Average Surface Air Temperature Research Articles

Reconstruction of the annual average values of the Earth’s albedo

The problem of reconstruction of a many-year series of values of the Earth’s spherical albedo is considered. The model developed reconstructs the annual average values of the albedo based on the annual average surface air temperature and thermal inertia of the hydrosphere. Tolerance of the model to variations in the input data is proved and confirmed by a series from 1880. The albedo reconstruction accuracy is assessed over the interval 1984–1999.

Moderation of Summertime Heat Island Phenomena via Modification of the Urban Form in the Tokyo Metropolitan Area

AbstractThis study investigated the moderation of the urban heat island via changes in the urban form in the Tokyo metropolitan area (TMA). Two urban scenarios with the same population as that of the current urban form were used for sensitivity experiments: the dispersed-city and compact-city scenarios. Numerical experiments using the two urban scenarios as well as an experiment using the current urban form were conducted using a regional climate model coupled with a single-layer urban canopy model. The averaged nighttime surface air temperature in TMA increased by ~0.34°C in the dispersed-city scenario and decreased by ~0.1°C in the compact-city scenario. Therefore, the compact-city scenario had significant potential for moderating the mean areal heat-island effect in the entire TMA. Alternatively, in the central part of the TMA, these two urban-form scenarios produced opposite effects on the surface air temperature; that is, severe thermal conditions worsened further in the compact-city scenario because of the denser population. This result suggests that the compact-city form is not always appropriate for moderation of the urban-heat-island effect. This scenario would need to combine with other mitigation strategies, such as the additional greening of urban areas, especially in the central area. This study suggests that it is important to design a plan to adapt to higher urban temperatures, which are likely to ensue from future global warming and the urban heat island, from several perspectives; that is, designs should take into account not only climatological aspects but also impacts on urban inhabitants.

Northern Hemisphere Climatology and Trends of Statistical Moments Documented from GHCN-Daily Surface Air Temperature Station Data from 1950 to 2010

Abstract The first four statistical moments and their trends are calculated for the average daily surface air temperature (SAT) from 1950 to 2010 using the Global Historical Climatology Network–Daily station data for each season relative to the 1961–90 climatology over the Northern Hemisphere. Temporal variation of daily SAT probability distributions are represented as generalized linear regression coefficients on the mean, standard deviation, skewness, and kurtosis calculated for each 10-yr moving time window from 1950–59 to 2001–10. The climatology and trends of these statistical moments suggest that daily SAT probability distributions are non-Gaussian and are changing in time. The climatology of the first four statistical moments has distinct spatial patterns with large coherent structure for mean and standard deviation and relatively smaller and more regionalized patterns for skewness and kurtosis. The linear temporal trends from 1950 to 2010 of the first four moments also have coherent spatial patterns. The linear temporal trends in the characterizing statistical moments are statistically significant at most locations and have differing spatial patterns for different moments. The regionalized variations specific to higher moments may be related to the climate dynamics that contribute to extremes. The nonzero skewness and kurtosis makes this detailed documentation on the higher statistical moments useful for quantifying climate changes and assessing climate model uncertainties.

Irrigation as an historical climate forcing

Irrigation is the single largest anthropogenic water use, a modification of the land surface that significantly affects surface energy budgets, the water cycle, and climate. Irrigation, however, is typically not included in standard historical general circulation model (GCM) simulations along with other anthropogenic and natural forcings. To investigate the importance of irrigation as an anthropogenic climate forcing, we conduct two 5-member ensemble GCM experiments. Both are setup identical to the historical forced (anthropogenic plus natural) scenario used in version 5 of the Coupled Model Intercomparison Project, but in one experiment we also add water to the land surface using a dataset of historically estimated irrigation rates. Irrigation has a negligible effect on the global average radiative balance at the top of the atmosphere, but causes significant cooling of global average surface air temperatures over land and dampens regional warming trends. This cooling is regionally focused and is especially strong in Western North America, the Mediterranean, the Middle East, and Asia. Irrigation enhances cloud cover and precipitation in these same regions, except for summer in parts of Monsoon Asia, where irrigation causes a reduction in monsoon season precipitation. Irrigation cools the surface, reducing upward fluxes of longwave radiation (increasing net longwave), and increases cloud cover, enhancing shortwave reflection (reducing net shortwave). The relative magnitude of these two processes causes regional increases (northern India) or decreases (Central Asia, China) in energy availability at the surface and top of the atmosphere. Despite these changes in net radiation, however, climate responses are due primarily to larger magnitude shifts in the Bowen ratio from sensible to latent heating. Irrigation impacts on temperature, precipitation, and other climate variables are regionally significant, even while other anthropogenic forcings (anthropogenic aerosols, greenhouse gases, etc.) dominate the long term climate evolution in the simulations. To better constrain the magnitude and uncertainties of irrigation-forced climate anomalies, irrigation should therefore be considered as another important anthropogenic climate forcing in the next generation of historical climate simulations and multi-model assessments.

