Now there’s one less ‘dirty weather’ claim for the bloviator in chief, Al Gore.
A new paper just published and available for preview for the upcoming issue of Nature demonstrates that hyped claims that drought has increased aren’t founded in science. Plotting the Palmer Drought Severity Index globally over the past 60 years they show little change in drought.
Drought is expected to increase in frequency and severity in the future as a result of climate change, mainly as a consequence of decreases in regional precipitation but also because of increasing evaporation driven by global warming. Previous assessments of historic changes in drought over the late twentieth and early twenty-first centuries indicate that this may already be happening globally. In particular, calculations of the Palmer Drought Severity Index (PDSI) show a decrease in moisture globally since the 1970s with a commensurate increase in the area in drought that is attributed, in part, to global warming. The simplicity of the PDSI, which is calculated from a simple water-balance model forced by monthly precipitation and temperature data, makes it an attractive tool in large-scale drought assessments, but may give biased results in the context of climate change. Here we show that the previously reported increase in global drought is overestimated because the PDSI uses a simplified model of potential evaporation7 that responds only to changes in temperature and thus responds incorrectly to global warming in recent decades. More realistic calculations, based on the underlying physical principles8 that take into account changes in available energy, humidity and wind speed, suggest that there has been little change in drought over the past 60 years.
Hmmm where have we seen this before?
And here is another:
Hoerling et al. in Journal of Climate: Is a Transition to Semi-Permanent Drought Conditions Imminent in the U.S. Great Plains?
“We conclude that projections of acute and chronic PDSI decline in the 21st Century are likely an exaggerated indicator for future Great Plains drought severity.”
Abstract:
How Great Plains climate will respond under global warming continues to be a key unresolved question. There has been, for instance, considerable speculation that the Great Plains is embarking upon a period of increasing drought frequency and intensity that will lead to a semi-permanent Dust Bowl in coming decades. This view draws on a single line of inference of how climate change may affect surface water balance based on sensitivity of the Palmer Drought Severity Index (PDSI). A different view foresees a more modest climate change impact on Great Plains surface moisture balances. This draws on direct lines of analysis using land surface models to predict runoff and soil moisture, the results of which do not reveal an ominous fate for the Great Plains. Our study presents a parallel diagnosis of projected changes in drought as inferred from PDSI and soil moisture indicators in order to understand causes for such a disparity, and to shed light on the uncertainties. PDSI is shown to be an excellent proxy indicator for Great Plains soil moisture in the 20th Century; however, its suitability breaks down in the 21st Century with the PDSI severely overstating surface water imbalances and implied agricultural stresses. Several lines of evidence and physical considerations indicate that simplifying assumptions regarding temperature effects on water balances especially concerning evapotranspiration in Palmer’s formulation compromise its suitability as drought indicator in a warming climate. We conclude that projections of acute and chronic PDSI decline in the 21st Century are likely an exaggerated indicator for future Great Plains drought severity.
Corresponding author address: M. Hoerling, NOAA/Earth System Research Laboratory
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Anthony could use that argument in his 2012 Draft Paper, which has been objected to by a denizen of SkS on the grounds that it can’t be known that poor quality stations NOW were poor quality stations THEN.
slightly clearer image on
http://www.nature.com/nature/journal/v491/n7424/images_article/nature11575-f1.2.jpg
Surely everybody knows that climate change in the time of the Mayan civilisation was linked to human sacrifice? Have modern climate scientists incorporated that variable into their models?
Not so long ago we were told about more drought in the UK and permanent drought in Australia. The good news is that Warmists were shamed by the wet facts on the ground. The UK had record rain this year and as for Australia they had Biblical floods last year. What did Warmists do?: blame global warming. They have no shame and simply ignore their earlier pronouncements as if no one was looking.
“Freak storms, flash floods, record rain – and there’s more to come”
http://www.guardian.co.uk/uk/2012/jul/08/summer-unending-rain
“‘Biblical’ floods hit Queensland and leave tens of thousands homeless”
http://www.guardian.co.uk/world/2011/jan/02/queensland-biblical-floods-australia
You are assuming that the lighter colored areas around the line in more recent times is a depiction of error bars. Without access to the paper this is an unsupported assumption.
Another interpretation of this is that they only have smothed data prior to 1960 and post 1960 they are showing both the smothed data plus the full range of volitility in the raw observations.
Sure, if you like. I’m just interpreting the caption of the figure above in the most reasonable way.
But no matter how the light shading is interpreted, it isn’t reasonable that it would be less “uncertainty” in the 60s than today, given improvements in the instrumentation and the enormous amount of money that has been funnelled into climate research in the meantime. The instrumentation today is surely better. It is supported by radar, collected electronically, produced from standardized and tested apparatus that can screw up, I’m sure, but in general is likely to screw up LESS and be recorded MORE CONSISTENTLY than whatever was used in the 50’s. Even if the number of stations decreased from 7000 to 1000, that should do no more than roughly double the statistical uncertainties (square root of N, not N).
Under no circumstances is this indicative of a believable result. It is a pointless result, that boils down to “using the stations and methods we included in this study, we haven’t the foggiest idea if drought increased or decreased over the period indicated, or if (most likely) it remained about the same”. Which is the null hypothesis in the first place. This study does nothing to change that.
So I reiterate: a) Bo-ring. b) Probably wrong or based on poor methodology if modern uncertainties are larger than pre-satellite uncertainties from the 50’s.
rgb
Surely everybody knows that climate change in the time of the Mayan civilisation was linked to human sacrifice? Have modern climate scientists incorporated that variable into their models?
Modern data correlates it with the fractional population of the Earth consisting of pirates, not human sacrifice. Sorry. Fewer pirates equals more global warming. Ar.
rgb
Hmmm, during the end of the LIA, the southern Great Plains and southern Rocky Mountains endured 15 or so years of severe drought (1850 – 1865). The mid-1890s were also grim, and apparently less than optimal precipitation during the period from 1450-1550 caused regional depopulation before the arrival of Europeans and European diseases.
Alas, I have yet to find the PDSI records kept by the Antelope Creek, Rio Grande Pueblo, or Athapaskan (Diné) peoples of the region in order to make an apples-to-apples comparison.
TXRed says:
November 17, 2012 at 11:33 am
….Alas, I have yet to find the PDSI records kept by the Antelope Creek, Rio Grande Pueblo, or Athapaskan (Diné) peoples of the region in order to make an apples-to-apples comparison.
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You forgot the Tree Rings. Those magical mannian tree rings that can tell us anything and everything about climate.
Basically, this paper is saying the Palmer Drought Severity Index is an old too simplified model that should be updated now that there is more data available to calculate dought conditions more accurately.
If that is done, there is little change in drought conditions.
The paper and new release also questions why the PDSI remains in use and is still used by the IPCC for example since this could have been fixed long ago. They say it is a “curiousity” that it is still in use.
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This is something that is becoming more common now. Some climate scientists feel more free now to correct the inaccurate vestiges of the science. Not long ago, they would have been drummed out of the field and/or fired for trying to do so.
Its a good development.
Let me recall that the wet climates are equatorial, and the dry climates are polar. Ask a penquin about drought. Never have seen a forecast that a “cold wet arctic air mass …” and how about those tripical storms…no water in those? Is there any simple obvious observation of common sense left?