: Although there was no clear significant effect in low DTR values, high values of DTR increase the risk of mortality in the cold season, in Tabriz, Iran.

Understanding the role of sea surface temperature-forcing for variability in global temperature and precipitation extremes

The oceans are a well-known source of natural variability in the climate system, although their ability to account for inter-annual variations of temperature and precipitation extremes over land remains unclear. In this study, the role of sea-surface temperature (SST)-forcing is investigated for variability and trends in a range of commonly used temperature and precipitation extreme indices over the period 1959 to 2013. Using atmospheric simulations forced by observed SST and sea-ice concentrations (SIC) from three models participating in the Climate of the Twentieth Century Plus (C20C+) Project, results show that oceanic boundary conditions drive a substantial fraction of inter-annual variability in global average temperature extreme indices, as well as, to a lower extent, for precipitation extremes. The observed trends in temperature extremes are generally well captured by the SST-forced simulations although some regional features such as the lack of warming in daytime warm temperature extremes over South America are not reproduced in the model simulations. Furthermore, the models simulate too strong increases in warm day frequency compared to observations over North America. For extreme precipitation trends, the accuracy of the simulated trend pattern is regionally variable, and a thorough assessment is difficult due to the lack of locally significant trends in the observations. This study shows that prescribing SST and SIC holds potential predictability for extremes in some (mainly tropical) regions at the inter-annual time-scale.

Causes of irregularities in trends of global mean surface temperature since the late 19th century.

The time series of monthly global mean surface temperature (GST) since 1891 is successfully reconstructed from known natural and anthropogenic forcing factors, including internal climate variability, using a multiple regression technique. Comparisons are made with the performance of 40 CMIP5 models in predicting GST. The relative contributions of the various forcing factors to GST changes vary in time, but most of the warming since 1891 is found to be attributable to the net influence of increasing greenhouse gases and anthropogenic aerosols. Separate statistically independent analyses are also carried out for three periods of GST slowdown (1896-1910, 1941-1975, and 1998-2013 and subperiods); two periods of strong warming (1911-1940 and 1976-1997) are also analyzed. A reduction in total incident solar radiation forcing played a significant cooling role over 2001-2010. The only serious disagreements between the reconstructions and observations occur during the Second World War, especially in the period 1944-1945, when observed near-worldwide sea surface temperatures (SSTs) may be significantly warm-biased. In contrast, reconstructions of near-worldwide SSTs were rather warmer than those observed between about 1907 and 1910. However, the generally high reconstruction accuracy shows that known external and internal forcing factors explain all the main variations in GST between 1891 and 2015, allowing for our current understanding of their uncertainties. Accordingly, no important additional factors are needed to explain the two main warming and three main slowdown periods during this epoch.

Is the global sea surface temperature rise accelerating?

This is an exploratory investigation to search for the presence of an acceleration in global sea surface temperature rise, which is essential to identify anthropogenic contributions to the climate change during the 20th century. A weighted statistical model with an acceleration parameter was built progressively to reconstruct the variations in the global sea surface temperature data considering statistically significant confounders and autoregressive disturbances in the process. From the preliminary residual analysis of a weighted regression model, emerged a parsimonious model with first order autoregressive disturbances with a deterministic trend, acceleration and periodicity of 69 yr and its 138 yr subharmonic. The final model solution, selected from 29 alternative combinations of the model parameters using Mallows's Cp metric, revealed a statistically significant deterministic trend, 0.40 ± 0.03 °C/c (p < 0.01), and acceleration, 0.67 ± 0.11 °C/c2 (p < 0.01) explaining 33% of the global sea surface temperature variations. The combined yearly trend and acceleration in global sea surface temperature as predicted by the model, exhibit a strong correlation with the yearly increase in the global CO2 concentrations observed during the 20th century.

A systematic wavelet-based exploratory analysis of climatic variables

Nonstationarity and time scale dependence are essential features of the climate system that may be dealt with simultaneously using wavelet analysis. In this study, we present a systematic analysis of a set of climate system variables, which include both natural and anthropogenic contributions, using wavelet-based exploratory methods. The tools of the continuous wavelet transform, the wavelet spectrum, coherence, and phase offer a comprehensive assessment of the characteristic modes of variability of climate system forcings and of the scale-based relationships of anthropogenic and natural climate variables with global surface temperature. Shorter-term variations in global surface temperature are associated with internally generated natural climate variability and external climate forcings, while longer-term variations are strongly related to human-induced changes only. In this respect, a long-term component of the net radiative forcing of human activities longer than 30 years displays a statistically significant relationship with global warming and cooling periods identified in the climate change literature.

