31   The last thing we should talk about

Capturing carbon dioxide from thin air is the last thing we should talk about.

When I say this, I am deliberately expressing a double meaning. First,
the energy requirements for carbon capture from thin air are so enormous,
it seems almost absurd to talk about it (and there’s the worry that raising
the possibility of fixing climate change by this sort of geoengineering might
promote inaction today). But second, I do think we should talk about it,
contemplate how best to do it, and fund research into how to do it better,
because capturing carbon from thin air may turn out to be our last line
of defense, if climate change is as bad as the climate scientists say, and if
humanity fails to take the cheaper and more sensible options that may still
be available today.

Before we discuss capturing carbon from thin air, we need to understand
the global carbon picture better.

Understanding CO2

When I first planned this book, my intention was to ignore climate change
altogether. In some circles, “Is climate change happening?” was a contro-
versial question. As were “Is it caused by humans?” and “Does it matter?”
And, dangling at the end of a chain of controversies, “What should we do
about it?” I felt that sustainable energy was a compelling issue by itself,
and it was best to avoid controversy. My argument was to be: “Never mind
when fossil fuels are going to run out; never mind whether climate change
is happening; burning fossil fuels is not sustainable anyway; let’s imagine liv-
ing sustainably, and figure out how much sustainable energy is available.”

However, climate change has risen into public consciousness, and it
raises all sorts of interesting back-of-envelope questions. So I decided to
discuss it a little in the preface and in this closing chapter. Not a complete
discussion, just a few interesting numbers.


Carbon pollution charges are usually measured in dollars or euros per ton
of CO2 so I’ll use the ton of CO2 as the main unit when talking about per-
capita carbon pollution, and the ton of CO2 per year to measure rates of
pollution. (The average European’s greenhouse emissions are equivalent
to 11 tons per year of CO2; or 30 kg per day of CO2.) But when talking
about carbon in fossil fuels, vegetation, soil, and water, I’ll talk about tons
of carbon. One ton of CO2 contains 12/44 tons of carbon, a bit more than
a quarter of a ton. On a planetary scale, I’ll talk about gigatons of carbon
(Gt C). A gigaton of carbon is a billion tons. Gigatons are hard to imagine,
but if you want to bring it down to a human scale, imagine burning one

Figure 31.1. The weights of an atom of carbon and a molecule of CO2 are in the ratio 12 to 44, because the carbon atom weighs 12 units and the two oxygen atoms weigh 16 each.
12 + 16 +16 = 44.