Trends in Tropospheric Water Vapor

[Snow_Miser]

Observations indicate that as the Earth has warmed, Water Vapor has increased at the surface, and in the troposphere. There was discussion going on about this on another part of the forum, but I think it's more appropriate for this area of the board.

 

http://www.sciencemag.org/content/310/5749/841

 

http://onlinelibrary.wiley.com/doi/10.1029/2010JD014192/abstract

 

http://journals.ametsoc.org/doi/abs/10.1175/2010JCLI3816.1

 

http://www.sciencemag.org/content/317/5835/233.abstract

 

http://onlinelibrary.wiley.com/doi/10.1029/2005GL025505/abstract

 

http://onlinelibrary.wiley.com/doi/10.1029/2005GL023624/abstract

 

The NCEP/NCAR reanalysis was not designed to measure changes in Water Vapor, and neither was the NVAP. The NVAP was designed to measure the spatial distribution of humidity. 

[Isotherm]

If one examines trends in specific humidity in the mid levels of the troposphere over the past 30 years, there's been a noticeable decrease globally (specific humidity is the ratio of water vapor content to the total air content on a mass basis).

 

1980s into the middle 90s:

 

 

 

2000s through 2013:

 

[Isotherm]

Specific humidity at the 300mb level has decreased with respect to normal from the 1980s to present.

 

 

 

 

[Snow_Miser]

Tom, that's using the NCEP Reanalysis data though, which is a huge anomaly with regard to the trends in upper tropospheric specific humidity when compared to other reanalyses.

 

http://onlinelibrary.wiley.com/doi/10.1029/2010JD014192/abstract

 

 

[Isotherm]

I see what you're saying; there are potential limitations. However, I wouldn't be so quick to write off the radiosonde derived data as inaccurate.

 

Take a look at the analysis / conclusion of the following scientific article when you get a chance. The satellite derived measurements from models could be more accurate, but it's also possible the radiosonde data might be detecting something unseen by satellites. A more thorough examination needs to be conducted in terms of deciphering the accuracy of these humidity measurements.

 

http://link.springer.com/article/10.1007%2Fs00704-009-0117-x

[Snow_Miser]

The NCEP Reanalysis is the only dataset showing a short term positive water vapor feedback while it shows a long term negative water vapor feedback according to the paper I posted above. That is highly implausible, and reason to be skeptical of the NCEP reanalysis.

[Isotherm]

The NCEP Reanalysis is the only dataset showing a short term positive water vapor feedback while it shows a long term negative water vapor feedback according to the paper I posted above. That is highly implausible, and reason to be skeptical of the NCEP reanalysis.

 

 

You can copy/paste the article's title into google to get it for free. Here's the conclusion from the one I posted. There is reason to refrain from completely writing off these radiosonde measurements.

 

The question is why is it implausible? Playing devil's advocate here. While the other datasets disagree, there is also a possibility that the satellite derived measurements for humidity could have issues.

 

"It is of course possible that the observed humidity trends from the NCEP data are simply the result of problems with the instrumentation and operation of the global radiosonde network from which the data are derived. The potential for such problems needs to be examined in detail in an effort rather similar to the effort now devoted to abstracting real surface temperature trends from the face-value data from individual stations of the interna- tional meteorological networks. As recommended by Elliot and Gaffen (1991) in their original study of the US radiosonde network, there needs to be a detailed examination of how radiosonde instrumentation, operating procedures, and recording practices of all nations have changed over the years and of how these changes may have impacted on the humidity data. In the meantime, it is important that the trends of water vapor shown by the NCEP data for the middle and upper troposphere should not be “written off” simply on the basis that they are not supported by climate models—or indeed on the basis that they are not supported by the few relevant satellite measurements. There are still many problems associated with satellite retrieval of the humidity informa- tion pertaining to a particular level of the atmosphere— particularly in the upper troposphere. Basically, this is because an individual radiometric measurement is a complicated function not only of temperature and humidity (and perhaps of cloud cover because “cloud clearing” algorithms are not perfect), but is also a function of the vertical distribution of those variables over considerable depths of atmosphere. It is difficult to assign a trend in such measurements to an individual cause. Since balloon data is the only alternative source of information on the past behavior of the middle and upper tropospheric humidity and since that behavior is the dominant control on water vapor feedback, it is important that as much information as possible be retrieved from within the “noise” of the potential errors."

