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Health on a Changing Planet

Filed under: — group @ 18 May 2011

by Jim and Rasmus

NOTE: The authors of the book are following this post. If you have questions on this broad topic, ask them!

In the big, wide-ranging world of global change effects, one would be hard pressed to find a topic that is more important–or of more interest to more people–than effects on human health. And in science, one can sometimes also be pressed to find books that smoothly integrate technical knowledge with the experiences and needs of human beings.

So, when you have someone with a lifetime of hands-on experience and academic training in international environmental health, describing the actual and potential impacts of global changes on the health of individuals, societies, and ecosystems, then you have something well worth paying attention to. This is certainly the case with Changing Planet, Changing Health, a new book from the University of California Press, authored by Paul Epstein and Dan Ferber, physician and writer, respectively. Written for a general audience, it deals with a number of current, and potential future, effects of global change—with an emphasis on climate change–on various health-related issues.


Senior author Paul Epstein has a strongly holistic/synthetic health perspective. Accordingly, the book is very wide ranging topically, covering issues from the discovery of the puzzling roots of cholera’s epidemiology, to the effects of large storms on the behavior of the insurance industry, to the social disruptions arising from hurricanes and warfare, to the roots of the problems with the global economic system–and much in between. The book does an outstanding job of connecting many otherwise disparate issues. These topics are all described in simple prose–there are no mathematics or model expositions, few acronyms and little jargon, etc. For these and other reasons, this book is an important and accessible contribution that many will want to read, and which many others really should.

Many of the discussions depict scenarios that are already happening, or could happen in the future, not necessarily what is likely to happen. That is, they provide examples of some possible effects, not an exhaustive attribution-oriented discussion of cause and effect, nor a model-based attempt to weigh future likelihoods of occurrence. The book is structured around chapters which integrate a particular climate change element’s effect on one or more health issues, often involving a personal story of some type. These situations include, for example, the discovery of the changing epidemiology of malaria in East Africa, crop disease and insect attacks in the United States, and the plights of the poor in Honduras.

Paul Epstein

This synthetic viewpoint stands in contrast to the narrower, reductionist perspective which permeates much of current medical science (or perhaps science in general). Accordingly, there is a short synopsis of the systems theory perspective in biology that was a central concept of the seminal work of Ludwig von Bertalanffy in the mid-20th century. It is also not surprising that the book extends the human health theme to the broader topic of system health in several places. In fact, two of the 13 chapters specifically address ecosystem stability issues, using disruptions of marine and forest ecosystems as examples, topics which may or may not have obvious ties to human health issues.

Relatedly, the book returns at several points to the general concept of cumulative effects. This first appears in a discussion of how ecologist Richard Levins of the Harvard School of Public Health influenced Epstein’s thinking on public health. It shows up later in discussions of the similar ways that plant and human pathogens’ virulence depend on the base health state of their hosts. This leads directly into a discussion of the spread of soybean rust throughout the world in the late 20th century, with its potential to greatly reduce yields and hence affect human food supplies. The idea returns yet later in discussions of the ongoing, multiple health stresses experienced by the rural poor in Honduras, making them less able to handle the effects of any additional stresses, such as those resulting from environmental disasters like Hurricane Mitch in 1998. This latter case speaks more generally to the susceptibility of the poor in general.

There are also discussions of potential surprises. For example, they describe the unexpectedly high amounts of beetle herbivory in soybeans in response to elevated atmospheric carbon dioxide, as evidenced by FACE experiments. Another example discusses ragweed pollen, a very important hay fever and asthma allergen. They describe research showing that the quantity of ragweed pollen produced in doubled CO2 environments is increased significantly (61 percent), not because of large increases in size (~ 10 percent) but rather (apparently) due to a changing internal allocation of resources. Life history characteristics of the genus might reasonably predict this result, and there are many factors in the real world that could alter it. But it still serves as a useful example that could otherwise fly completely under the radar.

