We're Pumping Out CO2 to the Point of No Return. It's Time to Alter Course

Until a few months ago, government
targets for cutting greenhouse gases at least had the virtue of being
wrong. They were the wrong targets, by the wrong dates, and they bore
no relationship to the stated aim of preventing more than 2C of global
warming. But they used a methodology that even their sternest critics
(myself included) believed could be improved until it delivered the
right results: the cuts just needed to be raised and accelerated.

Three papers released earlier this year changed all that. The first, published in Proceedings of the National Academy of Sciences
in February, showed that the climate change we cause today will be
"largely irreversible for 1,000 years after emissions stop". About 40%
of the carbon dioxide produced by humans this century will remain in
the atmosphere until at least the year 3000. Moreover, thanks to the
peculiar ways in which the oceans absorb heat from the atmosphere,
global average temperatures are likely to "remain approximately
constant ... until the end of the millennium despite zero further
emissions".

In other words, governments' hopes about the
trajectory of temperature change are ill-founded. Most, including the
UK's, are working on the assumption that we can overshoot the desired
targets for temperature and atmospheric concentrations of CO2, then
watch them settle back later. What this paper shows is that, wherever
temperatures peak, that is more or less where they will stay. There is
no going back.

The other two papers were published by Nature in
April. While governments and the United Nations set targets for cuts by
a certain date, these papers measured something quite different: the
total volume of carbon dioxide we can produce and still stand a good
chance of avoiding more than 2C of warming. One paper, from a team led
by Myles Allen,
shows that preventing more than 2C means producing a maximum of half a
trillion tonnes of carbon (1,830bn tonnes of carbon dioxide) between
now and 2500 - and probably much less. The other paper, written by a
team led by Malte Meinshausen, proposes that producing 1,000bn tonnes of CO2 between 2000 and 2050 would give a 25% chance of exceeding 2C of warming.

If
you want an idea of what this means, take a look at the global carbon
clock at www.know-the-number.com. The level of greenhouse gases in the
atmosphere is rising at the rate of 2bn tonnes a month (CO2
equivalent). The Allen paper suggests that the world can produce only
the equivalent of between 63 and 75 years of current emissions between
now and 2500 if we want to avoid more than 2C of warming.

Writing
elsewhere, the two teams gave us an idea of what this means. At current
rates of use, we will burn the ration that Allen set aside for the next
500 years in four decades. Meinshausen's carbon budget between now and
2050 will have been exhausted before 2030.

The World Energy
Council (WEC) publishes figures for global reserves of fossil fuels -
the minerals that have been identified and quantified, and which it is
cost-effective to exploit. The WEC says 848bn tonnes of coal, 177,000bn
cubic metres of natural gas and 162bn tonnes of crude oil are good to
go. We know roughly how much carbon a tonne of coal, a cubic metre of
gas and a barrel of oil contain. The calculations and references are on
my website: the result suggests that official reserves of coal, gas and
oil amount to 818bn tonnes of carbon.

The molecular weight of
carbon dioxide is 3.667 times that of carbon. This means that current
reserves of fossil fuel, even when we ignore unconventional sources
such as tar sands and oil shale, would produce 3,000bn tonnes of carbon
dioxide if they were burnt. So, in order not to exceed 2C of global
warming, we can burn, according to Allen's paper, a maximum of 60% of
current fossil fuel reserves by 2500. Meinshausen says we've already
used one-third of his 2050 budget since 2000, which suggests that we
can afford to burn only 22% of current reserves between now and 2050.
If you counted unconventional sources (the carbon content is much
harder to calculate), the proportion would be even smaller.

There
are some obvious conclusions from these three papers. The trajectory of
cuts is more important than the final destination. An 80% cut by 2050,
for instance, could produce very different outcomes. If most of the cut
were made towards the beginning of the period, the total emissions
entering the atmosphere would be much smaller than if it were made at
the end of the period. The peak atmospheric concentration must be as
low as possible and come as soon as possible, which means making most
of the reductions right now. Ensuring that we don't exceed the
cumulative emissions discussed in the Nature papers means setting an
absolute limit on the amount of fossil fuel we can burn, which, as my
rough sums show, is likely to be much smaller than the reserves already
identified. It means a global moratorium on prospecting and developing
new fields.

None of this is on the table. The targets and
methodology being used by governments and the United Nations - which
will form the basis of their negotiations at Copenhagen - are
irrelevant. Unless there is a radical change of plan between now and
December, world leaders will not only be discussing the alignment of
deckchairs on the Titanic, but disputing whose deckchairs they really
are and who is responsible for moving them. Fascinating as this
argument may be, it does nothing to alter the course of the liner.

But
someone, at least, has a radical new plan. This afternoon the team that
made the film The Age of Stupid is launching the 10:10 campaign, which
aims for a 10% cut in the UK's greenhouse gas emissions during 2010.
This seems to be roughly the trajectory needed to deliver a good chance
of averting 2C of warming. By encouraging people and businesses and
institutions to sign up, the campaign hopes to shame the UK government
into adopting this as its national target. This would give the
government the moral leverage to demand immediate sharp cuts from other
nations, based on current science rather than political convenience.

I
don't agree with everything the campaign proposes. It allows businesses
to claim reductions in carbon intensity as if they were real cuts: in
other words, they can measure their reductions relative to turnover
rather than in absolute terms. There's an uncomfortable precedent for
this: cutting carbon intensity was George Bush's proposal for tackling
climate change. As economic growth is the major cause of rising
emissions, this looks like a cop-out. The cuts will not be
independently audited, which might undermine their credibility with the
government.

But these are quibbles. 10:10 is the best shot we
have left. It may not be enough, it may not work, but at least it's
relevant. I take the pledge. Will you?

• Sign up for 10:10 now