Impacts of Climate Change
At first global warming sounded like a good idea, especially to people
in Northern climes. But starting in the 1960s, scientists recognized long-range
problems, concentrating at first on sea-level rise and a threat to food
supplies. New items were gradually added to the list, ranging from the
degradation of ecosystems to threats to human health. Experts in fields
from forestry to economics, even national security experts, pitched in
to assess the range of possible consequences. It was impossible to make
solid predictions given the complexity of the global system, the differences
from one region to another, and the ways human society itself might try
to adapt to the changes. But by the start of the 21st century, it was
clear that climate change would bring serious harm to many regions —
some more than others. Indeed many kinds of damage were already beginning
to appear. (This essay does not try to cover the entire history of impact
studies, but sketches some examples. Current scientific understanding
of impacts is summarized at the end).
Through the first half of the
20th century, when global warming from the greenhouse effect was
only a speculation, the handful of scientists who thought about
it supposed any warming would be for the good. Svante Arrhenius,
who published the first calculations, claimed that nations like
his native Sweden "may hope to enjoy ages with more equable and
better climates."(1) Most people assumed that a "balance of nature"
made catastrophic consequences impossible, and if any change did
result from the "progress" of human industry, it would be all to
the good. In any case nobody worried about the impacts of a climate
change that scientists expected would only affect their remote descendents,
several centuries in the future, if it happened at all. |
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LINKS -
for more on this see
<=Public
opinion
|
A few scientists took a closer look in the
late 1950s when they realized that the level of carbon dioxide gas
(CO2) in the atmosphere might be rising, suggesting
that the average global temperature might climb a few degrees Celsius
before the end of the 21st century. Roger Revelle, the most senior
of these researchers, publicly speculated that in the 21st century
the greenhouse effect might exert "a violent effect on the earth's
climate" (as Time magazine put it). He thought the temperature
rise might eventually melt the Greenland and Antarctic icecaps, raising
sea level enough to flood coastlines. Noting that climate had changed
abruptly in the past, perhaps bringing the downfall of entire civilizations
in the ancient world, in 1957 Revelle told a Congressional committee
that the greenhouse effect might someday turn Southern California
and Texas into "real deserts." He also remarked that the
Arctic Ocean might become ice-free, to Russia's advantage. Everyone
understood this was all speculation, more science fiction than scientific
prediction. Another senior scientist, more cautious, told his colleagues
that they should take seriously the possibility of "warming,
and possible changes in rainfall and cloudiness" by the early
21st century. Meanwhile a pair of graduate students reported that
the CO2 greenhouse effect "could raise
such problems as coastal flooding due to rise in sea level and increased
aridity in certain areas." |
<=>Revelle's result |
More scientists began to look at the matter after 1960, when
observations showed the level of CO2 in the
atmosphere was indeed rising rapidly. In 1963 a path-breaking meeting
on "Implications of Rising Carbon Dioxide Content of the Atmosphere"
was convened by the private Conservation Foundation. "Conservation"
was the traditional term for a movement that was developing into
"environmentalism," centered on the growing realization that human
activities had expanded to the point where they could damage vital
ecosystems on a global scale. Participants in the meeting began
to frame greenhouse warming as an environmental problem —
something "potentially dangerous" to biological systems as well
as to humans.(2)
|
|
The meeting set the pattern for many later exercises. It brought together experts in carbon dioxide and climate (in fact the only experts at that time: Gil Plass and Dave Keeling) with a handful of experts in fisheries, agriculture and so forth. And it resulted in a "consensus" report, which warned that if fossil fuel burning continued, "the earth will be changed, more than likely for the worse." But the group, like many later ones, admitted ignorance, and called for more research. They could scarcely say what dangers might await a century ahead. They suspected forest productivity would improve, which did not sound bad, and that the distribution of species including commercial fisheries would change, which could be bad or good. The only thing they felt confident about was that rising temperatures would increase melting of the world's glaciers, raising the sea level and bringing "immense flooding" of low-lying areas.(2a*) |
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Global warming caught the attention
of the U.S. President's Science Advisory Committee. In 1965 they
reported that "By the year 2000 the increase in atmospheric CO2
... may be sufficient to produce measurable and perhaps marked changes
in climate..." Without attempting to say anything specific, they
remarked dryly that the resulting changes "could be deleterious
from the point of view of human beings."(3)
The following year, a panel of the U.S. National Academy of Sciences
warned against "dire predictions of drastic climatic changes." Dire
predictions of one or another climate catastrophe had in fact been a staple of the popular press for decades,
as magazines, books and other media peddled colorful speculations
of every variety. The Academy
panel remarked that the geological record showed swings of temperature
comparable to what the greenhouse effect might cause, and "although
some of the natural climatic changes have had locally catastrophic
effects, they did not stop the steady evolution of civilization."(4) |
<=>Government |
That was not entirely reassuring. Concern grew among the few scientists who paid attention to climate theories. Meanwhile the rise of environmentalism was raising public doubts about the benefits of human activity for the planet; smoke in city air and pesticides on farms were no longer tokens of "progress" but instigators of regional or even global harm. A landmark study on "Man's Impact on the Global
Environment," conducted at the Massachusetts Institute of Technology
in 1970, suggested that greenhouse warming might bring "widespread
droughts, changes of the ocean level, and so forth," but could not
get beyond such vague worries(5). A meeting in Stockholm the following
year came to similar conclusions, and added that we might pass a
point of no return if the Arctic Ocean's ice cover disappeared.
