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Hi, this talk started out of a Twitter conversation.
I haven't decided whether to be embarrassed
about that or not.
But I was on Twitter one day and
a relatively prominent left of centre pundit,
piped up and said
"You know, climate change seems like a really big deal,
why are so few people talking about it?
Why have so few thought leaders made it
their signature issue?"
And another reasonably prominent
left of centre pundit piped up
and said "Well, for my part,
the reason I don't talk about it is it seems really complicated,
I don't feel like I have a good grasp on all the science
and so I just don't feel qualified to go out
and assert things publicly about it."
You know, anybody who has ever so much as mentioned
climate change on television or on the internet
will understand why this person thinks the way they do.
Any time you mention it,
the hordes descend, bearing complicated stories
about the medieval ice age, or sunspots, or water vapour,
and, you know, there is a lot of myths about climate change
borne by these climate sceptics
but to debunk those myths you have to know, you know,
you have to go online, and research, and read,
and be able to respond to them in detail,
and a lot of people just find that prospect dreary,
and so they don't bother.
And this, of course, drives me crazy,
so I piped up on Twitter and said
"You know, climate change is not actually that complicated.
What you need to know to be able
to speak out publicly about it,
just about the basic structure of the problem,
is really not that complicated,
I could explain it to you in 15 minutes" so,
let this be a lesson to you:
don't go talk smack on Twitter,
unless you are willing to back it up.
So, one thing led to another, and here I am
with 15 minutes to explain climate change to you.
So, let's get started.
Why is the Earth not a cold dead rock floating in space?
The reason is that it is enveloped by this tiny,
tiny thin layer of gases and chemicals
that we call our atmosphere.
So, the Sun's energy,
rather than just coming down and bouncing right back off,
it comes down and is held
close to the surface of the Earth for a while
and then bounces off,
and then this simple process is why we have evaporation,
and precipitation, and photosynthesis,
and life on our planet.
So, scientists discovered, well over a hundred years ago,
that the atmosphere and the systems on Earth
are in this dynamic relationship
and you can change the chemical composition of the atmosphere
and hold more of the Sun's energy for longer.
The energy still has to escape, of course,
but in the meantime it will cause changes
in these biophysical systems of the Earth.
And, you know, you often hear people say,
"The Earth has always changed,
the climate has always changed",
and that's true, it has.
This relationship between the atmosphere and the systems,
they go through cycles,
but these cycles have typically taken
hundreds of thousand of years,
millions of years.
The key thing to know first is that
for the last 10,000 years on Earth,
the climate has been relatively stable, unusually stable,
and by stable I mean temperature has varied,
it's gone up and down,
but it's stayed on a fairly narrow band
of about plus or minus 1 degree Celsius,
and all of advanced human civilisation
has taken place during these 10,000 years,
the development of agriculture, the written word,
the wheel, the iPhone, everything we know,
everything we have built,
we have done in this period of relative climate stability.
So, what we have been doing
for the last couple of hundred years
is digging up carbon out of the earth,
and throwing it up into the atmosphere,
and changing the chemical composition of the atmosphere,
like has happened in the past
except for extremely faster.
In geological time, the blink of an eye,
we are substantially changing
the chemical composition of the atmosphere
and all of climate science has been about,
"What's going to happen?
What is the Earth going to do in response to this?"
And so, we've already seen that the process is underway,
we have measured, we have witnessed,
observed with our eyes and our thermometers
about a 0.8ºC rise in global average temperature
since before the industrial age,
since before we started digging all this carbon up.
And this may not seem like a lot -- less than 1ºC --
but the thing to know about it is
these greenhouse gases we throw up
stay in the atmosphere for a very long time,
there are very long time lags involved here
so this 0.8º temperature rise is a response
to what we were doing 50-100 years ago,
and what we see in the first half of this century
will be a response to what we've done in the last 50 years
and what we'll see in the latter half of this century
will be a response to decisions we make today.