While the use of ecosystem complexity to illustrate the potential for surprises is certainly valid, it can also be a double edged sword. There will very likely be surprises that have unexpectedly positive results as well, and the overall balance between positive and negative is highly uncertain. My (Jim) one criticism is that I would like to have seen this this point made, with reference to experimental or model results. The plant ecology and/or agriculture discussions would have been a good place to do so, given the complexities/uncertainties involved. The authors’ strongest points are arguably those dealing directly with well-defined and direct human health concerns having demonstrated relationships with well understood climate dynamics.

Several important points of the book relate to biological thresholds. These are ubiquitous in biology at all scales and are illustrated nicely in several places; a particularly good example is the effect of temperature changes on malarial epidemiology. Malaria is caused by species of single-celled parasites in the genus Plasmodium, vectored by mosquitoes primarily in the genera Aedes and Anopheles between many vertebrate hosts, including humans. Debilitating to lethal in effects, the disease also comprises a fascinating scientific story. This includes for example, the effects of weather/climate on the population dynamics of rapidly reproducing, cold-blooded organisms, and the epidemiology of disease spread (and interesting textbook cases in genetics and evolution as well).

Dan Ferber

Epstein and Ferber describe how small changes in temperature can lead to large changes in malarial dynamics. This is a function of both insect and parasite life cycle development time–both of which are typically non-linear. These in turn have non-linear effects on malarial epidemiology, via changing spatial patterns of temperature and precipitation combined with the spatial pattern of human populations and the genetic resistance to malaria therein. So, full Plasmodium falciparum development that takes 56 days at 18 degrees C, but only 19 days at 22 degrees, has very significant implications for a mosquito host that lives only 3 weeks maximum: it allows the full development of malarial parasites which are not possible at the lower temperature. The insect population dynamic also matters, which in an aquatic breeder like mosquitoes, will be a function of both temperature and the existence of water reservoirs having a 3+ week lifetime, which in turn are a function of precipitation intensity and frequency. Insect population threshold effects are also discussed in a later chapter devoted to the topic of tree mortality and bark beetle dynamics in western North America.

The forest that really should not be missed for the trees here, is the importance of these non-linear dynamics in response to climate change.  Considering that many biophysical systems are webs that are considerably more complex than the examples provided, it takes little imagination to realize the potentially high levels of unpredictability that are quickly reached. And this should give any reasonable person–and society–concern about the consequences of forcing the climate into a state that is without precedent in modern society. Science is difficult enough when equilibrium states are the study focus, let alone when strongly forced and thus, transient.

Environmental health also includes non-biological stressors, such as environmental chemicals, food, water and air quality, social upheavals, etc. Epstein and Ferber address these broader issues as well. For example, one chapter is devoted entirely to air quality/composition and its effects on a wide ranging and chronic disease, asthma. They also recognize that global change is not just climatic. They describe, for example, the multiple causes of health effects in places like Honduras, resulting from the combined effects of mangrove clearing and shrimp farming, gold mining, El-Nino changes, and hurricanes, each contributing its part to an unhealthy and unsustainable condition.

Drs. Paul Epstein and Steve Gloyd, and a Mozambican colleague in Caia, Mozambique, in 1978 (L to R; Figure 1 from book)

The book is also not shy about engaging controversial topics or discussing the disinformation campaign. For example, Kenyan malarial epidemiologist Andrew Githeko was targeted a decade ago after his model-based predictions of the spread of malaria into the highlands of East Africa, where it is currently expanding but was historically absent due to the temperature limitations that altitude brings. Several of the tactics of denial that are well known to RC readers, are discussed. Nor are the authors afraid to discuss issues in the socio-political world that drive many of the human behaviors that are leading to climate change as well as the unequal suffering that will be experienced due to inequalities in wealth. And neither are they reluctant to address the multiple social and environmental costs of fossil fuels, such as coal. Once trained in making connections across disciplines, well, the habit tends to express itself.

In the discussions of climate per se, there are a few minor inaccuracies in an otherwise sound discussion of what is known. However, none of these has any bearing on the bigger picture portrayed. For instance, the book discusses the (essentially non-existent) effect of El Nino Southern Oscillation on the Gulf stream; it is possible that the authors actually had the ocean currents off the Peruvian and Equatorial coasts in mind. There is also a misconception in the book’s introduction about the strength of a greenhouse and the thickness of the glass panes, but this does not translate to the greenhouse effect. This is, however, noted later in the book, so the inconsistency is just a glitch. The book also asserts that global warming will lead to more storms, which is still a disputed issue. The situation regarding glaciers on Mt. Kenya is probably more complicated than just a question about temperature – changes in precipitation pattern will also affect their mass balance.