That would change the world's weather in ways that the scientists
could not guess at, but that they thought might be serious. Their
main point in bringing up the Arctic ice, however, was simply to
illustrate "the sensitivity of a complex and perhaps unstable system
that man might significantly alter."(6) |
<=>Public
opinion |
Up to this point, scientists
expected that greenhouse warming, if it happened at all, would bring
no serious impacts until well into the 21st century. And the 21st
century seemed so far away! But was climate change really so distant?
In the early 1970's the world saw vivid illustrations of climate
fluctuations as savage droughts afflicted the American Midwest,
devastated the Russian wheat crop and brought starvation upon millions
in Africa. Studies of climate were still in their infancy, and scientists
were debating whether the greenhouse effect from CO2
emissions might be overwhelmed by the cooling caused by other forms
of pollution. A few scientists speculated that industrial emissions of aerosols might cause severe cooling, while others suspected that natural cycles might bring a new ice age within the next few centuries. Nobody knew whether warming or cooling was more likely. |

Sahel
drought 1972
<=>Public
opinion |
Studies of the impacts of climate change therefore tended to address
generalities such as how a given type of crop would respond to either
a rise or a drop in temperature. An example was a 1974 report commissioned
by the U.S. Central Intelligence Agency (CIA). (link from below) What if the climate altered radically within
a few decades — perhaps the sudden freeze that some journalists
warned might grip the planet? The report concluded that the entire
world's food supply might be imperilled. There would be mass migrations,
perhaps even wars as starving nations fought for the remaining resources.
Scientists scoffed at the scenario, for none of them expected a
radical climate shift, whether warming or cooling, could come so
swiftly. But for a more distant future, the grim speculations could
not be entirely dismissed. |
|
Governments were now putting some of the environmental movement's
demands into law; that created a practical need for formal "environmental
impact" assessments. A new industry of expert consultants strove
to forecast effects on the natural environment of everything from
building a dam to regulating factory emissions. On a broader scale,
people concerned about the environment applied increasingly sophisticated
scientific tools to study the impacts of deforestation, acid rain,
and many other large-scale activities. They looked at impacts not
only on natural ecosystems but on human health and economic activities.
Assessing the long-term impact of greenhouse gases fitted easily
into this model. |
|
One example was a 1977 report on "Energy and Climate" from a
panel of geophysicists convened by the U.S. National Academy of
Sciences. By this time the speculations about cooling had faded away, while many scientists felt that greenhouse warming was a strong possibility. The panel got fairly specific about
the potential consequences. On the positive side, the Arctic Ocean
might eventually be opened to shipping. On the negative side, there
would be "significant effects in the geographic extent and location
of important commercial fisheries... marine ecosystems might be
seriously disrupted." Stresses on the polar ice caps might lead
to a surge of ice into the sea, bringing a "rise in sea level of
about 4 meters within 300 years." As for agriculture, there would
be "far-reaching consequences" which "we cannot specify... We can
only suggest some of the possible effects. A few of these would
be beneficial; others would be disruptive." There could be terrible
"human disasters" like the recent African droughts. However, the
panel made clear they could not foresee what might actually happen.
They concluded vaguely that "world society could probably adjust
itself, given sufficient time and a sufficient degree of international
cooperation. But over shorter times, the effects might be adverse,
perhaps even catastrophic."(7)
Two years later another Academy panel said much the same, and took
brief note of an additional threat — the rise of CO2
in the atmosphere would make the oceans more acidic. Here too they
found the consequences beyond guessing. Overall the experts could
only conclude that as the world warmed, "the socioeconomic consequences
may well be significant, but... cannot yet be adequately projected."(8) |
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Economists and social scientists were just beginning to take an
interest in the topic. In 1980 the Academy appointed an "Ad
hoc Study Panel on Economic and Social Aspects of Carbon Dioxide
Increase," the first semi-official attempt to address these
aspects directly, separate from the science. The panel's lame conclusion
was that any problems would come so slowly that they would be overtaken
by unpredictable technological and social changes. At worst, people
who found themselves in a region with worsening climate could migrate
to a better place, as had often happened in the past. This was supposed
to be reassuring. |
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As studies proliferated, the
topic of "climate impact studies" was starting to look like a respectable
field of research. The
significant reports of the late 1970s had all been American, and
many scientists wanted to internationalize impact studies. An attempt
was initiated by the International Council of Scientific Unions
(ICSU), the United Nations Environmental Programme (UNEP) and the
World Meteorological Organization (WMO) — the march of acronyms
signals the increasing levels of complexity and bureaucracy that
were coming into play. However, a one-week meeting in Villach, Austria,
in 1980 did not get any farther than the earlier U.S. Academy studies,
and its report was not widely circulated. "The 'internationalisation'
of the assessment effort was not very successful," admitted
one of the leaders, Bert Bolin. A more substantial team effort,
assembled in Stockholm, again reached the same conclusions as the
American panels — global warming would have profound consequences
for ecosystems, agriculture, water resources, the sea level and
so forth.(9)
|
|
More categories of impacts emerged, each attracting its own little band
of specialists. For example, an elaborate 1983 study by the U.S.
