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Lecture 6a - The ocean, climate, and humans
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En provenance du cours de University of Arizona
Biosphere 2 Science for the Future of Our Planet
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Sea Changes in our Marine Environment
Why are coral reefs in peril, and what can we do about it? In Module 6, discover the immense role that oceans play in global climate, heat distribution, and human livelihoods. Learn why global warming is sometimes called ocean warming, how ocean acidification affects marine life, and innovative ways in which the ocean is studied. With Dr. Julia Cole, U. of Michigan, UA Biosphere 2 Marine Research.
Rencontrer les enseignants
Kevin E. Bonine, PhDDirector of Education and Outreach
Biosphere 2
[MUSIC]
Hello, and welcome back to this Biosphere 2 course on Science for
the Future of our Planet.
My name is Julia Cole.
I'm the Research Director for the Ocean at the Biosphere 2, and
I'm a professor of Earth and Environmental Sciences at the University of Michigan.
I'll be talking today about the ocean's
role in this big topic of Earth system change that we've been discussing.
I'll be looking at the ocean as part of the climate system.
We'll talk a little bit about the changes that the ocean is going through as
a result of climate and environmental change.
And then we'll look at some of the science that we plan to do with the biosphere.
That will help us understand those changes better and ideally avoid some of the worst
consequences of ongoing environmental change in the ocean.
Today, for
the first part, I'll be talking about the oceans role in the climate system.
So we think of the climate as a system comprising many parts.
It includes not just the ocean, which scientists often call the hydrosphere.
That's the liquid part of the climate system, but
that is basically the ocean, with a little bit of freshwater thrown in.
We also have the atmosphere.
We've got the biosphere.
The biosphere is the living component of the climate system.
And on this image of Earth from space, you can see the biosphere as the green parts.
And then the cryosphere, the cryosphere is the frozen part of the climate system.
That would be the polar ice sheets and sea ice and ice that forms on land.
So in all this interconnected climate system,
the ocean plays a really important role.
It moves heat around.
It’s a source of memory, in the sense that when it absorbs heat and
becomes warm, it doesn’t release that very easily.
And it’s a source of water vapor to the atmosphere.
So we’ll walk through some of those things that the ocean does as part of
the climate system and how the ocean moderates our weather and climate.
I'll also talk a little bit about how the ocean is important for humans.
Okay, so the climate system on Earth gets its energy from the sun.
And the sun's energy strikes the Earth differently at different latitudes.
In the tropics, at low latitudes, the sun's energy is coming in directly, and
so it's very intense on any given area of land.
At higher latitudes, that same amount of sun's energy is spread out.
Because instead of striking directly on the surface of the Earth,
it's striking the top of a sphere, and so that energy gets spread out more.
So the high latitudes on the Earth receive less energy
per unit area than the low latitudes.
And if that energy didn't get moved around,
we would have much hotter tropics and much colder poles than we do.
It's the moving of that energy around the Earth system that creates weather and
climate for us.
The ocean plays a really important role in that.
So here's what ocean temperatures look like on the surface of the Earth.
We've got warmer temperatures across the low latitudes here, and
we've colder temperatures at the higher latitudes.
But again, the ocean is moving that heat around to minimize that difference,
believe it or not.
[LAUGH] This is a animation of a current that does that moving around for us.
So it's an animation of the Gulf Stream in the North Atlantic.
But I should point out that every ocean basin has its own current that
does the same things that I'm going to describe here from the North Atlantic.
So what we're seeing is this current moves from areas
of warm water in the southern part, in low latitudes.
And it moves that heat in a complicated, meandering path into the North Atlantic.
And this Gulf Stream is one of the strongest currents on the planet.
And one of the strongest currents, for
sure the strongest current in the North Atlantic surface.
Okay, so as it moves that heat northward, it warms the ocean there.
Also over the warm parts of the ocean in all the ocean basins,
we have a lot of evaporation of water.
That evaporation of water is really important for climate and
weather on the planet.
The ocean is a fundamental part of the global hydrologic cycle.
By evaporating water from the ocean surface, that moisture is carried inland
by weather systems and precipitated out as rain or snow.
Ad that's what allows us to have plants on the surface of the land,
to grow food, and to inhabit the land surface.
So the ocean's a really important part of the hydrological cycle as well.
Most of the evaporation that occurs in the ocean happens in the warmer parts because
evaporation is stronger under warm conditions.
Another thing that happens in the warm parts of the ocean is that tropical storms
can develop and grow and
potentially become major threats to coastal communities and ecosystems.
So here's an example of that.
This is showing us the ocean temperatures in the color.
This is a map of the Southeastern US with the Gulf of Mexico right here.
And over these warm waters,
we see a very large tropical storm that's developed here.
This is Hurricane Katrina that slammed into the Gulf Coast in
2005 with devastating consequences.
So it developed over the warm parts of the water, it accelerated and
grew in strength as it passed over warmer water.
And it's the warm oceans that allows these storms to reach the size that they do.
Okay, so important roles in climate,
important roles in the hydrologic cycle, important roles in weather.
The ocean is key to all of those things.
As well, the ocean provides us with resources and benefits that we need.
Something like 17% of the world's animal protein is provided by ocean fish.
And so it's an important component of the diet globally.
And in coastal communities,
the proportion of fish as a part of the animal protein diet can be over half.
So fish is a really important part of human's diet,
no matter where they live mostly.
So a lot of the supply of fish has been growing
due to industrial fishing practices.
Large boats that are able to go out for months at a time store their catches
frozen and come back, rather than artisanal fisheries that might be
catching on a daily basis, coming back and selling their catch.
These industrial fishing operations, like this one here for
herring, are not always done in the most sustainable way.
And so an additional pressure that the ocean is facing right now is that of
overfishing in many of the fish stocks of the world.
People like to live on the ocean.
It provides a lot of benefits.
It's beautiful.
There are many coastal cities that grew up as port cities but now are large,
vibrant, commercial, industrial, cultural centers.
And so living on the coast is desireable, and
coastal communities are growing much faster than inland communities.
There is a net migration of people from inland to coast on most continents in
the world.
This, of course, puts us at risk for coastal threats.
And this figure just shows one of those many coastal threats.
This is erosion from rising sea level and
storms that are undercutting these houses along the coast of California.
So people are placed at risk not only by coastal erosion, but
of course by the kinds of storms that we saw with Katrina.
And in low lying areas, rising sea levels are posing increasing risks
related to nuisance flooding that is becoming more and more common and
will soon be just flooding.
So the oceans are something that we can think about as,
if we think about them at all, we think of them as so vast an imperturbable that
what we are doing on land couldn't possibly affect them in any major way.
But that's not true.
Our activities are changing the ocean in very measurable and
mostly detrimental ways.
And those are the kinds of changes that I'm going to be talking about in
the next two sections of this class.
So when we come back, we'll talk a little bit about global warming and
ocean warming.
Thank you.
[MUSIC]
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