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The cryosphere plays a major role in earth's climate system. Most cryospheric assessments focus on one or more of its components and their response to climate change. However, to date, there has not been a comprehensive evaluation of the entire global cryosphere. We therefore determine such a holistic estimate and quantify changes to the hemispheric and global cryosphere due to climate change, by synthesizing sea ice, snow cover, and frozen ground extents into one global cryospheric extent data set. The 1981–2010 climatology of daily global cryospheric extent ranges from 45.7 ± 0.7 × 106 to 87.2 ± 2.0 × 106 km2 (9.0%–17.1%), from 13.3 ± 0.8 × 106–66.3 ± 1.7 × 106 km2 (5.2%–26.0%) in the Northern Hemisphere (NH), and from 17.9 ± 0.3 × 106 to 33.6 ± 0.4 × 106 km2 (7.0%–13.2%) in the Southern Hemisphere (SH). The monthly maximum cryospheric extent of 85.84 ± 1.91 × 106 km2 occurs in December, whereas minimum occurs in July with 45.92 ± 0.70 × 106 km2. During 1979–2016, global cryospheric area extent lost approximately 87 ± 11 × 103 km2/yr, with a decrease of 102 ± 9.7 × 103 km2/yr in the NH that was partly offset by an increase of 14.6 ± 4.4 × 103 km2/yr in the SH. The first day of cryospheric cover was delayed by 3.6 days at a rate of 0.95 days/decade, and the last day advanced by 5.7 days, at a rate of 1.5 days/decade. The duration and number of cryospheric cover days decreased by 8.7 days and 7.6 days over the study period, respectively. These variations of global cryospheric extent are correlated with rising air temperatures. Our findings highlight the importance of assessing the cryosphere as a whole, and provide a way to quantitatively estimate its overall changes.

Surface air temperatures affect a diverse set of physical and biological systems in many parts of the world. For regional‐scale studies, gridded surface air temperature data sets are frequently used as input variables. Here we evaluate 10 commonly used gridded air temperature products with spatial resolutions ranging from 0.1° × 0.1° to 5.0° × 5.0°, relative to observations from in situ weather stations on the Tibetan Plateau. Gridded temperatures are consistently lower, with mean annual air temperature biases ranging from −4.68 °C to −1.72 °C, and root mean square error (RMSE) from 3.24 °C to 6.11 °C. The mean biases of mean seasonal air temperatures for spring, summer, autumn, and winter are −3.21 °C, −2.98 °C, −2.89 °C, and −2.98 °C, respectively, and RMSEs of 4.81 °C, 4.39 °C, 4.3 °C, and 4.7 °C. Of all 10 products, the China meteorological forcing data set compares best with observations. Annual and season temperatures all increase significantly during 1980–2018 on the Tibetan Plateau, with winter dominating the warming rate.

Vegetation is closely tied to climate change, hydrological processes, the carbon cycle, and the energy balance. However, in cold regions, both climate and vegetation changes are also closely coupled to permafrost. The association between amplified warming and greening in Northern Hemisphere permafrost regions is not clearly understood. We therefore produce an extended 1982-2015 normalized difference vegetation index record based on concatenated Global Inventory Modeling and Mapping Studies and Moderate-Resolution Imaging Spectroradiometer data to quantify the spatiotemporal patterns of vegetation variability. We also establish spatiotemporal permafrost warming patterns based on a thawing index, active layer thickness, soil temperature, the first thaw date, and thawing days. Next, we establish the association between vegetation and warming permafrost. We find that normalized difference vegetation index increases in approximately 70% of Northern Hemisphere permafrost regions during the growing season (April-October) and in 72% of the region during autumn. Warming permafrost shows a positive relationship with greening. A higher thawing index, greater active layer thickness, higher soil temperature, and also increased precipitation are linked with the observed greening. An earlier first thaw date and an increased number of thawing days also correlate with vegetation greening. These findings underscore the sensitivity of vegetation to warming permafrost. Continued permafrost warming will result in further greening of Northern Hemisphere cold regions (and vice versa), with important implications for the permafrost soil-vegetation-atmosphere carbon cycles, and the water, nutrient, and energy budgets.

