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