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We identify and remove the main natural perturbations (e.g. volcanic activity, ENSOs) from the global mean lower tropospheric temperatures (T LT ) over January 1979 - June 2017 to estimate the underlying, potentially human-forced trend. The unaltered value is +0.155 K dec−1 while the adjusted trend is +0.096 K dec−1, related primarily to the removal of volcanic cooling in the early part of the record. This is essentially the same value we determined in 1994 (+0.09 K dec−1, Christy and McNider, 1994) using only 15 years of data. If the warming rate of +0.096 K dec−1 represents the net T LT response to increasing greenhouse radiative forcings, this implies that the T LT tropospheric transient climate response (ΔT LT at the time CO2 doubles) is +1.10 ± 0.26 K which is about half of the average of the IPCC AR5 climate models of 2.31 ± 0.20 K. Assuming that the net remaining unknown internal and external natural forcing over this period is near zero, the mismatch since 1979 between observations and CMIP-5 model values suggests that excessive sensitivity to enhanced radiative forcing in the models can be appreciable. The tropical region is mainly responsible for this discrepancy suggesting processes that are the likely sources of the extra sensitivity are (a) the parameterized hydrology of the deep atmosphere, (b) the parameterized heat-partitioning at the oceanatmosphere interface and/or (c) unknown natural variations.

This paper explores the link between the anomalous warming hole in the southeastern United States and a major land-use/land-cover (LULC) change in the region. Land surface and satellite observations were analyzed to estimate the net radiative forcing due to LULC change. Albedo and latent energy were specifically addressed for the dominant LULC change of agriculture to forests. It was assumed that in the energy-limited environment of the region, the partition of changes in available energy due to albedo will mostly impact the sensible heat. The results show that in the southeastern United States, for the period of 1920 to 1992, the changes in sensible (as a result of albedo) and latent energies are in direct competition with each other. In the spring and early summer months, the croplands are in peak production and the latent energy associated with their evapotranspiration (ET) is comparable to that of the forests so the decrease in radiation due to albedo dominates the signal. However, during the late summer and fall months, most major crops have matured, thus reducing their transpiration rate while forests (particularly evergreens) maintain their foliage and with their deep roots are able to continue to transpire as long as atmospheric conditions are favorable. This later influence of latent energy appears to more than offset the increased radiative forcing from the spring and early summer. Overall, a mean annual net radiative forcing resulting from a LULC change from cropland to forests was estimated to be −1.06 W m−2 and thus a probable contribution to the “warming hole” over the Southeast during the majority of the twentieth century.

Simulated stratospheric temperatures over the period 1979–2016 in models from the Chemistry-Climate Model Initiative are compared with recently updated and extended satellite data sets. The multimodel mean global temperature trends over 1979–2005 are -0.88 ± 0.23, -0.70 ± 0.16, and -0.50 ± 0.12 K/decade for the Stratospheric Sounding Unit (SSU) channels 3 (~40–50 km), 2 (~35–45 km), and 1 (~25–35 km), respectively (with 95% confidence intervals). These are within the uncertainty bounds of the observed temperature trends from two reprocessed SSU data sets. In the lower stratosphere, the multimodel mean trend in global temperature for the Microwave Sounding Unit channel 4 (~13–22 km) is -0.25 ± 0.12 K/decade over 1979–2005, consistent with observed estimates from three versions of this satellite record. The models and an extended satellite data set comprised of SSU with the Advanced Microwave Sounding Unit-A show weaker global stratospheric cooling over 1998–2016 compared to the period of intensive ozone depletion (1979–1997). This is due to the reduction in ozone-induced cooling from the slowdown of ozone trends and the onset of ozone recovery since the late 1990s. In summary, the results show much better consistency between simulated and satellite-observed stratospheric temperature trends than was reported by Thompson et al. (2012, https://doi.org/10.1038/nature11579) for the previous versions of the SSU record and chemistry-climate models. The improved agreement mainly comes from updates to the satellite records; the range of stratospheric temperature trends over 1979–2005 simulated in Chemistry-Climate Model Initiative models is comparable to the previous generation of chemistry-climate models.

