At the other end of the world, Pockely (2001) reports the results of a survey of the plants and animals on Australia's Heard Island, a little piece of real estate located some 4,000 kilometers southwest of Perth.  Over the past fifty years this sub-Antarctic island has experienced a local warming of approximately 1°C that has resulted in a modest retreat of its glaciers; and now, for the first time in a decade, scientists are documenting what this warming and melting has done to the ecology of the island.  Pockley begins by reporting on the "rapid increases in flora and fauna" that have accompanied the warming, quoting Dana Bergstrom, an ecologist at the University of Queensland in Brisbane, as saying that areas that previously had been poorly vegetated are now "lush with large expanses of plants," and to this information he adds that populations of fur seals have also expanded rapidly.  In fact, he cites Eric Woehler of Australia's environment department as informing him that fur seals have emerged from "near extinction" to a population of 28,000 adults and 1,000 pups.

In between these far-flung chilly regions (where warming would be expected to enhance the abilities of land mammals to survive and reproduce), Lawler (1998) examined biogeographic relationships of mammals that are typically found on mountaintops in the Great Basin of western North America, which effort was undertaken with the objective of determining their future well-being in the face of predicted climate-driven changes in their environment.  Interestingly, and contrary to the conclusions of earlier more simplistic studies that predicted dramatic global warming-induced reductions in the numbers of mammals in this region, Lawlor concluded that "virtually no extinctions can be expected from a projected 3°C rise in temperature."  The results of this study, as well as those of Grayson (2000) and Grayson and Madson (2000) stand in stark contrast to the doom-and-gloom predictions of climate alarmists, who incessantly claim that global warming will lead to a mass extinction of species nearly everywhere on earth because, as they say, plants and animals will not be able to migrate rapidly enough to keep up with the shifting climatic zones to which they are currently accustomed, or that they will literally "run out of places to run," as in the case of mountain-top dwellers.  As logical as that hypothesis might sound, however, more complex studies, such as the one reviewed here, indicate that it is wrong, simply because earth's plants and animals are not the simpletons climate alarmists make them out to be, possessing a wide array of strategies for coping with environmental change and re-colonizing former territories after having once been forced out of them.

Somewhat similar relationships to those that have been observed in colder locations on land have also been identified in colder marine environments. Heide-Jorgensen and Laidre (2004), for example, examined changes in the fraction of open-water found within various pack-ice microhabitats of Canada's Foxe Basin, Hudson Bay, Hudson Strait, Baffin Bay-Davis Strait, northern Baffin Bay and Lancaster Sound over a 23-year interval (1979-2001), using remotely-sensed microwave measurements of sea-ice extent, after which they related the trends they discovered to the winter success and survival of various marine animals, including the cetaceans (water mammals, such as whales, porpoises and dolphins).

The two scientists report that Foxe Basin, Hudson Bay and Hudson Strait showed small increasing trends in the fraction of open-water, with upward trends at all microhabitats studied ranging from 0.2 to 0.7% per decade.  In Baffin Bay-Davis Straight and northern Baffin Bay, on the other hand, the open-water trend was downward, and at a mean rate for all open-water microhabitats studied of fully 1% per decade, while the trend in all Lancaster Sound open-water microhabitats was also downward, in this case at a mean rate of 0.6% per decade.  In addition, Heide-Jorgensen and Laidre report that "increasing trends in sea ice coverage in Baffin Bay and Davis Strait (resulting in declining open-water) were as high as 7.5% per decade between 1979-1999 (Parkinson et al., 1999; Deser et al., 2000; Parkinson, 2000a,b; Parkinson and Cavalieri, 2002) and comparable significant increases have been detected back to 1953 (Stern and Heide-Jorgensen, 2003)."  They also note that similar trends in sea ice have been detected locally along the West Greenland coast, with slightly lower increases of 2.8% per decade (Stern and Heide-Jorgensen, 2003).

With respect to these observations, the two scientists note that "two types of vulnerability have been identified relative to increasing sea ice: i) the direct physical impact of sea ice as a barrier for air-breathing foraging animals; and ii) the cascading effects of changes in marine productivity."