CMIP5 multi‐model hindcasts for the mid‐1970s shift and early 2000s hiatus and predictions for 2016–2035

AbstractCompared to uninitialized climate change projections, a multi‐model ensemble from the CMIP5 10 year decadal prediction experiments produces more warming during the mid‐1970s climate shift and less warming in the early 2000s hiatus in both the tropical Indo‐Pacific region and globally averaged surface air temperature (TAS) in closer agreement with observations. Assuming bias in TAS has stabilized in the 10 year predictions, after bias adjustment, TAS anomalies for the 2016–2035 period in the 30 year predictions initialized in 2006 are about 16% less than the uninitialized projections. One contributing factor for the improved climate simulation is the bias adjustment, which corrects the models' systematic errors and higher‐than‐observed decadal warming trend. Another important factor is the initialization with observations which constrains the ocean such that the starting points of the initialized simulations are close to the observed initial states.

Climatological study on mesoscale extreme high temperature events in the inland of the Tokyo Metropolitan Area, Japan, during the past 22 years

Over the past 22 years (1990–2011), the inland part of the Tokyo metropolitan area has had 75 days with an extreme high temperature (EHT) higher than 37.2 °C in Kumagaya, Saitama Prefecture. To determine the synoptic-scale and mesoscale conditions for such EHT events, a statistical analysis was conducted using observational and objective analysis data. The results show that all the EHT events satisfy the conditions of a daily minimum surface air temperature above 21.4 °C on Kumagaya and an air temperature at 850 hPa above 18.8 °C on Tsukuba. The EHT days satisfying these conditions were categorized into 27 types according to different combinations of synoptic-pressure patterns, surface wind patterns, and the number of consecutive preceding clear-sky days. The most frequent type occurred eight times (10.7% of days) and was the ‘WHALE’ (tail of a whale) pressure pattern with a southeast (SE) surface wind, with at least four (4+) consecutive preceding clear-sky days. However, the type with the highest average maximum surface air temperature had a different wind direction, which was WHALE with a northwest (NW) surface wind and 4+ consecutive preceding clear-sky days. This type appeared only twice but produced the average maximum temperature of 39.7 °C.

Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus

The slowdown in global average surface warming has recently been linked to sea surface cooling in the eastern Pacific Ocean. This work shows that strengthening trade winds caused a reduction in the 2012 global average surface air temperature of 0.1–0.2 °C. This may account for much of the warming hiatus and is a result of increased subsurface ocean heat uptake.

A Model Simulation of Future Oceanic Conditions along the British Columbia Continental Shelf. Part I: Forcing Fields and Initial Conditions

Techniques for, and the results of, downscaling forcing and initial fields for an ocean-only regional climate model of the British Columbia continental shelf are presented. Fields from one regional-global model combination within the North American Regional Climate Change Assessment Program archive are shown to be representative of a larger ensemble of eight. Because model winds over the baseline period of 1970 to 1999 represent upwelling favourable conditions poorly, a strategy of computing future-minus-contemporary anomalies and adding them to the analogous values used in a recent hindcast simulation for the same region is justified and adopted. Average surface air temperatures over the future period of 2040 to 2069 are projected to be warmer for all months, with those in January generally having the highest increases and those in June the lowest. Because average precipitation is generally projected to increase in winter and decrease in summer, total freshwater discharges follow a similar pattern, increasing by about 10% in all months except June to August when they are projected to decrease by up to 10%. Though projected changes to the seasonally averaged heat flux are shown here, the consequence of applying all these forcing and initial fields to a circulation model of the British Columbia continental shelf is described in a subsequent companion manuscript.

