杏吧原创

ONE of the concepts that climate science has bequeathed the wider world is the tipping point: a description of how a complex system can change gradually, almost imperceptibly, then suddenly flip into a new, stable state. Climate tipping points tend to be things we really don鈥檛 want to go past, such as the irreversible conversion of the Amazon rainforest to savannah or, heaven forfend, the Gulf Stream shutting down. Like in the climate disaster movie The Day After Tomorrow. That one ends especially badly.

The existence of climate tipping points and where they lie, however, . Climate scientists have rowed back from , though are increasingly concerned about unstoppable methane release from melting permafrost.

More recently, though, the tipping point concept has found a new application in climate science as a way to explain, and possibly engineer, . The way changes in attitude creep along at a glacial pace before suddenly bursting forth to take root across society is a classic tipping point. This process is useful because it moves ideas that were once on the fringes of mainstream opinion rapidly to the centre; ideas such as the need for deep economic and technological changes to avoid a real-life climate disaster movie.

Whether by accident or design, we recently passed one such social tipping point. In narrow terms, it is the sudden, widespread embrace of net zero. In broader terms, it means final realisation from all levels of society that we must take radical action or face dire, possibly terminal, consequences.

A year ago, when I first wrote about it in this column, net zero was creeping into the mainstream. Greta Thunberg was talking about it; two countries 鈥� Suriname and Bhutan 鈥� had achieved it, and four more, including the UK, had passed laws to aim for it. A dozen or so others were thinking about it.

Today, the picture has changed dramatically. Suriname and Bhutan still stand alone as the heroes of zero, but legislation has been passed or is pending in 21 other countries, plus the European Union. Three of the world鈥檚 four-biggest emitters 鈥� China, the EU and Japan 鈥� are in the club. If the US consummates its new relationship with the planet, that will be four out of four. According to the Energy & Climate Intelligence Unit鈥檚 Net , the US is one of around 100 countries in which net-zero laws are under discussion. Even Australia, which just , has . Countries on the outside look increasingly like a rogues鈥� gallery of backward-looking petrostates: Brazil, Saudi Arabia, Iran, Russia, Venezuela and Nigeria. You might call them the axis of ev-oil.

鈥淢aybe the power of net zero to win over wider society lies in the fact that it is an easy concept to grasp鈥�

At subnational levels, enthusiasm is spreading too. According to Kaya Axelsson at the University of Oxford鈥檚 Net Zero initiative, 452 cities, 22 regions, more than 1100 big companies, nearly 50 investment funds and 550 universities have pledged to go net zero globally, with more joining every day. Axelsson says when she goes to talk to private companies, she finds she is pushing at an open door.

Even families can make a pledge at a website called . I will look into this and report back in a later column.

鈥淭here鈥檚 now a big, broad societal consensus about the need to do something about climate change,鈥� says Sam Fankhauser at the London School of Economics. 鈥淭wo years ago or so, you had to make the case for climate action. That narrative has really shifted.鈥�

Maybe the power of net zero to win over wider society lies in the fact that it is easy to grasp. The basic concept is actually the simplest part of it, according to one of its originators, Myles Allen at the University of Oxford. In order to keep a lid on global heating at whatever upper limit we choose, we will eventually have to stop adding carbon dioxide and other warming gases to the atmosphere.

A complete cessation is probably impossible, so emissions that cannot be avoided must be offset by planting trees and other nature-based solutions that remove carbon from the air. But these won鈥檛 be enough, so we also need what Allen calls 鈥渞e-fossilising鈥�: capturing CO₂ released from the combustion of fossil fuels and burying it underground from whence it came. Overall, no new greenhouse gases are added to the atmosphere. Hence 鈥渘et鈥� zero.

Of course, pledging and achieving are two different things. Three decades of hard graft still lie ahead. We urgently need to speed up emission reductions; only a handful of countries are actually on a trajectory towards net zero. The UK鈥檚 recent approval of a new coal mine shows how easy it is even for net-zero pledgers to slip back into old ways. But something has tipped, and there is now a fighting chance that the climate won鈥檛. Let鈥檚 face it: we have zero other options.