Japan has one of, if not the, strictest emission control regimes in the world. Upon purchase, when a car is three years old, and every two years after that, each car must undergo a rigorous and sometimes costly Sha-ken inspection. These ensure that it meets tough emission standards and is in sound mechanical condition.
Sha-ken makes it expensive for Japanese car owners to keep an older car on the road. Yet these regular inspections, combined with other factors - congested roads that ensure most cars have very low mileage, a relatively temperate climate, underground parking - mean that a five or seven year old Japanese car is typically in excellent condition. The net result is that Japan exports used cars at low prices to Australia, New Zealand, India, South Africa, Botswana, Zambia, and just about every country where right-hand-drive (RHD) cars are used.
From a narrow, national perspective, Japan's emission control regime appears to protect the environment. Yet by encouraging Japanese car owners to abandon perfectly good vehicles, which are then dumped on other countries, effectively it subsidizes car exports. From a global perspective, therefore, the environmental impacts of Japan's emissions control regime are far less clear.
An increase in the supply of cars would be expected to increase the quantity of cars on the road. But does increased car ownership automatically increase greenhouse gas emissions? It depends upon the alternatives. Is the alternative to a "new reconditioned" Japanese car a 50 year-old Chevy with a V8 engine held together with wire and prayers? A methane belching team of oxen? A solar-powered monorail system? On balance, my guess is that the increased supply of cars leads to increased emissions, but I don't have solid empirical evidence.
Even if importing cheap Japanese used cars into, say, Zambia leads to increased emissions, is it a bad thing? Zambians love their "new reconditioned" Japanese cars, just as Canadians would, if we were able to tap the cheap used Japanese car market. [We drive on the right, Japan drives on the left, and although some high end specialty used Japanese cars can be found in Vancouver, they are rarely seen elsewhere in Canada.]
Cars are a key part of Zambia's transport system. "Traders", mostly women, drive around the country, and make money through arbitrage - buying goods that are relatively cheap in Lusaka, driving down to Livingstone and reselling them, then stocking up with whatever is relatively cheap in Livingstone, and driving back to Lusaka. Cars also play a key role in the tourism industry - every taxi is a Japanese import.
One could argue that cheap cars fuel economic development. Even if they lead to an increase in Zambian carbon emissions, so what - Zambians still produce relatively few carbon emissions on a per capita basis. From a global perspective, surely the responsibility for reductions in carbon emissions should lie with those, like globe-trotting academics, who produce high levels of emissions - concern for the environment shouldn't trap Africans in poverty.
In short, it's complicated. But like any economist, I'm a sucker for an example of a policy with unintended consequences.