How does rising atmospheric CO2 affect marine organisms?

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The Response of Ecosystem Water Balance to Climate Warming
Pangle, L.A., Gregg, J.W. and McDonnell, J.J. 2014. Rainfall seasonality and an ecohydrological feedback offset the potential impact of climate warming on evapotranspiration and groundwater recharge. Water Resources Research 50: 1308-1321.

The authors write that "the potential impact of projected climate warming on the terrestrial hydrologic cycle is uncertain," having "evaded experimentalists due to the overwhelming challenge of measuring the entire water budget and introducing experimental warming treatments in open environmental systems."

What was done
In addressing this enormous challenge, Pangle et al. "present new data from a mesocosm experiment that examined the combined responses of evapotranspiration (ET), soil moisture, and potential groundwater recharge (R; lysimeter drainage) to a 3.5°C temperature increase in a grassland ecosystem experiencing a Mediterranean climate," where "the temperature increase was applied both symmetrically throughout the day, and asymmetrically such that daily minimum temperature was 5°C greater than ambient and daily maximum temperature was 2°C greater than ambient."

What was learned
The three researchers report that their results, spanning three years, "show that symmetric and asymmetric warming enhanced ET during the spring," but they say that "this increase in ET reduced soil moisture more rapidly, resulting in less ET during the summer than occurred under ambient temperature," such that there was "no difference in total ET during the combined spring and summer (March to October)." In addition, they indicate that "groundwater recharge was reduced during late-spring storms relative to the ambient temperature treatment," but they found that "these reductions were less than 4% of total annual R, and were offset by slightly greater R in the fall under both warming treatments."

What it means
In the concluding sentence of their paper, Pangle et al. write that their results "confirm the general view that interactions and feedbacks between climate, vegetation, and soil moisture ultimately dictate the ecosystem water balance response to warming," which in the case of their study resulted in no net change in annual ecosystem water balance.

Reviewed 23 July 2014