 

[Snow_Miser]

The question is why is it implausible? Playing devil's advocate here. While the other datasets disagree, there is also a possibility that the satellite derived measurements for humidity could have issues.

 

 

It's one thing for only satellite measurements to disagree with the NCEP Reanalysis. However, all of the other reanalyses disagree with the NCEP trend as well, making it highly unlikely that the NCEP trend is real. In addition there are other indicators as well that argue against a strong negative water vapor feedback like the NCEP reanalysis shows. Dessler and Davis explain why it is highly unlikely that the short term feedback can be positive while the long term feedback can be negative in their paper. 

 

 

Past paleoclimate change is also inconsistent with a negative water vapor feedback, since a very low climate sensitivity cannot explain the huge variations in temperature over the past 800,000 years.

 

http://epic.awi.de/19079/1/Khl2008d.pdf

 

 

[bluewave]

These are the most recent studies that I can find on the subject:

 

http://www.sciencedaily.com/releases/2014/02/140202111055.htm

 

 

Can naturally occurring processes selectively buffer the full brunt of global warming caused by greenhouse gas emissions resulting from human activities?

 

Yes, find researchers from the Hebrew University of Jerusalem, Johns Hopkins University in the US and NASA's Goddard Space Flight Center.

As the globe warms, ocean temperatures rise, leading to increased water vapor escaping into the atmosphere. Water vapor is the most important greenhouse gas, and its impact on climate is amplified in the stratosphere.

In a detailed study, the researchers from the three institutions examined the causes of changes in the temperatures and water vapor in the tropical tropopause layer (TTL). The TTL is a critical region of our atmosphere with characteristics of both the troposphere below and the stratosphere above.

The TTL can have significant influences on both atmospheric chemistry and climate, as its temperature determines how much water vapor can enter the stratosphere. Therefore, understanding any changes in the temperature of the TTL and what might be causing them is an important scientific question of significant societal relevance, say the researchers.

The Israeli and US scientists used measurements from satellite observations and output from chemistry-climate models to understand recent temperature trends in the TTL. Temperature measurements show where significant changes have taken place since 1979.

The satellite observations have shown that warming of the tropical Indian Ocean and tropical Western Pacific Ocean -- with resulting increased precipitation and water vapor there -- causes the opposite effect of cooling in the TTL region above the warming sea surface. Once the TTL cools, less water vapor is present in the TTL and also above in the stratosphere.

Since water vapor is a very strong greenhouse gas, this effect leads to a negative feedback on climate change. That is, the increase in water vapor due to enhanced evaporation from the warming oceans is confined to the near- surface area, while the stratosphere becomes drier. Hence, this effect may actually slightly weaken the more dire forecasted aspects of an increasing warming of our climate, the scientists say.

The researchers are Dr. Chaim Garfinkel of the Fredy and Nadine Herrmann Institute of Earth Sciences at the Hebrew University and formerly of Johns Hopkins University, Dr. D. W. Waugh and Dr. L. Wang of Johns Hopkins, and Dr. L. D. Oman and Dr. M. M. Hurwitz of the Goddard Space Flight Center. Their findings have been published in the Journal of Geophysical Research: Atmospheres, and the research was also highlighted in Nature Climate Change.

 

Story Source:

The above story is based on materials provided by Hebrew University of Jerusalem.Note: Materials may be edited for content and length.