Analysis of Temperature Trends in Sutluj River Basin, India

Surface air temperature is an important climatic variable that drives the hydrological cycle. Precipitation and runoff production are impacted by surface air temperature changes and are, therefore, important for water resources planning, irrigation and agriculture. Focusing on the Sutlej Basin in the Himalayan region, the present research is aimed at utilizing observational evidence to evaluate the response of the region to global warming through investigation of temperature trends. Trends in long-term average annual and seasonal surface air temperature, and several temperature indices at eight stations in the Sutlej River basin have been examined using Mann-Kendall non-parametric test. Six stations exhibited increasing trends in annual average maximum temperature with two being statistically significant. The trends in annual average minimum temperature were mixed; three of eight stations exhibited statistically significant decreasing trends. Some higher elevation stations exhibited clear warming trends both in maximum and minimum temperatures. Analysis of seasonal temperature data indicated that the warming was more pronounced in winter and spring than in summer and autumn. Trends in temperature indices considered in this paper were predominantly increasing. The predominant pattern of increased warming in the basin could have implications for water availability as the snow and glacier melt contribution to annual runoff at Bhakra reservoir is estimated at 59%. The analysis shows that even within a small area, there is variability in the magnitude and direction of historic temperature trends. Some of these variations could be partially attributed to data reliability.

Isoprene emission variability through the twentieth century

AbstractA biochemical model of isoprene emission embedded within a global chemistry‐climate simulation framework is applied to investigate the transient response to environmental change over the past century. In the model, the isoprene production is directly coupled to photosynthesis and depends on intercellular carbon dioxide concentration (CO2), atmospheric CO2, and canopy temperature. Sensitivity runs are performed to isolate the relative roles of individual global change drivers: CO2, physical climate, and anthropogenic land cover change (ALCC). Between 1880 and 2000, atmospheric CO2 increased by ~30% from 291 to 370 ppmv, global average surface air temperature increased by 0.7°C, and the crop cover fraction of vegetated land area more than doubled from 15 to 37%. Over the past century, isoprene emission has decreased globally by 20% from 534 to 449 Tg C/yr, while gross primary productivity has increased by 15% from 107 to 124 Pg C/yr mostly due to CO2 fertilization. In terms of individual drivers, the global isoprene source increased by 7% due to the atmospheric CO2 concentration rise (including the opposing effects of CO2 fertilization and CO2 inhibition), decreased by 22% due to ALCC, and increased by only 3% due to physical climate change. Thus, ALCC is the dominant driver of isoprene emission change. Modeled global isoprene emissions were higher in the preindustrial than in the present day. In the industrial era, isoprene emission change represents a human‐induced climate forcing, analogous to land use‐driven CO2 emission, not a climate feedback because temperature‐driven increase was a relatively weak driver of isoprene emission change from 1880 to 2000.

