Air conditioning is almost universal in the US and Japan — but not elsewhere

Most high-income countries have reduced road deaths substantially over the past decades. But the United States has made much less progress than other rich countries, and has even gone backward since the mid-2010s.

In this chart, I compare the trends for the US and a selection of other high-income countries to illustrate this point.

Consider Germany, which provides a useful comparison. In 1980, the US had about 25 road deaths per 100,000 people, and Germany had 22. But in the decades that followed, Germany’s rate fell steadily, while the US rate declined more slowly, and even rose again. In 2023, the last year in the data, the US rate was more than 4 times Germany’s.

In 2024, the National Academies of Sciences, Engineering, and Medicine in the US published a report that traces the gap to a mix of road-safety measures that other rich countries use more widely, such as speed and red-light cameras or lower limits where people walk.

There’s also a connection with how much Americans use their cars. In the US, people drive much more. However, that doesn’t fully explain the gap — US roads are also significantly more dangerous than those in Germany per kilometer traveled.

What we pay for something in a shop often doesn’t reflect its true cost. Producing goods causes damage through carbon emissions that drive climate change, but the receipts for that damage rarely show up in the price. The costs are often hidden and diffuse, but that doesn’t mean it isn’t real.

One way to make people pay the full cost is to introduce a carbon price. This can take the form of a carbon tax or a trading system, which caps emissions and lets companies buy and sell permits.

Many countries now do this. Around 30% of the world’s carbon dioxide (CO₂) emissions have a carbon price. In the chart, you can see that this has doubled in the last decade. The biggest part of this rise came from China’s introduction of a trading system in its electricity sector.

While more and more of the world’s production has a carbon price, most prices are incredibly low. In a recent article, we showed that most priced emissions were valued at $10 or lower. That’s well below most estimates of the “social cost of carbon”, which tend to be greater than $100 per tonne.

Simply having a carbon price is not enough. It also needs to be high enough to change what people buy and make low-carbon alternatives worth investing in.

Renewables supplied around 6% of Morocco’s electricity in 2000; by 2025, that share was four times as high.

That’s what the chart shows: the growing share of electricity production that comes from renewables.

Morocco’s rise stands out in the region for how it got there – several other African countries with rising renewables shares, like Sudan, have relied primarily on hydropower. Morocco, by contrast, has achieved it with wind and solar production, as part of a targeted policy push.

This has made Morocco’s electricity mix cleaner: each unit of electricity now comes with a larger contribution from renewables. But total fossil-fuel generation has not fallen. New solar and wind production has gone toward meeting rising demand, rather than displacing coal.

Morocco still burns nearly three times as much coal for electricity as it did in 2000, although coal generation appears to have plateaued in recent years.

Improved crop yields have allowed the world to feed billions more people while sparing forests and other land from agriculture.

Global yields of cereal crops have tripled since 1961. As you can see in the chart, they have increased in all regions.

However, yields across most African countries have lagged behind. At 1.7 tonnes per hectare, they’re still less than half the global average of 4.2 tonnes.

This is bad for farmers: they get much smaller harvests and live on much lower incomes. It makes it harder for countries to feed their populations. And it’s a problem for biodiversity: lower yields mean that farmland has to expand into wild habitats.

Increasing agricultural productivity — particularly across Africa — is one of the biggest challenges of this century.

In recent decades, sub-Saharan Africa has been the world’s fastest-urbanizing region.

The region’s most populous country, Nigeria, shows the scale of that change. In 1950, only around 1 in 10 Nigerians lived in a city. Today, it is nearly 1 in 2.

As you can see in the chart, over the same period, the share living in rural areas fell, but so did the share living in towns and suburbs, which had been the largest group in 1950 by a substantial margin.

Nigeria’s population became much more concentrated in cities — both because people migrated into established cities, and because new ones emerged as towns and suburbs grew dense and large enough to be classified as cities.

In early-industrializing countries, rapid urbanization was often closely tied to industrialization. Today, in many lower-income countries, including across much of sub-Saharan Africa, it is happening under different conditions.

Since the agricultural revolution, the majority of the labor force in countries like France, the United Kingdom, Italy, and the Netherlands worked in farming.

But over the last few centuries, this share has plummeted. Today, less than 5% of the workforce is employed in agriculture, and in many cases, it’s just a few percent.

This trend is shown clearly in the chart, which is based on data from the International Labour Organization and historical reconstructions by Broadberry and Gardner (2013).

The chart also includes the even steeper decline in agricultural employment in China over the last 40 years, as people have shifted to manufacturing and services.

Many other middle-income countries are on a similar trajectory, moving through this transition faster than European countries did in the past.