Environmental Protection Agency, with more than 100 reviewers, studied
sea-level rise. The experts concluded that by the end of the 21st
century they "could confidently expect major coastal impacts,
including shoreline retreat... flooding, saltwater intrusion, and
various economic effects." A big step forward was a 1983 U.S.
Academy report, the most detailed assessment up till then. It not only included
familiar categories like agriculture and sea-level rise,
but also pointed out that an increase in extreme summer temperatures
would worsen the "excess human death and illness" that
came with heat waves. Also, melting of permafrost in the Arctic
could require adaptations in engineering. Also, climate shifts "may
change the habitats of disease vectors." Finally and most important,
"In our calm assessments we may be overlooking things that
should alarm us." For there might be effects that no expert
could predict or even imagine, effects all the more dangerous because
they would take the world by surprise. Nevertheless the Academy,as usual, did not recommend
any actual policy initiatives, aside from the scientists' customary
plea for more research.
|
<=Government |
Meanwhile, in 1982 Bolin spoke about an
international effort with Dr. Mustafa Tolba, the dynamic executive director
of UNEP. Tolba, a former professor of biology at Cairo University,
wanted to go beyond physical climate studies to bring attention
to global ecosystems. That was the sort of "environmental"
study that UNEP could support. Later WMO was brought in, and ICSU
agreed to publish the results to help them become widely read. The
resulting 560-page report, Bolin was proud to say, brought the greenhouse
problem "much more to the forefront in the scientific community
than earlier assessments had done, particularly amongst those engaged
in analysis of the terrestrial ecosystems." The sequel was
a 1985 UNEP/WMO/ICSU conference in Villach, energetically chaired
by Tolba, which further publicized the scientists' warnings. The
assembled experts went on to call for policy initiatives—not
to restrict greenhouse gases, to be sure, but at least to mobilize
an internationally coordinated effort to study policy options.(9a*) |
<=>International
|
The studies to this point had
used a simple cause-and-effect model. Physical scientists would
run computer models to predict changes in precipitation and the
like. Others would follow by calculating immediate consequences,
for example using historical records to predict how crop yields
would vary with the weather. But if farmers could no longer get
good results from corn, wouldn't they plant something more suited
to their new climate? During the 1980s, some impact studies began
to take account of how humans might adapt to climate change. By
the end of the decade, some studies were linking models of crop
responses with economic models. Complex interactions were no less
crucial in natural ecosystems. Life scientists began to calculate
how forests, coral reefs and so forth might respond to the rise
of greenhouse gases. For example, could tree species move their
ranges poleward fast enough to keep up with the temperature rise?
At a still higher level of complexity, some studies began to account
for the way one type of climate impact might interact with another. |
<=>Simple models |
These more sophisticated approaches
guided the first comprehensive official U.S. government report, ordered up by
Congress from the Environmental Protection Agency. The EPA's findings
continued the trend toward predicting more numerous and more specific
kinds of damage. The experts concluded (as summarized by New
York Times in 1989) that "Some ecological systems, particularly
forests... may be unable to adapt quickly enough to a rapid increase
in temperature... most of the nation's coastal marshes and swamps
would be inundated by salt water... an earlier snowmelt and runoff
could disrupt water management systems... Diseases borne by insects,
including malaria and Rocky Mountain spotted fever, could spread
as warmer weather expanded the range of the insects." Some of this
was already vaguely grasped by the minority of people who followed
scientific news closely. Other predictions, notably the expansion
of diseases, had been mentioned in passing before but were only
now coming under detailed discussion.(10*) |
=>Public
opinion |
Studies of how climate change
might affect human health expanded particularly swiftly in the 1990s,
catching the attention not only of experts but the public. Here
as in some other categories, the work was increasingly supervised
not by a particular government but by international organizations,
from the venerable World Health Organization to the new International
Panel on Climate Change (IPCC, established 1988). Yet here as in some other categories,
it was becoming clear that global generalizations were of little
value compared with studies at a regional level. For example, insect
vectors of tropical diseases like dengue fever and malaria (which
already affected half a billion people) would expand their ranges.
The main impacts would be felt in developing nations, but people
in the developed world tended to worry chiefly about how such diseases
might spread to the temperate zones.(11) |
<=International |
Any regional analysis had to
start with the climate changes that would result from a given level of greenhouse gases, as calculated by computer models. But although the
increasingly sophisticated models had come to a rough agreement
on global features like the rise of average temperature, they differed
in the details. In places where many factors balanced one another,
for example the Sahel region between the Sahara desert and the African
rain-forest, one model might predict a benign increase of rainfall
and another, terrible droughts. Policy-makers did not much care
about the average global temperature — they wanted to know
how things would change in their own locality. |
<=Models
(GCMs) |
Unable to make quantitative predictions of just what might happen in each region, the IPCC decided to study "vulnerabilities," that
is, the nature of damage that a given system might sustain from
any of the likely sorts of climate change. This was in line with
an established practice of vulnerability studies in many other areas,
from food supplies to earthquakes. The experts also considered benefits,
but the very term "vulnerability" showed that by now most
of them believed the net effects of greenhouse warming would be
harmful. Some disagreed, leading to a serious controversy during
the discussions leading to the IPCC's initial report of 1990. The
eminent Russian climatologist Mikhail Budyko argued, on the basis
of his reconstruction of climates in the distant past, that warming
would have important benefits. For Siberia, at least, he had a point
— so long as the warming did not soar higher than in the earlier
interglacial epochs he had studied. In the usual IPCC fashion, the
experts papered over their disagreements, inserting some polite
phrases accepting that there could be beneficial results in some
northern locales.
