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The word Mitigation means to soften or make mild. 

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The way it's used in the climate 
change context is

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to talk about ways of avoiding emitting 
CO2 which is the cause of the problem. 

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And the question of what it would take 

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to avoid emitting CO2, to mitigate climate 
change 

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depends very much on the time 
frame on which you're asking the question. 

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In the near term, the Intergovernmental 
Panel on Climate Change

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put together a whole report 
on mitigation. 

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And they added up what they could see as 
various amounts of carbon emissions in 

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gigatons of carbon per year that could be 
avoided a cost of $100 per ton of CO2. 

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One issue here is, you have to watch out for,

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Is that a ton of carbon, as we've used before, is 
not the 

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same as a ton of C02, because of the mass 
of the oxygen. 

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Just something to keep in mind. 

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But anyway, the relative numbers are 
these. 

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for changes in energy supply at this 
cost,

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they came up without about 1 gigaton of 
carbon per year that could be saved. 

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Transportation, another gigaton per year. 

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The built 
environment, another gigaton. 

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Industry, another gigaton, and then 
agriculture, 1 more. 

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There're a couple of interesting things 
to notice here. 

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Most of this comes from efficiency, 
rather than new energy sources. 

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Most of the low-hanging fruit today, can 
be 

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gained by using our energy more 
efficiently, 

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because it's never been all that much of a 
priority in the past. 

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There's a lot of low-hanging fruit 

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in the built environment, the 
architectural sector. 

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There's a lot of carbon emissions that 
could be accomplished at 

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a net negative cost, that means it would 
pay for itself. 

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You put in more insulation when you 
build the building, and you have to 

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pay for that, but then you save money in 
the long term heating the building. 

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And the agricultural sector, mostly what 
they're talking about is 

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changes in agricultural practices that 
would allow carbon to build 

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up in the soil, such as no-till 
agriculture 

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There's no single 
magic bullet,

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no single change, that can accomplish the 
mitigation of climate change. 

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What they talk about is a 
portfolio of solutions 

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is how the Intergovernmental Panel on 
Climate Change puts it. 

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Or as Pacala and Socolow, Science 305: 968-972 (2004) put it, 

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they call these wedges. 
Imagine that here is business as usual 

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A rate of CO2 emission through time that's 
growing with time, and here let's call 

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this stabilization, if we could keep the 
CO2 emissions from growing

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for a while, that would be a good thing. 

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There's no single change in our 
practices or 

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lifestyles, that could get you from here 
to here. 

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But, you can divide this up into smaller 
pieces. 

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Each one of which they call a wedge. 

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Defined as ramping up from zero today to 
a saving of 

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about a gigaton of carbon per year by the 
year 2050. 

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And the cool thing about this is that 
there are many 

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wedges available with currently available 
technology. 

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If our automobiles got 60 miles a 
gallon 

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instead of 30, and assuming that by the 
year 

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2050 there will be about 3 times as many 

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automobiles as there are today, that would 
be a wedge. 

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Traditional windmills could scale up to be 
a wedge. 

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Nuclear power could be a wedge. 
Carbon capture and sequestration. 

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Actually, this paper came up with 

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15 wedges with currently available 
technology. 

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00:04:06,504 --> 00:04:09,744 
and concluded that we would only need 
implement 

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seven of those to begin to stabilize CO2 
emissions