How does rising atmospheric CO2 affect marine organisms?

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Volume 2 Number 20:  15 October 1999

The Fortunate Coupling of Atmospheric CO2 and Temperature Trends: Although there are a number of exceptions to the rule, there has been a general tendency for near-surface air temperature and atmospheric CO2 concentration to vary hand-in-hand across the past half-million or so years that we have been able to reconstruct their temporal histories from analyses of ice core data.  Throughout most of the planet's most recent great ice ages, for example, the air's CO2 content has been relatively low; while during the intervening interglacials it has been significantly higher.  This is good news, says Sharon A. Cowling of the Institute of Ecology's Climate Impacts Group at Lund University in Sweden; for in the absence of such a relationship, most of earth's plant life would be in a world of hurt during times of global warming...

Journal Reviews
The Non-Anthropogenic-Induced Retreat of the WAIS: Evidence of the deglacial retreat of the West Antarctic Ice Sheet indicates that its modern retreat is "not a consequence of anthropogenic warming."

Hurricane Statistics of the Atlantic Basin: Several hurricane indices examined for the Atlantic basin since 1944 reveal trends toward fewer and less intense hurricanes.

Assessing Atlantic Hurricane Damage in the USA: Hurricane-related storm damage was found to be half as great in warmer El Niņo years as opposed to cooler La Niņa years for the Atlantic coastal region of the United States over the years 1925-1997.

Global Warming and Floods: Several demonstrable fallacies associated with floods are noted in this paper, one of which is the oft-repeated claim that "damaging flooding in recent years is unprecedented because of 'global warming.'"

Rising CO2 Affects Ocean Carbon Pumps: The authors review the status of our knowledge relative to the direct effects of atmospheric CO2 enrichment on the marine biota, concluding that they have three major impacts that all tend to act as negative feedbacks to anthropogenic CO2 increase.

Water-Use Efficiency of North American Trees Over the Past Two Centuries: A study of 23 carbon isotope tree-ring chronologies obtained from trees growing in natural forests in western North America reveals a 10 to 25% increase in plant intrinsic water use efficiency from 1750 to 1970, over which time period the air's CO2 concentration rose by approximately 16%.

Density-Dependent Growth Response of an Agricultural Weed to Elevated CO2: Field mustard grown at atmospheric CO2 concentrations of 350 and 700 ppm exhibited CO2-induced increases in aboveground biomass that varied with density and time.  Early in stand development, for example, the CO2-induced growth response was quite large.  However, as stands matured, the growth response declined, but ultimately stabilized at 34% across a wide range of densities, which is similar to the CO2-induced growth response of most herbaceous plants.

Photosynthetic Response of Sun and Shade Leaves to Elevated CO2: In a FACE study implemented in a natural forest ecosystem in North Carolina, USA, sweetgum trees exhibited significant photosynthetic increases in both sun and shade leaves in response to atmospheric CO2 enrichment.  In addition, this photosynthetic stimulation was enhanced with environmental conditions of high temperature and reduced soil moisture, indicating that less than optimal growing conditions will not negate the positive effects of elevated CO2 on photosynthesis on this species.

Acclimation to Elevated CO2 Increases Photosynthetic Nitrogen-Use Efficiency in Grassland Species: Three economically important species (common to the grasslands of the lower United Kingdom) that were grown in open-top chambers for two years at an atmospheric CO2 concentration of 700 ppm displayed photosynthetic acclimation to elevated CO2, as indicated by reductions in rubisco activity of nearly 30%.  Despite these reductions, most species still exhibited greater photosynthetic rates when grown in elevated CO2, regardless of soil fertility.  In fact, the CO2-induced increases in photosynthesis and photosynthetic nitrogen-use efficiency were typically greater under conditions of low soil fertility than they were under conditions of moderate soil fertility.

Up-Regulation of Enzyme in Response to Elevated CO2: Atmospheric CO2 enrichment of rice plants led to the up-regulation of sucrose phosphate synthase, a key regulatory enzyme involved in sucrose synthesis, throughout the entire growing season.  This phenomenon is suggested to be another mechanism for acclimating to elevated CO2, as it allows for increased carbohydrate export from source leaves to match the increased carbohydrate production that occurs there.