bob326

I know I've already asked several questions on the water vapor feedback before, and I've personally found the evidence of a positive WV feedback quite compelling for some time now, but a paper was recently accepted to JGR atmos which effectively rebuts the Paltridge 2009 paper on humidity trends from the NCEP reanalysis:http://www.gerkynet.com/meteo/paltrigde08.pdf

P09 purported to find negative trends in specific humidity above 850 hPa, meaning a negative water vapor feedback. However, in their new paper "Trends in tropospheric humidity from reanalysis systems", Dessler et al. study other, more modern reanalyses, and discuss the many issues with the NCEP reanalysis data. They conclude:

"P09 calculated trends of specific humidity with time over the past few decades in the NCEP/NCAR reanalysis and found that the specific humidity, in particular in the tropical mid and upper troposphere, was decreasing. They concluded that this potentially cast doubt on the general consensus that the global water vapor feedback was strongly positive [e.g., Dessler and Sherwood, 2009]. We have extended the analysis of P09 by addressing two crucial issues, namely whether other reanalyses reproduce this and what time scale of climate fluctuation is associated with the negative water vapor trends. We have analyzed five different reanalyses, including the NCEP/NCAR

reanalysis. Rather than calculate trends with time, as P09 did, we instead regressed atmospheric humidity against surface temperatures for the tropics and mid-latitudes. In response to short time-scale climate variations (e.g., ENSO cycles), there is good agreement among the reanalyses on the connection between atmospheric water vapor and surface temperature: specific humidity increases with increasing surface temperature in the tropical mid and upper troposphere, as well as almost everywhere else. This is in good agreement with both theory and observation.

The picture is different when long-term climate variations are considered. The NCEP/NCAR reanalysis shows decreases in specific humidity in the tropical mid and upper troposphere with increasing tropical surface temperature. Such behavior implies that the water vapor feedback in response to long-term climate fluctuations would be negative, and would therefore have a different sign depending on the time-scale of the climate variation. No theory or model supports this, nor do analyses of long-term water vapor measurements or paleoclimate data.

In addition, the other reanayses, including the newest reanalyses (ERA-interim and MERRA), which were specifically designed to better reproduce long-term trends, do not manifest this behavior. Finally, we pointed out that the NCEP/NCAR reanalysis contains large biases in the tropical mid and upper tropospheric specific humidity, and does not reproduce the moistening of the tropical upper troposphere during the strong 1998 El Nino, further casting doubt on that reanalysis’ water vapor fields in that region.

Based on the available evidence, it is our judgment that negative trends in the tropical mid and upper troposphere in response to long-term climate change are spurious. This is clearly the most parsimonious explanation, and it is in accord with virtually all of the independent lines of evidence (models, observations, theory, newer reanalyses)."

Add this to the studies using satellite data; e.g.

Soden 2005: http://www.gfy.ku.dk/~kaas/forc&feedb2008/Articles...

Dessler and Zhang 2008: http://www.agu.org/pubs/crossref/2008/2008GL035333...

And it looks like the case for a strong and positive water vapor feedback is becoming harder and harder to deny.

Thoughts? Any other useful references on the topic?

In his most recent paper (2010), "Can thin cirrus clouds in the tropics provide a solution to the Faint Young Sun paradox?", Richard Lindzen notes the following

"Recent studies suggest that the strong positive water vapor feedback implied by the invariance of relative humidity may be within reasonable agreement with satellite observations [Dessler et al., 2008], even though the vertical profile of relative humidity is not strictly conserved."

By Dessler 2008, he's referring to:

http://geotest.tamu.edu/userfiles/216/Dessler2008b...

Which studied satellite trends in humidity over the period 2003-2008. They find a strong positive feedback consistent with a constant RH, as predicted by models.

Soden 2005 studied 22 years worth of satellite humidity, and also found roughly constant RH:

http://www.gfy.ku.dk/~kaas/Bornoecourse/Material/s...

On the other hand, we have Paltridge 2009 which uses the NCEP reanalysis and finds not only a decreasing RH, but a decreasing q, and thus, a negative WV feedback.

http://www.springerlink.com/content/m2054qq6126802...

But, as mentioned in the study, the NCEP reanalysis has known problems with model bias, and radiosondes have issues with instrumentation changes and poor ocean coverage.

