This course introduces the academic approach of Sustainability and explores how today’s human societies can endure in the face of global change, ecosystem degradation and resource limitations. The course focuses on key knowledge areas of sustainability theory and practice, including population, ecosystems, global change, energy, agriculture, water, environmental economics and policy, ethics, and cultural history. This subject is of vital importance, seeking as it does to uncover the principles of the long-term welfare of all the peoples of the planet. As sustainability is a cross-disciplinary field of study, this foundation requires intellectual breadth: as I describe it in the class text, understanding our motivations requires the humanities, measuring the challenges of sustainability requires knowledge of the sciences (both natural and social), and building solutions requires technical insight into systems (such as provided by engineering, planning, and management).
Modern Climate Change
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從本節課中
Ecosystems and Climate Change
In this module, we will see that the Earth faces many environmental pressures that result from human exploitation of natural resources. We will also look at the issue of climate change.
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Dr. Jonathan TomkinAssociate Director
School of Earth, Society and Environment
I'm Jonathan Tomkin from the University of Illinois.
In this lecture, we're looking at recent, current, and future climate change.
This figure shows a lot of data, let's examine it.
There are three sets. All that data shows the difference in the
temperature degree Celsius. And so remember, one degree Celsius is
about two degrees Fahrenheit. Compared to the average global temperature
in 1950, so a value of minus one on the Y axis means that it was one degree cooler
than it was in 1950. This is known as a temperature anomaly.
The top graph is a compilation of several different sets of instrumental data.
And these record information over the last 300 years is every since we had
instruments before this there was no reliable instrumental data.
We didn't have reliable thermometers. Let's focus on this set of information
first the black, red and yellow lines are different calculations for the temperature
normally, and they're from different sources.
They do show the limitations. An instrumental data, we only had precise
climate measurements since industrialization.
So the global instrument record only goes back to around 1850.
Before that, we only had spotty data. And although there is a longer set of data
from Europe, note the yellow line here Even that doesn't go back too far.
What has the change in temperature been over the last 150 years?
The black line is increased from normally around -three degrees Celsius in 1850 to
around +.5 degrees Celsius in 2005. This means there has been increase of just
under one degree Celsius, or about one and a half degrees Fahrenheit, in the last 400
years. Let's focus on the middle figure.
This goes much further back in time to before 800 AD, so over 1,200 years ago.
The black line is instrument data, and as you can see, it runs out.
But we have different sets of proxy data. The colored lines, that go back much
further. These proxies are less precise of an
instrumentator. They allow making assumptions, about how
the climate change natural processes. But they provide climate out of the data
that goes much further. So they're very important to our
understanding of those earlier periods of those climate.
From this data, we can see that different proxies vary, suggesting that there is
maybe error in this proxy data. Or that different places in the earth
experience different change in climates. Not all climate change is global.
Sometimes there are local climate changes from place to place.
Interestingly, the proxy data broadly agrees, with itself and with instrumental
data. The proxy data suggests that the past was
generally cooler than it is today. Between one and zero degrees Celsius, or
between one and two degrees Fahrenheit. Notice that there was a big change in both
the proxy data and the instrumental data around 1850 when the anomaly, instead of
being a negative number became positive. We see this big increase in the
temperature of around just under one degree Celsius.
The reason why global temperature has change so much since 1850, is because of
industrialization. The vast majority of climate scientists
believe that the addition of additional greenhouse gases to the Earth's atmosphere
has increased the Earth's temperature. Examples of greenhouse gases from
industrialization include methane and, crucially, carbon dioxide.
The Industrial Revolution became widespread in Europe in the nineteenth
century. But then spread to much of the rest of the
world. And in fact it's global today.
Industrialization requires fossil fuel energy sources and by using these sources,
by burning oil, gas, coal we've added carbon dioxide to the Earth's atmosphere.
As we can see in the figure, the amount of energy that we've used by burning coal has
increased steadily from the 1850s. But other energy sources have also become
very important. Particularly in the twentieth century,
natural gas and oil, and these have become ever-increasing contributors to the
Earth's natural greenhouse by adding carbon dioxide to the atmosphere.
Here we have a figure taken from an ice core.
This ice core trapped bubbles of air from the atmosphere over 400,000 years, and so
by measuring the concentrations of carbon dioxide in each of these bubbles, we can
see how the amount of carbon dioxide has changed.
In 1950, there was around 280 parts per million of carbon dioxide in the
atmosphere. Today, we're at over 380 parts per
million. And looking at this figure, you can see
that the level in 1950 was already quite high to begin with.
In fact, there is more carbon dioxide in the Earth's atmosphere today, then there
has ever been in the history of human life on Earth.
I should point out that there have been periods in the Earth's past before humans
had evolved that had higher levels of carbon dioxide than are currently
observed. Carbon dioxide in the Earth's atmosphere
has steadily increased in concentration over the last few decades.
This is instrumental data from the observatory in Hawaii.
The light blue line is the monthly values, or the dark blue one is the yearly
average. The yearly average continues to go up.