Updated tropical lower tropospheric temperature datasets covering the period 1979–2009 are presented and assessed for accuracy based upon recent publications and several analyses conducted here. We conclude that the lower tropospheric temperature (TLT) trend over these 31 years is +0.09 ± 0.03 °C decade−1. Given that the surface temperature (Tsfc) trends from three different groups agree extremely closely among themselves (~ +0.12 °C decade−1) this indicates that the “scaling ratio” (SR, or ratio of atmospheric trend to surface trend: TLT/Tsfc) of the observations is ~0.8 ± 0.3. This is significantly different from the average SR calculated from the IPCC AR4 model simulations which is ~1.4. This result indicates the majority of AR4 simulations tend to portray significantly greater warming in the troposphere relative to the surface than is found in observations. The SR, as an internal, normalized metric of model behavior, largely avoids the confounding influence of short-term fluctuations such as El Niños which make direct comparison of trend magnitudes less confident, even over multi-decadal periods.

The problems inherent in the estimation of global tropospheric temperature trends from a combination of near-nadir Microwave Sounding Unit (MSU) channel-2 and -4 data are described. The authors show that insufficient overlap between those two channels’ weighting functions prevents a physical removal of the stratospheric influence on tropospheric channel 2 from the stratospheric channel 4. Instead, correlations between stratospheric and tropospheric temperature fluctuations based upon ancillary (e.g., radiosonde) information can be used to statistically estimate a correction for the stratospheric influence on MSU 2 from MSU 4. Fu et al. developed such a regression relationship from radiosonde data using the 850–300-hPa layer as the target predictand. There are large errors in the resulting fit of the two MSU channels to the tropospheric target layer, so the correlations from the ancillary data must be relied upon to provide a statistical minimization of the resulting errors. Such relationships depend upon the accuracy of the particular training dataset as well as the dataset time period and its global representativeness (i.e., temporal and spatial stationarity of the statistics). It is concluded that near-nadir MSU channels 2 and 4 cannot be combined to provide a tropospheric temperature measure without substantial uncertainty resulting from a necessary dependence on ancillary information regarding the vertical profile of temperature variations, which are, in general, not well known on a global basis.

Deep-layer temperatures derived from satellite-borne microwave sensors since 1979 are revised (version 5.0) to account for 1) a change from microwave sounding units (MSUs) to the advanced MSUs (AMSUs) and 2) an improved diurnal drift adjustment for tropospheric products. AMSU data, beginning in 1998, show characteristics indistinguishable from the earlier MSU products. MSU–AMSU error estimates are calculated through comparisons with radiosonde-simulated bulk temperatures for the low–middle troposphere (TLT), midtroposphere (TMT), and lower stratosphere (TLS.) Monthly (annual) standard errors for global mean anomalies of TLT satellite temperatures are estimated at 0.10°C (0.07°C). The TLT (TMT) trend for January 1979 to April 2002 is estimated as +0.06° (+0.02°) ±0.05°C decade–1 (95% confidence interval). Error estimates for TLS temperatures are less well characterized due to significant heterogeneities in the radiosonde data at high altitudes, though evidence is presented to suggest that since 19...

Two deep-layer tropospheric temperature products, one for the lower troposphere (T2LT) and one for the midtroposphere (T2, which includes some stratospheric emissions), are based on the observations of channel 2 of the microwave sounding unit on National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites. Revisions to version C of these datasets have been explicitly applied to account for the effects of orbit decay (loss of satellite altitude) and orbit drift (east–west movement). Orbit decay introduces an artificial cooling in T2LT, while the effects of orbit drift introduce artificial warming in both T2LT and T2. The key issues for orbit drift are 1) accounting for the diurnal cycle and 2) the adjustment needed to correct for spurious effects related to the temperature of the instrument. In addition, new calibration coefficients for NOAA-12 have been applied. The net global effect of these revisions (version D) is small, having little impact on the year-to-year anomalies. T...

