there are exactly enough clockwork officials to process one thousand pas-
sengers per hour. There’s a modest queue, but because of the match of
arrival rate to service rate, the queue isn’t getting any longer. Now imag-
ine that owing to fog an extra stream of flights is diverted here from a
smaller airport. This stream adds an extra 50 passengers per hour to the
arrivals lobby – a small addition compared to the original arrival rate of
one thousand per hour. Initially at least, the authorities don’t increase the
number of officials, and the officials carry on processing just one thousand
passengers per hour. So what happens? Slowly but surely, the queue grows.
Burning fossil fuels is undeniably increasing the CO2 concentration in the
atmosphere and in the surface oceans. No climate scientist disputes this
fact. When it comes to CO2 concentrations, man is significant.

OK. Fossil fuel burning increases CO2 concentrations significantly. But
does it matter? “Carbon is nature!”, the oilspinners remind us, “Carbon is
life!” If CO2 had no harmful effects, then indeed carbon emissions would
not matter. However, carbon dioxide is a greenhouse gas. Not the strongest
greenhouse gas, but a significant one nonetheless. Put more of it in the
atmosphere, and it does what greenhouse gases do: it absorbs infrared
radiation (heat) heading out from the earth and reemits it in a random di-
rection; the effect of this random redirection of the atmospheric heat traffic
is to impede the flow of heat from the planet, just like a quilt. So carbon
dioxide has a warming effect. This fact is based not on complex historical
records of global temperatures but on the simple physical properties of
CO2 molecules. Greenhouse gases are a quilt, and CO2 is one layer of the

So, if humanity succeeds in doubling or tripling CO2 concentrations
(which is where we are certainly heading, under business as usual), what
happens? Here, there is a lot of uncertainty. Climate science is difficult.
The climate is a complex, twitchy beast, and exactly how much warming
CO2 -doubling would produce is uncertain. The consensus of the best cli-
mate models seems to be that doubling the CO2 concentration would have
roughly the same effect as increasing the intensity of the sun by 2%, and
would bump up the global mean temperature by something like 3°C. This
would be what historians call a Bad Thing. I won’t recite the whole litany
of probable drastic effects, as I am sure you’ve heard it before. The litany
begins “the Greenland icecap would gradually melt, and, over a period of
a few 100 years, sea-level would rise by about 7 metres.” The brunt of the
litany falls on future generations. Such temperatures have not been seen
on earth for at least 100000 years, and it’s conceivable that the ecosystem
would be so significantly altered that the earth would stop supplying some
of the goods and services that we currently take for granted.