The impact of climate change on runoff in the southeastern Tibetan Plateau

The Tibetan Plateau (TP) is the “water tower of Asia” and strongly influences both the hydrology and climate of southern and eastern Asia. Exploring the impact of climate change on the runoff of TP rivers is critical to improve water resources management. However, thorough studies on the runoff response to climate change are seldom conducted on large TP river systems. To complement the current body of work, this study uses two rainfall–runoff models (SIMHYD and GR4J) to simulate the monthly and annual runoff across the Yarlung Tsangpo River (YTR) basin in the southeastern TP (i.e., upstream of the Brahmaputra) under historical (1962–2002) and future (up to approximately 2030) climate conditions. The future climate series are obtained by using 20 Global Climate Models (GCMs) outputs from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) to reflect a 1 °C increase in the global average surface air temperature. The two rainfall–runoff models successfully simulate the historical runoff for the eight catchments in the YTR basins with median monthly runoff Nash–Sutcliffe Efficiencies (NSE) of 0.86 for SIMHYD and 0.83 for GR4J. The mean annual future precipitation and runoff across the region are projected to increase by most of the modeling results. The mean annual precipitation changes obtained from the 20 GCMs are −15%, 7% and 16% for the 10th percentile, median and 90th percentile of GCM outputs, respectively, and the corresponding changes in the simulated mean annual runoffs are −24%, 13% and 29% for the SIMHYD model outputs and −22%, 11% and 26% for the GR4J model outputs. The projected increase in the runoff at the median percentile mainly occurs in the middle reaches of the YTR and its two tributaries, the Lhasa River and the Nyangqu River, with a 12% increase in annual runoff that mainly occurs in the wet season from May to September. The present work is the first comprehensive study on the hydrological response to climate change covering the entire upstream area of the Brahmaputra, and the results found in this study are not only helpful for local water resource management but also for the lower reaches of the Brahmaputra.

Analysis of the effect of climate change on the Nakdong river stream flow using indicators of hydrological alteration

This study models the effect of climate change on runoff in southeast Korea using the TANK conceptual rainfall-runoff model. The results are assessed using the indicators of hydrological alteration (IHA) developed by U.S. Nature Conservancy. Future climate time series are obtained by scaling historical series, provided by four global climate models (GCMs, IPCC, 2007) and three greenhouse gas (GHG) emissions scenarios (IPCC, 2000), to reflect a maximum increase of 3.6 °C in the average surface air temperature and 33% in the annual precipitation. To this end, the spatio-temporal change factor method is used, which considers changes in the future mean seasonal rainfall and potential evapotranspiration as well as the daily rainfall distribution. In this study, the variance range for precipitation is from +3.55% to +33.44% compared to the present for years between 2071 and 2100. The variance range for the daily mean temperature is estimated between +1.59 °C and +3.58 °C. Although the simulation results from different GCMs and GHG emissions scenarios indicate different responses of the flows to the climate change, the majority of modeling results show that there will be more runoff in southeast Korea in the future. According to the analysis results, the predicted impacts of hydrological alteration caused by climate change on the aquatic ecosystem are as follows: 1) an increase in the availability of aquatic ecosystem habitats in Nakdong River in future summers and winters, 2) an increase in stress on the aquatic ecosystem due to extremely high stream flow, 3) an increase in the stress duration of flood events for the Nakdong River downstream and 4) an increase in aquatic ecosystem stress caused by rapid increases or decreases in stream flow.

Externally Forced and Internally Generated Decadal Climate Variability Associated with the Interdecadal Pacific Oscillation

AbstractGlobally averaged surface air temperatures in some decades show rapid increases (accelerated warming decades), and in other decades there is no warming trend (hiatus decades). A previous study showed that the net energy imbalance at the top of the atmosphere of about 1 W m−2 is associated with greater increases of deep ocean heat content below 750 m during the hiatus decades, while there is little globally averaged surface temperature increase or warming in the upper ocean layers. Here the authors examine processes involved with accelerated warming decades and address the relative roles of external forcing from increasing greenhouse gases and internally generated decadal climate variability associated with interdecadal Pacific oscillation (IPO). Model results from the Community Climate System Model, version 4 (CCSM4), show that accelerated warming decades are characterized by rapid warming of globally averaged surface air temperature, greater increases of heat content in the upper ocean layers, and less heat content increase in the deep ocean, opposite to the hiatus decades. In addition to contributions from processes potentially linked to Antarctic Bottom Water (AABW) formation and the Atlantic meridional overturning circulation (AMOC), the positive phase of the IPO, adding to the response to external forcing, is usually associated with accelerated warming decades. Conversely, hiatus decades typically occur with the negative phase of the IPO, when warming from the external forcing is overwhelmed by internally generated cooling in the tropical Pacific. Internally generated hiatus periods of up to 15 years with zero global warming trend are present in the future climate simulations. This suggests that there is a chance that the current observed hiatus could extend for several more years.

