Oceans in Crisis - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 177

the most rapid large-scale release of carbon dioxide the Earth has ever
experienced.
Another century on and where will we be? We are in the realm of
the various scenarios produced by the Inter-Governmental Panel on
Climate Change and others—and, for now, are at the higher end of the
range of projections. Currently, each year adds another 3 ppm. If that
continues, the Earth will see 700 ppm by the end of the century. That
will be an atmosphere more like that at the time of the dinosaurs than
that of today.
The Earth now has a thicker blanket, and it is perceptibly warming.
It warmed by the order of a degree in the last century, globally, albeit
with ups and downs. Much of the extra warmth retained by the Earth
has gone into the oceans (which has stopped air temperatures rising
so quickly), and this has probably caused about half of the 30 centi-
metres of global sea level rise that has taken place over the past
century. Given how long it takes the ocean waters to circulate and
mix, much of this extra warmth is still at the surface. It will take cen-
turies for it to slowly spread through into deep waters, and begin to
raise them above their current frigid state. The near-surface warming
is most strikingly visible around the poles, partly because these are
the parts of the world that are warming most quickly, and partly
because the sea ice of the polar regions is a highly tangible indicator
of temperature change.
The declines in Arctic sea ice over the past couple of decades caught
everyone by surprise, not least the oceanographers: the computer
models that they had painstakingly built to try to peer into the warmer
world to come had suggested that a good cover of Arctic ice should
persist into the end of this century. The figures that then emerged
from the year-by-year satellite surveys alarmed them. Between 1979,
when the satellite surveys began, and 2012, the area of sea ice remain-
ing at the end of the summer melt had almost halved. The figures for