If emissions of heat-trapping gases continue to accumulate in the atmosphere
at the current rate, there may be many centuries of warming and a near-total
loss of Arctic tundra, according to a new climate study.
Over all, the world would experience profound transformations, some potentially
beneficial but many disruptive, and all at a pace rarely seen in nature, said
the authors of the study, being published today in The Journal of Climate.
"The question is no longer whether we will need to address this problem,
but when we will need to address the problem," said Kenneth Caldeira, an
author of the study and a climate expert at the Carnegie Institution's Department
of Global Ecology, based at Stanford University.
"We can either address it now, before we severely and irreversibly damage
our climate, or we can wait until irreversible damage manifests itself strongly,"
Dr. Caldeira said. "If all we do is try to adapt, things will get worse
The paper's lead author, Bala Govindasamy of the Energy Department's Lawrence
Livermore National Laboratory, said it might take 20 or 30 years before the
scope of the human-caused changes becomes evident, but from then on there is
likely to be no debate.
The researchers ran a computer model that simulates both the climate system
and the flow of heat-trapping carbon into the air in the form of carbon dioxide,
then back into soils and the ocean.
Most simulations of the potential human impact on climate have been confined
to studying the next 100 years or so, but in this case the scientists started
the calculations in 1870 and let the computers churn away through 2300.
The authors stressed that the uncertainties were high over such a time span,
and said the study was intended to illustrate broad consequences rather than
project specific ones.
They programmed the model to run as if the atmospheric concentration of carbon
dioxide rose about 0.45 percent a year through 2300. That is slightly less than
the current rate, about 0.5 percent.
In the simulation, the concentration of carbon dioxide doubles from pre-industrial
levels in 2070, triples in 2120, and quadruples in 2160.
The results are sobering, Dr. Caldeira and other climate experts said, because
the computer model used in this study tends to produce less warming from a greenhouse-gas
buildup than many of the other climate simulations being run by other research
It also presumes that plants and the ocean will continue to sop up carbon dioxide
in the future, limiting the amount retained in the atmosphere. Many other independently
developed models calculate that at some point, chemical and biological shifts
caused by warming would reverse that flow and cause even more greenhouse gases
to flood into the atmosphere.
Consistent with many other studies, the model showed that the Arctic would
see the most warming, with average annual temperatures in many parts of Arctic
Russia and northern North America rising more than 25 degrees Fahrenheit around
Antarctica would follow suit later, with temperatures there rising sharply
The impact on vegetation and landscapes would transform large areas
of the earth.
In the simulation, at least one ecosystem, the scrubby Arctic tundra largely
vanishes as climate zones shift hundreds of miles north. Tundra would decline
from about 8 percent of the world's land area to 1.8 percent.
Alaska, in the model, loses almost all of its evergreen boreal forests and
becomes a largely temperate state.
But vast stretches of land that were once locked beneath permanent ice cover
would open up. The area locked beneath ice would diminish to 4.8 percent of
the planet's total land area, from 13.3 percent.
Several climate scientists not associated with the study said its main benefit
was akin to the murky visions of possible futures experienced by Ebenezer Scrooge
in "A Christmas Carol."
"It's a cautionary tale," said Gerald A. Meehl, a climate modeler
at the National Center for Atmospheric Research in Boulder, Colo., who has conducted
"The message is not to give up because the changes appear overwhelming,
but instead the message should be the longer we wait to do something, the worse