So the question is, "Temperature's rising,
how high does it have to rise before we need to worry,
before we're in danger,
before bad things start happening?"
The typical answer to this question has been "2ºC."
Anyone who has followed climate change discussions knows
that this 2º number has taken on a kind of iconic quality.
Typically, climate scientists who model impacts
of what's going to happen, model 2ºC rise,
typically economists who try to model what it would cost
to do something about climate change or what it's worth
or what various policies would cost, model 2º centigrade.
So obviously, what counts as not dangerous vs dangerous,
is not a hard scientific question, it's a political question,
and this was a political decision to take this 2C number,
mainly made by European climate negotiators
well over 10 years ago,
and it's just sort of stuck since then.
All the countries involved in climate negotiations
have basically signed on saying
"Yes, this is what we want to avoid, 2ºC temperature rise."
The bad news on this 2C number is twofold:
first of all, all the latest science done in the last 10-15 years
has pointed to the conclusion that those impacts
we thought were going to happen around 2ºC
are in fact going to happen much earlier than that,
the climate is more sensitive
to these added greenhouse gases than we thought.
So, if those were the impacts we were worried about,
then the real threshold of safety
ought to be something like 1.5ºC.
James Hansen is the climate scientist
most famously known for raising these warnings,
but it's a growing scientific consensus that
2º is, in fact, dangerously high,
which is bad, because
we are almost certainly going to blow past 2ºC.
There's some reason to believe
a recent study said that
even if we stopped our carbon emissions tomorrow,
we're still going to get more than 3º this century
just from momentum from the previous emissions.
But stopping at 2º now would take a level
of global coordination and ambition
that is nowhere in evidence.
So, a lot of climate scientists don't really want to tell you this
because they don't want to depress you,
but I am just a blogger, so I am happy to depress you:
2ºC is probably off the table.
So, then the question becomes
"Well, what would it look like if temperature goes higher than that?
What would, say, 4ºC look like?"
Oddly, there hadn't really been
a lot of concerted scientific attention to that question
because climate scientists honestly thought
we wouldn't do that to ourselves,
but we are doing it to ourselves.
So, in 2009,
several climate change research groups in England
drew together a group of scientists,
commissioned some papers and
had them really take a hard look for the first time.
What would 4ºC look like?
There are a lot of papers, a lot of equations,
a lot of talk and complexity I have hopefully paraphrased
here for you, to make it easier to grasp.
4ºC temperature rise would look ugly.
Among other things,
that would be the hottest the Earth has been
in 30 million years.
Sea-levels would rise at least 3-6 feet,
and this excludes some really tail end possibilities,
but 3-6 feet at least.
And persistent drought would cover about 40%
of the currently occupied land on Earth,
which would wreak havoc on agriculture
in East Asia, Africa, South America, Western US.
Well this combined will produce
hundreds of millions of people
who have been driven from their homes
either by their cities being swamped by sea-level rise or
by hunger or by all the attended ills
that come along with those things.
And, to boot, probably somewhere around half of
the known species on Earth would go extinct.
This question of pinning down the exact number of species
is very difficult, this is very much an approximation,
but some substantial chunk of life on Earth
would be wiped out.
The final bit of bad news...
that's not true, there's more bad news to come,
a middle bit of bad news is that, according to a recent paper
by the International Energy Agency,
we are currently on track
-- if we keep doing what we are now doing,
if we go on with business as usual, as it's called --
we are now on track for 6ºC temperature rise this century;
something, 5-7, these are obviously estimations.
So, if 4º is hell on Earth,
I'll let your imaginations filling the blanks on 6º
but, one danger that comes up
when we contemplate going this high with our temperature
is the possibility that
climate change will become irreversable.
I think when people typically think about climate change,
they think, "Oh, temperature is going to rise X amount,
circumstances will change, some places will get warmer,
some places will get wetter,
we'll adjust, we'll move our farms around,
people will migrate from one city to another,
we'll get resettled and we'll go on with life.