We examine to what degree we can expect to obtain accurate temperature trends for the last two decades near the surface and in the lower troposphere. We compare temperatures obtained from surface observations and radiosondes as well as satellite-based measurements from the Microwave Soundings Units (MSU), which have been adjusted for orbital decay and non-linear instrument-body effects, and reanalyses from the European Centre for Medium-Range Weather Forecasts (ERA) and the National Centre for Environmental Prediction (NCEP). In regions with abundant conventional data coverage, where the MSU has no major influence on the reanalysis, temperature anomalies obtained from microwave sounders, radiosondes and from both reanalyses agree reasonably. Where coverage is insufficient, in particular over the tropical oceans, large differences are found between the MSU and either reanalysis. These differences apparently relate to changes in the satellite data availability and to differing satellite retrieval methodologies, to which both reanalyses are quite sensitive over the oceans. For NCEP, this results from the use of raw radiances directly incorporated into the analysis, which make the reanalysis sensitive to changes in the underlying algorithms, e.g. those introduced in August 1992. For ERA, the bias-correction of the one-dimensional variational analysis may introduce an error when the satellite relative to which the correction is calculated is biased itself or when radiances change on a time scale longer than a couple of months, e.g. due to orbit decay. ERA inhomogeneities are apparent in April 1985, October/November 1986 and April 1989. These dates can be identified with the replacements of satellites. It is possible that a negative bias in the sea surface temperatures (SSTs) used in the reanalyses may have been introduced over the period of the satellite record. This could have resulted from a decrease in the number of ship measurements, a concomitant increase in the importance of satellite-derived SSTs, and a likely cold bias in the latter. Alternately, a warm bias in SSTs could have been caused by an increase in the percentage of buoy measurements (relative to deeper ship intake measurements) in the tropical Pacific. No indications for uncorrected inhomogeneities of land surface temperatures could be found. Near-surface temperatures have biases in the boundary layer in both reanalyses, presumably due to the incorrect treatment of snow cover. The increase of near-surface compared to lower tropospheric temperatures in the last two decades may be due to a combination of several factors, including high-latitude near-surface winter warming due to an enhanced NAO and upper-tropospheric cooling due to stratospheric ozone decrease.

Trends in global lower tropospheric temperature derived from satellite observations since 1979 show less warming than trends based on surface meteorological observations. Independent radiosonde observations of surface and tropospheric temperatures confirm that, since 1979, there has been greater warming at the surface than aloft in the tropics. Associated lapse-rate changes show a decrease in the static stability of the atmosphere, which exceeds unforced static stability variations in climate simulations with state-of-the-art coupled ocean-atmosphere models. The differential temperature trends and lapse-rate changes seen during the satellite era are not sustained back to 1960.

We monitor and model the effects on world-wide temperatures of the June 1991 volcanic eruption of Mount Pinatubo in the Philippines. Global mean air temperatures were reduced, by up to 0·5°C at the surface and 0·6°C in the troposphere, for some months in mid-1992, in approximate accord with model predictions. Differences from these predictions occurred in the Northern Hemisphere winters of 1991–1992 and 1992–1993, as a result of atmospheric circulation changes that yielded continental surface warmings not fully reproduced by the model. The effects of the eruption were less evident by 1994. A superposed-epoch composite for five major tropical eruptions shows significant global post-eruption cooling at the surface when the effects of the El Ni7o–Southern Oscillation are removed from the data. Stratospheric warmth following Pinatubo lasted until early 1993 according to Microwave Sounding Unit data.

Monitoring the earth system has traditionally focused on measurements at the earth's surface because this is where we live and perform our most obvious life sustaining functions. In just the past few decades, however, efforts have been initiated to assess the character of the atmosphere above the surface. Regular upper-air measurements by balloon ascents in scattered locations began in the 1940's and observations from satellites generally began in 1979. The upper air is important in the climate context because changes in these higher levels may offer more discernible relationships to such phenomena as global warming due to the enhanced greenhouse effect than seen at other levels. The probability that climate-change trends in the mid-troposphere (5-8 km) will be more clearly evident against the background of natural variability than at, for example, the surface. Indeed, results from coupled ocean-atmosphere models indicate that in terms of a global mean quantity the troposphere will actually warm at a rate greater than that of the surface temperature. At higher elevations, above 12 km, the IPCC (Intergovernmental Panel on Climate Change) 1990 indicates there is a high degree of certainty that a greenhouse-gas induced decrease in stratospheric temperatures will occur. The measure of change in these upper atmospheric layers, in combination with quantities observed at the surface, provide an ensemble of information to give the most robust opportunity for climate change detection.

