· Biological diversity -- the source of enormous environmental, economic, and cultural value -- will be threatened by rapid climate change.
There is little empirical evidence to suggest that the rising CO2 content of earth's atmosphere will induce rapid climate change over the next century.  But even if the planet warms as predicted, the contemporaneous rise in atmospheric CO2 concentration will act to maintain, if not enhance, biological diversity.

This information sheet begins by stating how current climate zones would shift poleward in latitude and upward in altitude for a given amount of warming.  With this claim we have no argument.  However, we do have a problem with the declaration that these climatic changes will necessarily lead to changes in "the composition and geographic distribution of unmanaged ecosystems," especially when these changes are suggested to lead to species extinctions.

As we have already outlined in our discussion of Point 2 of Information Sheet 10, the temperatures at which plants perform at their optimum generally rise with an increase in atmospheric CO2; and a number of theoretical and experimental studies have demonstrated that for 95% of earth's vegetation (its C3 plants), the increase in plant optimum temperature that would accompany a 300 ppm increase in the air's CO2 content would likely be even larger than the predicted temperature rise for the worst-case scenario of CO2-induced global warming.  Hence, even if the planet warmed as predicted for a doubling of the air's CO2 content, the great bulk of earth's vegetation would "prefer" those warmer conditions; and there would be no reason for it to migrate poleward or upward.  In addition, the other 5% of earth's plant life (its C4 and CAM plants) is already adapted to earth's warmer environments (De Jong et al., 1982; Drake, 1989; Johnson et al., 1993), which are expected to warm much less than the other portions of the globe (Houghton et al., 1996); and those plants may also experience an increase (albeit more modest) in their optimum temperatures in response to an increase in atmospheric CO2 (Chen et al., 1994).  Furthermore, warming itself often produces upward shifts in plant optimum growth temperature (Seeman et al., 1984; Veres et al., 1984; El-Sharkawy et al., 1992).  Clearly, therefore, a warming of the globe would not produce the impetus for plant migration that is often put forth as a reason for believing that earth's biodiversity would be threatened by an increase in atmospheric CO2 concentration.  Yet this is only the beginning of the story; for a number of studies have actually directly addressed the effects of atmospheric CO2 enrichment on ecosystem biodiversity.

Taylor and Potvin (1998), for example, reported no significant effect of elevated CO2 on species richness in managed prairies near Montreal, Quebec.  Moreover, elevated CO2 did not favor the growth and colonization of Chenopodium album (a common C3 agricultural weed) at the expense of slower growing native prairie species following soil disturbance.  A similar result was reported by Luscher et al. (1998), who exposed multiple genotypes of twelve fertile grassland species common to Switzerland to double the concentration of atmospheric CO2 for three years and observed that elevated CO2 did not act as a natural selective factor among them.  In both of these situations, therefore, the data suggest that elevated CO2 would, at a minimum, maintain biological diversity.

In another study, Arp et al. (1998) grew six perennial plants common to The Netherlands in treatment combinations of low and high soil nitrogen, low and high soil water, and ambient and elevated atmospheric CO2 for two full years.  Their results indicated that "elevated CO2 tends to favor species already best adapted to their environments."  Moreover, they stated that "a rise in CO2 would not change the relationships between plant species in the natural environment, but would reinforce existing ones."

So why is the species status quo maintained in situations such as these?  Some insights may be gained from the recent study of Simard et al. (1997), who studied nutrient transfer among trees in a temperate forest and discovered that nutrients are passed along a complex network of fungal mycelium from trees that have an abundance of nutrients at their disposal to those that are lacking them, regardless of species.  This finding suggests that competition among plants may not play as great a role in natural ecosystems as once believed, as this nutrient-sharing phenomenon would appear to promote species coexistence and maintain, or even enhance, ecosystem biodiversity.

Within this context, it is instructive to note that elevated levels of atmospheric CO2 enhance belowground growth and stimulate the root activities of most plants (Curtis et al., 1990, 1994; Idso and Kimball, 1992; Norby, 1994; Prior et al., 1995; King et al., 1996).  One such CO2-enhanced process is the exudation of nutrients and carbon compounds (Rogers et al., 1992), which stimulates microbial and fungal activities in the vicinity of plant roots (Lamborg et al., 1983; Pregitzer et al., 1995; Tingey et al., 1996; Lazarovits and Nowak, 1997; Ringelberg et al, 1997).  Consequently, as the air's CO2 content continues to rise, these phenomena should lead to the development of ever better mycelial networks for distributing nutrients among plants, enhancing their transfer from the "haves" to the "have-nots," including C3, C4 and CAM species.  And this observation calls the whole concept of competition into question, suggesting that cooperation may be the more fitting term to describe interspecies interactions in a future world of higher CO2.

