One of the many projected impacts of global warming, or climate change if you prefer, is species extinction. And according to the IPCC AR4, as reported in Wikipedia, the impacts of climate change on species are potentially catastrophic:
There is medium confidence that approximately 20-30% of species assessed so far are likely to be at increased risk of extinction if increases in global average warming exceed 1.5-2.5 °C (relative to 1980-1999). As global average temperature increase exceeds about 3.5 °C, model projections suggest significant extinctions (40-70% of species assessed) around the globe.
It’s also been reported that some species have already been driven to extinction by climate change, with the implication being that we’re already seeing the thin end of the wedge. But are these reports true? Are the species definitely extinct, and if so was climate change really to blame? Here we will review three of the better-known reported extinctions to see what the data tell us. In order of disappearance, the three victims are:
1. The golden toad (extinct ~1989)
2. The Aldabra banded snail (extinct ~1997)
3. The white lemuroid possum (extinct ~2005)
Here is where they lived:
And in Section 2 the real reason for the disappearance of the banded snail from Aldabra Atoll will be revealed for the first time.
1. The Golden Toad
• EXTINCT: Golden toad (Bufo periglenes). Along with the Monteverde harlequin frog (Atelopus varius), also of Central America … Last seen in 1989, the golden frog lived in mountaintop cloud forests that have disappeared due to drought and other climatic changes. (Source: IPCC AR5 Working Group II 2014 report, as quoted in National Geographic)
The IPCC’s first claim is that mountaintop cloud forests have disappeared. This is true in some areas, but the golden toad’s habitat was the Monte Verde cloud forest of Costa Rica, which is indisputably still there.
The next claim is that the extinction was preceded by drought and other climatic changes. We will begin with drought. The Global Historic Climate Network (GHCN) data base rainfall record for Monte Verde is shown below. It ends in 1986, a couple of years short of the reported extinction in 1989, but there’s no sign of drought. Also shown is the rainfall record from Puntarenas, about 20 miles south of Monte Verde, which covers 1987 and 1988 and later years. It shows no sign of drought either. (The GHCN records are available at KNMI Climate Explorer).
What about temperature? There’s no temperature record for Monteverde, but here are the records for Puntarenas and for Juan Santamaria airport, which is located about 40 miles east of Monte Verde. Apart from a few cold years in the 1960s Juan Santamaria temperatures show no significant change for a period of ~30 years before the golden toad’s extinction in 1989, and temperatures in Puntarenas were about a degree cooler in the late 1980s than they were in the early 1960s:
Clearly the extinction of the golden toad was not related to deforestation or climate change. So what caused it? The chytrid fungus, which causes a skin infection fatal to amphibians. (Interestingly, laboratory studies suggest that the infection can be cured by exposure to high temperatures.)
And the Monte Verde harlequin frog, which the IPCC also lists as extinct, isn’t. Small colonies still survive in the wild. (Note also that the golden toad will remain extinct only for so long as nobody finds one. Fifty years without a sighting is required before a species is officially listed as extinct.)
2. The Aldabra Banded Snail.
The only known population of the Aldabra banded snail Rhachistia aldabrae declined through the late twentieth century, leading to its extinction in the late 1990s. This occurred within a stable habitat and its extinction is attributable to decreasing rainfall on Aldabra atoll, associated with regional changes in rainfall patterns in the late twentieth and early twenty-first century. (Source: Gerlach 2007.)
This statement raises some questions, such as a) how did the habitat manage to remain stable during a drought severe enough to drive one of its inhabitants extinct and b) how can an extinction that occurred in the 20th century be associated with changing rainfall patterns in the 21st? But we’ll ignore them and move on. Here’s the extinction timeline:
Before 1976 – Snails abundant
After 1976 – “Dramatic drop in abundance”. Only adult snails found
1997 – Last live specimen collected
The extinction mechanism was interpreted to be a series of dry years – which if the snail population began to dwindle dramatically in 1976 must have begun around 1976 – that left the adult snails largely unharmed but killed the younger ones, leading to extinction through what is known as senescence.
Here now is the GHCN monthly rainfall record for Aldabra. Like the Monte Verde record it doesn’t quite make it to the extinction date, but there’s no sign of a series of unusually dry years beginning around 1976.
Figure 1(c) of the Gerlach report linked to above contains additional annual mean rainfall data, and here’s what we get when we combine them with the GHCN data (the two data sets give the same values in years where both have a value). I’ve added the extinction timeline for reference:
The combined data sets do show an overall decline in annual rainfall after 1976, but only when we include the years after 1997, when the snail was already extinct. Between 1968 and 1997 it’s hard to detect any significant change. (I’ve assumed, incidentally, that the 1958 and 1959 data are bad. If they aren’t we can make a case that it wasn’t a lack of rain that killed the snail, but too much of it.)