Variations in seasonal soil freeze/thaw state are important indicators of climate change and influence ground temperature, hydrological processes, surface energy, and the moisture balance. Previous studies mainly focused on the active layer and permafrost, while seasonally frozen ground research in nonpermafrost regions has received less attention. In this study, we investigate the response of changes in seasonal soil freeze/thaw state to changes in air temperatures by combining observations from more than 800 stations with gridded mean monthly air temperature data across China. The results show that mean annual air temperature (MAAT) increased statistically significantly by 0.29 ± 0.03°C/decade from 1967 to 2013, with greater warming on the Qinghai-Tibetan Plateau. There is a statistically significant decrease in the freeze/thaw cycle (FTC) at 0.39 ± 0.05 cycles/decade. In addition, there are strong negative correlations between FTC and MAAT. Estimating the soil freeze/thaw state classification based on the number of days in the month, we find that changes of mean annual area extent of seasonal soil freeze/thaw state decreased significantly for completely frozen (CF) ground, while the area extent of partially frozen (PF) and unfrozen (UF) ground both increased. Changes in mean monthly area extent of seasonal soil freeze/thaw state indicate that the extent of CF and UF area was decreasing and increasing, respectively. But for the extent of PF areas, both increasing and decreasing trends were observed. Quantifying the spatial pattern of the seasonal soil freeze/thaw, we find that CF and PF areas are located in northern China and the Tibetan Plateau from December to March, and UF areas are located in southern China. The variations of mean annual area extent departure of soil freeze/thaw states are consistent with MAAT changes in different land cover types across China.

Precipitation variability has great economic, social, and environmental impacts across the globe, and in particular in China. This paper evaluates the historical precipitation variability based on 20 general circulation models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) archive over the 20th century relative to two observational data sets and quantifies CMIP5 improvements over CMIP3. Multimodel ensemble means and individual models are assessed. Three future emission scenarios are used (representative concentration pathways (RCP) 8.5, RCP 4.5, and RCP 2.6), and 21st century CMIP5 estimates are put into context based on the 20th century biases. We find that CMIP5 models can reproduce the spatial pattern of precipitation over China during the 20th century, which represents an improvement over CMIP3. However, the models overestimate the magnitude of seasonal and annual precipitation in most regions of China, especially along the eastern edge of the Tibetan Plateau, and underestimate summer precipitation over southeastern China. For China as a whole, CMIP5's overestimation of annual precipitation is greater than CMIP3, which can be traced back to a greater underestimation of summer precipitation in CMIP3. There is a large spread among individual models, with the greatest uncertainties in simulating summer precipitation. Trends and correlations also suggest a better agreement of CMIP5 with observations than CMIP3. Throughout the 20th century, both the observations and models show an increasing trend in precipitation over parts of northwestern China and a decreasing trend over the Tibetan Plateau. There is poor agreement in precipitation trends over the southeast and northeast regions. In general, multimodel means cannot capture the amplitude of observed multidecadal precipitation variability. In the 21st century, precipitation is generally projected to increase across all of China under all three scenarios. RCP 8.5 exhibits the largest significant trend at a rate of +1.5 mm/yr, corresponding to 16% precipitation increase by the end of the century. The RCP 2.6 scenario shows the smallest increases, at +0.5 mm/yr (6%) by 2100. The greatest increases are projected to occur over the Tibetan Plateau and eastern China in summer, suggesting an altered monsoonal circulation in the future. However, due to the uncertainties in CMIP5, future precipitation projections should be interpreted with caution.