The first of these problems most affects the cetaceans, including over 50,000 narwhal, 20,000 beluga and many bowhead whales; and Heide-Jorgensen and Laidre say "there is sufficient evidence to detect a clear decline in the amount of open-water in several narwhal wintering microhabitats, including the Northern Wintering Ground, Southern Wintering Ground, Disko Bay, Store Hellefiske Bank, North Water and Cumberland Sound and adjacent offshore areas," several of which locations also serve as wintering grounds for beluga and bowhead whales.  A crisis of huge proportions appears to be building, as the sea ice of these regions continues to increase in response to regional cooling.  Also, increasing sea ice coverage in combination with environmental variability, as they describe it, "leads to an increased frequency of periodic complete freeze-over," and according to the two scientists from the Greenland Institute of Natural Resources, who are experts in the field, this phenomenon "can result in catastrophic mortalities that can affect population trajectories."  In the case of Disko Bay, for example, they report that "less than 5% open-water was observed on 89% of the days in March between 1992-1995, and during this period, 15% of these days had complete freeze-over."  Already, in fact, hundreds of narwhals have died during episodes of rapid sea ice formation caused by sudden cold periods (Siegastad and Heide-Jorgensen, 1994; Heide-Jorgensen et al., 2002).

Clearly, the decades-long cooling of these regions is becoming very dangerous for the marine mammals that inhabit them.  As described by Laidre and Heide-Jorgensen (2005), "cetacean occurrence is generally negatively correlated with dense or complete ice cover due to the need to breathe at the surface," and that "lacking the ability to break holes in the ice," narwhals are vulnerable to reductions in open water availability, as has been demonstrated by ice entrapment events "where hundreds of narwhals died during rapid sea ice formation caused by sudden cold periods," which events are becoming ever more likely as local temperatures continue to decline and sea ice cover and variability increase, which latter two trends were found by them to be "highly significant at or above the 95% confidence level."  Hence, they conclude that "with the evidence of changes in sea ice conditions that could impact foraging, prey availability, and of utmost importance, access to the surface to breathe, it is unclear how narwhal sub-populations will fare in light of [cooling-driven] changes in the high Arctic."

Returning to land mammals, we complete our summary with reports of two studies that broach somewhat different aspects of the CO2-climate-mammal connection.  In the first, which we discuss in our Editorial of 7 Aug 2002, we note that New Zealand scientists have demonstrated that condensed tannins, which are found in many pasture plants, can reduce methane emissions from grazing mammals such as sheep and cattle, and thereby reduce the global warming potential provided by this powerful greenhouse gas.  So what are condensed tannins, and what do they have to do with atmospheric CO2?

Condensed tannins are naturally-occurring compounds found in a number of different plants that sometimes act to deter herbivorous insects.  In New Zealand, the "legume lotus" is one of the primary sources of these substances; and scientists have determined that sheep and cattle feeding on it reduce their methane emissions by as much as 16%.  So thrilled are they by this finding, they are now talking, not only of using more tannin-producing species as animal forage, but of genetically introducing tannins into other pasture species as well.

The role of the ongoing rise in the air's CO2 content in this rapidly developing scenario may be deduced from a 1999 study of its effects on condensed tannin production in four genotypes of Lotus corniculatus, specimens of which were collected half a world away in meadows south of Paris, France.  In that study, Goverde et al. (1999) determined that a 350-ppm increase in the atmosphere's CO2 concentration increased tannin production in one lotus genotype by 17%, in a second genotype by 33%, in a third by 61%, and in a fourth by 140%.  It is interesting to note, in this regard, that whereas the world's scientists are just now discovering this significant means of combating one of the atmosphere's most powerful greenhouse gases, i.e., methane, nature has been employing the technique since the dawn of the Industrial Revolution, steadily boosting tannin production in plants that are eaten by ruminants as the air's CO2 content has gradually risen.

