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UNSW climate scientists shift goal posts, publish irrelevant “extreme hot days” trend

Posted By Joanne Nova On March 1, 2014 @ 1:48 am In Global Warming | Comments Disabled

The pause in global warming is so crippling, so crucial, that scientists will go to extremes to find any excuse to issue something that combines the magic terms “no pause” and “extreme temperatures”. This is the winning combination in climate bingo. But marvel how far these researchers have to stretch to get there.

Gaze upon  Seneviratne et al  (UNSW) declaring that there is no pause in the trend of “extreme hot temperature days”. Watch the pea (or rather peas).

Globally, on average, regions normally expect around 36.5 extremely hot days in a year. The observations showed that during the period from 1997-2012, regions that experienced 10, 30 or 50 extremely hot days above this average saw the greatest upward trends in extreme hot days over time and the area they impacted.

The consistently upward trend persisted right through the “hiatus” period from 1998-2012.

If the world was warming, they wouldn’t bother with this strained nonsense, would they? They are talking about 15 year trends in air over land, in summer, on the hottest 10% of days.

  1. Seneviratne et al acknowledge the pause in global temperatures. Therefore the models, and the theory is wrong. Every other incidental trend in smaller markers is a deckchair on the Clitanic.
  2. There is no causal connection with CO2. The greenhouse effect is supposed to be full time. It’s not like there are days when it doesn’t work. CO2 is either making the global average warmer as predicted or… it isn’t and their models are useless.
  3. The paper admits the summer extremes are warming over land, but not the warm winter extremes. So the greenhouse effect switches off in winter? That will be news. Wait, they also find there is a cooling effect in the mid-high latitudes of the northern hemisphere during the boreal winter? Isn’t that pretty close to when and where peak CO2 levels occur? I guess that’s only 10ppm of extra CO2, but this is not “parts of a jigsaw” coming together — it’s cherry picking.
  4. Extreme heat doesn’t necessarily mean hot. Looks like some of these extreme warm days occurred in places like Russia, Alaska and Greenland. As far as I can tell, they define “hottest extreme days” as being the hottest 10% of all days in a grid cell from 1979-2010. The average July temperature in Nuuk, Greenland is 10C (50F)  so the top 10% of “extreme hot weather” there is not so scary.
  5. Are they serious? A 15 year noisy trend in 30 year dataset is irrelevant. The graphs start in 1979 (when satellites start) but that’s also near the start of the last long warming cycle. For all we know it is connected to the natural upswing in the 60 year PDO cycle. Indeed, if surface cooling of the ocean is reducing global averages now (the explanation Seneviratne offers for the lack of global warming), obviously surface warming of the ocean could have been doing the opposite before. Without longer records this is meaningless, mindless PR headline hunting with no scientific significance.
  6. Just because something is statistically significant doesn’t mean it is meaningful. Since it warmed for the first 20 years of the dataset and then paused at the warmer level, it’s hardly surprising that someone can still “discover” some short trends that are rising.

Are the UNSW scientists trying to learn something about the world, or are they trying to generate headlines with the words “extreme hot temperatures”? Judge them by their press releases….

Click to enlarge. Note big blue cooling areas in the DJF months (northern winter) and warming extremes in the Sahara. Note also the amount of “extreme” heat days in high cold latitudes from December to May.

They are discussing a 15 year trend in “hottest days” at the end of a natural variation which is something like this:

The graph ends 100 years ago. So extend that red line up 0.9C. Then whip up some panic about the last quarter millimeter.

Sure, this is GISP — one ice core from Greenland and not global temperatures. The truth is we have no idea whether the current level of “extreme” hot days is much different to the hot spells 1,000 years ago, 2,000 years ago, or 7,000 years ago. It is completely disingenuous to pretend that a 15 year trend in a data set this noisy tells us something that matters.

Forget global average temperatures — move those goal posts

This paper is very ambitious — they would like us to believe that global average temperatures aren’t that important now, really these heat extremes have more impact. And maybe heat extremes do have more impact (it’s debatable), but they don’t tell us about the cause.

The climate scientists really hate the term “pause” calling it “ill-chosen”, “misleading” and “erroneous”. (Who is in denial?)

Based on existing observational evidence, we highlight that the term pause, as applied to the recent evolution of global annual mean temperatures, is ill-chosen and even misleading in the context of climate change.
Indeed, an apparently static global mean temperature can mask large trends in temperatures at both regional4 and seasonal11 scales.

These results have several important implications. First, they show that it would be erroneous to interpret the recent slowdown of the global annual mean temperature increase as a general slowdown of climate change.

They admit they don’t understand the causes:

As usual the caveats are carefully couched in the fine print that no journalist will bother to read:

This conclusion also applies to climate change projections, which are often expressed as changes in the global mean surface temperature1, although some of the most relevant impacts are related to temperature extremes over land rather than changes in mean temperature per se. In this context, a better understanding of the full complexity of changes resulting from greenhouse gas emissions, focusing on the identification of individual processes contributing to the global-scale response, is necessary.

“Hottest extreme days” is just another way to measure climate, one of an infinity of indicators. They were wrong on global averages. So they’re looking to report on anything “getting worse”. This is cherry picking a mindless statistic.

And Nature thought it was worth publishing.

The news: Climate change: No warming hiatus for extreme hot temperatures

EXTRA POINTS: I could go on…

*See Fig 1b, am I imagining it — is that a 15 year flat trend til 1997 followed by a 15 year rising one? Wasn’t CO2 increasing the whole time?

** They use the ERA-Interim dataset. It’s reanalysis using models. That’s just another layer of estimates and assumptions.

***You might think that this is about hot days measured by thermometers or that it means “days over 40C” or something like that. Not so. You’ll need to read the Supplementary information to even start to understand what they mean by land area, or “extreme” heat.

S1. Calculation of extreme warm day exceedances (ExD10, ExD30, ExD50) for
ERA-Interim and HadEX2 datasets

We calculated indices representing exceedances of warm days at each grid box for Figure 1. These are based on the 90th percentile warm day frequency (TX90p) as defined by the Expert Team for Climate Change Detection and Indices1,2, which counts the annual number of days with daily maximum temperature above the 90th percentile. The percentile threshold for each day is calculated using a five-day window (centered on each calendar day), using a bootstrapping method3 to avoid inhomogeneities at the beginning and end of the percentile base period. The reference number of extreme warm days (ExDref) is calculated at each location as the TX90p average over the 1979-
2010 time period. The yearly timeseries of extreme warm day exceedances (ExD10, ExD30, ExD50) are computed with respect to ExDref. They indicate the land area ratio in each year (using a weighted area sum according to the size of the respective grid cells), affected by an exceedance of 10 (ExD10), 30 (ExD30), and 50 (ExD50) extreme warm days, respectively. A ratio of 1 indicates that the land area fraction affected by a given exceedance corresponds to the 1979-2010 reference value, a ratio of 2 indicates a doubling (see Fig. 1). [And there's a lot more....]

 

REFERENCE

Sonia I. Seneviratne, Markus G. Donat, Brigitte Mueller & Lisa V. Alexander (2014) No pause in the increase of hot temperature extremes, Nature Climate Change, vol 4, p 161–163, doi:10.1038/nclimate2145

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