Papers on water vapor feedback observations

This is a list of papers about the observations of the water vapor feedback. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (February 14, 2018): Serreze et al. (2012) and Gordon et al. (2013) added and some dead links corrected.
UPDATE (March 29, 2012): Raval & Ramanathan (1989) and Yang & Tung (1998) added.
UPDATE (June 4, 2011): Paltridge et al. (2009) and Dessler & Davis (2010) added.
UPDATE (March 20, 2010): Held & Soden (2000) added.
UPDATE (December 9, 2009): Dessler & Wong (2009) added.
UPDATE (November 23, 2009): Wentz & Schabel (2000) and Wentz et al. (2007) added, and a broken link fixed. Thanks to PeterPan for pointing these out, see the comment section below.
UPDATE (November 6, 2009): Soden et al. (2002) and Soden et al. (2005) added. Thanks to PeterPan for pointing these out, see the comment section below.
UPDATE (October 30, 2009): Huang & Ramaswamy (2008) added.

An observationally based constraint on the water-vapor feedback – Gordon et al. (2013)
Abstract: The increase in atmospheric concentrations of water vapor with global warming is a large positive feedback in the climate system. Thus, even relatively small errors in its magnitude can lead to large uncertainties in predicting climate response to anthropogenic forcing. This study incorporates observed variability of water vapor over 2002–2009 from the Atmospheric Infrared Sounder instrument into a radiative transfer scheme to provide constraints on this feedback. We derive a short-term water vapor feedback of 2.2 ± 0.4 Wm⁻²K⁻¹. Based on the relationship between feedback derived over short and long timescales in twentieth century simulations of 14 climate models, we estimate a range of likely values for the long-term twentieth century water vapor feedback of 1.9 to 2.8 Wm⁻²K⁻¹. We use the twentieth century simulations to determine the record length necessary for the short-term feedback to approach the long-term value. In most of the climate models we analyze, the short-term feedback converges to within 15% of its long-term value after 25 years, implying that a longer observational record is necessary to accurately estimate the water vapor feedback.
Citation: Gordon, N. D., A. K. Jonko, P. M. Forster, and K. M. Shell (2013), An observationally based constraint on the water-vapor feedback, J. Geophys. Res. Atmos., 118, 12,435–12,443, doi:10.1002/2013JD020184. [Full text]

Recent changes in tropospheric water vapor over the Arctic as assessed from radiosondes and atmospheric reanalyses – Serreze et al. (2012)
Abstract: Changes in tropospheric water vapor over the Arctic are examined for the period 1979 to 2010 using humidity and temperature data from nine high latitude radiosonde stations north of 70°N with nearly complete records, and from six atmospheric reanalyses, emphasizing the three most modern efforts, MERRA, CFSR and ERA-Interim. Based on comparisons with the radiosonde profiles, the reanalyses as a group have positive cold-season humidity and temperature biases below the 850 hPa level and consequently do not capture observed low-level humidity and temperature inversions. MERRA has the smallest biases. Trends in column-integrated (surface to 500 hPa) water vapor (precipitable water) computed using data from the radiosondes and from the three modern reanalyses at the radiosonde locations are mostly positive, but magnitudes and statistical significance vary widely between sites and seasons. Positive trends in precipitable water from MERRA, CFSR and ERA-Interim, largest in summer and early autumn, dominate the northern North Atlantic, including the Greenland, Norwegian and Barents seas, the Canadian Arctic Archipelago and (on the Pacific side) the Beaufort and Chukchi seas. This pattern is linked to positive anomalies in air and sea surface temperature and negative anomalies in end-of-summer sea ice extent. Trends from ERA-Interim are weaker than those from either MERRA or CFSR. As assessed for polar cap averages (the region north of 70°N), MERRA, CFSR and ERA-Interim all show increasing surface-500 hPa precipitable over the analysis period encompassing most months, consistent with increases in 850 hPa air temperature and 850 hPa specific humidity. Data from all of the reanalyses point to strong interannual and decadal variability. The MERRA record in particular shows evidence of artifacts likely introduced by changes in assimilation data streams. A focus on the most recent decade (2001–2010) reveals large differences between the three reanalyses in the vertical structure of specific humidity and temperature anomalies.
Citation: Serreze, M. C., A. P. Barrett, and J. Stroeve (2012), Recent changes in tropospheric water vapor over the Arctic as assessed from radiosondes and atmospheric reanalyses, J. Geophys. Res., 117, D10104, doi:10.1029/2011JD017421. [Full text]