Considered in their entirety, these several observations provide no substantive basis for believing that biodiversity will decrease as the air's CO2 content continues to rise.  If anything, they point to the tantalizing possibility that plants will fare even better in the future than they do now, and that they may actually help each other to some degree, as opportunities for cooperation among species increase with increasing root growth and fungal networking in the belowground environment in response to the rising carbon dioxide content of the atmosphere.

· Forests adapt slowly to changing conditions.
This section of the information sheet is basically a continuation of the previous section, but with an emphasis on trees, essentially all of which are C3 plants.  Hence, its negative predictions are rebutted by the information we have just reviewed.  In addition, woody plants typically respond to atmospheric CO2 enrichment even better than non-woody plants (Wullschleger et al., 1995; Curtis and Wang, 1998; Saxe et al., 1998); and they experience all the CO2-induced stress-relieving phenomena that commonly occur at elevated CO2 concentrations, including the ability to better deal with drought and high temperatures (Idso and Idso, 1994).  Consequently, entire forests will not disappear if air temperatures slightly rise in response to an increase in the air's CO2 content.  In fact, trees would likely thrive in such an environment, as they have in the past.  Long ago in the Tertiary, for example, when the CO2 content of the air was much higher than it is today, many montane taxa grew among mixed conifers and broadleaf species, producing "super" ecosystems that were much richer than any that currently exist (Axelrod, 1944a, b, 1956, 1976, 1987, 1988).

· Forests play an important role in the climate system.
This section of the information sheet continues to beat the same dead horse as the two prior sections, stating that "large quantities of carbon may be emitted into the atmosphere during transitions from one forest type to another because mortality releases carbon faster than growth absorbs it."  What we have already written suffices to demonstrate that you can not get there (to large-scale forest death via CO2-induced global warming) from here (the scientific facts).

· Deserts and arid and semi-arid ecosystems may become more extreme.
Once again, even if this were to occur, which is certainly questionable in light of the fact that most climate models predict an intensification of the hydrologic cycle under elevated CO2 conditions, it would pose little problem for plants.  As we have noted previously, for example, as the air's CO2 content rises, most plants reduce their stomatal apertures, thereby lowering their rates of transpirational water loss (Saxe et al., 1998; Sgherri et al., 1998; Tognetti et al., 1998) and boosting their water-use efficiencies.  And this physiological adjustment is not something small; it typically doubles in response to a doubling of the atmospheric CO2 concentration (Idso et al., 1985; Valle et al., 1985; Fernandez et al., 1998).  Hence, it should clearly allow vegetation in water-limited regions to not only persist there, but to expand into even drier areas where they cannot currently survive.

BassiriRad et al. (1998), for example, reported that atmospheric CO2 enrichment increased the total biomass of two perennial C3 desert shrubs by approximately 62% and that of a perennial C4 desert grass by 25% relative to plants grown in normal air.  Moreover, Tuba et al. (1998) documented that three different desiccation-tolerant plants (a woody shrub, lichen and moss) all responded positively to a 700 ppm increase in atmospheric CO2 concentration during an extensive desiccation treatment by prolonging the period of time they were able to maintain positive rates of carbon uptake via photosynthesis.  This observation prompted the authors to state that "desiccation-tolerant plants will be among the main beneficiaries of a high CO2 future," in agreement with Arp et al. (1998) who concluded that "elevated CO2 tends to favor species already best adapted to their environments."

Consequently, in a future world of higher atmospheric CO2 concentration, it is not likely that either higher temperatures or greater water deficits will threaten the existence of plants growing in deserts and semi-arid regions.  In fact, atmospheric CO2 enrichment will likely increase their biomass, growth rates, heat-tolerance, desiccation-tolerance and water-use efficiencies and actually lead to what could be called "reverse desertification."

· Rangelands may experience altered growing seasons.
In this section it is stated that presumed CO2-induced changes in the evapotranspiration cycle "could strongly affect productivity and the mix of species."  The first of these claims is almost certainly correct, but not in the way the information sheet intends.  Rather than being a negative response, it should be positive, as elevated CO2 generally increases the optimal growth temperatures of plants and increases their water-use efficiencies.

