The Loom

A Complicated Death

harlequin%20frog.jpgLast 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.


  1. #1 Joseph K.
    January 11, 2006
  2. #2 Mark Paris
    January 11, 2006

    This illustrates a point I have made in comments on some blogs regarding the the difficulty of exactly predicting the effects of global warming. Global warming deniers or contrarians use this uncertainty to argue that we don’t need to do anything. I argue that the uncertainty makes it all the more important to do something before we make global changes that might take decades or even centuries to undo. Some have argued that global warming might be beneificial, but it makes little sense to bet the planet on that possibility, since the potential effects range from beneficial to disasterous. In this case, the frogs might be our miners’ canaries.

  3. #3 Seth
    January 11, 2006

    I wonder if the changing affects of the temperature, this nighttime warming and daytime cooling, are as new as when scientists began to notice (make a link) between rising temperatures, fungus growth, and this frog species? That is, I wonder if this 1980s-present timeline is the right timeline to begin to correlate with global warming changes…what is the right timeline to think about how global warming could cause species extinction?

  4. #4 Ian Gibson
    January 11, 2006

    I think the problem is that we have to get across the potential seriousness of global warming, without overstating the case and having the doubters jump on it. But at the same time it’s not like a lab experiment where you can take your time and replicate everything – there’s only one Earth so we need to trade off a little accuracy for speed sometimes. This obviously is a difficult compromise.

  5. #5 David B. Benson
    January 13, 2006

    Related to global warming, I recommend

    W.F. Ruddiman, “Plows, Plagues, and Petroleum”

  6. #6 Brian S.
    January 13, 2006

    Seems like there’s another timeline problem here – while current warming levels are unprecedented for a historical timeline of 1000+ years, they’re not unprecedented for the many thousands/million year timeline of a species like a frog.

    The frogs have dealt with these temperatures before, which presumably had the same local climate effects. Why is it killing them off now?

    I don’t have a subscription to Nature, so I don’t know if it addresses this issue.

  7. #7 Daniel Newby
    January 13, 2006

    Mark Paris said “I argue that the uncertainty makes it all the more important to do something before we make global changes that might take decades or even centuries to undo.

    Brian S. asks: “The frogs have dealt with these temperatures before, which presumably had the same local climate effects. Why is it killing them off now?

    You are implicitly assuming that preindustrial Earth was a stationary equilibrium, a joyous final utopia perfected by mother Gaia gently working for eons.

    It was not. Every time the ice swept out from the poles, vast swaths of forest were killed, then ground into dust by glaciers. And then when it swept back, all the efficient fluffy white creatures baked to death. A straits plugged up and its inland sea evaporated into salty hell, taking all the fish and most of the amphibians with it. Then the straits eroded open again and the valley creatures drowned. Krakatoa erupted, wiping out who knows how many species of rare gnat and orchid. Then it erupted again, wiping out all new rare species. Islands sink into the sea, others rise up in the middle of migratory routes.

    That’s life. Species die all the time. Other species are born when opportunities open up.

    The lesson for the human race is not “never do anything” but rather “don’t travel by bulldozer when sneakers will do”.

  8. #8 Francois Ouellette
    January 18, 2006
  9. #9 John
    January 18, 2006

    It can be very confusing because all change is inevitable and why all things evolutionary are so surprising (except in absolute retrospect). I guess what to take is just that while climate changes ARE inevitable, with the attending loss of species, let’s not HASTEN it with our own actions. But even this is confusing because there are now 6 billion of us and WHATEVER we do will have enormous consequences – and those consequences will bring more change and change equals loss of species. A few hundred years ago there was only a billion of us. THAT ALONE is an ENORMOUS change… even discounting the technological changes that our higher intelligence will continue to unleash.

  10. #10 Filipe
    January 18, 2006

    Carl Zimmer writes again on problems related to global warming. This post is mostly about consequences, not the mechanism, but people’s biases are again evident here in the comment section. I find it strange that many people who probably are unable to critically read a scientific paper on the subject feel that have authority to insult people who think that the issue is not settled. I find particularly offensive the comparison to creationists in a previous post, and the contempt implicit in the term naysayers in one comment above.

    Global warming is a well established fact but one must be aware that the assumption of an origin due to the greenhouse effect from human activity is based in semi-empirical models with many unknowns, including those related to the major heat and carbon sink: the oceans. Sorry but I have a lot of problems believing any long term previsions from those models. First we need to better understand the oceans. It is a good idea to start taking measures (changing the atmosphere content of CO2 can’t be a good thing) based on our current understanding of the phenomenon but this is a new scientific field and more resources are needed.

    A serious problem, although remote, is what will happen to people’s perception of science if the effect starts reversing. One of the most interesting coincidences in Earth’s recent past is the little ice age during the Maunder minimum of solar activity. The problem here is the lack of a physical mechanism which would link solar activity and temperatures at the Earth’s Atmosphere. Simple proxys like sunspot numbers and time between solar maxima, do not correlate eactly with temperature increase. It now seems that the important factor is Galactic Cosmic Rays (GCR) flux, which depends on solar activity (sunspots) but also on a parameter during solar minima (tilt of the neutral line). The relation of GCR flux and cloud cover is debatable but there is a slight possibility that this might contribute to climate change. We need to study this better but the political histeria that took over this topic makes it hard.

