New climate calculations give hope

BRITAIN: A group of prominent scientists yesterday created a potential whiplash moment for climate policy, suggesting that humanity could have considerably more time than previously thought to avoid a ‘‘dangerous’’ level of global warming.

The upward revision to the planet’s influential ‘‘carbon budget’’ was published by a number of researchers who have been deeply involved in studying the concept, making it all the more unexpected.

But other outside researchers raised questions about the work, leaving it unclear whether the new analysis – which, if correct, would have very large implications – will stick.

Ten researchers, led by Richard Millar of Oxford University, recalculated the carbon budget for limiting the Earth’s warming to 1.5 degrees Celsius above temper- atures from the late 19th century.

It had been widely assumed that this stringent target would prove unachievable, but the new study by scientists from New Zealand, Britain, Canada, Austria, Switzerland and Norway would appear to give us much more time to get our act together if we want to stay below it. ’’What this paper means is that keeping warming to 1.5C still remains a geophysical possi- bility, contrary to quite widespread belief,’’ Millar said.

But the new calculation diverged so much from what had gone before that other experts were still trying to figure out what to make of it.

‘‘When it’s such a substantial difference, you really need to sit back and ponder what that actually means,’’ Glen Peters, an expert on climate and emissions trajectories at the Centre for International Climate Research in Oslo, Norway, said. He was not involved in the research.

‘‘The implications are pretty profound,’’ Peters said. ‘‘But because of that, you’re going to have some extra eyes really scrutinising that this is a robust result.’’

That may have already begun, with at least one prominent climate scientist confessing he had a hard time believing the result.

‘‘It is very hard to see how we could still have a substantial CO2 emissions budget left for 1.5C, given we’re already at 1C. Thermal inertia means we’ll catch up with some more warming even without increased radiative forcing, and any CO2 emissions reductions inevitably comes with reduced aerosol load as well, the latter reduction causing some further warming,’’ Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany said.

Any substantial revision to the carbon budget would have major implications, changing our ideas of how rapidly countries will need to ratchet down their greenhouse gas emissions in coming years and, thus, the very workings of global climate policymaking. Limiting the Earth’s warming

1.5C above pre-industrial

to temperatures was the most ambitious goal cited in the 2015 Paris climate agreement.

It is of particular importance to vulnerable developing nations and small island states, which fear they could be submerged by rising seas.

Discussion up until now, however, has largely focused on how to avoid the more lenient but stillquite-difficult target of 2C. That is both because 1.5C was widely viewed as infeasible and because considerably less research had focused on studying the achievability of the target.

In 2013, the United Nations’ Intergovernmental Panel on Climate Change (IPCC) calculated that humanity could emit about a billion more tonnes of carbon dioxide from 2011 onward if it wanted a good chance of limiting warming to 2C – launching the highly influ- ential concept of the budget’’.

The allowable emissions or budget for 1.5C would, naturally, be lower. One 2015 study found they were 200 billion to 400 billion tonnes. And we currently emit about 41 billion tonnes a year, so every three years, more than 100 billion tonnes are gone.

No wonder a recent study put the chance of limiting warming to 1.5C at 1 per cent. Peters said that according to the prior paradigm, we basically would have used up the carbon budget for 1.5C by 2022.

That’s what makes the new result so surprising: It finds that we have more than 700 billion tonnes left to emit to keep warming within 1.5C, with a twothirds probability of success. ‘‘That’s about 20 years at presentday emissions,’ Millar said.

– Washington Post

‘‘carbon