With respect to the mix of species changing, our discussions of Points 1 and 2 of this information sheet suggest that decreasing biodiversity should not be a problem, and that increases in ecosystem species numbers could well occur.  As for the implications for livestock grazing, Bryant et al. (1998) have observed that several perennial rangeland species common to nutrient-poor soils in Europe typically "down regulate" their photosynthetic machinery to make more efficient use of scarce nitrogen reserves in atmospheres of higher-than-normal atmospheric CO2 concentration.  When much of their foliage was removed in a simulated grazing event, however, the plants exposed to elevated CO2 directed greater quantities of nitrogen back to their remaining leaves, where they could make better use of it and hasten the production of new foliage.  This chain of events suggests that atmospheric CO2 enrichment may help plants better withstand, as well as recover from, the debilitating effects of having their foliage eaten by either livestock or pests, even under conditions of less-than-optimum soil fertility.

· Mountain regions are already under considerable stress from human activities.
The gist of this section, once again, is that if CO2-induced global warming occurs "and species and ecosystems are forced to migrate uphill, those species whose climatic ranges are already limited to mountain tops may have nowhere to go and become extinct."  Once again, we say in response that elevated levels of atmospheric CO2 alleviate high temperature and water stress in essentially all plants, regardless of their habitats, by increasing their optimal growth temperatures and their water-use efficiencies.  The beauty of this phenomenon is that it not only boosts plant productivity, but it also decreases the severity of (and in some cases completely overcomes) most of the stressful phenomena that plants experience across the globe in various ecosystems and environments (Idso and Idso, 1994).  Hence, species will not be forced uphill to cooler regions if the globe warms in the future, because with more CO2 in the air, most plants will "prefer" to remain right where they are, and they'll grow even better there than they do today.

· The cryosphere will shrink.
There is that "will" again, which even we are beginning to take for granted.  It is clearly worth reporting, therefore, that no one knows that the cryosphere will shrink in the near future, or any time, especially as a result of a rise in the air's CO2 concentration.  What this section does, therefore, is merely address the potential consequences of the climate model prediction that "mountain glaciers could be reduced by one third to one half over the next 100 years."

Would such a shrinkage of the cryosphere be all that bad, even if it were to occur? Fresh water locked up in ice is fresh water unavailable for any useful purpose, such as feeding streams, rivers and groundwater.  And it makes the land it covers likewise unavailable.  Nevertheless, this section provides a long list of things that could be "affected" by it.  Needless to say, by now it should be clear that "affected" means "adversely affected" in the parlance of the United Nations.  And it should also be clear by now that just the opposite is likely to be true in the case of most of the items named.

· Non-tidal wetlands will also be reduced.
This bullet point suggests that "a warmer climate will contribute to the decline of wetlands."  How can that be, if the climate models predict more precipitation in a CO2-enriched world at the same time that they say that deserts are not projected to become wetter (Point 4 of this information sheet).  Where else can this extra precipitation fall but on average and wetter-than-average lands?  And what feeds wetlands?  It is the drainage from average and wetter-than-average lands, not deserts.  So, again, how could CO2-induced global warming contribute to the decline of wetlands?

This section suggests that it might do so by increasing wetland evaporation rates.  But evaporation would have to increase a lot to overpower the extra influx of water from drainage systems that supply watershed runoff to the wetlands, as the watersheds would be receiving more precipitation than they do now in a higher-CO2 world, and as their areas are typically much greater than those of the wetlands they supply with runoff.  Furthermore, higher atmospheric CO2 levels will insure that transpirational water loses from wetland vegetation will be reduced.

In addition to these considerations, atmospheric CO2 enrichment enhances vegetative productivity in wetland ecosystems (Jacob et al., 1995; Drake et al., 1996a,b); and it has been shown to reduce insect and fungal damage to wetland plants (Drake et al., 1996b).  Consequently, there should not be any reductions in wetland acreage due to any CO2-induced global warming that might occur in the future.

· Human actions can help natural ecosystems adapt to climate change.
Quite true.  But if the climate change is accompanied by a rise in atmospheric CO2, no human actions will be needed.  Indeed, none could even come close to supplying the benefits that are naturally provided by the increasing CO2 content of the air.

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