    The problem is that if the Sun also contributes to climate change and during the next solar cycles things change and temperatures start going down science will lose credibility among the public. Positions like Carl Zimmer putting all opponents in the field of crackpots and creationists do not help. Although there is a widely accepted view in the scientific community that human activity is to blame, there is still a lot to learn on the subject. In science one must always be prepared to accept the fact that consensus views may be wrong.

    The most disturbing thing about the paper discussed in the other post was the disclaimer that the authors had to put at the end. It would be important to know if it was there in the original version or if it was added on request from the referee. If I were the referee I would have asked them to take it, it’s an opinion not science. It is a bad sign when you are afraid to be labeled as an opponent to something in your field of research.

  11. #11 David B. Benson
    January 18, 2006

    Re #10 — Ruddiman’s book, cited in #5, offers
    an explaination of the so-called Little Ice Age.
    The text offers a, presumed causative, corrolation
    between human activity since the advent of
    agriculture and the climate record. The explaination looks plausible and does not require
    any deep aspect of the current attempts to do
    computer-based climate modelling.

    Much more on climate and global warming may be
    found on the
    web site, which seems a prefered place for discussions of climate, not the least because the climatologists who run the site promptly answer questions.

  12. #12 Filipe
    January 18, 2006

    about #11. The reference you give is mostly a just-so story, possible but not compelling. The remarkable thing about the little ice age is the incredible coincidence with the absence of sunspots. According to the author you read the Sun could explain from 0 to 100% of the climate change. How I wish we had a few hundred years of data to work with. The problem is that if we wait until we have enough data and this thing is due to human activity then it may be too late to do anything.

    Yes, I know, I go there sometimes. It is run by atmospheric people, so it is biased towards green house models (GHM).

    But this has nothing to do with frogs so I’ll stop here. I was just upset at the use of things like creationist in what should be a scientific debate. I enjoy this blog and was really disappointed by that post. Science needs controversy and opposing points of view to progress faster, ad-hominem is not the way to go.

  13. #13 John
    January 19, 2006


    From MSNBC tonight –

    WASHINGTON – Six former heads of the Environmental Protection Agency — five Republicans and one Democrat — accused the Bush administration Wednesday of neglecting global warming and other environmental problems.

    “I don’t think there’s a commitment in this administration,” said Bill Ruckelshaus, who was EPA’s first administrator when the agency opened its doors in 1970 under President Nixon and headed it again under President Reagan in the 1980s.

    For full article go to –

  14. #14 Filipe
    January 19, 2006

    To #13, John thanks for the link. Climate studies should be a priority, there could be dramatic changes during a period corresponding to a human lifetime. We need to better understand the consequences and the mechanisms of this thing, and we need it fast.

    Getting back to frogs, I just read the Nature article and I can not understand how that paper got published. It’s mostly wishful thinking. When I read the paper I entered in referee mode and made a series of annotations which I expected the original referees should have caught. In my view the paper data proves the contrary of what is in the title, namely that global warming had very little impact in the frogs demise.

    I’m not an expert in this particular field but finding trends in noisy data is similar in many fields, and it puzzled me that at least some researchers in this area were not trashing this paper. Apparently they are. Francois in #8 gives a link which I advise everyone to read. The authors in that page find exactly the same problems that I had found, and conclude that the frog’s extinctions had very little to do with climate change. The authors suggest that the frog’s problems may in fact be due to spread of the fungus from transport by ecotourists. It still wold be the humans fault, but related to a different aspect of modern human life, not to the pouring of CO2 in the atmosphere and raising the planet’s temperature.

    Politics tends to get into the way of good science, and anything that can only vaguely be related to global warming will be linked to it. My problem here is how this will affect people’s perception of science, since press reports are biased towards the scientists who present the scariest possible alternative.

  15. #15 John
    January 19, 2006

    My gut tells me that most thoughtful people understand that the complete picture of global warmimn is far from clear, but what concerns many of the folks that you refer is simply that the current administration, and the GOP in general, seem to be not only turning a blind eye toward the issue (presumably because it may bring up things that “aren’t good for business as usual”) but, worse, actually putting roadblocks in the path of those who want the problem discussed freely and openly. Hell, I’m fine if the bulk of research proves conclusively that human activities have very little to do with global warming. I just want the people who are experts in it to have support in their research and then have their findings made available without being overtly or covertly censored.

    The results of scientific findings don’t scare me. The politicization of them do.

  16. #16 Filipe
    January 19, 2006

    John after reading the puppet masters post maybe those in the administration are irrational because global warming is good for some parasite in control of those people. That post and this one about the poor frogs demise depress me.

