than CO2 does.

This isn’t the place to discuss the uncertainties of climate change in any
more detail. I highly recommend the books Avoiding Dangerous Climate
(Schellnhuber et al., 2006) and Global Climate Change (Dessler and
Parson, 2006). Also the papers by Hansen et al. (2007) and Charney et al.

The purpose of this chapter is to discuss the idea of fixing climate
change by sucking carbon dioxide from thin air; we discuss the energy
cost of this sucking next.

The cost of sucking

Today, pumping carbon out of the ground is big bucks. In the future, per-
haps pumping carbon into the ground is going to be big bucks. Assuming
that inadequate action is taken now to halt global carbon pollution, perhaps
a coalition of the willing will in a few decades pay to create a giant
vacuum cleaner, and clean up everyone’s mess.

Before we go into details of how to capture carbon from thin air, let’s
discuss the unavoidable energy cost of carbon capture. Whatever technolo-
gies we use, they have to respect the laws of physics, and unfortunately
grabbing CO2 from thin air and concentrating it requires energy. The laws
of physics say that the energy required must be at least 0.2 kWh per kg of
CO2 (table 31.5). Given that real processes are typically 35% efficient at
best, I’d be amazed if the energy cost of carbon capture is ever reduced
below 0.55 kWh per kg.

Now, let’s assume that we wish to neutralize a typical European’s CO2
output of 11 tons per year, which is 30 kg per day per person. The energy
required, assuming a cost of 0.55 kWh per kg of CO2, is 16.5 kWh per day
per person
. This is exactly the same as British electricity consumption. So
powering the giant vacuum cleaner may require us to double our electricity
production – or at least, to somehow obtain extra power equal to our
current electricity production.

If the cost of running giant vacuum cleaners can be brought down,
brilliant, let’s make them. But no amount of research and development
can get round the laws of physics, which say that grabbing CO2 from thin
air and concentrating it into liquid CO2 requires at least 0.2 kWh per kg of

Now, what’s the best way to suck CO2 from thin air? I’ll discuss four
technologies for building the giant vacuum cleaner:

A. chemical pumps;

B. trees;

C. accelerated weathering of rocks;

D. ocean nourishment.