Journal References:

1. C. I. Garfinkel, D. W. Waugh, L. D. Oman, L. Wang, M. M. Hurwitz. Temperature trends in the tropical upper troposphere and lower stratosphere: Connections with sea surface temperatures and implications for water vapor and ozone.Journal of Geophysical Research: Atmospheres, 2013; 118 (17): 9658 DOI:10.1002/jgrd.50772
2. Qiang Fu. Ocean–atmosphere interactions: Bottom up in the tropics. Nature Climate Change, 2013; 3 (11): 957 DOI: 10.1038/nclimate2039

 

 

http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50772/abstract

 

] Satellite observations and chemistry-climate model experiments are used to understand the zonal structure of tropical lower stratospheric temperature, water vapor, and ozone trends. The warming in the tropical upper troposphere over the past 30 years is strongest near the Indo-Pacific warm pool, while the warming trend in the western and central Pacific is much weaker. In the lower stratosphere, these trends are reversed: the historical cooling trend is strongest over the Indo-Pacific warm pool and is weakest in the western and central Pacific. These zonal variations are stronger than the zonal-mean response in boreal winter. Targeted experiments with a chemistry-climate model are used to demonstrate that sea surface temperature (hereafter SST) trends are driving the zonal asymmetry in upper tropospheric and lower stratospheric tropical temperature trends. Warming SSTs in the Indian Ocean and in the warm pool region have led to enhanced moist heating in the upper troposphere, and in turn to a Gill-like response that extends into the lower stratosphere. The anomalous circulation has led to zonal structure in the ozone and water vapor trends near the tropopause, and subsequently to less water vapor entering the stratosphere. The radiative impact of these changes in trace gases is smaller than the direct impact of the moist heating. Projected future SSTs appear to drive a temperature and water vapor response whose zonal structure is similar to the historical response. In the lower stratosphere, the changes in water vapor and temperature due to projected future SSTs are of similar strength to, though slightly weaker than, that due directly to projected future CO₂, ozone, and methane.

 

http://www.nature.com/nclimate/journal/v3/n11/full/nclimate2039.html

 

 

A study reveals that recent warming in the Indian Ocean and in the Pacific 'warm pool' has caused a cooling near the top of the tropical troposphere above, leading to less water vapour entering the stratosphere.

 

http://www.atmos.washington.edu/~qfu/Publications/ncc.fu.2013.pdf

 

 

Water vapour in the stratosphere is a greenhouse gas. It is constrained from entering the

stratosphere in the tropics by the thermal boundary between the stratosphere and troposphere1 — the tropical tropopause, the coldest point in the lower atmosphere. Cold-point temperatures at the tropical tropopause (Fig. 1a) have important implications for both stratospheric chemistry2 and global climate change3. The importance of the spatial distribution of temperature (Fig. 1b) is well recognized,

as the temperature minimum is relevant to cloud formation and subsequent dehydration through atmospheric circulation4. In the boreal winter, for example, the lowest cold-point temperatures over the warm pool in the tropical western Pacific govern the amount of water vapour that enters the stratosphere5. It is thus critically important to understand how the zonal (longitudinal) structure of the tropical cold-point temperature would respond

to global warming. Now, reporting in thJournal of Geophysical Research, Garfinkel and co-workers6 find that the warming in the tropical upper troposphere over the past 30 years has been strongest over the Indo-Pacific warm pool, where cooling near the tropopause has been strongest. They suggest that warming in the Indian Ocean and the Pacific warm pool has led to zonal asymmetry in atmospheric temperature trends, and that such trends may continue in the future.

Temperatures near the tropical tropopause are determined by a complex combination of stratospheric (top-down) and tropospheric (bottom-up) processes7. The zonal structures at 100 hPa (Fig.1b) closely resemble the mean pattern of the equatorial planetary waves — large-scale perturbations of the atmospheric dynamical structure. These are driven by massive convection over the Indo-Pacific warm pool8, with the lowest temperatures and largest cirrus cloud fractions over the western Pacific and Maritime Continent (which includes the islands of Indonesia,

 

