This is not a course on climate science or
on the ways in which human activities affect the climate.
There are several offerings on Coursera that provide a solid foundation on
the science of how Earth systems operate and
on the technology of how energy is produced and consumed.
In this course, we're more interested in the connections between these systems.
That's where sustainability becomes something more than climate or
energy or other existing specialties than in the systems themselves.
And so, we're going to assert some things about, for example, climate change and
point you towards sources for more detailed evidence and arguments.
But because climate change is the galvanizing force for much of your
Generation S, this lecture will provide a quick summary of our understanding
of the science of climate change and some of its implications for sustainability.
Let's start with carbon dioxide,
widely referred to by its chemical composition, CO2.
CO2 and other so-called greenhouse gases make possible life on Earth by capturing
some of the Sun's energy and raising the temperature on the Earth's surface.
CO2 is one of several greenhouse gases including methane,
which is CH4 and nitrous oxide, which is N2O.
These gases make different contributions to the greenhouse effect based on how
effective they are at radiative forcing, which prevents the Sun's energy from
escaping the Earth's atmosphere, and how long the gases remain in the atmosphere.
For example, methane is 72 times more powerful in
warming than carbon dioxide over 20 years.
About one-half of CO2 leaves the atmosphere after about 100 years, but
one-fifth remains after thousands of years.
Because CO2 is the most prevalent greenhouse gas,
it receives the most attention.
Scientists use a variety of techniques to estimate how much CO2 existed in
the atmosphere hundreds or millions of years ago.
But since 1958, scientists at the Mauna Loa observatory in
Hawaii have been directly measuring the concentration.
Just a few months ago on May 9th, 2013, the CO2 concentration
passed a symbolic threshold, reaching 400 parts per million for
the first time since observations at the observatory began.
Scientists estimate that the pre-industrial, around 1780,
level of CO2 in the atmosphere was about 280 parts per million.
And the last time it was at 400 parts per million was about 3 million years ago,
which was long before humans appeared on Earth, about 200,000 years ago, and
agriculture appeared about 10,000 years ago.
We actually know quite a bit about where this CO2 and
other so-called greenhouse gases are coming from.
This kind of diagram is called a Sankey diagram and is used to describe flows.
The size of the arrow is proportional to the amount of
material being transferred in the flow.
So it's a very useful way to display the movement of energy through an economy.
A link to this chart of the 2010 emissions flows is available on the course website
and is worth some closer study, but for now, note some of the bigger arrows.
For example, the use of coal in industrial processes,
the release of CO2 through deforestation, and
the tight connection between oil, transportation and carbon dioxide.
Now, the reason they're called greenhouse gases is that greater concentrations in
the atmosphere should raise temperatures on
the Earth's surface in the so-called greenhouse.
And indeed, temperatures are rising.
This diagram compares temperatures with a baseline from the 1980 average.
The surface temperature has warmed about 0.6 degrees centigrade,
which is about one degree Hahrenheit, in the last 30 years.
Given the rapid concentration of CO2 in the last 50 years,
you may be surprised that there's not an even larger than one
degree Fahenheit rise in average surface temperature.
And here, the climate science gets complicated.
It has to do with the sensitivity of the climate to our CO2 emissions.
But one relatively simple explanation for
the modest temperature increases so far can be found here in this diagram.
The oceans have been absorbing the vast majority of increased heat
thus far, 20 times in the oceans than in the land and air combined.
And that has significant consequences for marine life, Arctic ice and
sea level rises.
But another consequence is that there's more warming underway than most of
us can easily discern.
So let's pull back from even this quick summary of the climate science and
return to our main focus.
97% of climate scientists believe that we are affecting the Earth's climate.
This is really the main point, this quote.
When it comes to complex science, whether it be climate science or heart surgery or
how a plane manages to stay up in the air,
we defer to the experts who do this stuff for a living.
The reason why there's a consensus of scientists is
because there's a consensus of evidence.
Close quote.
The scientific consensus is that a CO2 concentration of 450 parts per million has
about a 50 50 chance of raising average global surface temperature by
two degrees Celsius by the year 2050.