The really dangerous possibility is that what are called --
the Earth has several of what are called
positive feedback systems,
so, for instance, in Siberia there is this permanent ice,
the permafrost and it contains a bunch of methane in it.
As it melts, it releases that methane,
the methane causes more warming,
which melts more ice, which releases more methane,
it's a self-sustaining process;
or sea ice melts, ice is white, it reflects energy,
when it melts becomes dark blue and absorbs more energy,
which heats the oceans, which melts more ice,
which creates more dark surfaces.
You see, there's a number of these systems
that are self-perpetuating,
and the danger, the great danger of climate change,
that towers above all these other more specific dangers,
is that these positive feedback systems will take on
a momentum of their own that becomes unstoppable,
and human beings will lose any ability to control it at all,
even if we'd stop all our climate emissions on a dime.
Will that happen at 2º?
Probably not though there is a real chance of it
and there is a lot of debate about that;
will it happen at 4º?
Well, it looks a lot more likely at 4º.
Will it happen at 6º?
Almost certainly.
So, if we continue on our present course,
climate change will probably take on a life of its own,
spiral out of control and,
according to a recent paper,
by 2300, we could see temperature rise of up to 12ºC.
Now if that happened,
something like half the Earth's currently inhabited land
would become too hot to survive on;
and when I say too hot to survive on
I don't mean it's difficult to grow beans
or air conditioning bills are inconveniently high,
I mean if you go outside you die of hotness.
I mean, places that were an average of 80ºF
would be now an average of 170-180ºF,
literally too hot for human beings to go outside and survive.
So, will there still be human civilization
under those circumstances?
Who knows, I mean,
maybe we'll live in underground climate controlled caves,
maybe we'll grow food in test tubes,
but that wouldn't look anything like Earth as we now know it,
it would look a lot more like Newt Gingrich's moon colony,
assuming any human beings,
or at least enough to make a civilization
survived in those circumstances.
So, when I say "Climate change is simple."
-- I know this has been bugging you,
you are not used to thinking in Celsius,
those strange European metric temperatures,
so here is good American Fahrenheit, it's just as ugly.
So this is what I mean by climate change being simple:
There are many complicated and fascinating discussions
to be had about what to do about it,
or about what effect our actions might have on the climate
and when, or which policies are best
based on cost benefit analyses.
There is complexity, plenty of complexity,
for those of you who like complexity,
but we now know to a fair degree of certainty
that if we keep doing what we are now doing,
we will face unthinkable catastrophe;
that's the bumper sticker,
that's the take home message,
and that, you know, saying
"I don't want to talk about that because I don't know the ins and outs"
is like saying, "I don't want to raise alarms
about Hitler's army being a hundred miles out,
because I don't know the thread count of their uniforms,
or, I don't know the average calorie intake of a German soldier."
You don't need to know those things
to be scared that the army's on the march
and to raise alarms about it.
Similarly, if we keep doing what we are now doing,
we are screwed,
this we know now.
To stabilize temperature,
and I don't mean stabilize temperature at 2º, or 4º, or 6º,
I mean to ever have a hope of
ever again having a stable temperature, of any kind,
global climate change emissions need to peak,
stop growing, peak and start falling
rapidly in the next 5-10 years.
Every year we do not get started on this,
we add, according to the International Energy Agency,
an extra 500 billion, with a B, dollars
to the price tag of what it is going to cost us to do this,
eventually, every year we wait.
That's $500 billion down the drain.
Now, you and I look around at current politics,
particularly US politics,
and massive coordinated intelligent ambitious action
does not strike us as particularly plausible.
In fact, it might strike us as impossible,
but that is where we are,
stuck between the impossible and the unthinkable.
So, your job, anyone who hears this,
for the rest of your life, your job is
to make the impossible possible.
Thank you!
(Applause)
コツ:単語をクリックしてすぐ意味を調べられます!

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【TEDx】Climate change is simple: David Roberts at TEDxTheEvergreenStateCollege

3735 タグ追加 保存
阿多賓 2014 年 3 月 9 日 に公開
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