Posted on 01/12/2006 7:40:32 AM PST by cogitator
Last year was the hottest on record, or the second hottest, depending on the records climatologists look at. The planet has warmed .8 degrees C over the past 150 years, and scientists are generally agreed that greenhouse gases have played a major part in that warming. They also agree that the warming will continue in the decades to come. Many experts are concerned that warming may make two unpleasant things more common: extinctions and diseases. In tomorrow's issue of Nature (link to come here), a team of scientists report on a case that ties these two dangers together: frogs have become extinct as climate change spreads a deadly fungus. It's an important study, but it can't be boiled down to simple slogans. It highlights the dangers of global warming, but it shows that global warming's effects can be counterintuitive and unpredictable.
Since the 1980s, scientists have observed that frogs and toads have been disappearing. Species that live in mountain cloud forests in the tropics have been particularly hard hit. Take Harlequin frogs (Atelopus). Scientists have described 110 species from Central and South America. But they can no longer find a single individual from 67% of those species. They've been identifying potential agents of the extinctions. It's been much harder to pinpoint the actual culprit (or culprits).
Climate change was one suspect. Species that live in mountains may be particularly vulnerable to warming temperatures because they live in small ranges. If it's too hot for an animal at 5,000 feet, it may respond by moving uphill. But it can't go uphill forever, and before long its range may simply vanish. Another leading suspect was a fatal fungus, which has been sweeping through frog populations in recent years.
There was some reason to think that the two suspects might be working together. Scientists have found some evidence that warmer temperatures encourages the spread of diseases. Pathogens that might be killed off by cold weather can thrive if the climate changes. It was also possible that warmer temperatures were putting stress on the frogs, making them more vulnerable to attack.
This might all sound quite logical, but some evidence didn't seem to fit in. In one Australian study, for example, the fungus proved deadlier at cooler temperatures. When scientists exposed 16 frogs to the fungus at 17 degrees C all died. But only 4 out of 8 frogs died at 27 degrees C.
A network of 75 scientists came together to sort this mystery out. They gathered data on almost all the harlequin frog species, including weather records for their ranges. If a major force has been driving a lot of species to extinction, it should be easier to pinpoint than the cause of a single species's disappearance.
The results indicate that global warming has had a hand in the extinctions. The warmer the average temperature is in the tropics in a given year, the more likely that frogs are going to disappear in the following year.
But the results also clash with simple notions of how global warming can drive extinctions. The most vulnerable harlequin frog species live between 1,000 and 2400 meters. Harlequin frogs living at higher elevations have actually suffered fewer extinctions. So vanishing real estate is not to blame (at least in this case).
The study is also a vivid illustration of the fact that global warming can lead to lots of strange local climate change. At several research stations in the study, scientists have found that the maximum daytime temperature has actually gone down. At night, on the other hand, the minimum temperature has been going up. Clouds may be causing this pattern. Global warming causes more water to evaporate, creating more clouds in mountain forests. At night these clouds may trap heat, keeping the forests warm. But in the daytime, incoming sunlight may bounce off the clouds, leading to cooler days.
It's these local peculiarities of climate change, the scientists argue, that may be helping the fungus kill harlequin frogs. The fungus doesn't like temperatures over 28 degrees C and dies at 30 degrees C. It can't survive in lowland forests, and even a harlequin frog living on a mountain could cure itself with a good bake in the sun. But these days that frog is less likely to find a spot of sun, thanks to the increasing cloud cover. On the other hand, very cold temperatures keep the fungus from growing. The highest elevations are still cold enough to block its spread, the scientists argue, which is why harlequin frogs have suffered fewer extinctions there. But as nights get warmer, the mid-elevation forests are becoming the perfect breeding ground for the fungus. And harlequin frogs there have paid the price.
