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PROFESSOR: In the last several years
the impacts of climate change have moved from something
we worried about in the future to something
we see happening all around us right now.
The bushfires in Australia in 2019 and 2020
where some of the largest and most damaging ever seen.
This is a photo of the aftermath of the Paradise
wildfire in California in 2018.
It killed dozens of people, was the costliest wildfire
in California history, and the most costly natural disaster
in the world in 2018.
This is a photo of flooding in Jakarta
in early 2020, when 14.8 inches of rain fell in a single day.
And this is a photograph of the aftermath of Hurricane Dorian
in the Bahamas, which delivered the most intense wind
speed ever measured in the Atlantic Ocean.
More droughts and wildfires, more intense rainfall,
and more damaging hurricanes are all consequences
of rising temperatures caused by human-induced climate change.
Many of you have seen this chart before.
It's called the Keeling Curve.
And it measures the atmospheric concentration
of carbon dioxide, which has been steadily rising
for decades.
This is the main driver of changes
in our climate in recent years.
And we're seeing the consequences
in rising temperatures.
After stalling in mid-century, we've
seen average global temperatures already climb
more than 1 degrees Celsius over pre-industrial levels.
In addition to the steady rise in temperatures,
there are growing worries about tipping points
in the climate system that might drive changes on their own,
preventing us from controlling emissions,
even if we attempted to.
One example of this is melting permafrost.
As permafrost, frozen soil in northern latitudes
melts, it emits methane, a powerful greenhouse gas.
This methane causes more warming,
which accelerates melting, releasing more methane.
This is just one example of potential positive feedbacks
in the climate system that raise the potential risks.
All of this has led to growing calls
to reduce and ultimately bring to zero
our emissions of greenhouse gases
in order to limit the global temperature
rise to less than 2 degrees Celsius,
and ideally keep it closer to 1.5 degrees Celsius.
Those were the goals enshrined in the Paris Agreement in 2015.
But limiting emissions to 2 degrees Celsius will be hard.
And it gets harder the longer we wait.
This graph illustrates that the longer we wait,
the faster we need to decarbonize.
Because carbon dioxide is essentially
permanent in the Earth's atmosphere on human timescales,
there's only a fixed budget of CO2 we can emit.
And we're rapidly running through it.
Keeping warming to 1.5 degrees Celsius
will require even steeper and more dramatic
reductions in greenhouse gas emissions,
starting immediately and rapidly heading towards zero.
The commitments made by countries in the Paris Accord,
even if met, won't get us there, as you
can see on this chart, where the orange lines indicate
emissions pathways with all Paris commitments implemented.
We'll need to be progressively ratcheting
up these reductions over time.
OK, that's climate.
But this is obviously a course about transportation.
So what role does transportation play in all of this?
Let's start with some numbers.
Transportation is not just a small part
of the climate problem.
In the United States, as in many other countries,
it is now the number one source of emissions.
The specific numbers vary by country,
but it's almost always a significant part
of the problem.
In the US, it's also true that the largest part
of transportation emissions come from cars and light
trucks, which are mostly SUVs.
These are the vehicles used for urban passenger transportation.
And that's the topic we're going to focus on here.
If you think the rapid decarbonization
of urban passenger transportation will be hard--
and it will be--
it's actually considered one of the easier
parts of the transportation problem,
with other elements like aviation and long distance
freight considered harder, because it's harder
to think about electrifying those sectors
in the short term.
So keep that in mind.
If we're going to fully decarbonize transportation,
urban passenger transportation, should be the part
we're able to do the quickest.
To be one level more specific, we're
talking here about mitigating climate change.
In other words, reducing emissions from urban passenger
transportation.
We're not going to deal with climate change
adaptation, an enormous topic in its own right.
Just as a reminder, in the US, urban passenger transportation
really means travel in private cars.
Other modes of travel like public transit,
are relatively small nationally, even
if they're important in the core of many larger cities.
This is an outlier when compared to other countries,
but helps to illustrate the main driver of the problem.
In Boston, where we're recording this lecture,
transportation emissions are not only
increasing in absolute terms, they
are increasing in per person terms.
So things are definitely trending the wrong way.
Globally too, many trends are making this problem worse.
Over the last 20 years, the share
of cars that are heavier and more polluting SUVs
has increased across the world, driving up
emissions per passenger mile, and moving things
in the wrong direction at precisely the wrong time.
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