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
lose 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
and if we can only stop treating it like dirt.
Climate change is happening,
the Earth's atmosphere is warming,
because of an 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 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 health, 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, 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 permafrosts 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 mille" 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 is 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)