These findings are truly welcome, yet they are only part of the good news reported by the New Zealand scientists, who note that tannins "have a variety of other animal related benefits, such as improved milk yields, increased liveweight gain, decreased internal parasite burden and reduced occurrence of bloat, dags and fly strike."  And, again, all of these tannin-induced benefits would be expected to be significantly enhanced by the increases in the air's CO2 content that increase forage tannin concentrations.  In addition, it is important to note that there are a great number of grazing mammals in addition to sheep and cattle, including antelope, bison, buffalo, camel, deer, giraffe, goat, llama, etc., and that these mammals eat a number of other types of plants, which may also experience increases in leaf tannin production as the air's CO2 content rises, as has in fact been found to be true for a number of different plant species, including both deciduous and evergreen trees (Lindroth et al., 1993, 1995; Traw et al., 1996; Hattenschwiler and Schafellner, 1999) and grasses (Goverde et al., 2002).

In light of these several observations, it can be appreciated that many mammals, both wild and domesticated the world over, may be participating in this important natural "program" for reducing methane emissions to the atmosphere.  Could it be they are partially responsible for the reduction in the rate-of-rise of the atmosphere's methane concentration that has been observed over the past few decades (see Methane (Atmospheric Concentrations) in our Subject Index)?  If so, we can expect to see more of the same as the air's CO2 content continues to climb; for the biosphere, it would seem, takes care of its own, as demonstrated by this unique negative feedback phenomenon that tempers greenhouse gas-induced global warming.

In closing out this Summary, we report the results of the study of Mattson et al. (2004), who grew one-year-old seedlings of silver birch trees in closed-top chambers for one summer and autumn in pots containing an unfertilized commercial peat maintained at three different soil nitrogen levels and two temperature regimes in air of either 362 or 700 ppm CO2, after which feeding trials with caged Eurasian hares were carried out and a number of chemical analyses made of the tops of the seedlings and the basal parts of their stems.  In a second experiment, they grew paper birch trees from seed for two 140-day growing seasons in well-watered and fertilized pots placed within FACE rings maintained at atmospheric CO2 concentrations of either 362 or 562 ppm, after which (in an unplanned aspect of the study) North American eastern cottontail rabbits fed ad libitum, consuming bark tissue down to and scoring the wood, on the basal third of the seedlings, which tissues were also tested for the presence of various herbivore-deterring chemical constituents.

So what did the scientists learn?  "As expected," in their words, "elevated CO2 substantially increased the above-ground woody biomass growth of both paper birch (63%) and silver birch (21%)."  In addition, noting that "numerous studies have shown that elevated atmospheric CO2 often, but not always, elicits increases in carbon partitioning to carbon-based secondary plant compounds," which tend to act as deterrents to herbivory, they say their findings "confirm this general pattern in silver and paper birch."  Last of all, they report that high CO2 reduced hare feeding on silver birch shoots by as much as 48%, and that it reduced rabbit feeding on paper birch stems by about 51%, while neither temperature nor severe early-season defoliation (another experimental treatment) affected tree resistance against these mammalian herbivores.

Calling the anti-herbivory effect of elevated CO2 "remarkably strong," and noting that rabbits "overwhelmingly preferred ambient CO2 plants," Mattson et al. say their data "clearly suggest that the defensive biochemistry of paper birch twigs as well as the main stem were [positively] altered as the result of elevated CO2."  Hence, we can expect that as the air's CO2 content continues to rise, at least these two species of birch trees will have a significantly easier time getting established and growing to maturity, in that they likely will not be harmed nearly as much by rabbits and hares munching away at their trunks and branches while in their early growth years.  And, of course, this phenomenon should leave much more foliage for other ruminant mammals to feed upon.

In conclusion, we see that where warming-induced extinctions of mammals have often been predicted to occur, they are highly unlikely to be realized in nature, and that where warming may be expected to open up new territories for mammal range expansions, such does indeed take place.  We also see that warming may benefit many marine mammals that currently are threatened by extensive seasonal ice cover, and that rising atmospheric CO2 concentrations may lead to reductions in methane emissions from land mammals, while they simultaneously produce changes in the palatability of the trunk and branch tissues of certain trees that may protect them from being killed by voracious hares and rabbits.

References
Deser, C.J., Walsh, E. and Timlin, M.S.  2000.  Arctic sea ice variability in the context of recent atmospheric circulation trends.  Journal of Climate 13: 617-633.

Goverde, M., Bazin, A., Shykoff, J.A. and Erhardt, A.  1999.  Influence of leaf chemistry of Lotus corniculatus (Fabaceae) on larval development of Polyommatus icarus (Lepidoptera, Lycaenidae): effects of elevated CO2 and plant genotype.  Functional Ecology 13: 801-810.