Trends in tropospheric humidity from reanalysis systems – Dessler & Davis (2010) “A recent paper (Paltridge et al., 2009) found that specific humidity in the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis declined between 1973 and 2007, particularly in the tropical mid and upper troposphere, the region that plays the key role in the water vapor feedback. If borne out, this result suggests potential problems in the consensus view of a positive water vapor feedback. Here we consider whether this result holds in other reanalyses and what time scale of climate fluctuation is associated with the negative specific humidity trends. The five reanalyses analyzed here (the older NCEP/NCAR and ERA40 reanalyses and the more modern Japanese Reanalysis (JRA), Modern Era Retrospective-Analysis for Research and Applications (MERRA), and European Centre for Medium-Range Weather Forecasts (ECMWF)-interim reanalyses) unanimously agree that specific humidity generally increases in response to short-term climate variations (e.g., El Niño). In response to decadal climate fluctuations, the NCEP/NCAR reanalysis is unique in showing decreases in tropical mid and upper tropospheric specific humidity as the climate warms. All of the other reanalyses show that decadal warming is accompanied by increases in mid and upper tropospheric specific humidity. We conclude from this that it is doubtful that these negative long-term specific humidity trends in the NCEP/NCAR reanalysis are realistic for several reasons. First, the newer reanalyses include improvements specifically designed to increase the fidelity of long-term trends in their parameters, so the positive trends found there should be more reliable than in the older reanalyses. Second, all of the reanalyses except the NCEP/NCAR assimilate satellite radiances rather than being solely dependent on radiosonde humidity measurements to constrain upper tropospheric humidity. Third, the NCEP/NCAR reanalysis exhibits a large bias in tropical upper tropospheric specific humidity. And finally, we point out that there exists no theoretical support for having a positive short-term water vapor feedback and a negative long-term one.” Dessler, A. E., and S. M. Davis (2010), J. Geophys. Res., 115, D19127, doi:10.1029/2010JD014192. [Full text]

Trends in middle- and upper-level tropospheric humidity from NCEP reanalysis data – Paltridge et al. (2009) “The National Centers for Environmental Prediction (NCEP) reanalysis data on tropospheric humidity are examined for the period 1973 to 2007. It is accepted that radiosonde-derived humidity data must be treated with great caution, particularly at altitudes above the 500 hPa pressure level. With that caveat, the face-value 35-year trend in zonal-average annual-average specific humidity q is significantly negative at all altitudes above 850 hPa (roughly the top of the convective boundary layer) in the tropics and southern midlatitudes and at altitudes above 600 hPa in the northern midlatitudes. It is significantly positive below 850 hPa in all three zones, as might be expected in a mixed layer with rising temperatures over a moist surface. The results are qualitatively consistent with trends in NCEP atmospheric temperatures (which must also be treated with great caution) that show an increase in the stability of the convective boundary layer as the global temperature has risen over the period. The upper-level negative trends in q are inconsistent with climate-model calculations and are largely (but not completely) inconsistent with satellite data. Water vapor feedback in climate models is positive mainly because of their roughly constant relative humidity (i.e., increasing q) in the mid-to-upper troposphere as the planet warms. Negative trends in q as found in the NCEP data would imply that long-term water vapor feedback is negative—that it would reduce rather than amplify the response of the climate system to external forcing such as that from increasing atmospheric CO2. In this context, it is important to establish what (if any) aspects of the observed trends survive detailed examination of the impact of past changes of radiosonde instrumentation and protocol within the various international networks.” Garth Paltridge, Albert Arking and Michael Pook, Theoretical and Applied Climatology, Volume 98, Numbers 3-4, 351-359, DOI: 10.1007/s00704-009-0117-x. [Full text]

Estimates of the Water Vapor Climate Feedback during El Niño–Southern Oscillation – Dessler & Wong (2009) “The strength of the water vapor feedback has been estimated by analyzing the changes in tropospheric specific humidity during El Niño–Southern Oscillation (ENSO) cycles. This analysis is done in climate models driven by observed sea surface temperatures [Atmospheric Model Intercomparison Project (AMIP) runs], preindustrial runs of fully coupled climate models, and in two reanalysis products, the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) and the NASA Modern Era Retrospective-Analysis for Research and Applications (MERRA). The water vapor feedback during ENSO-driven climate variations in the AMIP models ranges from 1.9 to 3.7 W m⁻² K⁻¹, in the control runs it ranges from 1.4 to 3.9 W m⁻² K⁻¹, and in the ERA-40 and MERRA it is 3.7 and 4.7 W m⁻² K⁻¹, respectively.”