New Guinea and Malaysia, and the surrounding shallow seas)9. The signature of the equatorial planetary waves is also evident in the temperature variability over intraseasonal to interannual timescales9. The responses of temperature structures at 100 and 250 hPa are reversed in sign because the maximum amplitude of equatorial planetary waves with opposite phases occurs at these two levels. The temperatures and cloud fraction near the tropical tropopause are also strongly modulated by extra-tropical stratospheric waves. These drive the Brewer–Dobson circulation (BDC) — a large-scale latitudinal circulation in the stratosphere with air rising across the tropical tropopause, moving polewards and sinking towards the extra-tropical troposphere — which is particularly evident in their seasonal cycles9–11 (Fig.1c). In contrast to the equatorial planetary waves, the extra-tropical stratospheric waves are associated with zonally symmetric temperature anomalies in the lower stratosphere.Changes in the cold-point temperature would be expected to alter the amount of water vapour entering the stratosphere. The model simulation shows that less water vapour enters the stratosphere as a result of the cooling near the cold-point tropopause over the Indo-Pacific warm pool, driven

by the increased SST there6. However, their work does not explain the changes in lower-stratospheric water vapour content that have been observed in the past few decades. This could partly be because other factors — such as the change of the BDC13 — would also affect the cold point- temperatures (Fig.1c). In addition, the impact of the equatorial planetary waves and upward motion associated with the BDC on tropical thin cirrus clouds need to be investigated, and could have a warming feedback to the climate system14.

Past increases in the Indian Ocean SST have been directly linked to the global warming15 and may continue in the future. Garfinkel et al. show that there is a cooling near the tropical tropopause over the Indo-Pacific warm-pool region and thus less water vapour entering the stratosphere. This response to the SST change is due to the enhanced equatorial planetary waves. A decrease in stratospheric water vapour may lead to a slight cooling of global surface temperatures. This study demonstrates

that it is of paramount importance to pay attention to, and understand the cause of, the patterns of SST changes that are related to global warming. ❐

 

Temperatures in the lower stratosphere and upper troposphere have been changing during the past few decades. Although many studies have focused on the zonal mean component of temperature trends12, Garfinkel and co-workers concentrate on the zonally asymmetric component, and in particular on trends near the coldest point in the tropopause region. Satellite observations are used to document the zonal structure of the temperature trends, which is strongest in January, February and March. The lower stratosphere over the warm-pool region is found to have cooled more than the zonal mean, whereas the central and eastern Pacific have cooled less. However, the structure of the upper tropospheric trends is opposite in phase, with the largest warming over the warm pool. All atmospheric chemistry– climate models that are driven by observed sea surface temperature (SST) and external forcings are shown to accurately capture the observed zonal variations of these trends.

958To understand the cause of the zonal structure of atmospheric temperature trends in January–March, Garfinkel et al. use an atmospheric chemistry–climate model with observed SST as the only forcing that varies over time. The simulated structure of temperature trends is similar to those from more comprehensive model integrations and satellite observations, indicating that the SST changes have driven the zonal asymmetry. An increase in SST over the Indian Ocean and the

far western Pacific enhances the deep convection and thus the latent heat release in the upper troposphere that increases the amplitude of the equatorial planetary waves. This leads to warming near 250 hPa, but cooling near 100 hPa, over the Indo-Pacific warm pool. Their study represents the first effort to document and understand the cause of zonal structures in tropical atmospheric temperature trends since 1980.

[Snow_Miser]

Very interesting research bluewave. I know some have attributed the recent hiatus period at the surface to changes in stratospheric water vapor concentrations, though this is a decadal effect, and equally adds and subtracts to the long term warming trend.

 

http://www.sciencemag.org/content/327/5970/1219.abstract

 

 

[bluewave]

Very interesting research bluewave. I know some have attributed the recent hiatus period at the surface to changes in stratospheric water vapor concentrations, though this is a decadal effect, and equally adds and subtracts to the long term warming trend.

 

http://www.sciencemag.org/content/327/5970/1219.abstract

 

solomon 2010.gif

 

solomon 2010 2.gif

 

It may be that the Pacific climate shift after the 97-98 Super El Nino is the primary driver

of the hiatus. But this recent Nature commentary also asks some good questions.

 

http://www.see.ed.ac.uk/~shs/Climate%20change/Climate%20model%20results/over%20estimate.pdf