The authors are critical towards certain multinational corporations, discussing for example the role of ‘economic hit men’ (e.g. John Perkins). And although the book covers many topics, it does not discuss population growth, and it touches on communication issues only lightly in discussing why the world has so far failed to act on climate change. This is somewhat ironic, given that the book is one of the best examples we have yet seen regarding the effective communication of climate change issues. It suffices to mention “Climategate”, “Wikileaks”, and social networks (in recent developments in Northern Africa) to understand the power of information/disinformation and communication, in molding public opinion.

The book also mentions Norway as a shining example regarding the tackling of climate change, but the world is more nuanced; Norway also pushed for more oil drilling in the Arctic, and is involved in tar sands in Canada, as well as oil exploration in Libya. Also, much of the surplus that Norway gains from pumping oil is invested into the same kinds of corporations as those Epstein and Ferber describe as part of the problem.

But there is much more to be learned from the book than just the various technical issues discussed. Just as important is the very evident concern with human welfare and justice; these have clearly motivated a very large part of Epstein’s life work, as well as several of those discussed in the book. One particularly good example is the rather amazing story of the Honduran doctor Juan Almendares and his lifelong dedication to the welfare of rural and/or marginalized people there. The importance of this human aspect in solving the impending global climate change problem is most certainly not to be overlooked, and it in fact forms a kind of subliminal undercurrent upon which the various technical discussions in the book all ride.

Paul Epstein and Dan Ferber have created in this book an outstanding synthesis of climate change and human/environmental health concerns. It is born of a lifetime’s work, and addresses topics that will potentially affect a very large number of people. This is a great and needed contribution and we recommend it without reservation.

Handbook in Denialism

Filed under: — rasmus @ 4 May 2011

It would not surprise me if the denialists would deny the existence of the new book by Haydn Washington and John Cook (skepticalscience.com) ‘Climate Change Denial: Heads in the Sand‘. Somehow, I don’t think they will read it – but they are not target group of this book either. Anyway, denialism is, according to the book, a common human trait – we should all know somebody who deny one thing thing or another.

Furthermore, denial is not the same as being skeptical, either, and Washington and Cook argue it is quite the opposite. Hence, the term “skeptics” for these deniers can be described as Orwellian “doublespeak”“newspeak”.

Denial is apparently caused by our lizard brainstem. What coincidence then, when talking about fossil fuels from plants from the era of huge long dead lizards (the fossil fuels are not made of the dinosaurs), that denying evidence for anthropogenic global warming (AGW) is linked to that lizard part of the brain. So, what about using the labels ‘reptiles’ or ‘dinos’? Washington and Cook opt for ‘deniers’, and so will I hereafter.

More »

Unforced variations: Jan 2011

Filed under: — group @ 6 January 2011

After perusing the comments and suggestions made last week, we are going to try a new approach to dealing with comment thread disruptions. We are going to try and ensure that there is always an open thread for off-topic questions and discussions. They will be called (as this one) “Unforced Variation: [current month]” and we will try and move all off-topic comments on other threads to these threads. So if your comment seems to disappear from one thread, look for it here.

Additionally, we will institute a thread for all the troll-like comments to be called “The Bore Hole” (apologies to any actual borehole specialists) that won’t allow discussion, but will serve to show how silly and repetitive some of the nonsense that we have been moderating out is. (Note that truly offensive posts will still get deleted). If you think you’ve ended up there by mistake, please let us know.

With no further ado, please talk about anything climate science related you like.

Blog updates and suggestions

Filed under: — group @ 1 January 2011

New Year, new blog software.

You’ll notice the new preview function for comments, the AddThis button for distributing our content to your favorite social media sites, and various updates to the plugins and functionality you won’t notice at all.

This is always a work in progress, so feel free to comment on the blog as a whole, anything we’re missing, things that work well (or don’t), and perhaps how we might organise content differently in ways that could be more effective. (Note that comments from other threads discussing these issues were moved here).