[1] Sixty years of tropical cyclone precipitation (TCP) in Texas has been analyzed because of its importance in extreme hydrologic events and the hydrologic budget. We developed multiple linear regression models to provide seasonal forecasts for annual TCP, TCP's contribution (percentage) to total precipitation, and the number of TCP days in Texas. The regression models are based on three or fewer predictors with model fits ranging from 0.18 to 0.43 (R2) and cross-validation accuracy of 0.05–0.36 (R2). La Nina exhibits the most important control on TCP in Texas. It is the major driver in our models and acts to reduce the vertical shear in the Caribbean and the tropical Atlantic, thereby generating more precipitating storms in Texas. Lower maximum potential velocity, the theoretical maximum wind speed that storms can attain, in the Gulf of Mexico, and low-level vorticity in the Atlantic hurricane main development region increased the modeled R2 by 20% or more. Both variables have negative coefficients in the TCP models. Lower maximum potential velocity and vorticity are associated with tropical cyclones with lower maximum wind speed and slower translation speed. Such weak TCs produce the majority of TCP and extreme TCP events in Texas. The quartiles of the TCs with strongest maximum wind speed and fastest translation speed are not associated with the largest mean daily precipitation based on observations in Texas. We have also shown that sea level pressure in the Gulf of Mexico, sea surface temperature in the Caribbean, and the North Atlantic Oscillation are potentially important predictors of seasonal TCP in Texas.

Atmospheric modification by anomalously dry or wet soils can both enhance and suppress convective activity. However, the local- and meso-scale feedbacks governing soil moisture–precipitation coupling are embedded within the larger synoptic-scale environment. Despite their importance, synoptic-scale atmospheric conditions are rarely considered in studies examining soil moisture-atmosphere interactions. We combine self-organizing maps (SOMs) of 500 hPa geopotential height, spatial synoptic classification, and Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model air mass trajectories to determine if the synoptic-scale environment affects the ability of the land surface to force unorganized convection in Oklahoma. We identify several synoptic patterns that significantly impact the frequency of unorganized convection. Synoptic patterns characterized by mid-level troughs over the Southern Great Plains are less frequently associated with unorganized convective events. These patterns exhibit cool air advection in the mid- and lower-levels of the atmosphere, and are linked to suppression of convective activity. The synoptic patterns characterized by 500 hPa ridging over the study region are more frequently associated with unorganized convective events. These patterns likely result in increased net radiation, vapor pressure deficit, and more homogenously dry soils. Unorganized convective events that occur during these synoptic conditions initiate preferentially over dry soils. We present evidence that the synoptic-scale environment can influence whether and how the land surface has an impact on convection.

The relationship between El Nino, the Southern Oscillation, and their joint effect (ENSO), and Northern Hemisphere 500 hPa midlatitude circulation for the 1946–1994 observational record is determined. Seasonally standardized vortex positions at a spatial resolution of 5° longitude are correlated with an equatorial Pacific sea surface temperature anomaly index and the Southern Oscillation Index (SOI). The 500 hPa circumpolar vortex is consistently expanded over the central Pacific during and for the entire year following warm ENSO periods. The vortex is contracted over North America concurrently with warm ENSO and to a lesser degree during the following season. Expansion/contraction variability is also evident over east Asia, although the linkages to warm or cold ENSO are weak. Sea surface temperatures have a stronger association with the vortex than does the SOI.

[1] The total extent of ice melt on the Greenland ice sheet has been increasing during the last three decades. The melt extent observed in 2007 in particular was the greatest on record according to several satellite-derived records of total Greenland melt extent. Total annual observed melt extent across the Greenland ice sheet has been shown to be strongly related to summer temperature measurements from stations located along Greenland's coast, as well as to variations in atmospheric circulation across the North Atlantic. We make use of these relationships along with historical temperature and circulation observations to develop a near-continuous 226 year reconstructed history of annual Greenland melt extent dating from 2009 back into the late eighteenth century. We find that the recent period of high-melt extent is similar in magnitude but, thus far, shorter in duration, than a period of high melt lasting from the early 1920s through the early 1960s. The greatest melt extent over the last 2 1/4 centuries occurred in 2007; however, this value is not statistically significantly different from the reconstructed melt extent during 20 other melt seasons, primarily during 1923–1961.

