Saturday, March 14, 2009

Troposhpere Temps from Satellites and Surface Temps

In an earlier post I took at look at MM07 versus S09. One of the interesting results was that the rate of post secondary education (PSE) in a country was inversely proportional to the rate of temperature increase in that country. Taking a deeper look I saw that if you take the top quartile of grid points based on PSE from the analysis that the surface warmed more slowly than the troposphere, while in the rest of the grid points the surface warmed much faster than the troposphere. (This is using HadCRUT for the surface and RSS for the troposphere.) I suppose you could shrug this off to coincidence except that according to the Model E data supplied by Dr. Schmidt the troposhpere is supposed to be generally warming faster than the surface everywhere.

Over the 440 grid cells of the analysis the Model E troposphere warmed faster than the surface (.16 degrees per decade versus .14) This contrasts with the measured data from HadCRUT and RSS where the surface warmed faster than the troposphere (.27 versus .23).

Looking at the segment with high PSE we can start with the US. Now I know there has been a lot of sniping about the US temperature network, but I'm guessing that it is really pretty good. Out of the 440 grid points 52 are in the US. For the these grid points the troposhpere is warming faster than the surface (.26 versus .24). There are 85 grid points in the top quartile outside the US. For those points the troposphere is also warming faster than the surface (.21 versus .19).

Now the truth is that this data is very convenient for me to look at because it was already layed out by others, and I haven't looked at any other time periods to confirm that this isn't some kind of fluke.

But I think it is pretty interesting that in the countries that probably have the best surface temperature networks the actual measurements are in line with the theory as proposed by the results of Model E. The conclusion would be that perhaps climate scientists ought to be focused on troposhperic temperatures as measured by satellite, and reduce their dependence on ground based measurements. Switching to satellite measurement seems to be happening elsewhere with a good example being sea level rise.

I should add that they ought to be noticing this type of agreement with models and be pleased with the vindication, but I don't sense that they are. I have a theory as to why.

When the satellite temperatures were first introduced by UAH they were used by climate skeptics to show that there was no warming. In addition Drs. Christy and Spencer aligned themselves to some degree with the skeptics camp. Even though subsequent events have corrected the satellite trends and there now is an independent satelitte measurement from RSS this seems to have put satellite measurements out of favor in this area. This is particularly true for the UAH data.

In fact you can get a hint of this from S09. At one point Dr. Schmidt comments that the differing regression results he got by using RSS versus UAH might be caused by the "higher trend" in RSS. In fact this is uncited and he provides no results to back this up. I think he just assumed it was true, because a quick test of the trends show that for this set of grid cells over this period RSS and UAH have identical average trends. The point being that Dr. Schmidt believed so strongly that of course UAH would show less warming than RSS that he didn't even test the conclusion.

I think it would be quite interesting if the climate modeling community would look at their results relative to the troposhperic measurements from RSS/UAH and deemphasize the surface network. There is plenty of warming in the satellite measurements, and they may be a whole lot more accurate

Follow Up on ERA-Interim from ECMWF

After looking at this post, Ryan Maue suggested that I do a further analysis of humidity trends using the ERA Interim data set of ECMWF. This is the most up to date information, although it covers a much shorter period than the ERA 40 data I used in the earlier analysis. The results are that over the 19 year period from 1989 to 2007 there are no significant trends in specific humidity (q) in this data set. Current theory would say that q should be increasing. Thus between the ERA 40 data, and the ERA Interim data there is no confirmation of the theory, and in fact many of the trends are negative, particularly over the NH mid latitudes, but not significant.

The data for this study is from the ERA interim data set downloaded from the ECMWF servers.

The results can be found here.

Wednesday, March 11, 2009

Humidity Trends from ECMWF

There was an interesting post on Climate Audit about a paper covering trends in atmospheric humidity. The substance of the post was discussing why a paper by Gareth Paltridge and others was rejected by the journal of climate. But I was quite interested to learn that there was long term trend data on humidity.

As most people who follow the issue understand a doubling of CO2 by itself should increase atmospheric temperature about 1 degree C at equilibrium. The big question is what feedback is caused by this temperature increase. The largest feedback is caused by an increase in water vapor as the temperature increases. The theory is that relative humidity (r) should remain constant, which would mean that as temperature increases specific humidity (q) would increase. This means that the total water vapor of the atmosphere would increase causing an increased forcing.

Over time I have seen a few papers which have confirmed that relative humidity is indeed staying constant. But these papers have had a lot of caveats and have covered limited areas and time frames. So I was interested in the paper by Dr. Paltridge which used a re-analysis data set called NCEP covering a 35 year period from 1973 to 2007.

I don't have access to the paper but the summary is that in this data set r decreased over the period in some relevant regions. This would be counter to theory, and interesting.

