MODERN TIMES
Art Hobson
ahobson@uark.edu
NWA Times 17 Feb 2007
Global
Warming: A Dose of Reality
One
reason I elected to become a scientist is that it
seemed to me that scientists are in the reality business. Richard Alley, a lead author of the
2007 Fourth Assessment Report of the U.N.Õs Intergovernmental Panel on Climate
Change (IPCC), Professor of Geosciences at Penn State University, and author of
a wonderful read titled ÒThe Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future,Ó is one
such scientist. His comment to
public servants and citizens about the IPCCÕs work is, ÒPolicy makers paid us
to do good science, and now we have high very scientific confidence in this
work—this is real, this is real, this is real. So now act, the ballÕs back in your court.Ó
Unlike
those who believe for religious, ideological, or other reasons that they
possess the absolute truth revealed directly to them by some higher authority,
scientists are never absolutely certain of their conclusions. And yet, there is no longer a
reasonable doubt that human activities are warming the planet at a dangerous
rate. This proposition is
sufficiently certain--Òvery likelyÓ according to the report--that it would be
decidedly foolish not to act on it.
The
Fourth Assessment might be the most comprehensive scientific report ever issued
on any topic. Written over a
six-year period, itÕs the most recent of four IPCC reports. ItÕs an assessment of the work of many
thousands of scientists appearing in hundreds of scientific journals
worldwide. Over 1200 scientists
and 2500 expert scientific reviewers summarized this work in the IPCC
report. The full report will be
published during 2007 in four sections dealing with (1) the scientific basis,
(2) its consequences, (3) options for slowing the trend, and (4) a final
synthesis report. The reportÕs
conclusions are conservative, for at least four reasons: science is always conservative because
scientists hate to be wrong and they love to spot the errors of other scientists; every word of the report had to be
agreed to by the IPCCÕs 130 participating governments; the IPCC is prohibited
by its charter from entering into speculation; and only scientific results
through 2005 were accepted.
This
document represents, for sure, the scientific consensus. The 21-page ÒSummary For PolicymakersÓ
of the scientific basis, drafted by 51 scientists including people like Alley
and Susan Solomon, co-discoverer of the Antarctic ozone hole and co-originator
of the chemical theory that correctly explains the hole, is available at http://www.ipcc.ch/. ItÕs written in English that everyone can read.
For
convincing confirmation that humans have significantly changed the atmosphere,
consider Figure 1 in the Summary.
It shows atmospheric concentrations of carbon dioxide and two other
global warming pollutants, during the past 10,000 years. All three graphs remain at relatively
unchanging levels right up until 150 years ago, when they zoom upward to radically
higher levels that are unprecedented in at least 650,000 years.
Other
conclusions: Global average
temperatures rose 1 degree Fahrenheit during the past century and will rise
another 2 to 11 degrees this century, with Arctic temperatures rising by twice
these amounts, if we donÕt severely reduce our emissions of global warming
pollution. Temperatures during the
past 50 years were the highest theyÕve been in at least 1300 years. Eleven of the past 12 years have been
among the 12 warmest since instruments began recording temperatures in
1850. Extreme weather (hot days
and nights, heat waves, hurricanes, heavy precipitation, drying, droughts) has
increased and will continue increasing. Permafrost and seasonally frozen ground
has significantly decreased and will continue decreasing. Mountain glaciers, snow pack, and snow
cover have declined and will continue declining. Summertime Arctic sea ice extent has decreased by over 20
percent and will decline until the Arctic ice cap disappears almost entirely
later in this century. Fresh
meltwater pouring into the Atlantic will cause the gulf stream to slow,
affecting global ocean flows, but this will not cause the feared sudden cooling
of Europe because global warming will dominate over any cooling effects.
Oceans
rose 7 inches during the past century because of melting mountain glaciers,
thermal expansion of seawater due to warming, and ice losses from the Greenland
and Antarctic ice sheets. Due only to mountain glaciers and thermal expansion,
oceans will rise an additional foot during this century. But one foot could be a big
underestimate, because although the Greenland and West Antarctic ice sheets are
showing signs of instability and rapid sliding toward the sea, these phenomena
were deemed too recent and too uncertain to be included in the report.
Going
somewhat beyond the conservative IPCC conclusions, many scientists believe that
we have as little as ten years left before setting the great ice sheets of
Greenland and West Antarctica on an irreversible path toward complete melting
or sliding into the sea, a long-term process that would eventually raise sea
levels by 23 feet if the Greenland ice sheet alone vanishes (this happened
during the previous Òinterglacial periodÓ 125,000 years ago when global
temperatures were only about 4 degrees above present levels). ÒIrreversibleÓ means that feedbacks
inherent within the climate system will inexorably melt these ice sheets,
regardless of how humans may manage to limit or reverse the increasing concentration
of global warming gases in the atmosphere.
Present
and future global warming pollution will continue contributing to warming and
sea level rise for more than 1000 years, due to the time required for removal
of these gases from the atmosphere. Where will this leave our grandchildren?
As
the planet warms, letÕs hope AmericaÕs political will rises faster than the
temperature readings.