On the Origin of the Surface Air Temperature Difference between the Hemispheres in Earth's Present-Day Climate

Abstract In today's climate, the annually averaged surface air temperature in the Northern Hemisphere (NH) is 1°–2°C higher than in the Southern Hemisphere (SH). Historically, this interhemispheric temperature difference has been attributed to a number of factors, including seasonal differences in insolation, the larger area of (tropical) land in the NH, the particularities of the Antarctic in terms of albedo and temperature, and northward heat transport by ocean circulation. A detailed investigation of these factors and their contribution to the temperature difference, however, has to the authors' knowledge not been performed so far. Here the origin of the interhemispheric temperature difference is traced using an assessment of climatological data and the observed energy budget of Earth as well as model simulations. It is found that for the preindustrial climate the temperature difference is predominantly due to meridional heat transport in the oceans, with an additional contribution from the albedo differences between the polar regions. The combination of these factors (that are to some extent coupled) governs the evolution of the temperature difference over the past millennium. Since the beginning of industrialization the interhemispheric temperature difference has increased due to melting of sea ice and snow in the NH. Furthermore, the predicted higher rate of warming over land as compared to the oceans contributes to this increase. Simulations for the twenty-first century show that the interhemispheric temperature difference continues to grow for the highest greenhouse gas emission scenarios due to the land–ocean warming contrast and the strong loss of Arctic sea ice, whereas the decrease in overturning strength dominates for the more moderate scenarios.

Which Emissions to Reduce?

Climate Science![Figure][1] CREDIT: © SCUBAZOO/SUPERSTOCK/CORBIS A fierce debate is being waged about the relative merits of controlling the anthropogenic emissions of climate-affecting pollutants with long atmospheric lifetimes, such as carbon dioxide, and those with shorter atmospheric lifetimes, such as methane or black carbon. Both classes of compounds have substantial radiative impacts, and arguments about which is more important to reduce have been made for each. By using a sophisticated global model, Smith and Mizrahi examined the potential climate effects of a strategy to mitigate the short-lived climate-forcing agents methane and black carbon and concluded that the likely benefits of such an approach are much more modest than had been suggested recently. Even assuming the maximally feasible reductions in emissions over the next decades, the rise in global average surface air temperature by the year 2050 would be only about one-half of the previous best estimate. Thus, a policy of focusing on reducing emissions of short-lived climate forcers, attractive to many because of its rapid effect and possibly easier and less costly implementation, may not be the silver bullet some have hoped it might be. Proc. Natl. Acad. Sci. U.S.A. 110 , 10.1073/pnas.1308470110 (2013). [1]: pending:yes

A modern Maunder Minimum would not stave off global warming

Roughly every 11 years, the Sun's activity swings, a peak‐to‐peak oscillation in the presence of sunspots on the solar surface. From around 1645 to 1715, however, researchers think that this largely reliable trend in solar activity stalled. Now known as the Maunder Minimum, the period saw not just a prolonged dearth of sunspot activity but also a likely reduction in the output of energy from the Sun. Researchers estimate that the Maunder Minimum could have caused a reduction in solar irradiance of around 0.01% to 0.25%, a shift that contributed to a drop of globally averaged surface air temperature of a few tenths of a degree.

On the effects of lag-times in networks constructed from similarities of monthly fluctuations of climate fields

The complex network framework has been successfully applied to the analysis of climatological data, providing, for example, a better understanding of the mechanisms underlying reduced predictability during El Niño or La Niña years. Despite the large interest that climate networks have attracted, several issues remain to be investigated. Here we focus on the influence of the periodic solar forcing in climate networks constructed via similarities of monthly averaged Surface Air Temperature (SAT) anomalies. We shift the time series in each pair of nodes such as to superpose their seasonal cycles. In this way, when two nodes are located in different hemispheres we are able to quantify the similarity of SAT anomalies during the winters and during the summers. We find that data time-shifting does not significantly modify the network Area Weighted Connectivity (AWC), which is the fraction of the total area of the Earth to which each node is connected. This unexpected network property can be understood in terms of how data time-shifting modifies the strength of the links connecting geographical regions in different hemispheres, and how these modifications are washed out by averaging the AWC.