Different Global Precipitation Responses to Solar, Volcanic, and Greenhouse Gas Forcings

AbstractUnderstanding climate change caused by different external forcings is an urgent need for crisis management and sustainable economic development. It remains unclear how differently global precipitation changes in response to global temperature variations induced by the change of individual solar, volcanic, or greenhouse gas (GHG) forcings. We address this issue by performing three last millennium simulations under each of these individual forcings with the Community Earth System Model version 1.0. The results show that all three forcings can excite strong low‐frequency variations that are longer than one decade, that is, global warming under strong solar radiation or high GHG concentration and global cooling under frequent volcanic eruptions. For a given global temperature change, the global precipitation change under volcanic forcing is larger than that under solar and GHG forcings. The reason is that the volcanic forcing induces the strongest solar irradiance change in the wet tropics. Among the three forcings we examined, the GHG forcing excites the strongest high‐latitude warming, especially the Arctic amplification of global warming. There is no Arctic amplification of temperature decrease under the volcanic forcing‐induced global cooling. The volcanic forcing weakens the Intertropical Convergence Zone and reduces precipitation. The results suggest that while volcanic eruptions can reduce precipitation, they do not mitigate the Arctic amplification of temperature increase under the GHG‐induced warming. The underlying mechanisms for these different climate responses are also discussed.

Global patterns of declining temperature variability from the Last Glacial Maximum to the Holocene.

Changes in climate variability are as important for society to address as are changes in mean climate. Contrasting temperature variability during the Last Glacial Maximum and the Holocene can provide insights into the relationship between the mean state of the climate and its variability. However, although glacial-interglacial changes in variability have been quantified for Greenland, a global view remains elusive. Here we use a network of marine and terrestrial temperature proxies to show that temperature variability decreased globally by a factor of four as the climate warmed by 3-8 degrees Celsius from the Last Glacial Maximum (around 21,000 years ago) to the Holocene epoch (the past 11,500 years). This decrease had a clear zonal pattern, with little change in the tropics (by a factor of only 1.6-2.8) and greater change in the mid-latitudes of both hemispheres (by a factor of 3.3-14). By contrast, Greenland ice-core records show a reduction in temperature variability by a factor of 73, suggesting influences beyond local temperature or a decoupling of atmospheric and global surface temperature variability for Greenland. The overall pattern of reduced variability can be explained by changes in the meridional temperature gradient, a mechanism that points to further decreases in temperature variability in a warmer future.

The Antarctic Centennial Oscillation: A Natural Paleoclimate Cycle in the Southern Hemisphere That Influences Global Temperature

We report a previously-unexplored natural temperature cycle recorded in ice cores from Antarctica—the Antarctic Centennial Oscillation (ACO)—that has oscillated for at least the last 226 millennia. Here we document the properties of the ACO and provide an initial assessment of its role in global climate. We analyzed open-source databases of stable isotopes of oxygen and hydrogen as proxies for paleo-temperatures. We find that centennial-scale spectral peaks from temperature-proxy records at Vostok over the last 10,000 years occur at the same frequencies (±2.4%) in three other paleoclimate records from drill sites distributed widely across the East Antarctic Plateau (EAP), and &gt;98% of individual ACOs evaluated at Vostok match 1:1 with homologous cycles at the other three EAP drill sites and conversely. Identified ACOs summate with millennial periodicity to form the Antarctic Isotope Maxima (AIMs) known to precede Dansgaard-Oeschger (D-O) oscillations recorded in Greenland ice cores. Homologous ACOs recorded at the four EAP drill sites during the last glacial maximum appeared first at lower elevations nearest the ocean and centuries later on the high EAP, with latencies that exceed dating uncertainty &gt;30-fold. ACO homologs at different drill sites became synchronous, however, during the warmer Holocene. Comparative spectral analysis suggests that the millennial-scale AIM cycle declined in period from 1500 to 800 years over the last 70 millennia. Similarly, over the last 226 millennia ACO repetition period (mean 352 years) declined by half while amplitude (mean 0.67 °C) approximately doubled. The period and amplitude of ACOs oscillate in phase with glacial cycles and related surface insolation associated with planetary orbital forces. We conclude that the ACO: encompasses at least the EAP; is the proximate source of D-O oscillations in the Northern Hemisphere; therefore affects global temperature; propagates with increased velocity as temperature increases; doubled in intensity over geologic time; is modulated by global temperature variations associated with planetary orbital cycles; and is the probable paleoclimate precursor of the contemporary Antarctic Oscillation (AAO). Properties of the ACO/AAO are capable of explaining the current global warming signal.

Emergent constraint on equilibrium climate sensitivity from global temperature variability.

