Sweden has had a prominent role in the natural sciences since the 18th century, with Carl Linnaeus founding systematic biology, and Anders Celsius inventing the 100-degree temperature scale. Since 1901, the city hosts the Nobel Prize ceremony. The rise of Nordic nationalism in the 19th century included appreciation of nature and outdoor life as a pastime; and the sparse population allowed the right to roam. Stockholm was redeveloped during the 1960s with an extensive system of highways (and sprawling suburbs) which was brought to a halt in the early 1970s with a rising environmentalist movement, as well as the 1973 oil crisis.
Sweden has no domestic fossil fuels (except peat) and has been phasing out coal and oil for strategic reasons already in the mid-20th century. As the climate agenda has become important, Sweden has a realistic aim for a carbon-free economy.
Stockholm, just as other large cities, used to be troubled by local pollution from industries, vehicle emissions, and sewage. Today the air is famously clean, and the water in lake Mälaren is good enough to drink.
While Stockholm has several airports nearby, a greener approach would be a train from Oslo or Copenhagen; see Rail and bus travel in Sweden. Stockholm can also be reached by sailing boat through Stockholm archipelago; see boating in the Baltic Sea.
Cars are subject to congestion tax, and some parts of the inner city require Euro 5 or higher emission standard (see Driving in Sweden). Taxis are rather expensive, and do not follow a fixed price. Driving in Stockholm is rarely necessary, in any case.