Greenland Ice Sheet Mass Balance Reconstruction. Part I: Net Snow Accumulation (1600–2009)

Abstract Ice core data are combined with Regional Atmospheric Climate Model version 2 (RACMO2) output (1958–2010) to develop a reconstruction of Greenland ice sheet net snow accumulation rate, Ât(G), spanning the years 1600–2009. Regression parameters from regional climate model (RCM) output regressed on 86 ice cores are used with available cores in a given year resulting in the reconstructed values. Each core site’s residual variance is used to inversely weight the cores’ respective contributions. The interannual amplitude of the reconstructed accumulation rate is damped by the regressions and is thus calibrated to match that of the RCM data. Uncertainty and significance of changes is measured using statistical models. A 12% or 86 Gt yr−1 increase in ice sheet accumulation rate is found from the end of the Little Ice Age in ~1840 to the last decade of the reconstruction. This 1840–1996 trend is 30% higher than that of 1600–2009, suggesting an accelerating accumulation rate. The correlation of Ât(G) with the average surface air temperature in the Northern Hemisphere (SATNHt) remains positive through time, while the correlation of Ât(G) with local near-surface air temperatures or North Atlantic sea surface temperatures is inconsistent, suggesting a hemispheric-scale climate connection. An annual sensitivity of Ât(G) to SATNHt of 6.8% K−1 or 51 Gt K−1 is found. The reconstuction, Ât(G), correlates consistently highly with the North Atlantic Oscillation index. However, at the 11-yr time scale, the sign of this correlation flips four times in the 1870–2005 period.

Could a future “Grand Solar Minimum” like the Maunder Minimum stop global warming?

A future Maunder Minimum type grand solar minimum, with total solar irradiance reduced by 0.25% over a 50 year period from 2020 to 2070, is imposed in a future climate change scenario experiment (RCP4.5) using, for the first time, a global coupled climate model that includes ozone chemistry and resolved stratospheric dynamics (Whole Atmosphere Community Climate Model). This model has been shown to simulate two amplifying mechanisms that produce regional signals of decadal climate variability comparable to observations, and thus is considered a credible tool to simulate the Sun's effects on Earth's climate. After the initial decrease of solar radiation in 2020, globally averaged surface air temperature cools relative to the reference simulation by up to several tenths of a degree Centigrade. By the end of the grand solar minimum in 2070, the warming nearly catches up to the reference simulation. Thus, a future grand solar minimum could slow down but not stop global warming.

Observational Evidence for Oceanic Forcing of Atmospheric Variability in the Nordic Seas Area

Abstract Substantial predictability of the wintertime atmospheric variability in the Nordic (Greenland–Iceland–Norwegian and Barents) seas region is reported based on oceanic observations and atmospheric reanalysis data. In particular, about 60% of the variance of the winter (December–March) regional average surface air temperature (SAT) and early-winter (November–February) zonal geostrophic winds over the western Barents Sea Opening (BSO) area in the period 1982–2006 is explained by the previous summer (June–September) Atlantic water temperature (AWT) anomalies in this area. The atmospheric response to oceanic heat anomalies mainly occurs in the marginal ice zone (MIZ), where the sea ice and corresponding surface heat flux (SHF) anomalies should be triggered by entrainment of subsurface heat anomalies into the deepening mixed layer and sustained through winter by anomalous oceanic heat transport. The latter should be caused by geostrophic current anomalies forced by anomalous ocean Ekman suction and/or onshore Ekman transport appearing as a feedback from the oceanically driven anomalous atmospheric circulation. The wintertime atmospheric links to the previous summer’s AWT anomalies in the BSO area reflect to a large extent a climate feedback from reemerging, atmospherically driven sea surface temperature (SST) anomalies. Indeed, about 70% of the variance of the winter average SAT over the Nordic seas and winter average surface wind vorticity in the MIZ area in the 1982–2006 (or extended 1982–2011) period is explained by the previous early-spring (February–May) SST anomalies in the open water area and the previous late-winter (January–April) SHF anomalies at the Barents Sea ice edge, respectively.