[1] We assess the correspondence between precipitation products from atmospheric reanalyses (ERA-40, NCEP-1, and NCEP-2), the Climate Prediction Center (CPC) Merged Analyses of Precipitation (CMAP-1 and CMAP-2), and the Global Precipitation Climatology Project Version 2 (GPCP-2) with adjusted observational precipitation (AOP) from China for 1979–2001 and also for ERA-40 and NCEP-1 over 1958–1978. In general, we conclude that CMAP-1 and GPCP-2 agree more closely with AOP than the reanalysis products do, although ERA-40 data agree more closely with AOP than NCEP data. The percentages of precipitation differences (PPDs) across China between annual ERA-40, NCEP-1, NCEP-2, CMAP-1, CMAP-2, and GPCP-2 data and AOP are −12, 22, 14, −8, −7, and −15%, respectively, for 1979–2001. Although relatively small biases are evident for China as a whole, maximum PPDs, usually occurring around the Qinghai-Tibetan Plateau, can exceed 1000%, indicating a strong terrain dependence of gridded precipitation data. GPCP-2, although characterized by greater underestimation for most of China compared with CMAP-1, exhibits a smaller biases range and hence may be better than CMAP-1. Compared with the NCEP-1 system, NCEP-2 represents an improvement as NCEP-2 precipitation agrees more closely with AOP than NCEP-1 data. However, the coherence of NCEP-2 precipitation needs further improvement. In addition, we find worse consistency and accuracy and larger positive biases in some parts of China for CMAP-2 versus CMAP-1, illustrating an advantage of including reanalysis data in CMAP, as CMAP-1 does. CMAP-1 could be further improved if they used the more skillful ERA-40 precipitation instead of the NCEP/NCAR data.

[1] In the paper ‘‘Evaluation of ERA-40, NCEP-1, and NCEP-2 reanalysis air temperatureswith ground-basedmeasurements in China’’ by L. Ma et al. (Journal of Geophysical Research, 113, D15115, doi:101.1029/2007JD009549), a printer error was introduced in the abstract, giving an incorrect year. The first sentence of the abstract should read as follows: We assess the correspondence of reanalysis air temperatures from ERA-40, NCEP-1, and NCEP-2 with homogenized observational data from China for 1958–2001 and 1979–2001. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, D18199, doi:10.1029/2008JD010981, 2008

[1] We assess the correspondence of reanalysis air temperatures from ERA-40, NCEP-1, and NCEP-2 with homogenized observational data from China for 1958–2001 and 1979–2001. Results indicate that climatologies for annual ERA-40, NCEP-1, and NCEP-2 air temperatures are lower than observations by −0.93°C, −2.78°C, and −2.27°C, respectively. Large negative differences for most of western China primarily contribute to this cool bias. Error analysis indicates that the internal coherence of ERA-40 data is better than NCEP-1 or NCEP-2. Although NCEP-2 air temperatures represent an improvement over NCEP-1, biases of NCEP-1 and NCEP-2 data relative to observations are still much larger than for ERA-40. Areas with positive/negative air temperature differences (dT) between reanalysis and observational data correspond to negative/positive elevation differences (dH). The high correlation coefficients of −0.94, −0.88, and −0.85 between dT and dH for ERA-40, NCEP-1, NCEP-2, and observations, respectively, illustrate that the air temperature differences between reanalysis data and observations are primarily related to elevation differences. Furthermore, a spatial and temporal comparison of trends also indicates that ERA-40 temperature changes correspond most closely to observed trends in China. In general, our comprehensive analysis of the three global reanalysis products indicates that, both on a seasonal and annual basis, ERA-40 temperatures correspond most closely to observations, and biases are due mainly to the elevation differences.