[1] One of the most significant signals in the thermometer-observed temperature record since 1900 is the decrease in the diurnal temperature range over land, largely due to rising of the minimum temperatures. Generally, climate models have not well replicated this change in diurnal temperature range. Thus, the cause for night-time warming in the observed temperatures has been attributed to a variety of external causes. We take an alternative approach to examine the role that the internal dynamics of the stable nocturnal boundary layer (SNBL) may play in affecting the response and sensitivity of minimum temperatures to added downward longwave forcing. As indicated by previous nonlinear analyses of a truncated two-layer equation system, the SNBL can be very sensitive to changes in greenhouse gas forcing, surface roughness, heat capacity, and wind speed. A new singlecolumn model growing out of these nonlinear studies is used to examine the SNBL. Specifically, budget analyses of the model are provided that evaluate the response of the boundary layer to forcing and sensitivity to mixing formulations. Based on these model analyses, it is likely that part of the observed long-term increase in minimum temperature is reflecting a redistribution of heat by changes in turbulence and not by an accumulation of heat in the boundary layer. Because of the sensitivity of the shelter level temperature to parameters and forcing, especially to uncertain turbulence parameterization in the SNBL, there should be caution about the use of minimum temperatures as a diagnostic global warming metric in either observations or models.

Satellite data from the microwave sounding unit (MSU) channel 4, when carefully merged, provide daily zonal anomalies of lower-stratosphere temperature with a level of precision between 0.01° and 0.08°C per 2.5° latitude band. Global averages of these daily zonal anomalies reveal the prominent warming events due to volcanic aerosol in 1982 (El Chichon) and 1991 (Mt. Pinatubo), which are on the order of 1°C. The quasibiennial oscillation (QBO) may be extracted from these zonal data by applying a spatial filter between 15°N and 15°S latitude, which resembles the meridional curvature. Previously published relationships between the QBO and the north polar stratospheric temperatures during northern winter are examined but were not found to be reproduced in the MSU4 data. Sudden stratospheric warmings in the north polar region are represented in the MSU4 data for latitudes poleward of 70°N. In the Southern Hemisphere, there appears to be a moderate relationship between total ozone concentration and MSU...

As a result of the eruption of Mt. Pinatubo (June 1991), direct solar radiation was observed to decrease by as much as 25–30% at four remote locations widely distributed in latitude. The average total aerosol optical depth for the first 10 months after the Pinatubo eruption at those sites is 1.7 times greater than that observed following the 1982 eruption of El Chichon. Monthly-mean clear-sky total solar irradiance at Mauna Loa, Hawaii, decreased by as much as 5% and averaged 2.4% and 2.7% in the first 10 months after the El Chichon and Pinatubo eruptions, respectively. By September 1992 the global and northern hemispheric lower tropospheric temperatures had decreased 0.5°C and 0.7°C, respectively compared to pre-Pinatubo levels. The temperature record examined consists of globally uniform observations from satellite microwave sounding units.

This paper describes a method for determining global atmospheric-temperature anomalies by means of satellite microwave radiometry. It is shown that microwave measurements of molecular oxygen thermal emission by the Microwave Sounding Units (MSUs) flying aboard the NOAA-6 and NOAA-7 can be used to monitor tropospheric temperature anomalies on global basis to a high level of precision. Comparisons between monthly MSU-derived hemispheric temperature anomalies with those computed from surface thermometer data show a very good agreement over the United States, although not for the hemispheres, especially the Southern Hemisphere. In this latter case, the poor agreement is ascribed to weaker thermal coupling between the ocean and the deep troposphere than that over the U.S. Annual anomalies for the hemispheres exhibit better correlations than do monthly anomalies.

Passive microwave radiometry from satellites provides more precise atmospheric temperature information than that obtained from the relatively sparse distribution of thermometers over the earth's surface. Accurate global atmospheric temperature estimates are needed for detection of possible greenhouse warming, evaluation of computer models of climate change, and for understanding important factors in the climate system. Analysis of the first 10 years (1979 to 1988) of satellite measurements of lower atmospheric temperature changes reveals a monthly precision of 0.01 degrees C, large temperature variability on time scales from weeks to several years, but no obvious trend for the 10-year period. The warmest years, in descending order, were 1987, 1988, 1983, and 1980. The years 1984, 1985, and 1986 were the coolest.

