person by 2050. This is such a deep cut, I suggest the best way to think
about it is no more fossil fuels.

One last thing about the climate-change motivation: while a range of
human activities cause greenhouse-gas emissions, the biggest cause by far
is energy use. Some people justify not doing anything about their energy
use by excuses such as “methane from burping cows causes more warming
than jet travel.” Yes, agricultural by-products contributed one eighth of
greenhouse-gas emissions in the year 2000. But energy-use contributed
three quarters (ﬁgure 1.9). The climate change problem is principally an
energy problem.

## Warnings to the reader

OK, enough about climate change. I’m going to assume we are motivated
to get off fossil fuels. Whatever your motivation, the aim of this book
is to help you ﬁgure out the numbers and do the arithmetic so that you
can evaluate policies; and to lay a factual foundation so that you can see
which proposals add up. I’m not claiming that the arithmetic and numbers
in this book are new; the books I’ve mentioned by Goodstein, Lomborg,
and Lovelock, for example, are full of interesting numbers and back-of-
envelope calculations, and there are many other helpful sources on the
internet too (see the notes at the end of each chapter).

What I’m aiming to do in this book is to make these numbers simple
and memorable; to show you how you can ﬁgure out the numbers for
yourself; and to make the situation so clear that any thinking reader will
be able to draw striking conclusions. I don’t want to feed you my own con-
clusions. Convictions are stronger if they are self-generated, rather than
taught. Understanding is a creative process. When you’ve read this book
I hope you’ll have reinforced the conﬁdence that you can ﬁgure anything
out.

I’d like to emphasize that the calculations we will do are deliberately
imprecise. Simpliﬁcation is a key to understanding. First, by rounding the
numbers, we can make them easier to remember. Second, rounded num-
bers allow quick calculations. For example, in this book, the population
of the United Kingdom is 60 million, and the population of the world is
6 billion. I’m perfectly capable of looking up more accurate ﬁgures, but
accuracy would get in the way of ﬂuent thought. For example, if we learn
that the world’s greenhouse gas emissions in 2000 were 34 billion tons of
CO2-equivalent per year, then we can instantly note, without a calculator,
that the average emissions per person are 5 or 6 tons of CO2-equivalent per
person per year. This rough answer is not exact, but it’s accurate enough to
inform interesting conversations. For instance, if you learn that a round-
trip intercontinental ﬂight emits nearly two tons of CO2 per passenger,
then knowing the average emissions yardstick (5-and-a-bit tons per year
per person) helps you realize that just one such plane-trip per year corre-

“Look – it’s Low Carbon Emission
Man”
Figure 1.10. Reproduced by kind permission of PRIVATE EYE / Peter Dredge www.private-eye.co.uk.
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