Now that Lindzen is on board with a strong WV feedback, are any scientists left? Is anyone skeptical of Lindzen's position?

That conclusion being that the climate sensitivity for 2xCO2 is between 2 and 4.5 K? Or at the very least that feedbacks will provide a net amplifying effect?

Lindzen and Spencer's hypothesis sounds great, but an insensitive climate system is *not* compatible with past climatic fluctuations -- the transitions to and from glacial periods, for instance.

If no, why?

Are there any observable phenomena in multidecadal climate that exhibit chaotic behavior? Or can we calculate temperature change from forcings alone without a proper understanding of initial conditions?

...especially if the fluctuations average out to roughly zero over time? This seems to be the crux behind the "It's ocean cycles!" argument and the recent slew of Spencer papers.

There was a recent question that asked about the tropical tropospheric 'hotspot', and someone brought up the Paltridge 2009 paper that purported to show a decrease in specific humidity above 850 hPa:

http://www.gerkynet.com/meteo/paltrigde08.pdf

I'm just wondering what kind of mechanism would allow for increasing T while decreasing q in the longterm. I can understand the argument for a negative trend in RH, but specific humidity?

I should also mention that the NCEP reanalysis is the only dataset that shows decreasing q both globally and in the tropics (IIRC). Both satellites and other reanalyses show differently

http://www.gfy.ku.dk/~kaas/Bornoecourse/Material/s...

http://geotest.tamu.edu/userfiles/229/Dessler_et_a...

http://journals.ametsoc.org/doi/abs/10.1175/2009JC...

This argument should have been put to rest long ago, but I still see it here, so let's try a little though experiment:

Say there is a planet A, with an atmosphere composed a single isothermal layer that--similar to Earth--is transparent to incoming SW radiation and opaque to outgoing LW. The flux density incident at the top of the atmosphere is 1 Wm^-2. What is the flux density incident on the surface of planet A? What happens when we add a second isothermal layer to the atmosphere?

You can assume that the surface and all layers of the atmosphere are in radiative equilibrium.

A particularly popular skeptical answer in another question said the following

"To the article:

'The earth’s climate system is warmed by 35 C due to the emission of downward infrared radiation by greenhouse gases in the atmosphere..'

IMO this is the basic mistake. Earth climate system is warmed by mere existence of the atmosphere (oceans), which keeps and distributes the day (summer) heat."

and

"But if we want to play the 33K game, lets go: Kiehl-Trenberths LW downward flux of 324 W/m2 causes +33K. Calculated increase of 2.4W/m2 (40% on the way to CO2 doubling) is equivalent to 0.24K increase in temperature, with no changes in water vapor or clouds. Doubling gives puny 0,4 K, the same number which Miskolczi or Lindzen came to from different directions."

Can anyone tell me why this is complete nonsense?

http://media.smh.com.au/news-video/national-times/...

Perhaps Monckton is a slightly more eloquent speaker, but in terms of substance, it's pretty clear who won to me (though I'm not a huge fan of Lambert in general).

As an aside, 300,000 ppm? What?

http://answers.yahoo.com/question/index;_ylt=Amf4I...

As a result of "climategate" and the denier's pronouncement that AGW has been "proven" to be a massive hoax, I've been posing a challenge of sorts to deniers:

"Explain to me specifically where QM fails; where thermo is wrong; where fluid dynamics, spectroscopy, atmospheric physics and chemistry got it wrong."

I have yet to receive a reasonable response, and the above link (obviously) is no different.

Does anyone have a good response?

This question has probably been asked before, and I know there have been several questions highlighting the various lines of evidence for AGW that still remain, but we continue to see questions by folks like the good Doctor that act like the UAE hack somehow means the end of climate science.

Specifically, what has changed?

Is QM now wrong? Is thermo a thing of the past? Sure, a few people said some things they shouldn't have, especially related to FOI requests and actions towards "skeptical" scientists, but can anyone here show how any evidence related to AGW has been falsified without resorting to ambiguous wording and context-deficient quotes?

And when will this end?

Dana recently brought up the topic of the water vapor feedback, pointing to the recent Dessler et al study here:

http://www.agu.org/pubs/crossref/2008/2008GL035333...