|
|
The IPCC got much farther in 1997 with a pioneering report on
"The Regional Impacts of Climate Change." Each region of the globe
got its own detailed account of vulnerabilities. At this level it
was obviously necessary to consider not only the local climate and
ecological systems, but also the local economic, social and political
conditions and trends, drawing in the social sciences as equal partners
with geophysics and biology. It was becoming a standard practice
to consider how people might adapt. For example,
the panel concluded that Africa was "the continent most vulnerable
to the impacts of projected changes." That was not just because
so many parts of Africa were already water-stressed, subject to
tropical diseases, and so forth, but still more because population
pressure and political failings were causing environmental degradation
that would multiply the problems of climate change. Above all, Africa's
"widespread poverty limits adaptation capabilities." By contrast,
the carefully managed agricultural systems of Europe and North America
might even contrive to benefit from a modest warming and rise in
the level of CO2 (which could act as a fertilizer
for some crops), although the developed nations would certainly
suffer some harmful impacts as well.(12)
|
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An elaborate assessment exercise
that the U.S. government pursued in the 1990s took a different approach.
The authors displayed, side by side, the results of two separate
computer models (one constructed in the United Kingdom and one in Canada).
In some regions the model predictions agreed; there seemed
little doubt, for example, that Southern California would get a
lot drier. In other regions they diverged, as when one model projected
more rain in the Southeast and the other, less. Overall, the American
experts agreed with the IPCC that highly managed ecosystems of farming
and forestry might do quite well in the first half century of serious
warming. On the other hand, nothing could prevent damaging changes
in some natural ecosystems and expensive difficulties along the
coasts. As for threats to health, there would be some problems but
"adaptation is likely to help protect much of the US population."
And finally, "some aspects and impacts of climate change will be
totally unanticipated," which people could interpret optimistically
or pessimistically, according to taste.(13)
Scientists in another major industrial country, chilly Russia, foresaw
even less worrisome results from global warming. These assessments,
and the publics they addressed, could see the impacts as manageable
because they were looking no more than half a century or so ahead.
The 22nd century was so far away! Surely by then, humanity would
have taken control of its emissions so that CO2
would not rise to three or four times the pre-industrial level...
wouldn’t we? |
<=>Government |
The future state of the climate would depend crucially on what emission
controls nations chose to impose. That exposed a problem with the
standard way of predicting impacts. Scientists had tried to look into
the future by extrapolating the visible trends and forces along a
single line, calculating a most likely outcome within a range of possibilities:
"global average temperature will rise three degrees plus or minus
50%" or the like. People would then estimate the consequences of a three-degree rise. |
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Professional "futurologists" in the
social sciences, and the policy-makers they advised, had abandoned
that method of prediction decades earlier, when they realized that
most of their predictions had been far off the mark. They turned to an approach practiced by military planners since the
1940s: instead of trying to predict the most likely future, imagine
a wide range of possible futures, and for each of these develop a
detailed “scenario”. The aim was to stimulate thinking
about how your operations should be structured so they would hold up under any of the likely contingencies. This approach was applied to environmental questions in the 1970s by studies that sketched out a set of very different possible futures for pollution, exhaustion of natural resources, food production and so forth, depending on just what policies governments might adopt.(13a) Since the 1980s most corporations and government agencies had used scenarios for their planning.. |
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The IPCC had taken up this method
from the outset, assembling experts to write scenarios in a lengthy intergovernmental process. The result, published in 1992, was a set of six different scenarios, each describing
a range of ways that the world's population, economies, and political
structures might evolve over the decades. Experts in various fields
of physical and social science could try to figure how much of each
of the various greenhouse gases would be emitted by the society
of a given scenario, then compute the likely climate changes, and
then estimate how that society would try to adapt. Much was omitted
from these scenarios, not least the feedback by which climate changes
might affect the socio-economic system and thereby the emissions
themselves. A second try in 1996 produced no fewer than 40 different
scenarios, grouped into families in terms of rate of economic growth,
sensitivity to environmental problems, degree of international cooperation
and so forth.(14) There were so many unknowns,
and so many differences from region to region with each region demanding its own detailed study, that the small community
of researchers could explore in depth only a few of the possibilities.
