The Copenhagen climate change summit

It's being billed as the meeting that will determine the future of humanity. Come
early December, we will be inundated with news from the Copenhagen summit.
Can it really save us from climate catastrophe? Catherine Brahic and Fred
Pearce sift through the mass of science and policy to pick out the key points
to watch

The Copenhagen climate change summit
Why this year? Two years ago in Bali, member nations of the UN Framework Convention on Climate Change (UNFCCC), which is convening the Copenhagen summit, agreed that they would accelerate their efforts and draft a long-term plan to avoid dangerous climate change. Their deadline for doing so is the close of this year's summit, on 14 December.

Hasn't the Kyoto protocol shown all this to be pointless? Not necessarily. The Kyoto protocol was always intended as a first step. There are a number of differences this time around, most notably that the US opted out of the Kyoto protocol but is very much engaged in the Copenhagen process.

Why 250,000 megatonnes? We have already emitted over 500,000 megatonnes of carbon - equivalent to about 1,800,000 megatonnes of carbon dioxide - mostly by burning fossil fuels and cutting down forests. This year, climate scientists calculated that if we emit no more than 750,000 megatonnes in total, we will have a 75 per cent chance of limiting global warming to 2 °C.

What is the significance of 2 °C? The objective of the UNFCCC is to prevent "dangerous" climate change. Although any amount of warming may have consequences - including biodiversity loss, changing weather patterns and disappearing coastlines - many climate scientists predict that some of those changes will be irreversible beyond 2 °C and others will pose a serious threat to millions of people. As a consequence, 2 °C has been adopted by politicians as the threshold for dangerous climate change.

Is 2 °C little enough? That all depends: little enough for what? No amount of warming is risk-free, and modelling studies indicate that at 2 °C an additional 1 billion people will suffer water shortages and most of the world's corals will be bleached. The world's poorest nations, which include a number of island states that are particularly vulnerable to sea-level rise, are campaigning to limit warming to 1.5 °C. Given the effort that is going to be required to reach the 2 °C target, this is unlikely to be achieved. Moreover, lags in climate systems, plus the removal from the atmosphere of the fine aerosol particles now cooling the world, mean past emissions are likely to result in a 1.9 °C warming.

WHAT NEEDS TO BE DONE

There are no two ways about it: to have any chance of avoiding the disastrous consequences of exceeding our carbon budget, we must usher in a new era of low-carbon societies.

How this is done will depend on what deal can be reached between rich and developing nations. Both must agree to cut emissions according to their means and historical responsibility.

Developing nations will also need money and technology to green their industrialisation. Where this will come from will be a key preoccupation for the Copenhagen negotiators THE HAVES...

must cut emissions by

BY 2020 BY 2050
NEED 25-40 % 80-95 %
AGREED SO FAR 10-24 % 40-80 %

AND HAVE NOTS

must cut emissions by
BY 2020 NEED 15-30 %
AGREED SO FAR 10-15 %

MONEY

It could cost the poorest nations hundreds of billions of dollars a year to curb their emissions and adapt to inevitable climate change.

Rich nations are responsible for most of the gases that are already heating the planet, and have a duty to help foot this bill. Negotiators in Copenhagen will have to agree on how.

Funds could be raised through taxes on emissions permits, for instance, or on international airline tickets. Or there could be a levy on all carbon emissions above certain national thresholds - as proposed by Switzerland.

The European Union agreed last week to push for a fund worth €100 billion a year by 2020.