    Politization is not what really scares me the most, I’m pessimistic and think people will prefer to adapt to global warming than try to prevent it unless it’s completely catastrophic (I don’t know many people willing to live without a car). Just for the record, I do believe that we are to blame for global warming, but I think we should cover other alternatives and not label opposing scientific views with names like creationist.

  17. #17 John
    January 20, 2006

    True. But let me ask you this – do you think the vast majority of creationists have little concern for the issue of global warming? Because if so, it would account for the confusion of those who label people who express doubts about global warming as being part of the creationist crowd. Clearly not all such folks are creationists, but I can see where some would confuse the two groups.

  18. #18 Filipe
    January 20, 2006

    John, Carl Zimmer comparison with creationists holds mostly due to a weakness in the media, including the so-labeled liberal media. The thing that most impressed me from the judge report on the Dover trial is that he clearly distinguished between one camp with scientists having peer-refereed publications in the field, and the other camp with no valid scientific work. The press generally does one of two things: (1) publishes the most scariest report or (2) tries to be fair and presents the views of someone for and someone against. The problem is that you can not put in equal terms a scientist and a crackpot that only says garbage. In science the debate must always be among scientists, and the scientists must be experts in the field. Unfortunately the media does not do that.

  19. #19 Carl Zimmer
    January 20, 2006

    Filipe, you are incorrect to suggest that my post on global warming makes a blanket statement about skeptics being equivalent to creationists. I point specifically to misleading “quote-mining” as a strategy used by both creationsits and a specific global warming skeptic.

  20. #20 Francois Ouellette
    January 20, 2006


    “Quote mining” is used by creationists and evolutionists, by global warming skeptics and global warming believers. When an issue becomes politicized, people like to use Science as an “objective” ally, and scientists themselves are not immune to that because they are also people with opinions.

  21. #21 Filipe
    January 20, 2006

    Carl, in regard to global warming most people don’t have real knowledge, only have opinions and fears, and both sides in the global warming debate are exploiting this. Quote mining is mostly due to the fact that very few people talking about this can critically read a scientific paper on the subject. People with political interests can be very biased for they know that their ignorance only shows to experts.

  22. #22 Rakan Al-Sabah
    January 21, 2006

    Global wamring is a problem that we as the problem have to solve. We have to take action and stop our pollution. We have to be men and women about it and accept that we are ruining our planet. There’s only one way to stop this and thats throught the people.

  23. #23 Luke Lea
    January 21, 2006

    Mark Paris says,

    “This illustrates a point I have made … regarding the the difficulty of exactly predicting the effects of global warming. Global warming deniers or contrarians use this uncertainty to argue that we don’t need to do anything. I argue that the uncertainty makes it all the more important to do something before we make global changes that might take decades or even centuries to undo. Some have argued that global warming might be beneficial, but it makes little sense to bet the planet on that possibility, since the potential effects range from beneficial to disastrous.”

    I think the real issue, which climatologist seem reluctant to face, is whether there is anything we can do — within reason — that would significantly slow the growth in emissions of carbon dioxide into the atmosphere? The answer, based on everything we know about the new world economy, would seem to be “not much.”

    In short, my hunch — and I may be mistaken about this — is that the climatological community, whose cultural roots lie in the countercultural radicalism of the 60’s with its Small-Is-Beautiful ethos, re reluctant to surrender their principled opposition our consumerist society along with the never ending-growth of the corporate-capitalist-industrial complex on which it depends. Again let me say that I might be wrong about this, so I would like to hear any comments from persons who are more intimately acquainted with this subculture, preferably someone who is not on the left. As an aside let me say that, in my opinion, the Small-Is-Beautiful ethos, which I share, being myself a child of the 60’s, is perfectly capable of reinventing itself within a capitalistic framework.

    Another possible source of reluctance is a fear, not entirely misplaced, that if the public attention turns away from the problems of mitigation and towards the problems adaptation, global climate modellers will no longer occupy center stage, and they may not receive the same level of funding. These fears are probably, not misplaced. But even so it is important to realize that climatological expertise will still be needed, but more on the regional rather than the global level: how high should sea walls be built in which parts of the world; in which areas will agricultural practices have to shift and by how much; whether and to what extent we might need to plan for the migration of populations away from the equator and closer to the poles — these are the kinds of questions that will have to be addressed..

    In short, whatever else they may be climatologist are human beings just like the rest of us; and like everybody else, including yours truly, they are prey to all the foibles and short-comings of human nature. It’s fun being at the center of attention, it’s not fun being down-sized, and nobody likes surrendering the dreams of their youth.

    Best wishes to all.

    Luke Lea

  24. #24 john
    January 22, 2006

    Call me Zimmer’s attack-dog –

    I carefully re-read Carl’s earlier post on global warming. It’s very clear that he in no way said that those who opposed the notion of human-caused global warming were creationists or even the same as creationists. He said that when he saw some of the quote-mining from them it gave him a sense of deja vu, as he has seen it so many times from creationists. He goes on to admonish them that if they don’t like the comparison, they should stop, and simply let their science do the talking.

    OK Carl, what’s my reward? I’ve never read Parasite Rex (hint).

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