[1] Soil temperature is an important indicator of frozen ground status, driven at least partly by air temperature variability. In this study we apply singular spectrum analysis (SSA) to detect trends and oscillations in annual and seasonal time series of surface air temperature (SAT) and soil temperature (ST). We investigate soil temperatures at depths of 0.4, 1.6, and 3.2 m for five permafrost-occupied regions in Russia. We use SAT data for 1902–1995 and ST data for 1960–1990. The trends show an increase in annual SAT and ST from the end of the 1960s across all five regions, and this warming exceeds that of the preceding period in the Central Siberian Plateau and Transbaikalia. Oscillations in annual SAT and ST time series are coincident in the West Siberian Plain (7.7 year period) and in the western Central Siberian Plateau and Transbaikalia (2.7 year period). In general, on a seasonal basis, 2–3 year oscillations in ST and SAT are coincident during winter, spring, and autumn across the regions and are also evident in the annual ST time series in the Central Siberian Plateau and Transbaikalia. We also find a decadal oscillation (9.8 year period), which is coincident for winter SAT and ST, over the western Central Siberian Plateau only. Although summer SAT and ST oscillations (5–8 year periods) are coincident for all investigated territories (except to the east of the Lena River), in the annual ST time series they are identified only for the West Siberian Plain. We document the degree to which SAT controls ST in each region and explore the causative factors for some of the dominant periods. The maximum effect of SAT increases on permafrost may be observed in the Central Siberian Plateau and Transbaikalia, while elsewhere the observed ST increases do not threaten permafrost areas.

[1] Changes in active layer thickness (ALT) over northern high-latitude permafrost regions have important impacts on the surface energy balance, hydrologic cycle, carbon exchange between the atmosphere and the land surface, plant growth, and ecosystems as a whole. This study examines the 20th century variations of ALT for the Ob, Yenisey, and Lena River basins. ALT is estimated from historical soil temperature measurements from 17 stations (1956–1990, Lena basin only), an annual thawing index based on both surface air temperature data (1901–2002) and numerical modeling (1980–2002). The latter two provide spatial fields. Based on the thawing index, the long-term average (1961–1990) ALT is about 1.87 m in the Ob, 1.67 in the Yenisey, and 1.69 m in the Lena basin. Over the past several decades, ALT over the three basins shows positive trends, but with different magnitudes. Based on the 17 stations, ALT increased about 0.32 m between 1956 and 1990 in the Lena. To the extent that results based on the soil temperatures represent ground “truth,” ALT obtained from both the thawing index and numerical modeling is underestimated. It is widely believed that ALT will increase with global warming. However, this hypothesis needs further refinement since ALT responds primarily to summer air temperature while observed warming has occurred mainly in winter and spring. It is also shown that ALT exhibits complex and inconsistent responses to variations in snow cover.

[1] Surface air temperature measurements from meteorological stations on the Tibetan Plateau are compared to 2-m temperatures from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-40) to assess the accuracy of this reanalysis product. We focus on ERA-40 grid cells containing at least four stations. The reanalysis temperatures are consistently lower, by as much as 7°C. However, temporal correlations are high, indicating that ERA-40 captures the interannual variability very well. The temperature bias is almost exclusively due to differences between the grid cell and the station elevations. We conclude that the ERA-40 temperatures provide better spatial fields of temperature than is possible with stations in this topographically complex, data-sparse area. Using this spatially and temporally continuous data set, we provide a temperature climatology and assess long-term climate trends. The high elevations of the western plateau are generally 10°C cooler than the eastern plateau. During winter, 2-m temperatures are below 0°C on the entire plateau, with summer values of only 0°C in the west and 10°C in the east. While station records point to a long-term climate warming trend, no trends are observed in ERA-40. This could be due to inadequacies of the reanalysis data, although we see no evidence of anomalous nonclimatic shifts. The significant trends in station data may reflect the extensive land use change and industrialization that has occurred on the Tibetan Plateau. Reanalysis data are less influenced by these local effects.

