Study Claiming Insect Decline Due To Global Warming ‘Based On Faulty Temperature Data’
Study Claiming Insect Decline Due To Global Warming Is Based On Faulty Temperature Data.
h/t Joe Public/Dave Ward
Many thanks to some real Sherlock Holmes work by Joe and Dave.
The article refers to this study by Brad Lister last year:
Arthropods, invertebrates including insects that have external skeletons, are declining at an alarming rate. While the tropics harbor the majority of arthropod species, little is known about trends in their abundance. We compared arthropod biomass in Puerto Rico’s Luquillo rainforest with data taken during the 1970s and found that biomass had fallen 10 to 60 times. Our analyses revealed synchronous declines in the lizards, frogs, and birds that eat arthropods. Over the past 30 years, forest temperatures have risen 2.0 °C, and our study indicates that climate warming is the driving force behind the collapse of the forest’s food web. If supported by further research, the impact of climate change on tropical ecosystems may be much greater than currently anticipated.
A number of studies indicate that tropical arthropods should be particularly vulnerable to climate warming. If these predictions are realized, climate warming may have a more profound impact on the functioning and diversity of tropical forests than currently anticipated. Although arthropods comprise over two-thirds of terrestrial species, information on their abundance and extinction rates in tropical habitats is severely limited. Here we analyze data on arthropod and insectivore abundances taken between 1976 and 2012 at two midelevation habitats in Puerto Rico’s Luquillo rainforest. During this time, mean maximum temperatures have risen by 2.0 °C.Using the same study area and methods employed by Lister in the 1970s, we discovered that the dry weight biomass of arthropods captured in sweep samples had declined 4 to 8 times, and 30 to 60 times in sticky traps. Analysis of long-term data on canopy arthropods and walking sticks taken as part of the Luquillo Long-Term Ecological Research program revealed sustained declines in abundance over two decades, as well as negative regressions of abundance on mean maximum temperatures. We also document parallel decreases in Luquillo’s insectivorous lizards, frogs, and birds. While El Niño/Southern Oscillation influences the abundance of forest arthropods, climate warming is the major driver of reductions in arthropod abundance, indirectly precipitating a bottom-up trophic cascade and consequent collapse of the forest food web.
Sounds like an open and shut case eh?
Lister even adds these temperature graphs to his paper:
Given that, as the paper itself admits, warming in the tropics in theory should be much less than elsewhere, claims of a 2C increase since the 1970s did not pass the sniff test. Fortunately Joe Public decided to go away and check the actual data used by Lister.
His findings should alarm anybody who believes in the integrity of science and peer review.
Let’s take a closer look at those graphs.
All the temperature data used comes from just two sites, El Verde and Bisley (not Bisely). But Bisley data only begins in 1993, so the comparisons with the 1970s rely solely on El Verde, the data for which is sourced from here.
And this is what the Station Metadata has to say:
In short, the data Lister uses prior to 1992 is worthless, and were substantially understated in comparison with those that followed.
If we begin the chart in 1992, we find that temperatures have actually been dropping, and not increasing.
The metadata states that temperatures showed an abrupt increase in 1997, as the adjustments were ended. However, this step up is not apparent on Lister’s graph. Rather, the step up is in 1992. This seems to indicate that Lister uses the unadjusted data.
The metadata also links to the dataset:
And this provides some handy graphs.
Below is the chart of annual temperatures from 1993 to 2013. [The data only runs to Feb 2014]
This shows the same pattern of declining temperatures since 1992. We know that the data since 1997 is fully reliable, and this too shows a declining trend. Note too that Lister’s graph indicates temperatures since 2013 have been lower still for three of the last four years.
This still leaves us the problem of Bisley, where data starts in Feb 1993. CLIMDB only have data till Nov 2010, so full annuals are only available from 1994 to 2009:
For some reason, Bisley shows a rather different picture to El Verde, although there is no obvious warming trend. Given that El Verde and Bisley are only a few miles apart, it is obvious that the divergence between the two is due to dodgy data and not real.
To sum up, we have a paper which makes bold claims that arthropods have been declining at an alarming rate since the 1970s, and that the cause is climate warming.
Yet these claims are based on long term temperature data, which, according to the organisation that actually maintains the data, is not reliable and should not be used for long term trends.
The only reliable data covers the period since 1992, and this shows declining temperatures. Even this dataset is not consistent with the Bisley one.
Clearly the whole study is worthless, and the paper should be withdrawn.
There are some alarming facts about all of this:
1) Why did the researchers not suspect that the temperature data looked hopelessly wrong at the outset?
2) Why did peer review not do the basic checks that I did?
3) The study carries out some mindbendingly complex statistical analysis, linking arthropod decline to rising temperatures. But how can this analysis have been robust, when the temperature data was hopelessly wrong?
The conclusion is that the faulty temperature data matched the researchers’ expectations of climate warming, and consequently they never bothered to crosscheck. It would after all have been extremely simple to have asked the people who maintain the data.
Whether or not arthropods are in decline I have no idea. But by blaming non existent climate warming, there is a very real danger that the true cause is being missed. Indeed, looking at those graphs, it may well be climate cooling that is responsible.
I plan to contact PNAS, who published the paper, to request that it be withdrawn.
I have also crosschecked the temperature data from 1975 to 1991, available here. This correlates with Lister’s graph.