I'm writing this post just before this paper goes public, and I'm cringing at the thought of how it will be spun. I've seen how pseudo-skeptics try to claim that we can't learn anything about extinctions or how they might be accelerated by future climate change (see my posts here, here, and here). On the other hand, it would be wrong to make a blanket statement that climate change triggers outbreaks because it makes the planet warmer. The equation is far from simple. If not for some cooling, fungi would not be such a threat to harlequin frogs. This interplay is not just complex but hard to forecast. Scientists have known about global warming and fungus outbreaks and frog extinctions for twenty years. But as far as I know, no one predicted that it would be nighttime warming and daytime cooling that would make the fungus so deadly. A commentary that accompanies the new paper in Nature points out that few computer models used to forecast climate-driven extinctions take parasites into account. And so we have no idea just what sort of future the Harlequin frogs are pointing us towards.
..eyep, I think it's the 50's that skews findings
Doogle
"But it must be true! I saw it on the NBC Nightly News last night!"
This requires them to link anything they possibly can to it.
They've just about used up all the easy ones, so now their claims will become more and more ridiculous as they have go to insane depths to come up with scare stories.
As we can see here:
Not all frogs are endangered.
I'd like to see the Nature authors respond to that article. It's a good response.
What's the big deal - it's just survival of the fittest.
Now the truth is out!
Global warming forced Anna
off the tennis tour!
Yes, but... one of the primary adaptations for climate change is to move. Because species' ranges and habitats have been restricted, it's harder for them to move, making extinction more likely. Leaving out climate change entirely, human activities have certainly restricted the range of a lot of species.
In the end it's still survival of the fittest as it was meant to be.
Excellent article. The Global WarmingTM true believers just don't like being held to acutal scientific standards.
I find it amazing that the climate never changed over thousands of years until Bush became President.
Frog extinction?? how did they manage to kill off the french?
Oh yeah---tell that to the nutria and fire ant (and thousands of other species whose range has been greatly expanded by human activity.
Climate changes, species go extinct---so what. It has happened since the planet cooled enough to have liquid water.
Change is the reality of the world--you "global warming" propagandists are trying to achieve stasis--which is flatly impossible.
I think you're over-reaching. As I said, I'd like to see the author's response to a fair criticism, and the article seems like a fair criticism. The biggest question, in my mind, is whether the coarse resolution cloud cover data cited would be able to detect trends of increasing cloud cover in a micro-climate like the Monte Verde cloud forest. This is a critical point. The temperature data for that location indicate a favorability toward increased cloud cover.
Just for grins, I've provided a map showing the study area (it's the "MonteVerde Reserve" northwest of San Jose. Compare that to the "study area" box shown on the cloud cover map in the World Climate Report article. (I may see if I can repost that here).
If I had a goal, it would be to limit, as much as possible, the loss of habitat and species tied to human activities. That's a vague and unquantified statement, but it acknowledges that stasis is impossible. However, some planning can mitigate avoidable losses.
So I would be interested in ways that the increasing cloud cover hypothesis put forward in the Nature article could be verified. If you're interested, I already found an article indicating that high-resolution estimates of cloud cover for a particular region differ significantly from low-resolution ISCCP data.
What about the huge disparity between the statistical difference of roughly 12% worst-case increase in extinctions determined by the refuting author vs the 60-ish% claimed by the author(s) of the Nature article? That is a glaring, significant difference.
The authors of the Nature article do not claim that the 69% loss is directly attributable to the change in local climate. They state two things of interest: one, that an increasing incidence of fungus infestation can lead to extinctions of populations still experiencing "normal" weather (i.e., climate change increases the chance of a fungus infestation entering the population and spreading); and two, that most of the extinctions have taken place at altitudes where the minimum temperature is shifting (upward) toward the growth optimum of the fungus.
Because World Climate Report is a climate change skeptical site (it's chief is Dr. Patrick Michaels), the "review" is certainly written to support their POV. But I also stated that its a fair criticism with points that deserve a response. I hope that the hypothesis put forth in the Nature article is critically examined, such that the points raised in the WCR article are addressed.
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