Obviously the snail didn’t go extinct because of drought. What about temperature? (“longer, hotter summers” are also cited as a culprit). The closest GHCN temperature record to Aldabra is Isles Glorieuses 160 miles to the south, and here it is. The first summer that might be classified as significantly longer and hotter than average was 1998, a year after the snail’s reported demise, and the trend line shows only 0.3C of warming over the last 60 years:
In short, there’s no evidence to support the argument that climate change drove the Aldabra banded snail extinct either. But if climate change didn’t kill it, what did? There’s no evidence that it was disease, loss of food supply, predators or habitat loss. Was there any event that coincided with the beginning of the snail’s decline?
Indeed there was. The arrival of the world’s most invasive species – man.
In 1966 the Royal Society mounted an exploratory expedition to Aldabra, liked what it saw, and in 1971 it opened a research station there. As a result RS scientists counted and collected snails on and off for ten years between 1966 and 1976, with activity peaking in 1975/76. The graph below superimposes their and other available shell count data on the extinction timeline. The timing is impeccable:
And don’t be misled by the small number of counts. The scale of collection was far greater. According to a Nature article “scientists were plucking snails off fresh leaves all over the Island 30 years ago” (which dates them as Royal Society scientists) and an Island Biodiversity article states that “in the 1970s traps that were set for insects (presumably also by RS scientists) ended up with loads of snails in them”. The arrival of the first shipload of tourists on Aldabra in 1970 on board the Lindblad Explorer, which made a number of repeat visits over the next few years, probably added to the depletion rate.
Even the last living snail, found in 1997, wasn’t left in peace. It was collected too.
So now we have an explanation that fits the facts and which requires no changes in the climate or anything else. The Aldabra banded snail was collected to death, as the Masirah cowrie seems to have been. But the evidence is circumstantial, insufficient to convict. What would we need to confirm beyond a reasonable doubt that this is in fact what happened?
We would need someone to go to a remote area of Aldabra with no history of snail collection and find a snail colony alive and well.
And on August 23, 2014, someone visited a remote part of Malabar island on the north side of Aldabra, and did exactly that.
Rhachistia aldabrae wasn’t extinct at all. It was just hiding.
3. The White Lemuroid Possum
Scientists say a white possum native to the Daintree rainforest in the Australian state of Queensland has become the first mammal to become extinct due to man-made global warming. The Brisbane, Queensland, Courier-Mail reports the white variety of the lemuroid ringtail possum, found only above 3,000 feet in the mountain forests of far north Queensland, has not been seen for three years. Experts fear climate change is to blame for the disappearance of the highly vulnerable strain thanks to a temperature rise of up to 1.5 degrees Fahrenheit. (Source: Fox News.)
Unlike the golden toad and the banded snail, hemibelideus lemuroides was claimed to have been a victim of temperature, not drought, being reportedly unable to survive for more than four or five hours at temperatures exceeding 30C. So let’s go straight to the GHCN temperature record for the city of Cairns, which is at the base of the mountains in which the white lemuroid possum lives, or used to:
It’s difficult to see a sustained rise of 1.5F (0.8C) anywhere (the most distinctive feature is the ~1C upward baseline shift in 1942, without which the record would show no warming since 1907). Moreover, the hottest summers on record occurred back in the 1920s. But the “temperature rise of up to 1.5 degrees F” that supposedly did for the possum occurred during the heatwave of 2005, so let’s zoom in on the period around 2005 to see if there’s anything exceptional about it:
When people talk of the “heatwave of 2005” in the Southern Hemisphere it’s not always clear whether they mean late 2004 and early 2005 or late 2005 and early 2006, but in this case it doesn’t matter. Neither summer was in any way exceptional, and the hottest month recorded in either period – December 2005 – was still only the 12th warmest month on record – the warmest was January 1924. And once more there’s no sign of a 1.5F (0.8C) temperature rise. (Do the scientists have a weather station up in the mountains above Cairns? One imagines they would have said something about it if they did.)
From these results we can conclude that abnormally high temperatures were not responsible for the extinction of the white lemuroid possum. Or at least they wouldn’t have been if the possum had indeed been extinct. But it stayed extinct only until 2009, when three live lemuroid possums were spotted in their natural habitat.
But these were brown lemuroid possums, not white ones. Doesn’t matter, said some, they’re both the same species; the white possum is just an unusual color variant. Does matter, said others. The white possum is a unique evolutionary unit, whether a separate species or not. Maybe this is why the white lemuroid possum has become known as the polar bear of the Southern Hemisphere. The polar bear isn’t a separate species either, but a subspecies of the brown bear.