Many research projects used only one scenario, a middle one with
emissions neither sharply restricted nor rising explosively.
|
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In its own reports, the IPCC not only laid out clearly the range
of scenarios it had investigated, but got increasingly specific
about whether the consensus of experts judged a given impact to
be "likely," "very likely," or "virtually
certain." There was plenty of uncertainty, not least because the laborious studies lagged behind the science; the panel's 2001 impact assessments relied on older computer model results that were derived from the still older 1992 emission scenarios. (It was only around 2009 that the impacts community figured out ways to work through the different stages in parallel rather than sequentially.)(14a) In the panel's 2001 and 2007 reports, the most impressive
parts resembled the earlier reports that simply laid out a variety
of the likely direct impacts, and suggested which regions would
be especially vulnerable. |
<=International
|
Scholars who studied the two-decade series of IPCC assessments reported
a clear trend toward more complex and interdisciplinary analysis,
in which climate impacts were combined with other stresses and with
potential adaptations. The trend responded to the evolving needs of
policy-makers. The scientists’ first goal had been to evaluate
the overall danger to the world associated with a given level of greenhouse
gases, in order to advise governments how much effort they should
make to restrict emissions. By the time that question was answered,
greenhouse gases had risen to a level where some serious impacts were
inevitable. Leaders in governments and business organizations were
now asking for detailed and precise assessments so they could shape
policies for adapting to the changes.(15) |
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The scientists' attempts at precision
could be misleading. For example, studies published from the 1970s
into the mid 1980s estimated that by 2100, the sea level might rise
anywhere from a few tenths of a meter to a few meters. The upper limit
dropped to about half a meter in the IPCC's 1995 report, and it stayed
there in later reports. But in fact, the range of scientific estimates
on how high the seas could rise in the 21st century remained broad.
The rise would exceed a meter if polar ice sheets began to surge into
the oceans in the next few decades. Most scientists had always considered
that quite unlikely, but there were always some who argued that it
was possible. The IPCC gave scant attention to such impacts that did
not seem at least fairly likely to happen, even if they would be catastrophic
in the event they did befall us. |
<=Sea rise & ice |
This was different from the
practice in many other kinds of impact studies. For example, the
building codes of cities in earthquake zones, and evacuation plans
for people living near nuclear reactors, dealt with problems that
might have less than one chance in a hundred of happening in the
next century or two. The IPCC, by contrast, was preoccupied with
impacts that were more likely than not. |
<=>Models
(GCMs) |
There were still people arguing that climate change would be beneficial.
These included a few scientists and a large number of conservatives,
amply funded by right-wing private American institutes. For example,
a Hoover Institution publication held that "Global warming, if
it were to occur, would probably benefit most Americans." There
would be lower heating bills and other energy savings, and besides,
"More people die of the cold than of the heat." Many asserted,
as a Heartland Institute publication declared, that "More carbon
dioxide in the air would lead to more luxuriant crop growth and greater
crop yields." Little if any hard analysis backed up such statements,
but there was some truth in them. As Russians in particular noticed,
a bit of warming would bring some benefits to cold regions. But even
in those regions the people, crops and entire ecosystems would eventually
suffer more harm than good, according to the voluminous and detailed
studies worked up by teams of economists, epidemiologists, agronomists
and other experts. The public, however, scarcely knew that these teams
existed and never read their reports. The experts' conclusions reached
ordinary people at most as a summary paragraph or two in a news story,
perhaps "balanced" by a statement from one of the institutions
committed to denying any problem existed. Meanwhile some media featured exaggerated warnings of doom. "Global heating will all but eliminate people from the Earth," exclaimed a well-known scientist; a high-ranking bank officer declared that inaction on emissions would bring "the extinction of the human race."(16) |
|
Reality descended
upon the abstract world of impact studies as actual consequences
of global warming began to appear. In the late 1990s, field surveys
of sensitive and well-studied groups like birds and butterflies
found them measurably shifting their ranges, or even facing extinction,
in just the ways that could be predicted from the observed warming.(17a*) In the early years of the 21st century, instead of future
possibilities some experts began to estimate the role that global
warming might have played in one or another actual disaster. It
turned out that because of unexpected complexities, the rich nations
were not as safe as some had thought. One example: in 2003 a heat
wave of unprecedented scope killed tens of thousands in Europe.
Nobody had foreseen that old people could not save themselves when
the traditional August vacation emptied the cities. Another example:
bark beetles, no longer controlled by winter freezes, devastated
millions of acres of forests from Alaska to Arizona, leaving the
weakened timber prey to an unprecedented outbreak of forest fires.
