More or Less

RCP 8.5: Why did the climate change model get it wrong?

Whether we like it or not, global warming is happening. The global temperature has already gone up, and it’s going to go up more, because the atmosphere is already full of carbon dioxide and other greenhouse gases, and we’re continuing to add to that stock. Quite how much it will increase by is a very important question for all of us. Until relatively recently, during much of the 2010s and into the 2020s, many scientists claimed that if we kept on going down the path we were on, if we just kept on with business as usual, then by the end of the century global temperatures would increase by almost five degrees centigrade. This projection was based on something called RCP 8.5, a statistical scenario used by scientists to model the future of the climate. You can still find scientific papers published in 2025 that make the same claim. However, there’s a good case that RCP 8.5 should never have been used as the business-as-usual scenario. And in hindsight it doesn’t look like an accurate vision of the future at all. So what’s going on? Dr Zeke Hausfather, a climate scientist and the climate research lead at Stripe, explains the argument. Presenter: Tim Harford Series producer: Tom Colls Sound mix: Donald MacDonald Editor: Richard Vadon

Is RFK right about US sperm counts?

Around the world, many countries are concerned about tackling the decline in birth rates and total fertility rates. The US is no exception. To tackle this issue the US government announced that it would provide subsidies for Americans seeking IVF treatment. The announcement was accompanied by one suspect sounding stat from US Health Secretary Robert F. Kennedy Jr. "Today the average teenager in this country has 50% of the sperm count, 50% of the testosterone as a 65-year-old man," he said. We speak to Professor Allan Pacey, Professor of Andrology at the University of Manchester, and Adith Arun, a researcher at Yale University to find out whether this statement is accurate. Producer/Presenter: Lizzy McNeill Series Producer: Tom Colls Editor: Richard Vadon Sound Mix: James Beard

Richard Thaler and The Winner’s Curse

In the later part of the 20th century, a pioneering group of economists started shaking up their academic field. These “behavioural economists” used findings from experimental psychology and everyday life to challenge the prevailing view that human beings were rational decision makers – acting in predictable ways to maximize their wealth. One of those pioneers was Richard Thaler, who noted down some of these “anomalies” in a column in the 1980s, which was turned into a book - The Winner’s Curse - first published in 1992. His work also won him the Nobel memorial prize in economics in 2017. More than 30 years on, he has returned to that book, publishing a new, updated version with co-author Alex Imas, which looks at whether those anomalies in rational thinking have stood the test of time. Tim asks him to set out two of his most famous ideas – the winner’s curse itself, and the idea of “mental accounting”. Presenter: Tim Harford Series producer: Tom Colls Sound mix: Donald MacDonald Editor: Richard Vadon

Is there a stock market crash coming?

For months, the share prices of tech companies have marched seemingly-ever upward, driven by fevered excitement about the potential of Artificial Intelligence. But many are now voicing fears that this surge might turn out to be a bubble, which could burst with damaging effects. So do we have to rely on vibes? Or can we use data to tell us about the risk that AI might go pop? Nathan Gower discovers what the numbers tell us about the health of the stock market. Guests: Katie Martin, markets columnist at the Financial Times Simon French, Chief Economist and Head of Research at investment company Panmure Liberum Presenter and Producer: Nathan Gower Series Producer: Tom Colls Editor: Richard Vadon Sound Engineer: Andy Mills

Has there been a $50 trillion wealth transfer to the richest Americans?

Bernie Sanders says a vast amount of wealth - $50 trillion - has moved from 90% of the population to the wealthiest Americans since the 1970s. The figure comes from a study by Carter Price, a senior mathematician at nonprofit research institute the RAND Corporation. Tim Harford speaks to Carter to understand how he calculated his figures and what they really mean. If you’ve seen a number in the news you think we should take a look at, email moreorless@bbc.co.uk Presenter: Tim Harford Producer: Nicolas Barrett Series producer: Tom Colls Sound mix: Giles Aspen Editor: Richard Vadon