Notice that the monthly value also rise, can you guess why?
It turns out that natural processes are still involved in regulating the Earth's
atmosphere. The large northern hemisphere's deciduous
forests absorb carbon dioxide in the spring months, but then they emit it again
in the fall as leaves decay. This demonstrates that the natural system
also influences the composition of the earth's atmosphere but it also shows the
limitation of that natural system. The natural process of the earth can react
quickly enough to absorb all the additional carbon dioxide that human
activities are adding to the atmosphere. As we learned in previous lectures, adding
carbon dioxide, a natural greenhouse gas, to the Earth's atmosphere should change
the Earth's climate. We've seen this data for temperature in
this lecture. The Earth's temperature is warmer today
than it was 125 years ago. But, can you think of other examples of
how increasing carbon dioxide, which should increase the natural greenhouse
effect, which should increase the average global temperature, should influence the
Earth? Lets look at some examples.
One thing that we would think is that warmer temperatures would mean less ice,
because ice would be more likely to melt. This has been observed in many different
places, one example is Arctic sea ice. This figure shows that 2007 had the lowest
Arctic sea ice ever recorded. And, in fact, this is the lowest amount of
Arctic sea ice in human memory. This trend has not changed.
In fact, this year 2012, so even lower amounts of ice in the Arctic than was
observed in 2007, a new record. This is the lowest amount of ice observed
in the sea ice in the Arctic in human history.
Similarly, mountain glaciers have also shrunk in size.
Although it varies from place to place, almost every region in the globe has seen
significant shrinkage in the size and extent of mountain glaciers.
Glacier National Park in the U.S. Has lost almost three-fourths of its ice
volume in the last 150 years. This sequence of photos shows the
shrinking of Gemel glacier. Note that the lake has appeared as the ice
has melted. And at the ice, which used to sit hundreds
of feet above the valley floor is now much lower.
Another consequence you might expect is rising sea levels.
This is partly because we're seeing land based ice melt and return water to the
oceans. But it's also a consequence of the thermal
expansion of water. When we make something warmer, it expands
and this is true with the oceans. Sea levels have increased around the world
and over the last 100 years, this has been about 200 millimeters.
So in other words, sea levels are around 200 millimeters higher.
That's about eight inches. Recent sea level rise has been faster than
was observed earlier in the twentieth century.
So, we expect that this rate of sea level rise should increase through the
twenty-first century. And of course there are many natural
biological systems that are key to the climate.
Using historical records, researchers have determined that Japanese cherry blossom
trees are blooming earlier now than they did in the nineteenth century, and we see
this in many other systems. So, what does this suggest for the future?
Well it turns out that this is tricky. Prediction is difficult because not only
do we need to understand the Earth's natural systems, but we also need to
predict what people will do. Will we continue to burn as much fossil
fuels or more in the future as we have in the past?
Or will we change our industrial methods? As a consequence, international bodies
have used different scenario estimates to determine what would happen to the Earth's
temperature if humanity decided to do different things.
Let's look at this figure. Here we can see the previous, the
twentieth century data in black, and then there are predictions for different
climate futures. The pink line suggests that we add no more
Carbon Dioxide in the future. So, in other words, we no longer burn
fossil fuels we don't use oil, coal, natural gas.
We don't produce cement. This would mean that the climate change
would be very minimal between now and the end of the century.
There would be a little bit of warming up as the Earth equilibriated at the new
temperature. Of course, this scenario is unlikely if
humanity survives and we have societies of the future.
Using more realistic social models, where we continue to use fossil fuels produces
high temperature estimates. On average, however, scientists predict
that the temperature would be markedly higher than it is today at the end of this
century, especially over land and in the Arctic.
This figure shows the world map with predicted increase totals.
They're around four degrees Celsius. That is around eight degrees Fahrenheit
warmer than today. If you look at this map, you can see where
you live. How much hotter is your place expected to
be at the end of the twenty-first century compared to the beginning?
Four degrees Celsius is a lot, that's more than 4x that we've observed over the
twentieth century, for example. This would suggest that the sort of
changes we've seen so far are going to be much smaller than the sort of changes
we're gonna see from climate change over this century.
So, we're gonna see very important consequential impacts from this increase
in temperature. So these impacts will include a loss of
permafrost. More loss of ice including sea ice and
glaciers, increased sea levels, Increased land-based temperatures.
Biological systems will have to change enormously.
As will our natural farming, as will our farming systems.
We might see places will get more or less precipitation than they do today.
As you can see from the reading. This picture here shows a picture of a
golden toad. Some scientists think that climate change
in its natural habitat, the cloud forest of Costa Rica, is at least partly
responsible for its disappearance. I wonder if the golden toad, would be the
first of many species, that might be made extinct, by climate change.
So the burning of fossil fuels is having an enormous impact on the planet.
Perhaps we can get away from burning so many fossil fuels by moving to a renewable
energy future. In next week's lectures, we'll see if
that's possible. Produced by OCE-ATLAS Digital Media at the
University of Illinois Urbana-Champaign.
