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Volume 3 Number 14:  15 July 2000

Two Types of Tree-Ring Response to Atmospheric CO2 Enrichment and Their Implications for Reconstructing Past Trends in Earth's Surface Air Temperature: In response to a reader's query, we explain the differential impacts of atmospheric CO2 enrichment on tree-ring density and width, demonstrating that prior reconstructions of earth's surface air temperature based on tree-ring density chronologies are correct for the entire period of the last millennium, while those based on tree-ring widths deviate dramatically from reality over the past 70 years.

Journal Reviews
The Current Status of Climate Modeling: A review of the state-of-the-art of climate modeling reveals that there are many important questions relating to potential global climate change for which the models do not yet have answers, but that in spite of this lack of definitive knowledge, governments are still using them to make policy.

Testing Climate Models Against Reality: What a Novel Idea!: A comparison of climate model predictions of the overall effect of clouds on surface temperature proves embarrassing for several models, particularly in the summer season of the year, when one of the models did not even get the sign of the effect correct, which leads us to ask, "Is it rational to revamp international energy policies on such a flimsy basis?

Palaeoclimate Histories May Need Some Adjustments: In a study of three of the most abundant high-latitude foraminifera that are used to infer past climatic conditions over polar and subpolar regions of the earth, it was found that these three "species" may well be three groupings of species, each separate species of which may have distinctive environmental/habitat preferences.  Hence, it is possible that certain palaeoclimate histories derived from assumptions about the original three "species" may have to be revised in light of what may be learned about the new entities.

A Two-Century History of Biospheric CO2 Exchange: Ice core and direct observations of atmospheric CO2 and 13C demonstrate that the size and/or prowess of the biosphere has been growing greater and greater over the past century in spite of all the bad things mankind has supposedly been foisting upon the planet.

Atmospheric CO2 and the Glacial Southern Ocean: Based on a new interpretation of proxy records of nutrient utilization in the polar Southern Ocean, Elderfield and Rickaby argue that the lower atmospheric CO2 concentration of the Last Glacial Maximum was not caused by enhanced phytoplanktonic productivity but rather by the insulating properties of a vastly expanded area of sea-ice.

Interactive Effects of Elevated CO2 and Ozone on Three Deciduous Tree Species: Black cherry, green ash, and yellow-poplar seedlings grown for 10 weeks at twice-ambient atmospheric CO2 concentrations exhibited significantly greater rates of photosynthesis than seedlings grown at ambient CO2 concentrations.  When exposed simultaneously to twice-ambient atmospheric CO2 and ozone concentrations, atmospheric CO2 enrichment tended to ameliorate the negative effects of ozone on this parameter and the CO2-induced increases in photosynthesis were nearly always greater than those exhibited under conditions of elevated CO2 alone.  Similarly, elevated CO2 increased total biomass in all three seedlings, and seedling biomass values attained in the treatment combination of elevated CO2 and elevated ozone were similar to those observed for seedlings grown in elevated CO2 alone.  Thus, it is likely that seedlings of these three deciduous tree species will not suffer the detrimental effects of ozone-induced growth reductions if the CO2 content of the air continues to increase in the future.

Interactive Effects of Elevated CO2, Ozone, and Leaf Rust Infection on Productivity in Wheat: Healthy and infected (inoculated with rust-causing fungal spores) wheat plants were grown to maturity in controlled environmental chambers receiving various concentrations of atmospheric CO2 and ozone.  Although pathogenic infection and elevated ozone typically reduced photosynthesis and yield, the greatest CO2-induced increases in these parameters generally occurred in infected plants exposed to high ozone concentrations.  Thus, elevated CO2 tended to ameliorate the detrimental effects of pathogenic infection and elevated ozone on photosynthesis and yield in this important grain-producing crop.

Effects of Elevated CO2 and Temperature on Ponderosa Pine: Ponderosa pine seedlings grown for six months at an atmospheric CO2 concentration of 1100 ppm displayed 42 and 62% more total biomass than seedlings grown at 350 ppm CO2 at low and high temperature regimes, respectively.  Thus, future increases in the air's CO2 content should significantly stimulate biomass production in ponderosa pine seedlings, and this stimulation will likely be greater at higher, rather than lower, air temperatures.  Consequently, it is unlikely that this coniferous --or any tree-- species will have to migrate towards the poles to cooler climates if air temperatures rise, for nearly all of earth's vegetation will grow better at warmer temperatures due to an upward shift in their optimal growth temperature brought about by elevated CO2 concentrations.

Photosynthetic and Growth Responses of Aspen Clones to Elevated Soil Temperature and Nutrient Availability: Aspen (Populus tremuloides) cuttings grown for 98 days at various combinations of soil temperature and soil nitrogen availability exhibited greater photosynthetic rates, biomass production, and root turn-over rates when subjected to high, rather than low, soil temperature, regardless of soil nitrogen content.  Consequently, even without an increase in the air's CO2 concentration, carbon sequestration should substantially increase in this species and in forest soils beneath their stands if the climate continues to warm in the future.  And if the CO2 content of the air continues to rise, the carbon sequestration prowess associated with this species will become even greater.

Learning from Ants: n a massive study conducted in North, Central and South America, it was found that ground ant abundance is positively correlated with site net primary productivity, which is invariably enhanced by atmospheric CO2 enrichment.