Here’s the story about climate that we liberals like to tell ourselves: once we get rid of dinosaur politicians like Trump, we’ll take on the fossil-fuel lobby and greedy corporations and vote through a “green new deal”.

It will fund clean, fast-growing industries: solar, wind, electric vehicles, sustainable clothes. That will be a win-win: we can green our societies and keep consuming. This story is called “green growth”.

Unfortunately, green growth probably doesn’t exist — at least not for the next couple of decades, during which time we’ll have to cut most of our carbon emissions to keep the planet habitable. Our generation has to choose: we can be green or we can have growth, but we can’t have both together.

Let’s start with the basics. We have to nearly halve current global carbon emissions by 2030 to have a chance of limiting the rise in the planet’s temperatures to 1.5C, says the Intergovernmental Panel on Climate Change.

Many climate scientists think the IPCC’s backward-looking, consensus-based estimates are too optimistic, but let’s accept that figure for a moment. It would require quite a turnround. Global emissions are still rising, hitting a record last year. Meanwhile, the world’s population is growing.

So we need to slash emissions while feeding and fuelling more people. But those people are also getting richer: global income per capita typically grows about 2 per cent a year.

And when people have money, they convert it into emissions. That’s what wealth is.

To achieve green growth, we’d have to emit radically less carbon per unit of gross domestic product. The amount of carbon required to produce one dollar of GDP has recently been dropping, by about 0.4 per cent a year.

But to keep temperature rises at safe levels, the carbon intensity of the global economy needs to fall at least 10 times faster, estimates the Renewable Energy Policy Network for the 21st Century (REN21), a think-tank.

Green-growthers will say: “Don’t worry, renewable energy is taking off.” And it’s true that modern renewables now account for more than 10 per cent of total energy consumption, according to REN21. By 2050, that figure could reach about 30 per cent.

But the IPCC estimates we’ll need to be at about double that by then. And global investment in clean energy projects fell to its lowest levels in six years in the first half of 2019, says Bloomberg New Energy Finance.

Green-growthers trumpet the transformation of European economies in recent decades: higher GDP, falling emissions. But that’s mostly because these countries have offshored their emissions: much of their stuff is now made in Asia.

Moreover, aviation and shipping aren’t counted against national carbon budgets. Once you factor in emissions embedded in imported goods, the EU’s carbon emissions are about 19 per cent higher than the bloc’s official figures, calculates the Global Carbon Project, a network of scientists; for many big cities, the gap is about 60 per cent.

The sad truth is that moving from dirty to green growth will take much more time than we have. The infrastructure we’ll be using these next crucial decades has largely already been built, and it isn’t green. Most of today’s planes and container ships will still be in use by 2040. There are no green alternatives yet, nor enough vegan burgers or sustainable clothes.

In 2040, too, most people will be living on much the same streets as today, still driving cars. Electric vehicles won’t save us: their lifetime emissions are unacceptably high. (Mining lithium, making car batteries, shipping cars and generating most electricity isn’t clean.)

Or picture the world’s biggest new infrastructure project: China’s Belt and Road is a web of highways, ports, cement plants, power plants (many coal-fired) and, yes, lots of greenish rail, built to shunt consumer goods across the world at pace. That’s growth, but it isn’t green.

It’s true we’re becoming more fuel-efficient. Ships, cars and planes have all reduced their energy consumption per mile.

But as William Jevons pointed out in 1865, when fuels become cheaper and more efficient, we use more of them. Note the global rise in car sales, increased ship speeds and the growing numbers flying each year. About four out of five people on earth have never taken a flight. Many of them cannot wait.

If green growth doesn’t exist, the only way to prevent climate catastrophe is “degrowth” now, not in 2050: stop most flying, meat-eating and clothes-buying until we have green alternatives, ban privately owned cars and abandon sprawling suburbs. A long economic depression might be enough to keep the planet habitable. We’d also need to divert money from consumption to building green infrastructure. This is essentially Greta Thunberg’s argument.

But that would put us in a new world. Economic growth, democracy and CO2 have always been intertwined. Growth and democracy barely existed until coal fuelled the industrial revolution. Can democracy survive without carbon?

We are not going to find out. No electorate will vote to decimate its own lifestyle. We can’t blame bad politicians or corporates. It’s us: we will always choose growth over climate.

Follow Simon on @KuperSimon or email him at simon.kuper@ft.com

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Letters in response to this column:

Global net zero will be tough but not impossible / From Richard Black, London, UK

Yes, elected leaders are tackling global warming / From David Miller, Director of International Diplomacy, C40 Cities, New York, NY, US

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