Geoscience Reference
In-Depth Information
Without the greenhouse effect, the planet would be so cold as to be uninhabitable. But,
by burning fossil fuels—coal, oil and gas—we are increasing the amount of CO
2
in the
atmosphere and thus, other things being equal, increasing the earth's temperature.
But four questions immediately arise, all of which need to be addressed, coolly and
rationally.
First, other things being equal, how much can increased atmospheric CO
2
be expected
to warm the earth? (This is known to scientists as climate sensitivity, or sometimes the
climate sensitivity of carbon.) This is highly uncertain, not least because clouds have an
important role to play, and the science of clouds is little understood. Until recently, the
majority opinion among climate scientists had been that clouds greatly amplify the basic
greenhouse effect. But there is a significant minority, including some of the most eminent
climate scientists, who strongly dispute this.
Second, are other things equal, anyway? We know that over millennia, the temperature
of the earth has varied a great deal, long before the arrival of fossil fuels. To take only the
past thousand years, a thousand years ago we were benefiting from the so-called medieval
warm period, when temperatures are thought to have been at least as warm, if not warmer,
than they are today. And during the Baroque era we were grimly suffering the cold of the
so-called Little Ice Age, when the Thames frequently froze in winter and substantial ice
fairs were held on it, which have been immortalised in contemporary prints.
Third, even if the earth were to warm, so far from this necessarily being a cause for
alarm, does it matter? It would, after all, be surprising if the planet were on a happy but
precarious temperature knife-edge, from which any change in either direction would be a
major disaster. In fact, we know that, if there were to be any future warming (and for the
reasonsalreadygiven,'if'iscorrect)therewouldbebothbenefitsandwhattheeconomists
call disbenefits. I shall discuss later where the balance might lie.
Andfourth,totheextentthatthereisaproblem,whatshouldwe,calmlyandrationally,
do about it?
It is probably best to take the first two questions together.
According to the temperature records kept by the UK Met Office (and other series
are much the same), over the past 150 years (that is, from the very beginnings of the
Industrial Revolution), mean global temperature has increased by a little under a degree
centigrade—accordingtotheMetOffice,0.8°C.Thishashappenedinfitsandstarts,which
are not fully understood. To begin with, to the extent that anyone noticed it, it was seen as
a welcome and natural recovery from the rigours of the Little Ice Age. But the great bulk
of it—0.5°C out of the 0.8°C—occurred during the last quarter of the twentieth century. It
was then that global warming alarmism was born.
But since then, and wholly contrary to the expectations of the overwhelming majority
of climate scientists, who confidently predicted that global warming would not merely