Thanks for sticking with us, and a happy new year to you all.

Seeing Red

Filed under: — Jim @ 24 October 2010

NOTE: The hijacking and spread of misinformation and slander by certain commenters has led to the closing of further comments on this article.  I am however, very thankful to those many who made good points, asked good questions and provided further references, thus contributing to better public education.  Jim.

Note: This is the first of two or more articles on the extensive tree mortality now being caused by bark beetles in western North America. The goal of this first post is simply to provide necessary background on the relevant biological/ecological processes involved, so that future articles discussing climatic and other possible influences, are more understandable.
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It’s mid autumn in the northern hemisphere, whose deciduous forests annually provide one of earth’s great spectacles. When deciduous trees prepare for their seasonal cold dormancy they partially recycle important elemental components of chlorophyll and the associated photosynthetic machinery, such as nitrogen, phosphorous and magnesium. Other more minor leaf pigments, which vary in abundance and spectral properties from species to species, are then temporarily exposed on the tree before leaf drop. The timing of the chlorophyll loss varies between trees, and when combined with the presence of evergreen conifers, gives the flamboyant array witnessed, typically heavy in the yellow to red pigments.

New Hampshire, USA, in the autumn

If you’ve never seen it, consider putting it on your list of worthwhile things to do in your life, as did the guy from San Francisco I once met on the Appalachian Trail in Vermont. Never mind that he carried most of his gear in a plastic garbage bag slung over his shoulder and wondered why the bears were bothering him at night when he didn’t hang his food (mostly a large hunk of cheese in a paper bag). We were instantly friends when he told me he was on the trail just to see the colors, up close and personal for a few days, in response to a magazine article he’d read.

In western North America, true deciduous forests are strictly riparian and therefore limited. The vast majority of upland forests and woodlands are dominated by conifers, all but one of which are evergreen. However, one highly important deciduous species—quaking aspen (Populus tremuloides), which turns brilliant yellow—forms groves that range in size from a few trees to vast forested expanses, typically on mid to high elevation mountain slopes with decent groundwater supply through the summer. [The largest known organism in the world is a large aspen stand in the West Elk Mountains of Colorado, USA (aspen is highly clonal, connected by rhizomes).] The greens and yellows provide a poor man’s version of fall color compared to an eastern hemlock-hardwood forest perhaps, but when combined with often colorful rock exposures, blue skies and rivers, and montane topography, the sight usually has its own magnificence.

Red foliage however, is one thing you’re not supposed to see a lot of in western North America, any time of year.

In many places in the west–particularly through the central and northern Rocky Mountains and British Columbia–there is now a lot of red foliage, but unfortunately, it’s not just in autumn, and is occurring on non-deciduous species. The proximate causes of this are (1) Dendroctonus spp. (literally, “tree killer”), the most destructive of several destructive bark beetle genera, and (2) tree physiological stress. God’s “inordinate fondness for beetles”*, combined with certain human activities, is now causing some serious problems indeed. Here I’ll try to give background on the issues related to bark beetle outbreaks, working from proximate to ultimate causes, and focusing on the one beetle species currently doing by far the most damage, the mountain pine beetle (MPB), Dendroctonus ponderosae. The MPB is attacking a set of highly important pine species (Pinus spp.) over a very large area of western North America, especially lodgepole pine (Pinus contorta), ponderosa pine (Pinus ponderosa) and whitebark pine (Pinus albicaulis), but also some of the other five needle pines (esp. limber pine). Other species of beetles in the genera Dendroctonus and Ips are also doing some serious damage to these and other species, albeit at smaller spatial scales and/or less intensively, and represent so many variations on the theme illustrated by the MPB.

