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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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lose 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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and if we can only stop
treating it like dirt.
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Climate change is happening,
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the Earth's atmosphere is warming,
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because of an 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 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
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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
in these kinds of associations
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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
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is health, 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
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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, soil use and degradation
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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
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at which we're releasing carbon
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, 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 permafrosts 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
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of carbon 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
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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 to be able
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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
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is known as the "4 per mille" 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 is 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)