Here's another article by Dessler on the same subject:

http://geotest.tamu.edu/userfiles/216/dessler09.pd...

And here's Dana's question:

http://answers.yahoo.com/question/index;_ylt=ApDyB...

And yet here is another recent study on the long term trends in tropospheric humidity:

http://www.springerlink.com/content/m2054qq6126802...

Which mentions

"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"

Thoughts?

http://www.guardian.co.uk/environment/2009/feb/11/...

Written by Vicky Pope, head of the climate prediction programme at the Hadley Centre. Like most scientists, she believes that the recent warming has been mostly man-made, but that extreme alarmist comments do no good for the cause.

Thoughts?

http://www.nature.com/ngeo/journal/v1/n11/abs/ngeo...

Of course, as many here on Y!A have pointed out, the warming on Mars is not a convincing argument against human induced warming here on Earth. Martian warming was mostly caused by changes in albedo and dust circulation. This study provides another possible driver.

http://www.independent.co.uk/environment/climate-c...

Even James Hansen was there. He didn't argue that the crew of 6 was innocent, that they hadn't vandalized the power station, just that the threat of GW is so great that breaking the law in the name of "fighting AGW" is surely forgivable. Does this seem ridiculous to anyone else?

Finishing up on Dana's question on the sun here:

http://answers.yahoo.com/question/index;_ylt=AlDL4...

I didn't get a chance to respond to his response, so

"bob326 - Meehl states 'radiative forcing from increasing greenhouse gases is dominant for the response in the late twentieth century' and discusses solar amplified by anthropogenic effects."

Wrong paper. The climate commitment study I was speaking of was:

http://www.sciencemag.org/cgi/content/abstract/307...

And yes, I know Meehl agrees with AGW theory and the study is about GHGs, but if you can think past that you can learn how even fixed forcing agents (meaning the sun in this case) can influence temperatures for centuries to come.

"Also, there is no 30 year solar lag. Thus a significant fraction of the recent warming cannot be blamed on the Sun, even by your own citations."

Of course there is no 30 year solar lag, but that isn't what I was arguing, and if you had read my post you would have understood that. I will repeat what was in my post: After the plateau in solar activity, most of the temperature response should occur in the first few decades, although arguably, that response was delayed by the causes of the midcentury cooling (aerosols, ocean circulations, etc..). All forcing agents, including CO2, have trouble explaining the mid-century cooling without bringing aerosols into the equation, and solar is no different.

Now onto the question: We are starting to find out that solar irradiance varies much less than previously thought (see J Leans earlier work vs. Svalgaard's more recent reconstruction), and yet we are very certain that these small changes in irradiance along with other solar variables can produce large changes in Earth temperatures and climate through a complex set of feedbacks. Much of this process is poorly understood.

So, given our level of understanding, can we be so sure that the sun isn't playing a larger role than the IPCC assigns it?

http://tamino.wordpress.com/

Clearly he is intelligent and has quite a bit of experience with data analysis. He even lets on that he has several papers in peer reviewed journals, but who is he?

http://www.cdc.noaa.gov/people/gilbert.p.compo/Com...

Here is Roger Pielke Sr.'s take on it: http://climatesci.org/2008/07/21/oceanic-influence...

Along with these papers:

http://www.uwm.edu/~aatsonis/2007GL030288.pdf

http://www.springerlink.com/content/j43817g947nq71...

http://www.agu.org/pubs/crossref/2007/2007GL029698...

http://ams.allenpress.com/perlserv/?request=get-ab...

http://www.sciencemag.org/cgi/content/abstract/295...

http://www.nerc-essc.ac.uk/~rpa/PAPERS/olr_grl.pdf

Roy Spencer's presentation (the new paper is to be published

soon):

http://climatesci.org/wp-content/uploads/spencer-p...

Spencer's paper from earlier this year:

http://ams.allenpress.com/perlserv/?request=get-ab...

"the vast numbers of people on yahoo answers who think people can do whatever they want to our planet with no consequence"

That is part of an answer to this question http://answers.yahoo.com/question/index;_ylt=Avc5k...

And I notice that it is a fairly prevalent opinion among "AGWers": that anyone who doubts the "consensus" must hate the environment and believe that nothing we do harms the environment.

I know that this isn't true for me, but I was wondering how many of you "doubters" think this way?