Not all carbon emissions find their way into Earth's
atmosphere—about half of it is absorbed by vegetation and the
world's oceans. On the one hand, that helps limit carbon's
climate-changing effects. But on the other, it can deliver what
a National Oceanic and Atmospheric Administration scientist
calls a "double whammy" to the oceans. That's because carbon
dioxide is a weak acid, and when it's absorbed by water, it
contributes to ocean acidification, which can kill coral reefs
and shellfish, wreaking havoc on undersea plant and animal life.
As humans have increased their carbon emissions over the past
100 years, vegetation and the world's surface oceans have been
working overtime to absorb about half of it, about the same
proportion as 50 years ago, according to the study, published
Wednesday in Nature. "Humanity is getting an assist on climate
change from natural systems, otherwise the carbon dioxide in the
atmosphere would be twice as high," says Pieter Tans, one of the
study's authors. "But CO2 is an acid