I pointed out a few posts ago that Antarctic temperatures had been declining during the period of satellite measurement.’ IPCC 4AR Second Draft says that “recent warming is strongly evident at all latitudes in SSTs over each of the oceans“.’ “Strongly” seems to be a new favorite word – think of all the times that Holland and Webster use it. Given the declining trend in Antarctic (satellite) temperatures, I wondered whether this statement was actually true.’ I looked at both Mears-Wentz and Christy data.’ Surprise, surprise – recent warming is not evident over all latitudes – much less “strongly evident”. Here’s a graph of trends from Mears and Wentz which shows increasing temperatures over most parts of the world, but declining trends in the Southern Ocean – which seems to flatly contradict the claim in the 2nd Draft (of course, they may cooper this up between now and then).
Figure 1. Gridcell temperature trends (Mears and Wentz)
Spencer and Christy have provided monthly averages for 5 ocean latitudinal bands, which I’ve plotted below, going from S to N, showing the decadal trend in deg C/decade. Again there is a slight declining trend in the South polar oceans, with slight increasing trends in the south extratropical oceans and tropical oceans.’ I would not be inclined to say that recent warming is “strongly evident” in the 2nd and 3rd panels and would be interested as to what test is implied for “strong evidence”.’ The results are quite different for the north extratropics and especially the north polar oceans. Squinting at the plot of the north polar ocean temperatures, the results don’t really show a uniform trend. Although the temperature increase is clear enough, it seems to occur almost in one step in the mid-1990s – this would seem to be as distinct as any of Holland and Webster’s regime changes. However, it’s a mug’s game trying to tell the difference.
Figure 2. Satellite temperatures for ocean latitudinal bands from MSU.’ http://vortex.nsstc.uah.edu/data/msu/t2lt/uahncdc.lt
Now it’s true that satellite evidence shows increases over most latitudes, but not all latitudes.’ They easily have had a substantial statement that avoided over-reaching. So why wouldn’t they simply report that southern oceans are an exception?’ I can’t help but think that it’s tied into the polar amplification thing. If high-latitude southern oceans show a cooling – contrary to expected polar amplification of warming – it doesn’t look good. So even though these oceans constitute a small portion of total ocean area and a relevant true statement could easily have been made, the statement is fudged (or is likely to have been fudged unless it’s coopered up). It’s the sort of thing that drives one crazy about IPCC.