The way it's used in the climate change context is
to talk about ways of avoiding emitting CO2 which is the cause of the problem.
And the question of what it would take
to avoid emitting CO2, to mitigate climate change
depends very much on the time frame on which you're asking the question.
In the near term, the Intergovernmental Panel on Climate Change
put together a whole report on mitigation.
And they added up what they could see as various amounts of carbon emissions in
gigatons of carbon per year that could be avoided a cost of $100 per ton of CO2.
One issue here is, you have to watch out for,
Is that a ton of carbon, as we've used before, is not the
same as a ton of C02, because of the mass of the oxygen.
Just something to keep in mind.
But anyway, the relative numbers are these.
for changes in energy supply at this cost,
they came up without about 1 gigaton of carbon per year that could be saved.
Transportation, another gigaton per year.
The built environment, another gigaton.
Industry, another gigaton, and then agriculture, 1 more.
There're a couple of interesting things to notice here.
Most of this comes from efficiency, rather than new energy sources.
Most of the low-hanging fruit today, can be
gained by using our energy more efficiently,
because it's never been all that much of a priority in the past.
There's a lot of low-hanging fruit
in the built environment, the architectural sector.
There's a lot of carbon emissions that could be accomplished at
a net negative cost, that means it would pay for itself.
You put in more insulation when you build the building, and you have to
pay for that, but then you save money in the long term heating the building.
And the agricultural sector, mostly what they're talking about is
changes in agricultural practices that would allow carbon to build
up in the soil, such as no-till agriculture
There's no single magic bullet,
no single change, that can accomplish the mitigation of climate change.
What they talk about is a portfolio of solutions
is how the Intergovernmental Panel on Climate Change puts it.
Or as Pacala and Socolow, Science 305: 968-972 (2004) put it,
they call these wedges. Imagine that here is business as usual
A rate of CO2 emission through time that's growing with time, and here let's call
this stabilization, if we could keep the CO2 emissions from growing
for a while, that would be a good thing.
There's no single change in our practices or
lifestyles, that could get you from here to here.
But, you can divide this up into smaller pieces.
Each one of which they call a wedge.
Defined as ramping up from zero today to a saving of
about a gigaton of carbon per year by the year 2050.
And the cool thing about this is that there are many
wedges available with currently available technology.
If our automobiles got 60 miles a gallon
instead of 30, and assuming that by the year
2050 there will be about 3 times as many
automobiles as there are today, that would be a wedge.
Traditional windmills could scale up to be a wedge.
Nuclear power could be a wedge. Carbon capture and sequestration.
Actually, this paper came up with
15 wedges with currently available technology.
and concluded that we would only need implement
seven of those to begin to stabilize CO2 emissions