And several prominent scientists believe that 450 parts per
million will raise the temperature more and faster than that.
Even a two centigrade rise will have significant impacts on many places and
people around the globe.
So this two degrees goal has been adopted by many national and
international groups, including the United Nations, the United States,
which recognized the scientific consensus regarding the two C goal in Copenhagen,
in the year 2009, and the G7 major economies.
At this point, I want to make a simple point about expert consensus.
This is a subject of much research and
argument, but I want to make just a simple point.
Even with a consensus among scientists about atmospheric chemistry and
even about the probabilities of future temperature and
other changes, there remains plenty of room for debate about the politics and
morality of the implications of these changes and how to respond to them.
Facts are arranged to tell a story,
whether that story is a scientific theory or a political argument.
There's nothing sinister about this.
Rather, it is how humans understand reality, by telling stories or
narratives, to use the current term.
There's a book I highly recommend if you're interested in
this subject by Deborah Stone called Policy Paradox.
Recommend reading this book to,
that, which goes deeper into the construction of narratives.
Let me give an example with a diagram using the same facts,
the CO2 emissions we've been discussing denominated by three different contexts.
The first panel displays emissions by national total,
which tells a story about obligation among the largest polluters.
China and the U.S. are the problem and the potential solution.
The second panel displays emissions by national population, which tells
a story about the unevenness of pollution depending on where people live.
For example, there aren't many Canadians, but they pollute as much as Americans.
The third panel displays emissions by national economic output,
which tells a story about carbon efficiency in different economies.
Here, Russia, China and
South Africa should move toward lower carbon economies to solve the problem.
Same data, three very different diagrams and
very different stories about 450 parts per million and the two C goal.
But it gets harder to achieve that two C goal with each passing year.
The International Energy Agency stated in 2012 that, quote,
almost four-fifths of the CO2 emissions allowable by 2035
are already locked in by existing power plants, factories, buildings, etc.
If action to reduce CO2 emissions is not taken before 2017,
all of the allowable CO2 emissions would be
locked in by energy infrastructure existing at that time, end quote.
Not more than one-third of proven reserves of fossil fuels can be consumed prior to
2050 if the world is to achieve the two C goal unless carbon capture and
storage technology is widely deployed.
We will explore the implications of this claim in later weeks of the course.
But again, the main point is that decisions we make
now will significantly influence the course of climate,
even recognizing the uncertainty of the situation.
This diagram from scientists at MIT describes both the uncertainty and
the influence.
The circle on the left displays the relative likelihood of
various temperature rises between now and 2100, the end of the century.
On the left, no change from our current path.
As you can see, we have virtually no chance of staying under two C.
Even with the aggressive policies described by the circle on the right,
the analysis shows that we are unlikely to stay below two C and
more like just below four C,
which is good because the newest scientific research that four C.
And remember, that only happens if we act fast and
very aggressively to limit carbon emissions.
Four C would create hellish conditions for humans and the rest of the ecosystem.
The journalists Dave Roberts has a great TED talk assembling recent
research estimating the consequences of such a future, which is summarized here.
This is a very sobering list.
Even more sobering is that many scientists are convinced that once temperatures
rise to some unknown point, increases will accel,
will accelerate and be irreversible no matter what measures we take.
So, in sum, while there are many interesting and open questions in
climate science, the most important science for most of us is settled.
It's happening, we're causing it, and it's bad for us and our descendents.
And increasingly, we don't even need to rely on climate science experts.
It's observable by any of us.
More than 32 million people fled their homes last year because of disasters such
as floods, storms, and earthquakes, exacerbated by the climate.
98% of this displacement is related to climate change.
Asia, and West and Central Africa bore the brunt.
Floods in India and Nigeria accounted for 41% of displacement.
Some 1.3 million people were displaced in rich countries as well, with the U.S.
particularly affected.
In conclusion, this course moves from the premise that climate risk is
sufficiently well established to motivate sustainability in practice across the U.S.
and around the world.
Our focus is on the issues that risk is creating and
on the varieties of practice being used to respond to those issues.
Our focus is introducing you to some of the roles to play in
the greatest challenge facing Generation S.