Not New Hampshire in autumn. MPB mortality on whitebark pine in western Wyoming’s Bridger-Teton National Forest. (Fig. 4 of Bentz et al, 2010)

Theological considerations aside, there are many hundreds of species of bark beetles worldwide, and the Curculionidae, or weevil family, of which bark beetles are a member, contains the largest number of species of any animal family. However, only a very small percentage of “aggressive” bark beetle species has the potential to cause extensive tree death during population outbreaks (“irruptions”). These species kill by overwhelming, with coordinated aggression and sheer numbers, a tree’s defenses, followed by a complete destruction of the tree’s ability to transport the products of photosynthesis (e.g. sucrose, amino acids, hormones, etc.) through its transport tissue, the phloem or inner bark. This is usually accompanied by an impaired ability to transport water to the leaves via the outer xylem (the sapwood), courtesy of blue stain fungi (e.g. Grosmannia or Ceratocystis spp.) carried and introduced by the beetles. As ecological systems go it’s very well studied, and contains the interesting wrinkles, non-linearities and feedbacks so typical of ecological systems, even relatively simple ones like this. Plant physiology and demography, insect population dynamics, insect-fungal symbioses, land management practices, and climate dynamics all play important roles in the overall outbreak process. Simplistic explanations of the causes of these dynamics are, as usual, to be avoided.

Whether or not an individual tree will survive a beetle attack is determined by its pre-attack nutritional and hydration states, and the number and timing of beetles that attack it. Conifers defend themselves with both pre-existing (“constitutive”) and de-novo (inducible) defense systems. In pines, resins–a large class of complex plant chemicals that function as antimicrobials, fungicides and insect toxins –are delivered primarily via a constitutive production/delivery system consisting of resin canals lined with resin-producing epithelial cells. Resins typically have strong and interesting odors (familiar to many in products like turpentine, a commercial resin derivative), and they cause the distinctive smell of a pine forest in the summer when they vaporize from leaves and bark. They are produced and delivered in solution, flowing through the ramifying canals in the outer sapwood (the mostly live, water conducting part of the wood) and phloem, which exist solely for that purpose. These solutions are typically highly viscous and sticky, not unlike the consistency of molasses or honey.

Adult mountain pine beetle, about 6 mm long.

Beetles attack by chewing straight through the outer bark into the phloem. If they sever a resin canal of a healthy, hydrated tree, there is an immediate and forceful flow of resin solution under hydrostatic pressure that often kills the beetle. This action represents a cost to the tree however, in both water and resin, the latter being metabolically highly expensive material. If the tree’s carbon balance has been suffering and/or the tree is not well hydrated–due to things such as drought stress, an extended beetle attack or low light levels–its ability to maintain resin solution pressure and/or chemical toxicity, is accordingly reduced. Inducible defenses are also important and involve gene activated cell death and a subsequent “walling off” of living cells/tissues via induced biochemical processes, to slow the beetles’ and fungus’ physical progress in the tree. Although many beetles will thus typically be killed or isolated during an attack, even a perfectly healthy tree can eventually have its defenses overcome by sheer beetle numbers. These trees then become breeding grounds for a repeat of the process on other, nearby trees. This leads directly to issues in beetle population dynamics, which are arguably the most critical element in the system’s dynamics.

Bark beetle population growth potential depends on forest structure and composition, tree vigor, and weather/climate. A key reason for the destructive potential of aggressive species like the MPB is plasticity in the number of generations produced per year, which correlates well with mean annual temperature. There are (at least) two direct temperature effects (and likely several other indirect ones) on beetle population processes. In the warm season, warmer temperatures accelerate development through several larval stages and pupation, and in the cold season they can reduce the kill of over-wintering larvae. In the MPB, two (or more) generations can be produced per year in warmer climates (“multivoltine” reproduction) while only one half generation per year may occur in more northerly or higher elevation populations. For equivalent food supply and fecundity rates, this variability in generation time will obviously have a very strong effect on the number of adult beetles emerging per unit time to attack new host trees (although the thermal requirements for the full developmental cycle can mitigate this somewhat). As a generalization, winter temperature controls are relatively more important in colder climates than in warm ones, so the thermal controls on population growth will vary with geography and physiography. Also, generation time has important implications for the potential rate of evolutionary adaptation to changing growth constraints (such as host defenses or climatic tolerances), via the total possible number of genetic recombination chances per unit time. Plants and their insect herbivores have been involved in this evolutionary battle for tens of millions of years, and have developed some fascinating defense and attack mechanisms in the process. It’s not at all easy being green.

