What happens to Steig et al's warming when you divide Antarctica into two distinct climate zones?

A week ago I made this comment to Jeff Id on The Air Vent regarding his reconstruction of the Steig et al Antarctic temperature trends paper. The idea was to treat Antarctica as two distinct climate zones. I should point out that this idea has not been accepted yet, but there are some good reasons to consider it.

As seen in the map above, currently Antarctica is classified per the Köppen climate classification system entirely as EF, or “Ice Cap”. But here is what it might look like if the peninsula was classified differently.

I’ve made some enhancements with inline images and links to my original comment on The Air Vent for WUWT readers:

Jeff, in looking at your output maps above something occurred to me about the climate the Antarctic peninsula.

The biggest problem I see with Antarctica in either yours or Steig’s reconstructions is the treatment of the continent as a single climate zone, when in fact the climate of the peninsula has a significantly different set of temperature and precipitation norms than the majority of the main continent.

Going back to basic climatology one can recall the Köppen climate classification system. Antarctica has been classified as EF

EF =Ice Cap Climate – All twelve months have average temperatures below 0 °C (32°F) There has been some discussion that the Aleutian peninsula might be better served if newly classified as EM (Maritime Polar) This would separate relatively mild marine locations such as Ushuaia, Argentina and the outer Aleutian Islands like Unalaska The climate of Unalaska from the colder, continental climates. The mean annual temperature for Unalaska is about 38 °F (3.4 °C), being about 30°F (−1.1°C) in January and about 52°F (11.1°C) in August. With about 250 rainy days a year.

Contrast that to interior Alaska temperatures which are not moderated by the presence of the sea. Fairbanks for example has an mean annual temperature for Fairbanks is 26.9°F (-2.8°C) and with 106 rainy days.

Using the Unalaska to Fairbanks comparison, the Antarctic peninsula would be a candidate for this new “Maritime Polar” (EM) classification IMHO.

In support of that, here is a seasonal temperature map submitted to Wikipedia by Stoat’s William Connelly:

Note how in winter the Antarctic peninsula is completely at the other end of the temperature scale from the interior just as we see in the Unalaska to Fairbanks comparison. In the summer, the effect is less, but the Antarctic peninsula agrees mostly with the sea temperature band surrounding the Antarctic continent.

Another piece of support evidence that the Antarctic peninsula climate is vastly different than the interior continent is precipitation, the other half of the Köppen climate classification system.

Here is a map of Antarctic precipitation:

Note once again that in terms of precipitation the Antarctic peninsula climate is also vastly different than the interior continent. It seems the Antarctic peninsula is an outlier when compared to the rest of the continent. The peninsula gets 400-600+ mm of precip while the interior gets 0-100mm.

As Köppen understood, places that are connected geographically and politically aren’t always connected by a common climate. Note another factor that you pointed out in this article:

http://noconsensus.wordpress.com/2009/02/15/aws-gridded-reconstruction/

Note that we have the majority of weather stations in Antarctica on the peninsula in your grid cell C, a total of 11. No other place in Antarctica comes close in the number of weather stations. Further, that grid cell also happens to be the one where the climate diverges from the interior of Antarctica the most.

So why is the obviously different Antarctic peninsula climatic zone being considered in the Steig study at all? The answers are: 1) it is connected geographically to the continent so that when saying “Antarctica is warming” the statement is true. 2)Treatment of the Antarctic peninsula climate zone as an outlier likely ruins the premise of the study in the first place.

Of course the counter argument would be that: “Antarctica is classified as one climate zone, thus our analysis in robust” but my counter argument would be that we could also likely find the same results from a study of the USA if we had the majority density of weather stations in the study based in the Florida keys and south Florida, with a remainder around the coastal cities of the USA and maybe a few in the interior. Could we accurately derive the climate trend of the USA from such and arrangement? Me thinks not.

To test this, I’d like to see what happens when the interior and the peninsula are are treated as separate climate zones. You could pick a delineation line right at the base, or go further out the peninsula, I doubt it would make much difference given the station weighting. Produce separate outputs showing the continent versus the peninsula.

I’ll bet the results will be obvious and telling.

Well, Jeff obliged and did the analysis I suggested. I thank him for that. While the decadal temperature  trend does switch from positive to negative, there is some new information that has emerged about the RegEM analysis.

Spatially Weighted Antarctic Temperatures – No Peninsula

Posted by Jeff Id “The Air Vent” on April 18, 2009

From this post and others I’ve determined that the temperature trend in the RegEM versioins of the Antarctic are not entirely created by smearing of the peninsula station’s data.

In order to interpret the RegEM results from the previous peninsula free reconstruction, we need to see a baseline reasonable reconstruction without the peninsula. These trends are based entirely on the surface station data. I saw several questions on WUWT about the improved accuracy of satellite temperatures. The satellite temperatures in this paper are of a different type than UAH or RSS use and these are affected substantially by clouds. The result is a much noisier and less trustworthy dataset than surface measurements.

In my opinion this sort of thing is about the best we can do in determining a total trend for the Antarctic over this timeframe. There are a few tweaks which might help but beyond that we have to accept that we don’t know any better than this method shows.

Now removing the peninsula does have basis in science because the ultra thin strip of land is primarily dependent on ocean temperatures and currents. It will be seen as cherry picking because I’ve clipped the part of the Antarctic warming the most. Before TCO or someone points out that I wouldn’t clip it if it didn’t have warming, keep in mind that I show it both with and without the peninsula and I make no claim that clipping the peninsula is the preferred method. It does make some sense though.

First the full trend.

Figure 1

Spatial trends with clipping region shown in black Figure 2.

Figure 2

As I’ve shown before, the trends from 1967 onward.

Figure 3

Spatial distribution 1967 onward.

Figure 4

If I’ve learned anything from all these plots, it’s that the Antarctic isn’t warming at 0.12 +/- 0.7 C/decade. It just isn’t. The actual trend is much lower than that and since 1967 it has even dropped a little across the continent.

Now from the other reconstructions we have the following.

Compared to the 0.12 that Steig et al. claims the real trends are pretty low. When the peninsula is removed in the properly weighted reconstruction presented here the trend drops by(0.52-.39)/.52 x100 =25%. This represents a very large contribution to the average simply because this tiny area has shown so much warming. It doesn’t seem reasonable to adjust the continent upward 25% based on this little strip of land.

Surprisingly, in RegEM the trend changes by an similar amount (0.108-0.074).0.08 x100 =31%. This is impressively similar to me as many have speculated that the positive trend in RegEM is created by smearing of peninsula trends. In my spatial reconstruction above, there is no smearing of the peninsula trend at all and there is a 25% trend drop when the peninsula is removed. This means to me that the RegEM high positive trend is not wholly created by the peninsula. Also, this does not mean the trends aren’t smeared by RegEM, they are.