[1] We explore the daily evolution of tropical intraseasonal oscillations in satellite-observed tropospheric temperature, precipitation, radiative fluxes, and cloud properties. The warm/rainy phase of a composited average of fifteen oscillations is accompanied by a net reduction in radiative input into the ocean-atmosphere system, with longwave heating anomalies transitioning to longwave cooling during the rainy phase. The increase in longwave cooling is traced to decreasing coverage by ice clouds, potentially supporting Lindzen’s ‘‘infrared iris’’ hypothesis of climate stabilization. These observations should be considered in the testing of cloud parameterizations in climate models, which remain sources of substantial uncertainty in global warming prediction. Citation: Spencer, R. W., W. D. Braswell, J. R. Christy, and J. Hnilo (2007), Cloud and radiation budget changes associated with tropical intraseasonal oscillations, Geophys. Res. Lett., 34, L15707, doi:10.1029/2007GL029698.

[1] We define the radiative forcings used in climate simulations with the SI2000 version of the Goddard Institute for Space Studies (GISS) global climate model. These include temporal variations of well-mixed greenhouse gases, stratospheric aerosols, solar irradiance, ozone, stratospheric water vapor, and tropospheric aerosols. Our illustrations focus on the period 1951–2050, but we make the full data sets available for those forcings for which we have earlier data. We illustrate the global response to these forcings for the SI2000 model with specified sea surface temperature and with a simple Q-flux ocean, thus helping to characterize the efficacy of each forcing. The model yields good agreement with observed global temperature change and heat storage in the ocean. This agreement does not yield an improved assessment of climate sensitivity or a confirmation of the net climate forcing because of possible compensations with opposite changes of these quantities. Nevertheless, the results imply that observed global temperature change during the past 50 years is primarily a response to radiative forcings. It is also inferred that the planet is now out of radiation balance by 0.5 to 1 W/m 2 and that additional global warming of about 0.5� C is already ‘‘in the pipeline.’’ INDEX TERMS: 1620 Global Change: Climate dynamics (3309); 1635 Global Change: Oceans (4203); 1650 Global Change: Solar variability

Three published data sets of upper-air global temperatures, two from radiosondes and one from satellites, are examined and compared for the lower stratosphere and troposphere.

One of the most significant signals in the thermometer-observed temperature record since 1900 is the decrease in the diurnal temperature range over land, largely due to warming of the minimum temperatures. While some data sets have indicated this asymmetrical warming has been reduced since 1979, regional analyses (e.g. East Africa) indicate that the nocturnal warming continues at a pace greater than daytime temperatures. The cause for this night time warming in the observed temperatures has been attributed to a variety of causes. Climate models have in general not replicated the change in diurnal temperature range well. Here we would like to try to distinguish between warming in the nocturnal boundary layer due to a redistribution of heat and warming due to the accumulation of heat. The temperature at night at shelter height is a result of competition between thermal stability and mechanical shear. If stability wins then turbulence is suppressed and the cooling surface becomes cut-off from the warmer air aloft, which leads to sharp decay in surface air temperature. If shear wins, then turbulence is maintained and warmer air from aloft is continually mixed to the surface, which leads to significantly lower cooling rates and warmer temperatures. This warming occurs due to a redistribution of heat. As will be shown by techniques of nonlinear analysis the winner of the stability and shear contest can be very sensitive to changes in greenhouse gas forcing, surface roughness, cloudiness, and surface heat capacity (including soil moisture). Further, the minimum temperatures measured in the nocturnal boundary layer represent only a very shallow layer of the atmosphere which is usually only a few hundred meters thick. It is likely that the observed warming in minimum temperature, whether caused by additional greenhouse forcing or land use changes or other land surface dynamics, is reflecting a redistribution of heat by turbulence-not an accumulation of heat. Because minimum temperatures in the stable boundary layer are not very robust measures of the heat content in the deep atmosphere and climate models do not predict minimum temperatures well, minimum temperatures should not be used as a surrogate for measures of deep atmosphere global warming.