[1] Seasonal freezing and thawing processes in cold regions play a major role in ecosystem diversity, productivity, and the Arctic hydrological system. Long-term changes in seasonal freeze and thaw depths are also important indicators of climate change. Only sparse historical measurements of seasonal freeze and thaw depths are available for permafrost and seasonally frozen ground regions. Using mean monthly soil temperature data for 1930–1990 for 242 stations located throughout Russia, we employed a linear interpolation method to determine the depth of the 0°C isotherm based on soil temperature data measured between 0.2 m and 3.2 m depth. The relationship between available observed annual maximum freeze and thaw depths and our interpolated values indicates a perfect correlation. A comprehensive evaluation of long-term trends in these new interpolated data for Russia indicates that in permafrost regions, active layer depths have been steadily increasing. In the period 1956–1990 the active layer exhibited a statistically significant deepening by approximately 20 cm. The changes in the seasonally frozen ground areas are even greater: The depth of the freezing layer decreased 34 cm between 1956 and 1990. Potential forcings of the observed changes include air temperature, freezing and thawing index, and snow depth. Correlation and multiple regression reveal that active layer depth is most strongly related to snow depth. Air temperature, both mean annual and thawing index, is also significantly related to changes in the active layer. Freeze depth is influenced most strongly by the freezing index and mean annual air temperature, although snow depth is also a significant contributor. Air temperature and snow depth have been changing less in the seasonally frozen ground regions of Russia compared to permafrost regions, although observed changes in freeze depth are greater than changes in active layer depth for 1930–1990. This indicates that the seasonally frozen ground regions of the Russian high latitudes are more susceptible to climate change than the Russian permafrost. However, as temperatures have been rising, especially in the high-latitude continental regions, both permafrost and seasonally frozen ground regions are being greatly impacted. These changes can potentially result in increased river runoff and changes in discharge throughout the Russian Arctic drainage basin, as well as changes in high-latitude ecosystems.

[1] Trends in the Northern Hemisphere circumpolar vortex at 700, 500, and 300 hPa are examined to assess the relationship between circulation variability and air temperature. A vortex climatology is developed for the period 1949–2000. At each pressure level, three geopotential height contours are used to quantify the size and position of the vortex at 5° longitude resolution within and both north and south of the primary hemispheric baroclinic zone. This combination of spatial specificity and the long temporal record makes this the most comprehensive vortex climatology to date. The overall and seasonal vortex time series for the Northern Hemisphere are created for northern, middle, and southern contours at each of the three levels in the atmosphere. From the beginning of the record until 1970, the vortex exhibits a statistically significant expansion, but the vortex has been contracting significantly since then at all levels. The pre-1970 expansion and subsequent contraction is strongest in the lower latitudes and weakest in the higher latitudes. The trends are also stronger in the upper troposphere than in the lower troposphere. Spatial examination of the vortex indicates that the pre-1970 expansion and post-1970 contraction were driven primarily by expansion/contraction over Asia, Europe, and North America with little change over the Northern Hemisphere oceans. Although significant climate change debate focuses on the discrepancy between positive trends in surface air temperature and little or no trends in Microwave Sounding Unit (MSU) satellite temperatures, contraction of the circumpolar vortex at every level of the atmosphere implies that the atmosphere is warming at depth since 1970. Comparisons with the MSU temperature history indicate that the Northern Hemisphere circulation as a whole, as represented by the circumpolar vortex, accounts for almost two thirds of the interannual variability in midlatitude MSU temperature, indicating that vortex size and position are coupled strongly to atmospheric temperature and could be a good indicator of climate change. On a latitude-by-latitude and level-by-level basis, the lower latitudes are associated most strongly with MSU temperature in the midtroposphere while the middle and higher latitudes are more closely associated with MSU temperature in the upper troposphere. The vortex trends are also similar to observed surface warming trends.

[1] The exact nature of the interaction between the Pacific Ocean and the climate of the Northern Hemisphere is still in large part uncertain. To investigate these interactions, canonical correlation analysis is applied to relate midlatitude atmospheric circulation variability with Pacific Ocean SST variability. The leading mode corresponds closely to decadal PDO-like variability and the second mode is comparable to ENSO. Consequently, we identified different atmospheric circulation patterns related to the spatially similar, but temporally different modes of SST variability. Circulation variability over Eurasia is linked with the decadal SST variability, while the interannual SST variability is linked to circulation variability over the eastern Pacific. This suggests that decadal SST variability, in part, could be forced by the atmosphere. Furthermore, while the PDO switched back into its negative phase in the late 1990s, the decadal SST variability as related to circulation did not. Instead, the interannual mode has shifted into a negative phase, indicating a change in the nature of ocean-atmosphere interaction in the late 1990s.