Nobody had prepared for this particular impact of global warming. By 2010 a world-wide increase in record-breaking and devastating heat waves, droughts and floods had convinced many insurance companies and ordinary citizens that something unprecedented was happening to the weather. |

A first harbinger
of
warming. More
=>Public
opinion
Trees killed by beetles
|
Drought emerged as probably the most severe problem for the near term, that is, the lifetimes of people already born. Record-breaking droughts in the American Southwest, Amazon basin, Australia and the Mediterranean looked like harbingers of permanent changes in precipitation and temperature patterns that could turn crucial agricultural areas into dust bowls. These regions and others from the Middle East to Southeast Asia seemed likely to suffer severely already by midcentury.(17b) |
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A description of impacts meant little to people unless it was translated
into specific human terms. For example, if an aquifer turned brackish
as the sea level rose, exactly what difference would that make to
anyone? Since the early 1970s, economists had been developing increasingly
detailed projections of the economic benefits and costs of global
warming, working up from regional examples to global estimates.Of course, it was not easy
to put a dollar value on longer summers or the destruction of the
world's coral reefs. In response to environmentalist warnings, a few free-market economists worked up calculations
that found negligible costs from climate change, and warned that taxing
or regulating emissions would wreck the economy. Others replied
with calculations that gave opposite results. Economic analysis took off in the early 1990s with increasingly numerous and sophisticated studies.(18*) |
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The most influential skeptical work came from Bjørn Lomborg,
a Danish political scientist who wrote a best-selling book and in
2004 assembled a panel of prominent economists to analyze various
approaches (the "Copenhagen Consensus"). Lomborg and his
panel argued that it would be far better for humanity to spend its
money on immediate problems like malaria than on long-term problems
like global warming — although they did say that governments
would do well to spend far more money on research on ways to reduce
greenhouse emissions.(19) The debate evolved into
a discussion of basic principles, exposing issues that the public
and policy-makers scarcely appreciated. Some economists pointed out
that the conventional methods of their field were not framed to deal
with such an issue, where the main consequences were many years ahead
and might bring anything from discomfort to devastation. Hardly any impact study looked farther ahead than 2100; the 22nd century just seemed too far away. |
|
Governmental and international
bodies stepped in, supporting elaborate professional studies. An outstanding
example was the Stern Review on the Economics of Climate Change,
produced for the British government in 2006 by Nicholas Stern, former
chief economist of the World Bank, with a staff of 20. Stern framed
the question in a businesslike "risk management" manner, studying
the worst case plausible enough to be worth buying insurance against
(under the assumption that the well-being of future generations had
significant value for us in the present). His team calculated that
if global warming in the 21st century was in the upper range of what
scientists thought likely, the direct effects would cut the annual
Global Domestic Product by some 5%. Indirect effects might possibly
raise that as high as 20%, equivalent to the Great Depression of the
1930s or the damage in one of the 20th century's world wars
maintained perpetually. The economists made a rough estimate of the
cost of preventing that, most likely a modest 1% reduction in Global
Domestic Product. (The IPCC's 2007 report reached a similar conclusion.)
"Climate change," Stern concluded, "is the greatest market failure
the world has ever seen."(20*) |
=>Public
opinion |
There was an even
more sobering way to frame climate change as a security threat.
For half a century, forward-looking military officers had considered
with increasing concern what global warming might mean in their area
of responsibility. They would surely be called upon, for example,
if weather disasters multiplied. In 2003, defense intellectuals in
the Pentagon commissioned a report on "An Abrupt Climate Change Scenario
and its Implications for United States National Security." As reported
in a leak to the press, the authors warned of a risk that "mega-droughts,
famine and widespread rioting will erupt across the world.... abrupt
climate change could bring the planet to the edge of anarchy as countries
develop a nuclear threat to defend and secure dwindling food, water
and energy supplies." The authors concluded that "the threat to global
stability vastly eclipses that of terrorism." The report was strikingly
similar to the CIA report prepared three decades before (see
above). Again the specific "worst-case"scenario, an abrupt change
in ocean circulation, was something scientists considered extremely
unlikely. By now, however, impact studies had sketched out a range
of more plausible scenarios that looked bad enough. If you thought
like a military officer, the IPCC's approach — concentrating
on what everyone could agree was likely, while ignoring less
likely but still possible scenarios — was not "conservative"
at all, but irresponsible. Many well-informed military officers and
other national security experts, along with many political leaders
and a majority of the world’s public, now believed that the
possible impacts of global warming ranked among the most dangerous
long-term risks that civilization faced.(21*) |
=>Government
<=>International
<=>Public
opinion |
What do we know about the impacts of global warming?
A large body of scientific studies, exhaustively reviewed, has produced
a long list of possibilities. Nobody can say that any of the items
on the list are certain to happen. But the world's climate experts almost all agree that the impacts listed below are
more likely than not to happen. For some items, the probabilities
range up to almost certain.
|
|
The following are the likely consequences of warming by a few
degrees Celsius — that is, what we may expect if humanity
manages to begin restraining its emissions soon, so that greenhouse
gases do not rise beyond twice the pre-industrial level. Without
strong action the doubling will come well before the end of this
century, bringing the planet to temperatures not seen since the
spread of agriculture. By 2007, many of the predicted changes were
observed to be actually happening. For details see reports referenced in this footnote: (22) |
|
* Most places will continue to get warmer, especially
at night and in winter. The temperature change will benefit some
regions while harming others — for example, patterns of tourism
will shift. The warmer winters will improve health and agriculture
in some areas, but globally, mortality will rise and food supplies
will be endangered due to more frequent and extreme summer heat
waves and other effects. Regions not directly harmed will suffer
indirectly from higher food prices and a press of refugees from
afflicted regions. |
|
* Sea levels will continue to rise
for many centuries. The last time the planet was 3°C
warmer than now, the sea level was at least 6 meters (20 feet) higher.(23) That
submerged coastlines where many millions of people now live, including
cities from New York to Shanghai. The rise will probably be so gradual
that later generations can simply abandon their parents' homes,
but a ruinously swift rise cannot be entirely ruled out. Meanwhile
storm surges will cause emergencies. |
<=Sea rise & ice |
* Weather patterns will keep changing toward
an intensified water cycle with stronger floods and droughts. Most
regions now subject to droughts will probably get drier (because
of warmth as well as less precipitation), and most wet regions will
get wetter. Extreme weather events will become more frequent and
worse. In particular, storms with more intense rainfall are liable
to bring worse floods. Some places will get more snowstorms, but most mountain glaciers and winter snowpack will
shrink, jeopardizing important water supply systems. Each of these things
has already begun to happen in some regions.(24) |

Drought in the 2060s
|
* Ecosystems will be stressed, although some
managed agricultural and forestry systems will benefit, at least
in the early decades of warming. Uncounted valuable species, especially
in the Arctic, mountain areas, and tropical seas, must shift their
ranges. Many that cannot will face extinction. A variety of pests
and tropical diseases are expected to spread to warmed regions.