Vertically integrated diabatic heating rate estimates (H) calculated from 32 months of European Center for Medium-Range Weather Forecasts daily analyses (May 1985-December 1987) are determined as residuals of the thermodynamic equation in pressure coordinates. Values for global, hemispheric, zonal, and grid point H are given as they vary over the time period examined. The distribution of H is compared with previous results and with outgoing longwave radiation (OLR) measurements. The most significant negative correlations between H and OLR occur for (1) tropical and Northern-Hemisphere mid-latitude oceanic areas and (2) zonal and hemispheric mean values for periods less than 90 days. Largest positive correlations are seen in periods greater than 90 days for the Northern Hemispheric mean and continental areas of North Africa, North America, northern Asia, and Antarctica. The physical basis for these relationships is discussed. An interyear comparison between 1986 and 1987 reveals the ENSO signal.

Two global data sets have been analyzed to determine the interannual variability of the zonal mean mass distribution. The first is a National Meteorological Center (NMC) global data set of sea level pressures beginning in December 1977 and surface pressures beginning in April 1979. The second is an 11-year (1972–1982) hybrid set of sea level pressures from the Australian southern hemisphere and U.S. Navy northern hemisphere analyses. The two sets are compared and evaluated by seeing how well they satisfy the constraint of conservation of mass. Anomalies in total mass due to changes in water vapor content of the atmosphere are lost in the data problems. Several inhomogeneities or discontinuities are found and are identified either with changes in analysis procedures in both data sets or the introduction of new orography and operational models at NMC. Consequently only limited periods of data are suitable for determining the dominant modes of variability. Nevertheless, hemispheric mean anomalies in mass in one hemisphere tend to be mirrored in the other, and it is clear that previously deduced fluctuations in hemispheric mean mass are mostly real. Predominant modes of variability of zonal means reveal systematic exchanges of mass (1) almost entirely confined within each hemisphere in isolation, (2) between the extratropics of each hemisphere with little impact on the tropics as an antisymmetric mode, and (3) between the tropics and extratropics in a symmetric mode. The second mode played a strong role in redistributing mass during April–July of 1979 during the First GARP Global Experiment (FGGE) and resulted in an exceptionally deep circumpolar trough over the southern hemisphere and record high pressures over the northern hemisphere. The possible origin of these modes is briefly considered.

Seven years of daily global surface pressure (Ps,) analyses derived from European Centre for Medium Range Forecasts (ECMWF) data are examined to describe more fully interhemispheric mass exchanges and intraseasonal variability. Extreme events in hemispheric mean Ps are determined, and composited grid point differences show that hemispheric anomalies are mainly determined by pressures in the North Pacific, western North Atlantic, northern Asia and the Southern Hemisphere (SH) circumpolar trough. Seasonal differences in the composites indicate that the regional anomalies occur farther poleward in the winter hemisphere, and the tropical anomalies tend to have the same sign as that of the summer hemispheric mean anomaly. Long-lasting, localized, extreme Ps anomalies are identified in 18 significant events of hemispheric mass imbalance, and are found to be highly favored when the hemispheric mean departs significantly from normal. The result implies that regionally persistent anomalies are related to ...

There is a substantial global redistribution of atmospheric mass associated with the mean annual cycle which results in large exchanges of mass between hemispheres. Interannual fluctuations in the distribution of mass both within each hemisphere and for the “hemispheric” mean over 17.5°–90° latitude are examined. The long-period (1899–1980) historical sea level pressures over the northern hemisphere are analyzed and found to exhibit three modes of interannual zonal mean mass redistribution that are common to all seasons. The first is one where mass is mostly redistributed within the hemisphere, while the other two modes imply that compensation of mass occurs south of 17.5°N. A similar analysis over the southern hemisphere for 1972–1983 reveals remarkably similar results. Large and significant fluctuations in the hemispheric mean sea level pressure are found. These include record anomalies during the northern spring and summer of 1979, the year of the Global Weather Experiment. Opposite anomalies in the southern hemisphere, through the constraint of conservation of mass, imply the reality of a substantial global-scale redistribution of atmospheric mass.