Long legacy of fossil fuels

The oceans have long memories. Researchers recently reported that even if humans change their carbon-producing ways, some of the impacts of anthropogenic climate change, such as higher ocean temperatures, will last for at least a century. Now it appears that the long-term legacy of burning fossil fuels may last for hundreds of thousands of years, according to new research published in Tellus B (DOI 10.1111/j.1600-0889.2007.00290.x) in September.

Toby Tyrrell and colleagues at Southampton University (U.K.) call the long-term effects of CO2 a "fossil fuel hangover". They modeled the movement of various forms of carbon through the ocean and the atmosphere. In the model, they imposed a huge dose of carbon on the planet from 1900 to 2300—a pulse of 4000 gigatons of carbon—to simulate the burning of all fossil fuel reserves.

At first, the modeled oceans became more acidic because of rising CO2. But over many millennia, the researchers found, oceans reached a different final steady state compared with preindustrial times. This new steady state had higher atmospheric CO2 levels than before fossil fuel burning, and the oceans were more alkaline and had higher levels of dissolved inorganic carbon (DIC). A feedback mechanism causes more carbonate to dissolve in seawater, pushing even more carbon back into the atmosphere. Depending on how much CO2 humans produce in coming centuries, DIC and alkalinity could increase by 50% over preindustrial levels and atmospheric carbon by 100%.

"The system converges to a new equilibrium," the authors write. This means that the earth won't be able to recover completely from recent industrial carbon emissions, as it did in the past when CO2 levels were high. Past high levels of atmospheric carbon have been attributed to changes in earth's orbit, which occur about every 100,000 years and trigger ice ages. According to Tyrrell and colleagues, should business-as-usual CO2 emissions continue, the planet's next ice age may not come to pass for at least a half million years.

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