Warmer world is the challenge of a generation

The chance to prevent the world warming by 2 ?C has gone, but that's no reason to give up fighting for a greener future

Editorial: "Durban climate summit must accept degrees of responsibility"

AS THE latest round of United Nations climate negotiations began in Durban, South Africa, on Monday, expectations could scarcely have been lower. A globally binding deal is further away than ever. That makes considerable warming from climate change inevitable.

In the last few weeks major reports by the International Energy Agency and the UN Environment Programme (UNEP) have concluded that we can still meet the UN's target of limiting warming to 2??C above preindustrial levels. But climate scientists are far less optimistic. Many say the chance to avoid a 2??C rise has been and gone, and we must now prepare for the damage to come.

To have a fair chance of keeping below 2??C, global emissions would have to peak by 2020 or so before falling. There's no sign of that:

they made their biggest-ever leap in 2010. Many countries promised to cut their emissions at the 2009 UN climate summit in Copenhagen, Denmark, but modelling carried out by climate consultancy Ecofys, based in the Netherlands, shows that even if those cuts were implemented in full we would still see 3.5??C of warming by 2100.

Read more: "Earth in balmy 2080"

To meet the 2??C target, even bigger cuts are needed. According to UNEP, nations must emit the equivalent of no more than 44 gigatonnes of carbon dioxide each year by 2020, but current pledges are 6 to 12 gigatonnes short. A UNEP report published last week says we can bridge this "emissions gap" by combining faster uptake of renewable energy, improved energy efficiency, and cuts to other greenhouse gases.

A second UNEP report points out that it is much easier to cut short-lived greenhouse gases like methane, and fine atmospheric particles like soot from inefficient stoves. Cutting these emissions could keep the thermostat from rising by 2??C until the middle of the century, buying us time to deal with CO₂.

It is the inertia in our society that is the problem, says the International Energy Agency in its 2011 World Energy Outlook report. The lifespan of existing power plants and factories commits us to 80 per cent of the total emissions that will take us to 2??C. Construction over the next five years commits us to the rest, so unless we switch our investments from fossil fuels to low-carbon technologies within five years, 2??C of warming is inevitable.

The reality is that the 2??C target is technically and economically feasible, but politically impossible. Saleemul Huq of the International Institute for Environment and Development says that countries would have to go to a war footing to do it. He compares the situation to the second world war, when nations like the UK transformed their economies to deal with an overwhelming threat. This single-minded commitment can work miracles, but no country has any such plans.

The UK's secretary of state for energy and climate change, Chris Huhne, says the deadline for an international deal is 2015. Other countries, like the US and India, want to delay even discussing a deal until then, leaving scant time to the desired emissions peak in 2020. And as Durban talks got under way this week, Canada announced it would not be participating in any successor to the Kyoto protocol.

What should we do if we cannot hit emissions targets? First, do not give up on cutting emissions, says Brian Hoskins of Imperial College London. We don't fully understand the climate, so we might emit more than is currently deemed "safe" and stay under 2??C by sheer luck.

And don't change the 2??C target. It's too early, says Corrine Le Qu?r?, director of the Tyndall Centre for Climate Change Research in the UK. The next IPCC report, due in 2013, could show that society can cope with a warmer world (see "Welcome to a world warmed by 2??C"). If it does, a small increment in the target might be justifiable, she says, but until then shifting goalposts would be premature and send the wrong message. "I haven't seen anything to suggest that 2??C is less dangerous now than it was when it was adopted," Le Qu?r? says. At all costs, Hoskins adds, we must avoid 4??C. Indeed, this could wipe out the Amazon rainforest and halt the Asian monsoon.

Finally, some form of geoengineering may be necessary. "We are going to have to look at CO₂ removal," says Tim Lenton of the University of Exeter, UK. Trees are already being planted to act as carbon sinks, and prototype technologies exist for sucking CO₂ from the atmosphere. Hoskins says they could be essential later in the century to keep temperatures down.

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