《可持续发展的时代》旨在让你了解可持续发展 所面临的关键挑战和实践途径 即兼顾社会包容性和环境可持续性的经济发展
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可持续发展的时代
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从本节课中
Curbing Climate Change
Professor Sachs provides an introduction to the science behind climate change, and describes the negotiations and policies that are necessary to mitigate and prevent the consequences.
与讲师见面
Jeffrey Sachs
Director, Earth Institute; Quetelet Professor of Sustainable Development; Professor of Health Policy and Management
[MUSIC].
Why should we care about human-induced climate change?
The fact of the matter is, we should be scared, truly scared.
Not so frightened that we're paralyzed, but rather scared into action because
the consequences on a business-as-usual trajectory
for this planet could absolutely be dire.
We are on a path of putting so much carbon dioxide, methane, nitrous oxide
into the atmosphere that the temperature increase on average on the planet
could be several degrees centigrade by the end of this century.
Four, five, six, eight, nine degrees centigrade, there's no absolute
precision on how big the increase could be
because we can't really say, first of all, how
much greenhouse gas we will be putting in, even
in a growing world economy on a business-as-usual path.
And there are also undoubted uncertainties about the Earth's processes.
And our climate models do not have the precision to be able to get
down to the decimal point of the likely increases of temperature.
But, because we have so much evidence coming from so many different directions,
the Paleoclimate, the statistical models used by climate scientists, the evidence
of what's already happening around the world, we can be pretty sure
that the consequences could be very, very dire indeed unless we change course.
One very useful way to view this was presented in an important report
on climate change produced by Lord Stern in the United Kingdom a few years ago.
And the Stern review of climate change
included the picture that you're looking at now.
Now, you see across the horizontal axis, zero degrees centigrade,
one degree, two degrees, three degrees, four degrees, five degrees centigrade.
This is showing all of the possibilities for
the increase of temperatures during the twenty-first century depending
on how much greenhouse gas we end up
emitting and how the Earth's systems respond to that.
Down the side axis, we have the kinds
of consequences that we should expect for different temperatures.
There will be consequences for the food supply.
There will be consequences for water.
There will be consequences for the functioning
of ecosystems and the survival of other species.
There will be consequences for extreme weather events such as droughts, floods,
mega heat waves, mega storms, big cyclones, typhoons, hurricanes.
There will be consequences and risks of very rapid, dramatic
changes to key Earth systems that could cause the climate,
not only to change as markedly as shown here, but
even more markedly through sudden alterations of the Earth's climate system.
What this graph shows is that for any of these categories, say food, as you look
at the consequences at one degree centigrade, compare
them with the consequences at two degrees centigrade.
Compare them at, for the consequences that would
occur at an increase of five degrees centigrade.
The more change there is in the average temperature caused by
bigger increases of greenhouse gasses, the bigger risks we face.
If we can head off a, a lot of
the greenhouse gas emissions by shifting from fossil fuels to
other kinds of energy, for example, then the consequences
will be smaller because the temperature increases will be smaller.
If, instead, we continue just going right along
our merry way with increasing oil, gas, coal, and
other greenhouse gases, and so we have a big
increase of temperature, the consequences could be completely disastrous.
Consider food, for example.
At one degree centigrade, one of the
consequences is severe impacts in the Sahel region.
The Sahel, remember, is the part of West Africa just below the Sahara Desert.
Mali, Niger, Chad, it's a dry region, could get dryer.
The consequences for the Sahel, even at a one
degree increase, which we basically already had, are quite serious.
What would happen at five degrees centigrade increase?
Well, according to the evidence, entire regions would experience major declines
in crop yields, up to one third decline of crop yields in Africa, for example.
That would be tantamount to mass hunger, even starvation in parts of the world.
If we just let things rip, and the temperatures, therefore, rise by
four or five degrees centigrade so that we're at the extreme danger end of this
graph, then the consequences are absolutely terrifying.
With water at one degree centigrade you
see that small mountain glaciers are disappearing.
And this will cause threats to the water supply in places
that depend on glacier melt for their water in the rivers.
But go over to five degrees centigrade, and you see that sea level rise
would threaten major world cities including London,
Shanghai, New York, Tokyo and Hong Kong.
Calamitous events possible with a mega rise in sea levels
even of several meters, possibly, if the big ice sheets
in West Antarctica and in Greenland melt sufficiently or break
up in ways that cause a mega rise in sea level.
And the Earth's history tells us absolutely possible because in
earlier episodes of high CO2 concentrations
in the Earth's paleohistory, the old climate,
the sea level was often many, many meters higher than it is on
the planet today because much less ice was trapped in the ice sheets
of Antarctica and Greenland and, instead, was filling
the ocean basin and raising the sea level.
Well, as we've talked about many, many times,
we've built our big cities right on the coast.
That's where the economy is best, where trade is best, where productivity is high.
And yet, those are the cities under incredible peril.
Well, in case after case, if we just let her rip, the dangers
for our ability to feed the planet, our ability for our cities
to remain safe from extreme hazards, our abilities to maintain public health, our
abilities to avoid other
calamitous dramatic change of earth's processes, for instance changes
in, in the ocean circulation or irreversible disintegration of parts of
the ice sheets is called into real threat.