Goverde, M., Erhardt, A. and Niklaus, P.A.  2002.  In situ development of a satyrid butterfly on calcareous grassland exposed to elevated carbon dioxide.  Ecology 83: 1399-1411.

Grayson, D.K.  2000.  Mammalian responses to Middle Holocene climatic change in the Great Basin of the western United States.  Journal of Biogeography 27: 181-192.

Grayson, D.K. and Madson, D.B.  2000.  Biogeographic implications of recent low-elevation recolonization by Neotoma cinerea in the Great Basin.  Journal of Mammalogy 81: 1100-1105.

Hattenschwiler, S. and Schafellner, C.  1999.  Opposing effects of elevated CO2 and N deposition on Lymantria monacha larvae feeding on spruce trees.  Oecologia 118: 210-217.

Heide-Jorgensen, M.P. and Laidre, K.L.  2004.  Declining extent of open-water refugia for top predators in Baffin Bay and adjacent waters.  Ambio 33: 487-494.

Heide-Jorgensen, M.P., Richard, P., Ramsay, M. and Akeeagok, S.  2002.  In: Three recent Ice Entrapments of Arctic Cetaceans in West Greenland and the Eastern Canadian High Arctic.  Volume 4, NAMMCO Scientific Publications, pp. 143-148.

Laidre, K.L. and Heide-Jorgensen, M.P.  2005.  Arctic sea ice trends and narwhal vulnerability.  Biological Conservation 121: 509-517.

Lawlor, T.E.  1998.  Biogeography of great mammals: Paradigm lost?  Journal of Mammalogy 79: 111-1130.

Lindroth, R.L., Kinney, K.K. and Platz, C.L.  1993.  Responses of deciduous trees to elevated atmospheric CO2: Productivity, phytochemistry, and insect performance.  Ecology 74: 763-777.

Lindroth, R.L., Arteel, G.E. and Kinney, K.K.  1995.  Responses of three saturniid species to paper birch grown under enriched CO2 atmospheres.  Functional Ecology 9: 306-311.

Mattson, W.J., Kuokkanen, K., Niemela, P., Julkunen-Tiitto, R., Kellomaki, S. and Tahvanainen, J.  2004.  Elevated CO2 alters birch resistance to Lagomorpha herbivores.  Global Change Biology 10: 1402-1413.

Norment, C.J., Hall, A. and Hendricks, P.  1999.  Important bird and mammal records in the Thelon River Valley, Northwest Territories: Range expansions and possible causes.  The Canadian Field-Naturalist 113: 375-385.

Parkinson, C.L.  2000a.  Variability of Arctic sea ice: the view from space, and 18-year record.  Arctic 53: 341-358.

Parkinson, C.L.  2000b.  Recent trend reversals in Arctic sea ice extents: possible connections to the North Atlantic Oscillation.  Polar Geography 24: 1-12.

Parkinson, C.L. and Cavalieri, D.J.  2002.  A 21-year record of Arctic sea-ice extents and their regional, seasonal and monthly variability and trends.  Annals of Glaciology 34: 441-446.

Parkinson, C.L., Cavalieri, D.J., Gloersen, P., Jay Zwally, H. and Comiso, J.C.  1999.  Arctic sea ice extents, areas, and trends, 1978-1996.  Journal of Geophysical Research 104: 20,837-20,856.

Pockely, P.  2001.  Climate change transforms island ecosystem.  Nature 410: 616.

Siegstad, H. and Heide-Jorgensen, M.P.  1994.  Ice entrapments of narwhals (Monodon monoceros) and white whales (Delphinapterus leucas) in Greenland.  Meddeleser om Gronland Bioscience 39: 151-160.

Stern, H.L. and Heide-Jorgensen, M.P.  2003.  Trends and variability of sea ice in Baffin Bay and Davis Strait.  Polar Research 22: 11-18.

Traw, M.B., Lindroth, R.L. and Bazzaz, F.A.  1996.  Decline in gypsy moth (Lymantria dispar) performance on an elevated CO2 atmosphere depends upon host plant species.  Oecologia 108: 113-120.