BBC Sounds, Music Radio Podcasts Thanks for downloading the more or less podcast from the BBC World Service and our annual tradition of taking a look back at the numbers of the year with me, Tim Harford. As numbers go, 2025 has been a big year for them. From climate temperature records and the 267th hope to, and unrelated, the viral question of whether 100 men could take on one gorilla. So we've gathered together some friends of the program to give us their top numbers of the year. First up we look to the United States, where in 2025 White House Wings came down and global import tariffs went up. Pay up President Trump's big beautiful year of tariffs certainly had its fluctuations. The Supreme Court is even reviewing their legality as we speak. The level of tariff imposed varied from country to country, industry to industry. So how do you choose just one number to sum up tariffs imposed across all countries? I'll leave that job to Thomas Sampson from the London School of Economics. My number of the year is 28%, which was the peak in the average US tariff rate following President Trump's reciprocal tariff announcements in April of this year. Finding this overall average tariff rate provides a good indicator for trying to work out what's going on with America's trade policies and economy. But as Thomas says, 28% was the peak. The number has actually fallen since April. Now some of those tariffs never ended up being implemented, so the average effective tariff rate by the end of October had declined to 18%, according to the Yale Budget Lab, but that's still substantially higher than the 2% level in January of this year. And the current 18% rate is still the highest average US tariff rate since the mid 1930s. But calculating this average is not as simple as you may think. There isn't a single tariff rate that the US imposes on imports from different countries and of different products. There are thousands of individual tariffs on each individual product coming from each different country. And the way that this number is computed is by averaging across products, but using imports shares in 2024 as weights. So if the US imported a lot from China in 2024, we give a bigger weight to tariffs on imports from China than on other countries. Taking the average this way, it peaked at 28% in April. This reflects the full cost consumers would have paid if the tariff had been imposed on last year's pattern of imports. There is, another way we could get to an average, because that pattern of imports will change in response to the tariff itself. When a big tariff is imposed on, for example, French cheese, American consumers will buy less French cheese. So an alternative average tariff looks at the tariffs collected in this new, fromage-less world. Another way to try and compute the same number is to look at how much tariff revenue the US actually collects and divide that by the total value of imports to get an average tariff rate based on revenue collected. When we do that, and the latest data I have for that is from July, the average tariff rate is 9.8%. That's about one third as big, much lower. Why? Partly because, well, that French cheese effect, but also because some of these tariffs just aren't being collected yet. And so, at least so far, is not collecting quite as much tariff revenue as one might have expected. Thank you, Thomas Sampson. Now, from percentages to wattages. I am Hannah Ritchie, and my number of the year is $1 trillion. So that's the number of watts of installed solar power that China surpassed this year, which is equivalent to what we'd call one terawatt. A terawatt sounds like a big number, but looking at installed solar power can also be a bit misleading when we consider how much power is being used. So first, why does Hannah think it's an important number? I think it really signifies how quickly solar power has been built out globally, but actually how much China is now dominating and really rapidly moving on solar power. Now, one trillion watts of solar power produces about 1,800 terawatt hours. But to give some context of how big that number is, India in total uses about 2,000 terawatt hours, right? So the solar output from that one trillion watts of solar is almost equivalent to the total electricity generation of the whole of India from all sources. Suffice to say that if you've installed almost enough solar capacity to run India, the world's most populous country, then you have installed a lot of solar. Solar photovoltaics have followed a learning curve. The more the world makes solar panels, the cheaper they get, and of course, the cheaper they get, the more people want to buy them. There's a huge boom in solar panels going on roofs and huge solar farms across China soaking up those rays. However, China's electricity demand is also growing. So can they build renewables fast enough to meet additional demand for electricity and also push coal and fossil fuels out of the electricity mix? This looks like it could be the first year where it's basically built enough to cover all of that additional electricity demand. To give some context on how much China's electricity is growing, it's adding about a UK-sized grid every single year to its electricity demand. And actually, the fact that it's now meeting all of that additional demand from new solar and wind actually speaks to the fact of how much and how quickly they're now deploying these sources. So is China getting most of its electricity from solar energy? Solar is around 10% of electricity demand. Some more of that comes from wind, some more of that comes from nuclear and hydro. But it's important to note that still China's electricity mix is still relatively dominated by fossil fuels and primarily coal. Although this share of electricity coming from coal has been decreasing over time as these new sources have increased. Is it a bird? Is it a plane? Is it an alien spaceship? No, it's our final number currently winging across our solar system. Hi, I'm Catherine Hamons. I'm a Professor of Astrophysics at the University of Edinburgh and the Astronomer at Royal for Scotland. I have chosen the number three to celebrate the discovery of the third interstellar object in our solar system. That interstellar object is three-eye atlas, a comet. Need a reminder of what a comet is? Well, NASA defines one as a cosmic snowball, frozen gas, rock and dust. As astronomers, we can't send probes outside our solar system to see what life is like outside in the rest of our galaxy. And so we rely on these interstellar visitors to bring with them a memory of where they've come from. And so this is why astronomers have been so excited and mapping the path, the journey of three-eye atlas as it goes through our solar system so they can learn more about what things are like across the galaxy. It's only the third we've ever discovered which has come from outside of our solar system. It was first spotted in July of this year. Astronomers looked at its trajectory and they realised that it hadn't come from just the outskirts of our solar system, it had come from another star within our own galaxy. Seeing as we can't ask the comet its age outright, that would be rude, we use good scientific know-how to work out how long it's been around. We think it's come from a very old part of the galaxy which means that it is over 7 billion years old which makes it 2 billion years older than anything else in our solar system. That's it for your numbers of the year. We'll be back with more in 2026 and until then, goodbye.
