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So one of the most important solutions
to the global challenge posed by climate change
lies right under our foot every day.
It's soil.
Soil's just the thin veil that covers the surface of land,
but it has the power to shape our planet's destiny.
See, a six-foot or so of soil,
loose soil material that covers the earth's surface,
represents the difference between life and lifelessness in the earth system,
and it can also help us combat climate change
if we can only stop treating it like dirt.
(Laughter)
Climate change is happening,
the earth's atmosphere is warming,
because of the increasing amount of greenhouse gases
we keep releasing into the atmosphere.
You all know that.
But what I assume you might not have heard
is that one of the most important things our human society could do
to address climate change
lies right there in the soil.
I'm a soil scientist who has been studying soil since I was 18,
because I'm interested in unlocking the secrets of soil
and helping people understand this really important climate change solution.
So here are the facts about climate.
The concentration of carbon dioxide in the earth's atmosphere
has increased by 40 percent
just in the last 150 years or so.
Human actions are now releasing 9.4 billion metric tons of carbon
into the atmosphere,
from activities such as burning fossil fuels
and intensive agricultural practices,
and other ways we change the way we use land,
including deforestation.
But the concentration of carbon dioxide that stays in the atmosphere
is only increasing by about half of that,
and that's because half of the carbon we keep releasing into the atmosphere
is currently being taken up by land and the seas
through a process we know as carbon sequestration.
So in essence, whatever consequence you think we're facing
from climate change right now,
we're only experiencing the consequence of 50 percent of our pollution,
because the natural ecosystems are bailing us out.
But don't get too comfortable,
because we have two major things working against us right now.
One: unless we do something big,
and then fast,
emissions will continue to rise.
And second: the ability of these natural ecosystems
to take up carbon dioxide from the atmosphere
and sequester it in the natural habitats
is currently getting compromised,
as they're experiencing serious degradation because of human actions.
So it's not entirely clear
that we will continue to get bailed out by these natural ecosystems
if we continue on this business-as-usual path that we've been.
Here's where the soil comes in:
there is about three thousand billion metric tons of carbon in the soil.
That's roughly about 315 times the amount of carbon
that we release into the atmosphere currently.
And there's twice more carbon in soil than there is in vegetation and air.
Think about that for a second.
There's more carbon in soil
than there is in all of the world's vegetation,
including the lush tropical rainforests and the giant sequoias,
the expansive grasslands,
all of the cultivated systems,
and every kind of flora you can imagine on the face of the earth,
plus all the carbon that's currently up in the atmosphere, combined,
and then twice over.
Hence, a very small change in the amount of carbon stored in soil
can make a big difference in maintenance of the earth's atmosphere.
But soil's not just simply a storage box for carbon, though.
It operates more like a bank account,
and the amount of carbon that's in soil at any given time
is a function of the amount of carbon coming in and out of the soil.
Carbon comes into the soil through the process of photosynthesis,
when green plants take carbon dioxide from the atmosphere
and use it to make their bodies,
and upon death, their bodies enter the soil.
And carbon leaves the soil
and goes right back up into the atmosphere
when the bodies of those formerly living organisms
decay in soil by the activity of microbes.
See, decomposition releases carbon dioxide into the atmosphere,
as well as other greenhouse gases such as methane and nitrous oxide,
but it also releases all the nutrients we all need to survive.
One of the things that makes soil such a fundamental component
of any climate change mitigation strategy
is because it represents a long-term storage of carbon.
Carbon that would have lasted maybe a year or two
in decaying residue if it was left on the surface
can stay in soil for hundreds of years, even thousands and more.
Soil biogeochemists like me
study exactly how the soil system makes this possible,
by locking away the carbon in physical association with minerals,
inside aggregates of soil minerals,
and formation of strong chemical bonds
that bind the carbon to the surfaces of the minerals.
See when carbon is entrapped in soil,
in these kinds of associations with soil minerals,
even the wiliest of the microbes can't easily degrade it.
And carbon that's not degrading fast
is carbon that's not going back into the atmosphere as greenhouse gases.
But the benefit of carbon sequestration
is not just limited to climate change mitigation.
Soil that stores large amounts of carbon is healthy, fertile, soft.
It's malleable. It's workable.
It makes it like a sponge.
It can hold on to a lot of water and nutrients.
Healthy and fertile soils like this