Ryan Maue, who is a student at Florida State made several comments and here on CA pointing out issues with the Paltridge paper. Essentially the objection is that prior to 1979 the data is based on a small radiosonde network, and that the subsequent data is based on a combination of satellites and radiosondes. He felt that at the minimum the results should be compared to other re-analysis data sets. He chose ECMWF as the best. He even commented that he would take a look himself.

So I thought I would go ahead and see if I could figure out how to download the ECMWF data and do a quick analysis. It turns out to be quite possible.

The ECMWF data covers parts of 46 years, but only 44 complete years from 1958 to 2001. So I downloaded the r and q data for all grid locations for those years. The results have something for everyone I suppose.

For completeness I started out looking at the trends for the entire period and the entire globe. In this case q is only negative at the very highest altitudes above 100hPa. Below 500hPa q is positive. R on the other hand is negative above 400hPa, and positive below 925hPa with the altitudes in between not being significant. Again according to theory the theory the trend in r is supposed to be zero and the trend in q is supposed to be positive.

But I get the impression that the global figure over this time period is not the most interesting. As Mr. Maue points out most of the radiosondes are in a small band in the Northern Hemisphere. So the trends that cover that area are called out both by Dr. Paltridge and By Mr. Maue in a subsequent post.

Looking at the NH results for the entire period q is significantly negative all the way down to 700mb. It only becomes significantly positive at 925hPa. In a result I don't completely understand r is negative above 400hPa and insignificant below that. I would have thought that in a warming atmosphere that if q was negative r would have to be negative as well. In any event the negative q trend over the NH which is where the majority of the real measurements would have been made in this time period seems to be different than theory and in line with the results from NCEP. Note that I tried two definitions of the Northern mid latitudes with no change in results.

In the SH the trends are largely positive for both q and insignificant for r which would be in line with theory. And this is true for the entire mid latitude and tropic region, which has negative r only for the altitudes above 400hPa.

In summary then over the 44 year period the area that shows negative q seems to be the mid latitudes of the Northern Hemisphere. Since the areas outside of the measurement regions are computed using climate models I'm not sure of the relationship of the "real" data to areas where there were no radiosondes.

I took a separate look at the "post satellite" period. Unfortunately this is a very short time in this data set since it ends in 2001 unlike the NCEP data which goes through 2007. The trends were not particularly significant over this period.

The R code for this analysis can be found here.

The data for this post is from ERA-40 and was graciously supplied by the ECMWF data server.

Tuesday, March 3, 2009

IPCC Sea Ice Forecasts

There has been a lot of discussion in recent years of the large drop in Arctic sea ice. People who are particularly concerned about CO2 induced global warming have pointed to this drop as clear current evidence that the effects of warming are accelerating. People who are generally skeptical about CO2 induced global warming have brought up the fact that Antarctic sea ice levels appear to be increasing as a counter argument. It has always seemed logical to me that global sea ice level was probably the most complete measure in this area, but I had read several informal documents that suggested that the Arctic was the true signature test for CO2 induced global warming.

In particular earlier this year a blogger wrote a post noting that global sea ice was at the same level as 1979. This generated a response from "Cryosphere Today." The response was that while the information was correct it was referring to the global trend and not on the Arctic trend. They point out that the reduced sea ice in the Arctic was being compensated for by increased ice in the Antarctic. The response includes the following. "In the context of climate change, GLOBAL sea ice area may not be the most relevant indicator. Almost all global climate models project a decrease in the Northern Hemisphere sea ice area over the next several decades under increasing greenhouse gas scenarios. But, the same model responses of the Southern Hemisphere sea ice are less certain."

I had heard statements like this before, but I had never looked to see what the basis of the statements might be. So I went to the AR4 WG1 report. On page 770 you can find chapter "Changes in Sea Ice Cover." In that section you can find the following. "In 20th and 21st-century simulations, antarctic sea ice cover is projected to decrease more slowly than in the Arctic (Figures 10.13c,d and 10.14)." I have copied figure 10.13 below.

The top two projections are for the Arctic, and the bottom two are for the Antarctic. The black line represents the ensemble mean for the various scenarios and models. What is obvious from looking at this picture is that while the Arctic sea ice is projected to decrease more rapidly, Antarctic sea ice is projected to decrease as well. Not only that but the decrease should have been occurring fairly steadily in the last few decades, and increasing at this point.

In that section, which it is true is quite short, I found no reference to higher uncertainty regarding Antarctic sea ice. The final paragraph of the section just refers to the general uncertainty of projections including the amount of climate change in the polar regions in general.

So what evidence did CT have for their assertion? They link to a single 2005 study discussing a simulation where increased snow fall in the Antarctic tends to preserve sea ice.

So the consensus view as established by the IPCC is that while the Arctic is expected to decline more rapidly we should see declining sea ice at both poles. This means that increased Antarctic sea ice over the last 30 years is not in line with these projections. Does this prove that increasing CO2 does not cause global warming? Not even a little. But it does mean that looking at global sea ice level is relevant, and that focusing exclusively on Arctic sea ice might reasonably be considered cherry picking.