How does rising atmospheric CO2 affect marine organisms?

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Volume 2 Number 23:  1 December 1999

Biospheric Carbon Sequestration: Does It Really Work?: Fred Pearce of Britain's New Scientist magazine thinks that planting new forests will not slow the rate of rise of the air's CO2 content.  We help him see the light!

Journal Reviews
The Instrumental Surface Air Temperature Record of the Past 150 Years: A comprehensive update and analysis of the surface air temperature record of the globe suggests that the earth has warmed slightly over the past century or so.

Length of Growing Season Variability and Consequences for Carbon Sequestration: An ecosystem model study of the impacts of observed changes in growing season length over the period 1900-1987 in the eastern deciduous broadleaf forest of the United States reveals recent observations of increased growing season length, which are often cited as evidence of CO2-induced climate change, to be "neither unusual nor necessarily a sign of permanent climate change."  The study also demonstrates that temperature-induced increases in growing season length, which lead to the sequestration of CO2, will overpower the release of CO2 to the atmosphere that is caused by temperature-induced increases in biotic respiration rates.

Megafloods of the Mississippi River: Analyses of several characteristics of hemipelagic muds in the northern Gulf of Mexico reveal the occurrence of large megafloods caused by "historically unprecedented precipitation and flooding in the Mississippi watershed" at 4700, 3500, 3000, 2500, 2000, 1200 and 300 years before present.  If such an episode of flooding were to occur in the near future - although it has been a common occurrence in the recent geologic past - it would certainly be used as a reason to coerce political action on reducing anthropogenic CO2 emissions, even though elevated CO2 concentrations may have had nothing to do with it, as they clearly had nothing to do with these dramatic events of the past.

Increases and Decreases in Salinity Negatively Impact Corals: A laboratory study of the effects of small increases and decreases in water salinity indicates that change alone, independent of its direction, can often be bad for corals.

Underestimation of Solar Radiation Absorption in GCM Atmospheres: An analysis of measurements of solar radiation fluxes at 720 surface sites and corresponding top-of-the-atmosphere locations demonstrates that four representative general circulation models of the atmosphere underestimate the amount of solar radiation absorbed by the atmosphere by close to 20%.

Genotypic Growth Responses of Spruce to Elevated CO2: Four genotypes of Sitka spruce growing in open-top chambers enriched with elevated CO2 for three growing seasons exhibited 42% more dry mass than control plants exposed to ambient CO2.  Although there were no significant dry mass differences between clones at ambient CO2, two southerly clones produced about 20% more dry mass than two northerly clones when grown at elevated CO2.  This CO2-induced growth advantage of southerly clones may be exploited by commercial foresters in Europe to increase their overall timber yields in the next century.

Genotypic Photosynthetic and Nitrogen-Use Responses of Spruce to Elevated CO2: Four genotypes of Sitka spruce growing in open-top chambers enriched with elevated CO2 for three growing seasons exhibited photosynthetic rates that were 62% greater than those displayed by control trees growing at ambient CO2, despite a 36% reduction in apparent rubisco activity.  Moreover, CO2-enriched saplings possessed significantly lower amounts of chlorophyll and leaf nitrogen than did ambiently-grown saplings.  Thus, because elevated CO2 increased photosynthetic rates and caused greater dry mass production in all genotypes, it significantly enhanced the nitrogen-use efficiency of all saplings.

Effects of Elevated CO2 on Earthworm Activities: Assessments of earthworm activities, including rates and cumulative weights of surface cast production, increased significantly with atmospheric CO2 enrichment in calcareous grasslands of Switzerland.  In addition, this phenomenon led to significantly greater soil fertility in CO2-enriched plots, suggesting that plant growth responses to elevated CO2 may be further enhanced due to increased soil nutrition.

Effects of Elevated CO2 and Earthworm Casts on Grassland Plant Species: The proximity of plant growth to nutrient-rich earthworm casts in calcareous grasslands of Switzerland was highly variable, regardless of atmospheric CO2 concentration.  However, plants growing closer to earthworm casts tended to produce more biomass than plants growing further away from them at both atmospheric CO2 concentrations.  Although plant associations with casts did not significantly influence their growth responses to elevated CO2, the average CO2-induced growth response of graminoid species was greater for those species growing closer to casts in comparison with those species growing further away from them, thus indicating that plant growth responses to elevated CO2 can be enhanced due to the presence of earthworm casts that enrich soil fertility at local microsites within plant communities.

Interactive Effects of Elevated CO2, Phosphorus, and Legumes on Community Productivity in a Simulated Grassland: Simulated nutrient poor grassland communities, characteristic of those existing in Switzerland, exhibited the greatest biomass production under conditions of atmospheric CO2 enrichment, supplemental phosphorus fertilization, and the inclusion of nitrogen-fixing legumes.  However, the greatest CO2-induced percentage stimulation in biomass production occurred for simulated communities that lacked fertilization and nitrogen-fixing legumes, suggesting that such communities should respond favorably to increasing concentrations of atmospheric CO2, despite their low fertility.