Water-vapor climate feedback inferred from climate fluctuations, 2003–2008 – Dessler et al. (2008) “Between 2003 and 2008, the global-average surface temperature of the Earth varied by 0.6°C. We analyze here the response of tropospheric water vapor to these variations. Height-resolved measurements of specific humidity (q) and relative humidity (RH) are obtained from NASA’s satelliteborne Atmospheric Infrared Sounder (AIRS). … The water-vapor feedback implied by these observations is strongly positive, with an average magnitude of [lambda]q = 2.04 W/m²/K, similar to that simulated by climate models.” [Full text]

Observed and simulated seasonal co-variations of outgoing longwave radiation spectrum and surface temperature – Huang & Ramaswamy (2008) “We analyze the seasonal variations of Outgoing Longwave Radiation (OLR) accompanying the variations in sea surface temperature (SST) from satellite observations and model simulations, focusing on the tropical oceans where the two quantities are strikingly anti-correlated. A spectral perspective of this “super-greenhouse effect” is provided, which demonstrates the roles of water vapor line and continuum absorptions at different altitudes and the influences due to clouds.” [Full text]

Observed and Simulated Upper-Tropospheric Water Vapor Feedback – Gettelman & Fu (2008) “Satellite measurements from the Atmospheric Infrared Sounder (AIRS) in the upper troposphere over 4.5 yr are used to assess the covariation of upper-tropospheric humidity and temperature with surface temperatures, which can be used to constrain the upper-tropospheric moistening due to the water vapor feedback. … Results indicate that the upper troposphere maintains nearly constant relative humidity for observed perturbations to ocean surface temperatures over the observed period, with increases in temperature ~ 1.5 times the changes at the surface, and corresponding increases in water vapor (specific humidity) of 10%–25% °C⁻¹. Increases in water vapor are largest at pressures below 400 hPa, but they have a double peak structure. Simulations reproduce these changes quantitatively and qualitatively.” [Full text]

Identification of human-induced changes in atmospheric moisture content – Santer et al. (2007) “Data from the satellite-based Special Sensor Microwave Imager (SSM/I) show that the total atmospheric moisture content over oceans has increased by 0.41 kg/m² per decade since 1988. … In a formal detection and attribution analysis using the pooled results from 22 different climate models, the simulated “fingerprint” pattern of anthropogenically caused changes in water vapor is identifiable with high statistical confidence in the SSM/I data. Experiments in which forcing factors are varied individually suggest that this fingerprint “match” is primarily due to human-caused increases in greenhouse gases and not to solar forcing or recovery from the eruption of Mount Pinatubo.” [Full text] [Supporting information]

How Much More Rain Will Global Warming Bring? – Wentz et al. (2007) “Climate models and satellite observations both indicate that the total amount of water in the atmosphere will increase at a rate of 7% per kelvin of surface warming. … Rather, the observations suggest that precipitation and total atmospheric water have increased at about the same rate over the past two decades.” [Full text]

Enhanced positive water vapor feedback associated with tropical deep convection: New evidence from Aura MLS – Su et al. (2006) “Recent simultaneous observations of upper tropospheric (UT) water vapor and cloud ice from the Microwave Limb Sounder (MLS) on the Aura satellite provide new evidence for tropical convective influence on UT water vapor and its associated greenhouse effect. … The moistening of the upper troposphere by deep convection leads to an enhanced positive water vapor feedback, about 3 times that implied solely by thermodynamics. Over tropical oceans when SST greater than ∼300 K, the ‘convective UT water vapor feedback’ inferred from the MLS observations contributes approximately 65% of the sensitivity of the clear-sky greenhouse parameter to SST.” [Full text]

The Radiative Signature of Upper Tropospheric Moistening – Soden et al. (2005) “Climate models predict that the concentration of water vapor in the upper troposphere could double by the end of the century as a result of increases in greenhouse gases. … We use satellite measurements to highlight a distinct radiative signature of upper tropospheric moistening over the period 1982 to 2004. The observed moistening is accurately captured by climate model simulations and lends further credence to model projections of future global warming.” [Full text]

Anthropogenic greenhouse forcing and strong water vapor feedback increase temperature in Europe – Philipona et al. (2005) “Surface radiation measurements in central Europe manifest anthropogenic greenhouse forcing and strong water vapor feedback, enhancing the forcing and temperature rise by about a factor of three.”