Equilibrium climate sensitivity (ECS) remains one of the most important unknowns in climate change science. ECS is defined as the global mean warming that would occur if the atmospheric carbon dioxide (CO2) concentration were instantly doubled and the climate were then brought to equilibrium with that new level of CO2. Despite its rather idealized definition, ECS has continuing relevance for international climate change agreements, which are often framed in terms of stabilization of global warming relative to the pre-industrial climate. However, the 'likely' range of ECS as stated by the Intergovernmental Panel on Climate Change (IPCC) has remained at 1.5-4.5 degrees Celsius for more than 25 years. The possibility of a value of ECS towards the upper end of this range reduces the feasibility of avoiding 2 degrees Celsius of global warming, as required by the Paris Agreement. Here we present a new emergent constraint on ECS that yields a central estimate of 2.8 degrees Celsius with 66 per cent confidence limits (equivalent to the IPCC 'likely' range) of 2.2-3.4 degrees Celsius. Our approach is to focus on the variability of temperature about long-term historical warming, rather than on the warming trend itself. We use an ensemble of climate models to define an emergent relationship between ECS and a theoretically informed metric of global temperature variability. This metric of variability can also be calculated from observational records of global warming, which enables tighter constraints to be placed on ECS, reducing the probability of ECS being less than 1.5 degrees Celsius to less than 3 per cent, and the probability of ECS exceeding 4.5 degrees Celsius to less than 1 per cent.

Theoretical foundations of emergent constraints: relationships between climate sensitivity and global temperature variability in conceptual models

There is as yet no theoretical framework to guide the search for emergent constraints. As a result, there are significant risks that indiscriminate data-mining of the multidimensional outputs from GCMs could lead to spurious correlations and less than robust constraints on future changes. To mitigate against this risk, Cox et al (hereafter CHW18) proposed a theory-motivated emergent constraint, using the one-box Hasselmann model to identify a linear relationship between ECS and a metric of global temperature variability involving both temperature standard deviation and autocorrelation ($\Psi$). A number of doubts have been raised about this approach, some concerning the theory and the application of the one-box model to understand relationships in complex GCMs which are known to have more than the single characteristic timescale. We illustrate theory driven testing of emergent constraints using this as an example, namely we demonstrate that the linear $\Psi$-ECS proportionality is not an artifact of the one-box model and rigorously features to a good approximation in more realistic, yet still analytically soluble conceptual models, namely the two-box and diffusion models. Each of the conceptual models predict different power spectra with only the diffusion model's pink spectrum being compatible with observations and the complex CMIP5 GCMs. We also show that the theoretically predicted $\Psi$-ECS relationship exists in the \texttt{piControl} as well as \texttt{historical} CMIP5 experiments and that the differing gradients of the proportionality are inversely related to the effective forcing in that experiment.

The Sensitivity of Daily Temperature Variability and Extremes to Dataset Choice

AbstractRobust conclusions regarding changes in the temperature distribution rely on the accuracy and reliability of the input datasets used. Differences between methodologies and datasets in previous studies add uncertainty when comparing and quantifying findings. Here, the authors investigate the sensitivity of assessing global and regional temperature variability and extremes over 1980–2014 in gridded datasets of daily temperature anomalies. A gridded in situ–based dataset, Hadley Centre Global Historical Climatology Network–Daily (HadGHCND), is compared against several commonly used reanalysis products by assessing both the entire distribution and the tails of the distribution. Empirical probability distribution functions show sensitivity to the input dataset when estimating aspects such as standard deviation and skewness, with the mean showing robust results for most regions, irrespective of dataset choice. Standard deviation is especially sensitive, with larger disagreements between datasets for some regions more than others, such as Africa and the Mediterranean region, and with larger differences in minimum temperatures compared with maximum temperatures. Estimates of extreme parameters also show sensitivity to dataset choice, particularly in the lower tails and for daily minimum temperature anomalies. Comparing changes in the means and the extremes of the temperature distributions, the cold extremes in the lower tails have been warming at a faster rate than the mean of the entire distribution for much of the Northern Hemisphere extratropics, with warm extremes warming at a faster rate than the mean in some subtropical regions. These documented sensitivities call for caution when assessing changes in temperature variability and extremes, as dataset choice can have substantial effects on results.

Recent United Kingdom and global temperature variations

Recent United Kingdom and global temperature variations

СОПОСТАВЛЕНИЕ ВАРИАЦИЙ ТЕМПЕРАТУРЫ ВОЗДУХА НА АФРИКАНСКОМ КОНТИНЕНТЕ И ИНТЕНСИВНОСТИ ШУМАНОВСКОГО РЕЗОНАНСА ПО ДОЛГОВРЕМЕННЫМ НАБЛЮДЕНИЯМ В AНТАРКТИКЕ

СОПОСТАВЛЕНИЕ ВАРИАЦИЙ ТЕМПЕРАТУРЫ ВОЗДУХА НА АФРИКАНСКОМ КОНТИНЕНТЕ И ИНТЕНСИВНОСТИ ШУМАНОВСКОГО РЕЗОНАНСА ПО ДОЛГОВРЕМЕННЫМ НАБЛЮДЕНИЯМ В AНТАРКТИКЕ