Monday, September 15, 2014

Anthony Watts gets (slam) dunked in the oceans by CSIRO and Nature

I know you don't need any more proof that Anthony Watts doesn't read what he posts about, but you're getting it anyway. Today he's gloatingly posted:
You might remember this claim from Australia’s CSIRO back in 2012 published in the Sydney Morning Herald. It’s been busted by a new paper:

Has the CSIRO paper been busted? Nope. Not at all. Just the opposite. It's findings have been confirmed.

The new paper Anthony is talking about is a study published in Nature Geoscience. Anthony doesn't provide a direct link to the press release, but here it is - at Eidgenössische Technische Hochschule Zürich. It says in part:

With a new analysis of land regions, ETH climate researcher are challenging the general climate change precept that dry regions are getting drier and wet regions are getting wetter. In some regions they are encountering divergent trends.
Based on models and observations, climate scientists have devised a simplified formula to describe one of the consequences of climate change: regions already marked by droughts will continue to dry out in the future climate. Regions that already have a moist climate will experience additional rainfall. In short: dry gets drier; wet gets wetter (DDWW).
However, this formula is less universally valid than previously assumed. 
...the researchers compared data from between 1948 and 1968 and 1984 to 2004.
The evaluation shows no obvious trend towards a drier or wetter climate across three-quarters of the land are[a]. There are solid trends for the remaining quarter. However, only half of this surface area follows the DDWW principle, i.e. one-eighth of the total landmass, while the trends seem to contradict this rule over the other half.

Land doesn't conform to expectations

That is, when comparing the two periods, 1948-1968 and 1984-2004 and just looking at land:

  • three quarters of the land area showed no obvious trend
  • one quarter of the land area shows solid trends
  • half the land areas in this quarter, or 1/8 of the land areas followed the dry getting drier, wet getting wetter pattern, and 
  • half showed the opposite. That is, 1/8 of the land areas showed dry getting wetter and wet getting drier.

The supplementary information seems to be different to the press release. It states in part:
In our study, we detect changes in the mean hydroclimatological conditions between the time periods 1948 to 1968 and 1985 to 2005.
This is different to what's stated in the press release.  Further, the supplementary info itself has more comparisons than the paper does.
However, in the interest of completeness we performed the same analysis comparing the first (1948-1968) and the last period (1985-2005) with the respective middle period (1968-1985, see Fig. S3). 

The oceans conform to expectations

The scientists also looked at the ocean areas. They reported that the principle of wet gets wetter and dry gets drier holds for the oceans.

Let's go back to the report in the Sydney Morning Herald that Anthony Watts scoffed at. What does it say. Well, this is what it said:
WET areas have become wetter and dry areas drier over the past 50 years due to global warming, a study of the saltiness of the world's oceans by a team including CSIRO researchers has shown.

Do you need to read it again? The CSIRO article was about a study of the world's oceans. Not a study of the land. It was confirmed, not rebutted by the new paper. 

Anthony got it wrong. No surprises there. 

Both bits of research show exactly the same thing: that as far as the oceans are concerned, the principle of the wet gets wetter and the dry gets drier holds.

Points of interest

Now the new research is interesting for more reasons than just the result for patterns of rainfall on land. It's interesting because it was able to get a result. The SMH report of the Paul Durack and co paper states:
Initial attempts to study this ''rich get richer'' effect, however, were hindered by a shortage of good rainfall records on land and a lack of long-term satellite measurements.
So Dr Durack studied the oceans.
Paul Durack and colleagues list some of the difficulties in collecting data about rainfall patterns in the 2012 Science paper itself as (my paras):
Given the above broad-scale model responses and the CC relationship, an intensification of ~4% in the global water cycle (E-P) is expected to already have occurred in response to the observed 0.5°C warming of Earth’s surface over the past 50 years (11).
However, obtaining a global view of historical long-term rainfall pattern changes is made difficult because of the spatially sparse and short observational record. Long, high-quality land-based records are few and Northern Hemisphere–biased (12). Direct high-quality long-term rainfall estimates over oceans [which comprise 71% of the global surface area and receive over 80% of global rainfall (13) (fig. S1)] are very scarce, with most global observational products dependent on data contributions from satellites, themselves sensitive to error (14, 15).
Additionally, because of the short temporal coverage (~15 to 30 years) by satellite missions, trends are likely affected by natural decadal modes of variability and may dominate much of the measured changes (3).
This challenge is exacerbated by the spatially and temporally sporadic nature of rainfall, making the derivation of broad-scale averages of small multidecadal changes from a sparse network of observing stations error-prone (16).
These difficulties are evident in the differing signs of long-term trends between reconstructed rainfall data sets (17, 18). Discrepancies among air-sea evaporative flux products (19) undermine their use in resolving long-term water cycle changes.
As a result, we do not yet have a definitive view on whether Earth’s water cycle has intensified over the past several decades from atmospheric observing networks (12, 20).

That was for a paper published in 2012. They bypassed the above problems by studying trends in sea surface salinity. However that meant they could only study trends for the oceans, not land.

Now I don't know how reliable is the data used for the new paper by Peter Greve and colleagues. Obviously the researchers think it's reliable enough. Whether they were able to come up with new techniques to determine precipitation on land, or whether it's that better data has become available in the past two years. Or maybe they overcame the data deficiencies in some other way. In the abstract they state:
Here we present an analysis of more than 300 combinations of various hydrological data sets of historical land dryness changes covering the period from 1948 to 2005. Each combination of data sets is benchmarked against an empirical relationship between evaporation, precipitation and aridity. 

The Nature Geoscience paper itself is paywalled, but there is a supplementary info file for people who may be familiar with the Budyko framework and are in a position to assess the reliability of the data. This new study did reference the Durack paper in Science, as well as other related studies.

From the WUWT comments

I can't be bothered. I just had another look through the latest (archived here) and so far not a single person at WUWT has noticed that, contrary to what Anthony Watts claimed, the new study confirmed the earlier study, which was about trends over the oceans.

Peter Greve, Boris Orlowsky, Brigitte Mueller, Justin Sheffield, Markus Reichstein & Sonia I. Seneviratne. "Global assessment of trends in wetting and drying over land." Nature Geoscience (2014) doi:10.1038/ngeo2247

Durack, Paul J., Susan E. Wijffels, and Richard J. Matear. "Ocean salinities reveal strong global water cycle intensification during 1950 to 2000." Science 336, no. 6080 (2012): 455-458. DOI: 10.1126/science.1212222

1 comment:

  1. "so far not a single person at WUWT has noticed that, contrary to what Anthony Watts claimed, the new study confirmed the earlier study, which was about trends over the oceans."

    That is why they are known as fake skeptics.


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