These problems have already been observed in numerous places.
|
|
* Increased carbon dioxide
levels will affect biological systems independent of climate
change. Some crops will be fertilized, as will some invasive weeds
(the balance of benefit vs. harm is uncertain). The oceans will
continue to become markedly more acidic, gravely endangering coral
reefs, and probably harming fisheries and other marine life. |
<=Biosphere |
* There will be significant unforeseen impacts.
Most of these will probably be harmful, since human and natural
systems are well adapted to the present climate. |
|
The climate system and ecosystems are complex and only partly
understood, so there is a chance that the impacts will not be as
bad as predicted. There is a similar chance of impacts grievously
worse than predicted. If the CO2 level keeps
rising to well beyond twice the pre-industrial level along with
a rise of other greenhouse gases, as must inevitably happen if we
do not take strong action soon, the results will certainly be worse.
Under a "business as usual" scenario,
recent calculations give even odds that global temperature will
rise 5°C or more by the end of the century — causing a
radical reorganization and impoverishment of many of the ecosystems
that sustain our civilization.(25) |
|
All this is projected to happen to people who are now alive. What of the more distant future? If emissions continue to rise for a century — whether because we fail to rein them in, or because we set off an unstoppable feedback loop in which the warming itself causes ever more greenhouse gases to be evaporated into the air — then the gases will reach a level that the Earth has not seen since tens of millions of years ago. The consequences will take several centuries to be fully realized, as the Earth settles into its new state. It is probable that, as in the distant geological eras with high CO2, sea levels will be many tens of meters higher and the average global temperature will soar far above the present value: a planet grossly unlike the one to which the human species is adapted. |
<=CO2 greenhouse
|
What can people do about global warming, and what should
we do? See my Personal Note and Links. |
|
1. Arrhenius (1908),
p. 63. BACK
2. Time (1956). Real
deserts: Revelle in United States Congress (85:2), House of Representatives,
Committee on Appropriations, Report on the International Geophysical
Year (Washington, D.C.: Government Printing Office, 1957), pp. 104-106. Ice-free:
see note below. Lloyd V. Berkner, "Horizons
of Meteorology," talk to American Meteorological Society and
American Geophysical Union, May 1, 1957, Am. Met. Soc. records, Box
12; my thanks to Alan Needell for this information. "Such problems":
Wallace Broecker and Bruno Giletti writing in the student magazine
Yale Scientific in 1957, according to " Broecker
and Kunzig (2008), p. 71. BACK
2a. Conservation Foundation
(1963).pp. 1, 5, 14. They also speculated (p. 6) that "many life forms would be annihilated" in the tropics if emissions continued unchecked for several centuries, a time too far away to mean much to anybody. BACK
3. President's Science
Advisory Committee (1965), pp. 126-27. BACK
4. National Academy
of Sciences (1966), Vol. 2, "Research and Development," p. 88.
BACK
5. SCEP (1970),
p. 18. BACK
6. Wilson (1971),
pp. 17, 182. BACK
7. National Academy
of Sciences (1977), pp. 8-14. BACK
8. National Academy
of Sciences (1979), pp. 3, 24-27. BACK
9. Ad hoc panel: Oreskes
et al. (2008b), p. 124; Bolin (2007),
p. 34. BACK
9a. Hoffman
et al. (1983) as cited by Oreskes et
al. (2008b), pp. 134-35, see also pp. 140-41. National
Academy of Sciences (1983), pp. 45, 50, 53, on pests see also
pp. 405-07. This followed a preliminary report, National
Research Council (1982). Here and below I draw especially on
Long and Iles (1997). They identify the
first World Climate Conference (Geneva, 1979) as "the first major
conference to address human health" (p. 8). Bolin
(1986), pp. 35-38. BACK
10. Philip Shabecoff, "Draft Report on Global
Warming Foresees Environmental Havoc in U.S.," New York Times,
October 20, 1988; United States, Environmental
Protection Agency (1989). My search of the
Google news archive found that newspaper and newsmagazine items
on disease spread by climate change and the threat to water supplies
from earlier snowmelt began to appear in 1988-89. Items on impacts
on water supplies due to the disappearance of glaciers started appearing
only in 1997. Harm to water supplies was noted, for example, by
Revelle and Waggoner (1983). BACK
11. Long and Iles
(1997), pp. 29-33. BACK
12. Budyko: Bolin (2007),
p. 64.Watson et al. (1997), quote p.
