The Economics of Climate Change
The Price of Tomorrow: Why Climate Change Is Really a Problem of Discounting
The most consequential number in all of climate economics isn't a temperature — it's a percentage rate that determines how much we think the future is worth.
The Idea
At the heart of climate economics sits a deceptively simple question: how much should we sacrifice today to prevent harm that arrives decades from now? The tool economists use to answer this is the discount rate — the rate at which future costs and benefits are translated back into present-day value. The higher the rate, the less we value the future. A cost of one million arriving in fifty years, discounted at five percent annually, shrinks to less than ninety thousand in today's terms. It practically disappears. This matters enormously for climate policy. When economists build models to assess whether aggressive action on emissions is worth the cost, their conclusions hinge almost entirely on what discount rate they feed in. The Stern Review, published in 2006, used a very low rate — around 1.4 percent — and concluded that spending heavily now to curb warming was an obvious bargain. Other economists, using rates closer to five or six percent, reached nearly the opposite conclusion. Neither camp was making an arithmetic error. They were making a philosophical choice: how much do we value people who haven't been born yet compared to people alive today? A high discount rate implicitly says future generations will be richer and more technologically capable, so they can handle the damage themselves. A low rate says a life in 2080 matters as much as a life in 2025. The maths of climate change forces this ethical question into the open whether economists like it or not.
In the World
In 2006, British economist Nicholas Stern handed the UK government a 700-page report that made headlines around the world — not because of its science, but because of a single number buried in its methodology. Stern used a 'pure time preference rate' of essentially zero, meaning he refused to value future lives less simply because they were future. Combined with a low expected growth rate, his effective discount rate landed around 1.4 percent. The result was a striking conclusion: the economic cost of unmitigated climate change could reach twenty percent of global GDP, while the cost of preventing it was only around one percent annually. The case for immediate, aggressive action was overwhelming. The backlash from economists was swift. Yale's William Nordhaus, who would later win the Nobel Prize for his own climate modelling work, argued that Stern's discount rate was far too low and out of step with how markets and real people actually value the future. Using rates closer to five percent, Nordhaus's own models suggested a far more gradual, incremental response was economically rational. The two men weren't disagreeing about climate science. They were disagreeing about moral philosophy — specifically, whether it is legitimate to discount the welfare of people who don't yet exist. Stern said no. Nordhaus said the market already does, and models should reflect reality. The debate still hasn't been resolved. But it permanently changed how economists, policymakers, and eventually central banks talk about long-run risk — and planted the question of intergenerational fairness squarely inside the spreadsheet.
Why It Matters
Most personal financial decisions involve a version of this same tension — spending now versus saving for a future self who feels, somehow, slightly abstract and distant. Research in behavioural economics consistently shows that people heavily discount their own futures, let alone the futures of strangers not yet born. Understanding that climate economics is fundamentally about discount rates rather than just emissions targets reframes how you read the news. When a government announces a net-zero target for 2050 or 2070, the implicit discount rate embedded in that deadline is doing most of the moral heavy lifting. A target thirty years away, discounted at even a modest rate, means relatively modest action is required today. It also sharpens your scepticism of anyone who frames climate action purely as an economic trade-off. The Stern-Nordhaus debate revealed that the numbers always rest on a values judgement first. Recognising that doesn't make the maths irrelevant — it makes you a more honest reader of it. And in a world where these models increasingly inform everything from infrastructure investment to central bank stress tests, that literacy is genuinely useful.
A Question to Ponder
If you had to put a number on how much less a stranger's wellbeing in 2075 matters to you than a stranger's wellbeing today, what would that number actually be — and could you defend it?
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