A new synthesis report, published by the U.S. federal Climate Change Science Program, finds that “climate changes are already affecting” U.S. water resources, agriculture, land resources, and biodiversity, and that significant impacts are “very likely” to continue over the next few decades and beyond. The 200-page “The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity” assessment summarizes scientific literature from more than 1,000 publications, including the reports of the Intergovernmental Panel on Climate Change (IPCC).

The assessment is notable not only for the U.S. Administration’s recognition of the “robust scientific consensus that human-induced climate change is occurring,” but also for its strong warning that the short term consequences of climate change are already irreversible and for its call for ecosystem monitoring systems specifically designed for detecting climate change effects.

According to the report, crop yields for agricultural commodities could be negatively affected by warmer temperatures. The authors cite recent studies indicating that increased temperature results in decreased maize (corn) yield, and propose that “a temperature rise of 1.2ºC over the next 30 years in the Midwest may de­crease yield by about 4 percent,” while further noting that some studies have recorded a -16% change per a 1ºC of temperature increase. These projected decreases could impact capacity to meet the regulatory mandate of 15 billion gallons of corn ethanol by 2015 and could further lead to continued increases in the price of maize, which reached more that $6/bushel in May 2008 (Forbes).

These trends could also influence sales of genetically modified or hybridized crop varieties designed to increase yields under restricted conditions, optimize water uptake, or even minimize the use of carbon and carbon-equivalent inputs. Monsanto, for example, sells corn hybrids with high ethanol yield capabilities and Wired magazine last week points to Arcadia Biosciences’ plan to award farmers offset credits for switching to more nitrogen-efficient rice.

Other findings on agriculture productivity indicate that grain and oilseed crops “will increasingly begin to experience failure;” that the marketable yields of fruit and vegetable crops are “very likely” to be affected; that weeds, pathogens, and parasites may proliferate; that higher temperatures will “very likely” reduce livestock production; and that changes in rangeland productivity will “likely” have a significant impact on livestock operations.

The report also suggests that, although much of the U.S. experienced “decreased drought severity and duration” over the past century, there will be a significant shift in water resource availability over the next 50 years, with the eastern U.S. experiencing “increased runoff” (indicating greater precipitation), while the interior of the West experiences “decreases in annual runoff” by as much as 20%. A graphic of the projected changes in water flows is available from The New York Times.

While not intended to provide concrete recommendations on adaptation to the projected trends, the report did assess whether the available environmental monitoring systems could detect changes caused by climate changes and found existing monitoring tools were not designed with the intention of monitoring impacts of climate change on natural resources, agriculture, and biodiversity. The authors expressed “limited confidence” in the current technical and institutional system to provide an early warning system or to provide information necessary to evaluate adaptation options.

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