Life cycle timing of the mountain pine beetle in British Columbia

Because a tree can recover from some limited number of beetle attacks–by restoring its carbon balance and/or hydration over time–aggressive species like the MPB do not allow this to happen. They do so by emerging from trees within a narrow window of time, roughly 2-3 weeks (also temperature dependent) and then coordinating their attacks using chemical communication (i.e. pheromones). For the MPB in southeast Wyoming’s Snowy Range for example, where there is currently one generation per year, emergence from lodgepole pine is typically in high summer (late July to early August) when trees are feeling the effects of summer water stress. The pheromones released by inititial colonizers signal to newly emerging beetles in flight that an attack is underway, drawing a critical mass of beetles into a coordinated attack on certain trees exceeding a minimum basal diameter. (Beetles reproduce far more effectively in larger trees and near the tree base, because the phloem food source is thicker there.) This creates an attack that would otherwise be far more diffuse and less effective, were beetles to just land randomly on potential hosts. Once tree defenses have been overwhelmed and the tree is certain to die, other pheromones are then produced which drive in-flight beetles away, thereby maximizing the food resource for the colonizing beetles and their coming offspring.

A tree under attack, with vigorous defense of resin exudate from entrance holes. This tree will not likely survive.

Tree physiological stress also plays a critical, climate-dependent role, especially in getting an outbreak started. A central tradeoff in all vascular plants is the unavoidable loss of water for a given gain of carbon dioxide, since both exchanges occur via stomatal pores on leaf surfaces. When plant water status drops below minimum levels required for cell functioning, stomates quickly close and carbon fixation thus stops. When light levels are low, carbon fixation also slows (albeit for different biochemical reasons). High tree densities can thus limit per-tree water and/or light availability, leading to lowered photosynthesis and consequent carbon balance problems that directly affect trees’ abilities to defend themselves from predation. An MPB population can very quickly irrupt in, and destroy, a stand of physiologically weakened trees. Healthy forest stands and landscapes, and mixed species and/or mixed size forests, stand a much better chance of at least slowing an outbreak down, especially at as the spatial scale increases. However, even then, large forested areas can eventually be overwhelmed by sheer beetle numbers, as is now happening in many places.

Much of western North America has elevated tree densities, relative to pre-settlement times, either for all trees, the largest tree classes thereof, or both. This is primarily due to active fire reduction/suppression policies over the last century or more by federal and state land managers, and/or timber harvesting practices. The resulting increased competition, without any increased climate stresses, would by itself increase tree physiological stress and affect beetle outbreak dynamics. The addition of warmer and/or dryer conditions simply magnifies this problem. Similarly, increased climatic stress unaccompanied by increased competition would also favor the beetles. Because natural fire regimes varied widely historically, and are complicated in many places by similar variability in logging practices and intensities, the effect of fire reductions on bark beetle outbreaks varies considerably and involves several issues of spatial and temporal scale variability. This makes the topic both interesting and difficult, and requires good information on past land management practices and forest stand dynamics. That topic however is fodder for another post.

*A famous quote, sometimes attributed to Charles Darwin, but formally attributed to evolutionary biologist J.B.S. Haldane (in: Hutchinson, G.E. (1959). Homage to Santa Rosalia, or why are there so many kinds of animals. American Naturalist 93 (870): 145-159): “There is a story, possibly apocryphal, of the distinguished British biologist, J.B.S. Haldane, who found himself in the company of a group of theologians. On being asked what one could conclude as to the nature of the Creator from a study of his creation, Haldane is said to have answered, “An inordinate fondness for beetles.””

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The next article will discuss the geography and dynamics of the beetle outbreaks in relation to likely causative factors, including climate. I encourage those interested to read the following recent paper:

Bentz, B.J. et al. 2010. Climate change and bark beetles of the Western United States and Canada: Direct and indirect effects. BioScience 60(8):602–613:

General References:

Raffa, K.F. 1988. The mountain pine beetle in western North America, pp. 505-530 in: Dynamics of Forest Insect Populations., A.A. Berryman ed. Plenum Press, New York.

Gibson et al., 2009. Mountain Pine Beetle. USDA Forest Insect and Disease Leaflet 2

Leatherman et al., 2010. Mountain Pine Beetle (Colorado State University Extension Fact Sheet)


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