We know that certain regions of the world are extraordinarily vulnerable like the
Sahel that you're looking at here where it is already prone to
massive, droughts and where the populations are already very poor.
We're seeing those dangers, not as potential threats of the future,
but as already clear and present dangers, because the Sahel
has lived through serious droughts in recent years with very serious
consequences for loss of life and for the onset of conflict.
The Mediterranean Basin, which includes the countries of southern Europe
Spain Italy, Greece, Yugoslavia, and the
countries of North Africa Morocco, Algeria, Libya, Tunisia,
Egypt and the eastern Mediterranean, this is a
region where the climate science tells us that a relatively
dry region that produces some of the,
the world's most beloved products, whether it's
the olive oils or the great wines of this region, could be devastated by drying.
And so, these are three of many regions
that have been identified as facing profound threats.
Mm, and this is not simply in the imagination of the
climatologists or, or even in the traces of their mathematical models.
This is what we're already observing
even with the limited human-induced climate change
that we've experienced now, which could be a small fraction of what's to come.
Have a look at the changes of of, of
rainfall experienced in the Mediterranean Basin over the last century.
The whole Mediterranean Basin has experienced a significant trend of drying.
And the record shows if we continue with business as usual, that it
could experience further dramatic drying with quite devastating consequences
to the economies, to the nature, to
the ecosystems, to food security even in this region.
The evidence from the mathematical models is that
the trends that we've been experiencing till now, for example, the drying in
the Sahel or the drying in the Mediterranean, foreshadow what
would happen if we continue as we're going, but
with consequences far more severe than what we've seen to date.
You're looking now at a map recently produced by a climate science
group that studies the propensity to drought on the planet.
And the map that you're looking at shows you in the red areas,
places likely to experience significant declines of rainfall
and significant increases of drought intensity and frequency.
It's an ugly picture because you see red everywhere.
A tremendous amount of the world's areas would
likely experience significant declines of soil moisture that they
need to grow food and would experience a significant
increase of intensity of drought at the same time.
Now we know that another consequence that could be devastating
is the rise of sea levels as ice sheets melt or just break apart
pushing ice or water into the open ocean and raising sea levels.
In the northeast of the United States where
I live, the estimate is that, over the last
century, the sea level has already increased by
about one foot or one third of a meter.
I, you might think that we'd get a uniform rise
of sea level in all parts of the world, but
topography and other geologic features mean that the rise of
sea levels will differ in differ, different parts of the world.
A one foot increase, what has already been experienced, played a major
role in the havoc of the massive floods that hit New York City, that we've
already looked at, and the whole Eastern Seaboard during superstorm Sandy.
Storm surges eh, coastal erosion are
already occurring as sea levels are rising.
But the new evidence suggests that by the
end of the century on a business-as-usual path,
sea levels could be a meter higher than
they are right now, three or four feet higher.
And if the worst case happened, which is a catastrophic loss of part of the West
Antarctic ice sheet, for example, the rise of sea level could even be several meters.
You put this together.
The consequences for urban areas,
hugging the oceans, for our food supplies around the world
are, are absolutely extraordinary, potentially devastating.
The map that you're looking at now attempts to ask what would happen to food
production if this combination of warmer temperatures
and and more drying were to take place.
And what you see here is South Asia and tropical Africa
in the absolute red zones, or red and pink zones meaning
major loss of agricultural production, so too the Southern
part of the United States and much of Latin America, much of Australia.
What are we doing?
We're putting the world's food supplies at great risk.
And again, it's not hypothetical because we've already had a serious
derangement of production in many places in the world as droughts
have hit in recent years and as higher temperatures have undermined
crop yield, sometimes killing crops or dramatically reducing the crop yields.
A final point that I would like to stress is that, even
if one put aside all of the climate-induced
changes coming from this human-induced rise of
carbon dioxide concentrations, all of the major storm events, the
rising sea levels, the rising temperatures the increased floods and
droughts, the loss of soil moisture needed to
grow food, it's a big, long, very threatening list.
Put all of that aside.
The basic physical fact that a higher CO2 concentration in the atmosphere will
lead to more carbon dioxide dissolving in the oceans causing acidity in
the ocean, by itself is frightening enough because, as I've discussed, as
the oceans become more acidic, and there's a lot more acidification on the way,
major parts of the marine ecosystems, the shellfish, the animals with exoskeletons,
the plankton with the calcareous exteriors, but part of the major food
chains in the world, the Coral Reefs, which are so vital for the marine
ecosystems, could experience, and are likely to experience, a massive dying.
We're playing with threats beyond our easy imagination.
We're in a kind of denial that is added to by, unfortunately,
propaganda by major vested interest groups, like big oil companies.
We are playing with the survival of millions of other species, adding
to this tremendous risk of the sixth great extinction on the planet
that we've looked at before; the other five caused by nature itself, this
one by humanity in it's thoughtlessness if we continue on this course.
We can see that we have every reason to change the
game, every reason to play for a control of these forces,
every reason to mitigate the human-induced climate change for our own
safety, for the safety of the planet, and for future generations.
How can these forces be reduced?
How can we mitigate human-induced climate change?
That's our next topic.
