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It’s not just the spilled oil: Since the Industrial Revolution, Earth’s oceans have been soaking up unprecedented levels of atmospheric carbon dioxide as well as runoff from manufacturing processes. In a new review, Woods Hole Oceanographic Institution scientist Scott Doney describes the impact of human activities on the open ocean and coastal waters. Observations and models show that up to 30% of the carbon released by fossil-fuel combustion is absorbed by the ocean; with that rise in subsurface CO₂, a weak acid in seawater, the ocean’s pH plummets. Measurements of CO₂ and pH collected over the past two decades off Hawaiian shores show that the ocean is becoming more acidic—30 to 100 times faster than what geological records report. The shift in the ocean’s acid-base equilibrium due to excess CO₂ also hinders the precipitation of calcium carbonate, which makes up the shells and skeletons of many marine species. Yet another concern is hypoxia—dangerously low levels of subsurface oxygen caused by climate-warming-induced degradation of organic matter—which leads to anaerobic respiration conditions and produces even more CO₂. And yes, oil spills, even naturally occurring seeps from oil wells, release pernicious hydrocarbons into the marine environment. Most such industrial chemicals are “woefully undersampled,” writes Doney, whose summary calls on the oceanographic community to better coordinate its monitoring of the ocean’s biogeochemical cycle. (S. C. Doney, Science 328, 1512, 2010.)—Jermey N. A. Matthews

With political sentiment growing in favor of greenhouse gas (GHG) restrictions, biofuels from plant cellulose are being considered among the alternatives to fossil fuels: Plants are renewable and biodegradable, and they sequester carbon. Yet a new report validates concerns that a global biofuels program could put intense pressure on land supply and distribution. To predict the impact of a biofuels-based economy on climate change, an international team of researchers from the US, Brazil, and China linked an economic model of land use with a terrestrial biogeochemical model of global GHG levels. The team considered two cases for cellulosic biofuel crop growth: The primary focus of case1 is on converting unfarmed areas such as forests, as shown in the image; of case 2, on exploiting existing farmland to the extent possible. In both cases, biofuel feedstock becomes a dominant global crop by year 2100, but in the process, total forest area is cut—by 56% in case 1 and by 24% in case 2. The loss of carbon-sequestering trees in case 1 results in a net release of carbon. In case 2, the gains from biofuel production ultimately lead to increased carbon sequestration in the farmed soil from the addition of nitrogen fertilizer, which paradoxically releases N₂O, another potent GHG. The research suggests that stabilizing GHG levels will require a limited and more efficient use of forests and fertilizers for biofuel crop production. (J. M. Melillo et al., Science Express, 22 October 2009, doi:10.1126/science.1180251. Image courtesy of Chris Neill, Marine Biological Laboratory, Woods Hole, MA.)—Jermey N. A. Matthews