6. BACK
13. National Assessment
Synthesis Team (2000-2001), quotes p. 9. BACK
13a. The influential pathbreaker was Meadows et al. (1972). BACK
14. J. Leggett, et al., "Emissions Scenarios
for the IPCC: An Update," in IPCC (1992),
pp. 68-95. The scenarios are available at the
IPCC Data Distribution Centre. 1996: IPCC Special Report on
Emissions Scenarios, online
here. BACK
14a. Moss et al. (2010), including an impacts studies historical timeline. BACK
15. Füssel
and Klein (2006). BACK
16. Conservative quotes from McCright
and Dunlap (2000), pp. 514-15. Lovelock (2009), p. 6; Kevin Parker, global head of Deutsche Bank Asset Management, quoted in John M. Broder, "Climate Deal Likely to Bear Big Price Tag," New York Times, Dec. 9, 2009. BACK
17a. Landmark studies included Parmesan
(1996), finding a latitude shift attributed to climate change
in a North American butterfly (Edith's Checkerspot, photo
(c) 2004 Jeffrey Pippen, by permission),
and Parmesan et al. (1999) with "the
first large-scale evidence of poleward shifts in entire species'
ranges" from Europe. BACK
17b. Romm (2011); Dai (2011). BACK
18. Discussions began with D'arge and Kogiku (1973), arguing that CO2 emissions should be restricted, and Nordhaus (1974), saying the greenhouse effect should not constrain energy growth in the near future at least. Long
and Iles (1997) point to the US Department of Transportation's
Climatic Impact Assessment Program (aimed not at the greenhouse
effect but aircraft emissions) for producing, in 1975, "the first
assessment to focus on social and economic measures," (p. 6) and
the 1989 US Environmental Protection Agency study as "the first
extensive appearance of an economic analysis of impacts." BACK
19. Lomborg
(2001); Lomborg (2004), see also
Lomborg(2007). For criticism of factual errors see http://www.lomborg-errors.dk and Friel (2010). BACK 20. Stern
(2006), p. 3. All these numbers were highly uncertain; Stern's estimated cost
of stabilizing CO2 at a level
he thought reasonably safe (550ppm) might be anywhere from 3.5% of GDP to -1% (net benefit),
p. xiv. IPCC (2007e), and check the IPCC
website for subsequent reports. Criticism by economists, much of it technical, centered on Stern’s use of a "0% discount." That bestowed as much value on costs to all later generations as costs to ourselves, and could be used to justify almost any expense. But the critics' preferred discounting, say at 3-4% per year, assumed the world economy was certain to expand indefinitely without a hitch — our grandchildren would be so fabulously wealthy that they could solve any problem, even as the environment deteriorated around them. And it ignored prudent insurance-style evaluation of the cost of altogether catastrophic impacts that scientists thought unlikely but entirely possible: a "fat tail" probability distribution, see Weitzman (2007), Weitzman (2009). BACK
21. In
1956 a leading scientist speculated that in a distant future we
might "find that the Arctic Ocean will become navigable...
If the Russian coastline increases by something like 2,000 miles
or so, the Russians will become a great maritime nation." Testimony
of Roger Revelle, US Congress, House 84 H1526-5, Committee on Appropriations,
Hearings on Second Supplemental Appropriation Bill (1956),
pp. 474 and 473. See also "Government" essay here.
Already in the 1970s, a couple of studies like the CIA study noted
above had framed global warming as a security
problem. Environmentalists since the early 1970s had argued more
generally that the world would be more secure if it spent less money
on military defense and more on defense against pollution and other
environmental dangers. The groundbreaking 1988
Toronto Conference concluded that changes in the atmosphere
were a major threat to global "security," and for climate change
in particular the "ultimate consequences could be second only to
a global nuclear war." For all this see Barnett
(2001), who gives the quote from World
Meteorological Organization (1989). Report for Pentagon: Schwartz
and Randall (2003), reported by Stipp
(2004); quote: Mark Townsend and Paul Harris, "Now the Pentagon
Tells Bush: Climate Change Will Destroy Us," The Observer,
February 22, 2004. An internet newspaper archive search will show,
e.g., the Science Advisor to UK Prime Minister Tony Blair, Sir David
King, calling climate change "the greatest threat facing mankind"
and "worse than terrorism." See report issued in 2007 by a group
of retired three- and four-star admirals and generals: CNA
corporation (2007) and report of a 2007 conference of academics
and serving officers, Pumphrey (2008).
At the request of Congress, in 2008 the CIA weighed in officially
with a classified report declaring climate change had a "potential
to seriously affect U.S. national security interests." Siobhan
Gorman, "Report Says U.S. Security Faces Challenges From Global
Warming," Wall Street Journal, June 25, 2008, online
here. The first substantial appearance of climate change in a top-level U.S. military policy document was in the 2010 Quadrenniel Defense Review, worrying about both political instability and disaster response. In 2007, 64% of all Americans felt that their country was
"in as much danger from environmental hazards, such as air pollution
and global warming, as it is from terrorists," source: Yale
Center for Environmental Law and Policy. For international opinion
see, e.g., 2007 Chicago Council on Global Affairs poll at worldpublicopinion.org.
BACK
22. IPCC
(2007c) summarizes knowledge as of mid 2006; for the latest
see the IPCC's website. For regional changes in the United States see the U.S. Global Change Research Program reports. Lynas
(2007) provides vivid pictures of various possible futures.
Note that reviews such as Grassl (2000)
have been only modestly revised by more recent work.
BACK
23. Kopp (2009). BACK
24. For North America, see Karl
et al. (2008). BACK
25. Sokolov
et al. (2009); for a summary see MIT
News Office press release, May 19, 2009. BACK
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copyright
© 2007-2011 Spencer Weart & American Institute of Physics
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