Trends and variability in column-integrated atmospheric water vapor – Trenberth et al. (2005) “An analysis and evaluation has been performed of global datasets on column-integrated water vapor (precipitable water). … The evidence from SSM/I for the global ocean suggests that recent trends in precipitable water are generally positive and, for 1988 through 2003, average 0.40±0.09 mm per decade or 1.3±0.3% per decade for the ocean as a whole, where the error bars are 95% confidence intervals. Over the oceans, the precipitable water variability relates very strongly to changes in SSTs, both in terms of spatial structure of trends and temporal variability (with a regression coefficient for 30°N–30°S of 7.8% K⁻¹) and is consistent with the assumption of fairly constant relative humidity.” [Full text]

Quantifying the water vapour feedback associated with post-Pinatubo global cooling – Forster & Collins (2004) “In this work we employ observations of water vapour changes, together with detailed radiative calculations to estimate the water vapour feedback for the case of the Mt. Pinatubo eruption. … The observed estimates are consistent with that found in the climate model,… Variability, both in the observed value and in the climate model’s feedback parameter, between different ensemble members, suggests that the long-term water vapour feedback associated with global climate change could still be a factor of 2 or 3 different than the mean observed value found here and the model water vapour feedback could be quite different from this value; although a small water vapour feedback appears unlikely.” [Full text]

Water Vapor Feedback in the Tropical Upper Troposphere: Model Results and Observations – Minschwaner & Dessler (2004) “These changes in upper-tropospheric humidity with respect to surface temperature are consistent with observed interannual variations in relative humidity and water vapor mixing ratio near 215 mb as measured by the Microwave Limb Sounder and the Halogen Occultation Experiment. The analysis suggests that models that maintain a fixed relative humidity above 250 mb are likely overestimating the contribution made by these levels to the water vapor feedback.” [Full text]

Global Cooling After the Eruption of Mount Pinatubo: A Test of Climate Feedback by Water Vapor – Soden et al. (2002) “We use the global cooling and drying of the atmosphere that was observed after the eruption of Mount Pinatubo to test model predictions of the climate feedback from water vapor. …. Then, by comparing model simulations with and without water vapor feedback, we demonstrate the importance of the atmospheric drying in amplifying the temperature change and show that, without the strong positive feedback from water vapor, the model is unable to reproduce the observed cooling. These results provide quantitative evidence of the reliability of water vapor feedback in current climate models, which is crucial to their use for global warming projections.” [Full text]

Precise climate monitoring using complementary satellite data sets – Wentz & Schabel (2000) “We find a strong association between sea surface temperature, lower-tropospheric air temperature and total column water-vapour content over large oceanic regions on both time scales. This lends observational support to the idea of a constant relative humidity model having a moist adiabatic lapse rate. On the decadal timescale, the combination of data sets shows a consistent warming and moistening trend of the marine atmosphere for 1987–1998.” [Full text]

Water vapor feedback and global warming – Held & Soden (2000) A review paper. “In this review, we describe the background behind the prevailing view on water vapor feedback and some of the arguments raised by its critics, and attempt to explain why these arguments have not modified the consensus within the climate research community.” [Full text]

Water Vapor, Surface Temperature, and the Greenhouse Effect—A Statistical Analysis of Tropical-Mean Data – Yang & Tung (1998) “Water vapor feedback is one of the important factors that determine the response of the atmosphere to surface warming. To take into account the compensating drying effects in downdraft regions, averaging over the whole Tropics is necessary. However, this operation drastically reduces the number of degrees of freedom and raises questions concerning the statistical significance of any correlative results obtained using observational data. A more involved statistical analysis is performed here, using multiple datasets, including the global water vapor datasets of Special Sensor for Microwave/Imaging (column water), upper-tropospheric relative humidity, the Television Infrared Observational Satellite Operational Vertical Sounder retrieved upper-tropospheric specific humidity, and the surface temperature data from the National Centers for Environmental Prediction–National Center for Atmospheric Research Reanalysis dataset. The tropical-mean correlations between relative humidity and surface temperature cannot be established, but those between specific humidity and the surface temperature are found to be positive and shown to be statistically significant. This conclusion holds even when the averaging is done on the natural logarithm of the upper-tropospheric water vapor content. The effect on the tropical-mean outgoing longwave radiation is also discussed.” Yang, Hu, Ka Kit Tung, 1998: Water Vapor, Surface Temperature, and the Greenhouse Effect—A Statistical Analysis of Tropical-Mean Data. J. Climate, 11, 2686–2697. doi: http://dx.doi.org/10.1175/1520-0442(1998)0112.0.CO;2. [Full text]

