Environmental Science and Technology
September 19, 2007

Long legacy of fossil fuels
Earth may not recover from CO2-induced climate
change for hundreds of thousands of years.

By NAOMI LUBICK

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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