With all the hyperbole with this week's climate marches, one would think we're dealing with settled science. That would certainly for those easily duped. According Steven E. Koonin, a theoretical physicist, former science adviser to the White House, and Director of the Center for Urban Science and Progress at New York University. We are very far from the knowledge needed to make good climate policy. He writes
The idea that “Climate science is settled” runs through today’s popular and policy discussions. Unfortunately, that claim is misguided.
It has not only distorted our public and policy debates on issues related to energy, greenhouse-gas emissions and the environment. But it also has inhibited the scientific and policy discussions that we need to have about our climate future.
My training as a computational physicist—together with a 40-year career of scientific research, advising and management in academia, government and the private sector—has afforded me an extended, up-close
perspective on climate science. Detailed technical discussions during
the past year with leading climate scientists have given me an even
better sense of what we know, and don’t know, about climate. I have come
to appreciate the daunting scientific challenge of answering the
questions that policy makers and the public are asking.
The crucial scientific question for policy isn’t whether the climate
is changing. That is a settled matter: The climate has always changed
and always will. Geological and historical records show the occurrence
of major climate shifts, sometimes over only a few decades. We know, for
instance, that during the 20th century the Earth’s global average
surface temperature rose 1.4 degrees Fahrenheit.
Nor is the crucial question whether humans are influencing the
climate. That is no hoax: There is little doubt in the scientific
community that continually growing amounts of greenhouse gases in the
atmosphere, due largely to carbon-dioxide emissions from the
conventional use of fossil fuels, are influencing the climate. There is
also little doubt that the carbon dioxide will persist in the atmosphere
for several centuries. The impact today of human activity appears to be
comparable to the intrinsic, natural variability of the climate system
itself.
Rather, the crucial, unsettled scientific question for policy is,
“How will the climate change over the next century under both natural
and human influences?” Answers to that question at the global and
regional levels, as well as to equally complex questions of how
ecosystems and human activities will be affected, should inform our
choices about energy and infrastructure.
But—here’s the catch—those questions are the hardest ones to answer.
They challenge, in a fundamental way, what science can tell us about
future climates.
Even though human influences could have serious consequences for the
climate, they are physically small in relation to the climate system as a
whole. For example, human additions to carbon dioxide in the atmosphere
by the middle of the 21st century are expected to directly shift the
atmosphere’s natural greenhouse effect by only 1% to 2%. Since the
climate system is highly variable on its own, that smallness sets a very
high bar for confidently projecting the consequences of human
influences.
A second challenge to “knowing” future climate is today’s poor
understanding of the oceans. The oceans, which change over decades and
centuries, hold most of the climate’s heat and strongly influence the
atmosphere. Unfortunately, precise, comprehensive observations of the
oceans are available only for the past few decades; the reliable record
is still far too short to adequately understand how the oceans will
change and how that will affect climate.
A third fundamental challenge arises from feedbacks that can
dramatically amplify or mute the climate’s response to human and natural
influences. One important feedback, which is thought to approximately
double the direct heating effect of carbon dioxide, involves water
vapor, clouds and temperature.
…
We often hear that there is a “scientific consensus” about climate
change. But as far as the computer models go, there isn’t a useful
consensus at the level of detail relevant to assessing human influences.
Since 1990, the United Nations Intergovernmental Panel on Climate
Change, or IPCC, has periodically surveyed the state of climate science.
Each successive report from that endeavor, with contributions from
thousands of scientists around the world, has come to be seen as the
definitive assessment of climate science at the time of its issue.
For the latest IPCC report (September 2013), its Working Group I,
which focuses on physical science, uses an ensemble of some 55 different
models. Although most of these models are tuned to reproduce the gross
features of the Earth’s climate, the marked differences in their details
and projections reflect all of the limitations that I have described.
For example:
• The models differ in their descriptions of the past century’s
global average surface temperature by more than three times the entire
warming recorded during that time. Such mismatches are also present in
many other basic climate factors, including rainfall, which is
fundamental to the atmosphere’s energy balance. As a result, the models
give widely varying descriptions of the climate’s inner workings. Since
they disagree so markedly, no more than one of them can be right.
• Although the Earth’s average surface temperature rose sharply by
0.9 degree Fahrenheit during the last quarter of the 20th century, it
has increased much more slowly for the past 16 years, even as the human
contribution to atmospheric carbon dioxide has risen by some 25%. This
surprising fact demonstrates directly that natural influences and
variability are powerful enough to counteract the present warming
influence exerted by human activity.
Yet the models famously fail to capture this slowing in the
temperature rise. Several dozen different explanations for this failure
have been offered, with ocean variability most likely playing a major
role. But the whole episode continues to highlight the limits of our
modeling.
• The models roughly describe the shrinking extent of Arctic sea ice
observed over the past two decades, but they fail to describe the
comparable growth of Antarctic sea ice, which is now at a record high.
• The models predict that the lower atmosphere in the tropics will
absorb much of the heat of the warming atmosphere. But that “hot spot”
has not been confidently observed, casting doubt on our understanding of
the crucial feedback of water vapor on temperature.
• Even though the human influence on climate was much smaller in the
past, the models do not account for the fact that the rate of global
sea-level rise 70 years ago was as large as what we observe today—about
one foot per century.
• A crucial measure of our knowledge of feedbacks is climate
sensitivity—that is, the warming induced by a hypothetical doubling of
carbon-dioxide concentration. Today’s best estimate of the sensitivity
(between 2.7 degrees Fahrenheit and 8.1 degrees Fahrenheit) is no
different, and no more certain, than it was 30 years ago. And this is
despite an heroic research effort costing billions of dollars.
Read the entire essay here: http://online.wsj.com/articles/climate-science-is-not-settled-1411143565
No comments:
Post a Comment