support the most dynamic, abundant and diverse habitat for living things
that we know of anywhere on the earth system.
It makes life possible for everything from the tiniest of the microbes,
such as bacteria and fungi,
all the way to higher plants,
and fulfills the food, feed and fiber needs for all animals,
including you and I.
So at this point, you would assume that we should be treating soil
like the precious resource that it is.
Unfortunately, that's not the case.
Soils around the world are experiencing unprecedented rates of degradation
through a variety of human actions that include deforestation,
intensive agricultural production systems,
overgrazing,
excessive application of agricultural chemicals,
erosion and similar things.
Half of the world's soils are currently considered degraded.
Soil degradation is bad for many reasons,
but let me just tell you a couple.
One: degraded soils have diminished potential to support plant productivity.
And hence, by degrading soil,
we're compromising our own abilities to provide the food and other resources
that we need for us
and every member of living things on the face of the earth.
And second:
soil use and degradation, just in the last 200 years or so,
has released 12 times more carbon into the atmosphere
compared to the rate at which we're releasing carbon
into the atmosphere right now.
I'm afraid there's even more bad news.
This is a story of soils at high latitudes.
Peatlands in polar environments
store about a third of the global soil carbon reserves.
These peatlands have a permanently frozen ground underneath,
the permafrost,
and the carbon was able to build up in these soils over long periods of time
because even though plants are able to photosynthesize during the short,
warm summer months,
the environment quickly turns cold and dark,
and then microbes are not able to efficiently break down the residue.
So the soil carbon bank in these polar environments
built up over hundreds of thousands of years.
But right now, with atmospheric warming,
the permafrost is thawing and draining.
And when permafrost thaws and drains,
it makes it possible for microbes to come in
and rather quickly decompose all this carbon,
with the potential to release hundreds of billions of metric tons of carbon
into the atmosphere in the form of greenhouse gases.
And this release of additional greenhouse gases into the atmosphere
will only contribute to further warming
that makes this predicament even worse,
as it starts a self-reinforcing positive feedback loop
that could go on and on and on,
dramatically changing our climate future.
Fortunately, I can also tell you that there is a solution
for these two wicked problems of soil degradation and climate change.
Just like we created these problems,
we do know the solution,
and the solution lies in simultaneously working
to address these two things together,
through what we call climate-smart land management practices.
What do I mean here?
I mean managing land in a way that's smart
about maximizing how much carbon we store in soil.
And we can accomplish this
by putting in place deep-rooted perennial plants,
putting back forests whenever possible,
reducing tillage and other disturbances from agricultural practices,
including optimizing the use of agricultural chemicals and grazing
and even adding carbon to soil, whenever possible,
from recycled resources such as compost and even human waste.
This kind of land stewardship is not a radical idea.
It's what made it possible for fertile soils
to be able to support human civilizations since time immemorial.
In fact, some are doing it just right now.
There's a global effort underway to accomplish exactly this goal.
This effort that started in France is known as the "4 per 1000" effort,
and it sets an aspirational goal
to increase the amount of carbon stored in soil by 0.4 percent annually,
using the same kind of climate-smart land management practices
I mentioned earlier.
And if this effort's fully successful,
it can offset a third of the global emissions
of fossil-fuel-derived carbon into the atmosphere.
But even if this effort is not fully successful,
but we just start heading in that direction,
we still end up with soils that are healthier, more fertile,
are able to produce all the food and resources that we need
for human populations and more,
and also soils that are better capable
of sequestering carbon dioxide from the atmosphere
and helping with climate change mitigation.
I'm pretty sure that's what politicians call a win-win solution.
And we all can have a role to play here.
We can start by treating the soil with the respect that it deserves:
respect for its ability as the basis of all life on earth,
respect for its ability to serve as a carbon bank
and respect for its ability to control our climate.
And if we do so,
we can then simultaneously address
two of the most pressing global challenges of our time:
climate change and soil degradation.
And in the process, we would be able to provide food and nutritional security
to our growing human family.
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！

読み込み中…

B1 中級 米

【TED】A climate change solution that's right under our feet | Asmeret Asefaw Berhe:

86 タグ追加 保存
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林宜悉 2019 年 9 月 27 日 に公開

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