Water vapor feedback over the Arctic Ocean – Curry et al. (1995) “Results of this study indicate that water vapor feedback over the Arctic Ocean is substantially more complex than in other regions because of the relative lack of convective coupling between the surface and the atmosphere and the different thermodynamic and radiative environment in the Arctic. In particular, the effect of water vapor on the net flux of radiation is complicated by low temperatures, low amounts of water vapor, and the presence of temperature and humidity inversions. During winter a “hyper” water vapor feedback arises from the control of ice saturation on the lower tropospheric humidity and a water vapor “window” in the rotation band at low atmospheric humidities.” Curry, J. A., J. L. Schramm, M. C. Serreze, and E. E. Ebert (1995), Water vapor feedback over the Arctic Ocean, J. Geophys. Res., 100(D7), 14,223–14,229, doi:10.1029/95JD00824. [Full text]

Observed dependence of the water vapor and clear-sky greenhouse effect on sea surface temperature: comparison with climate warming experiments – Bony et al. (1995) “One part of the coupling between the surface temperature, the water vapor and the clear-sky greenhouse effect is explained by the dependence of the saturation water vapor pressure on the atmospheric temperature. However, the analysis of observed and simulated fields shows that the coupling is very different according to the type of region under consideration and the type of climate forcing that is applied to the Earth-atmosphere system. This difference, due to the variability of the vertical structure of the atmosphere, is analyzed in detail by considering the temperature lapse rate and the vertical profile of relative humidity. Our results suggest that extrapolating the feedbacks inferred from seasonal and short-term interannual climate variability to longer-term climate changes requires great caution.” Sandrine Bony, Jean-Philippe Duvel and Hervé Trent, Climate Dynamics, Volume 11, Number 5, 307-320, DOI: 10.1007/BF00211682.

Positive water vapour feedback in climate models confirmed by satellite data – Rind et al. (1991) “CHIEFamong the mechanisms thought to amplify the global climate response to increased concentrations of trace gases is the atmospheric water vapour feedback. As the oceans and atmosphere warm, there is increased evaporation, and it has been generally thought that the additional moisture then adds to the greenhouse effect by trapping more infrared radiation. Recently, it has been suggested that general circulation models used for evaluating climate change overestimate this response, and that increased convection in a warmer climate would actually dry the middle and upper troposphere by means of associated compensatory subsidence. We use some new satellite-generated water vapour data to investigate this question. From a comparison of summer and winter moisture values in regions of the middle and upper troposphere that have previously been difficult to observe with confidence, we find that, as the hemispheres warm, increased convection leads to increased water vapour above 500 mbar in approximate quantitative agreement with the results from current climate models. The same conclusion is reached by comparing the tropical western and eastern Pacific regions. Thus, we conclude that the water vapour feedback is not overestimated in models and should amplify the climate response to increased trace-gas concentrations.” D. Rind, E.-W. Chiou, W. Chu, J. Larsen, S. Oltmans, J. Lerner, M. P. McCormkk & L. McMaster, Nature 349, 500 – 503 (07 February 1991); doi:10.1038/349500a0.

Observational determination of the greenhouse effect – Raval & Ramanathan (1989) “Satellite measurements are used to quantify the atmospheric greenhouse effect, defined here as the infrared radiation energy trapped by atmospheric gases and clouds. The greenhouse effect is found to increase significantly with sea surface temperature. The rate of increase gives compelling evidence for the positive feedback between surface temperature, water vapour and the green-house effect; the magnitude of the feedback is consistent with that predicted by climate models. This study demonstrates an effective method for directly monitoring, from space, future changes in the greenhouse effect.” A. Raval & V. Ramanathan, Nature 342, 758 – 761 (14 December 1989); doi:10.1038/342758a0.