There are many ways to measure air pollution, but a key indicator is called "PM 2.5" — one of the most harmful classes of airborne pollutants.
The "PM" stands for "particulate matter," and the "2.5" stands for 2.5 microns in diameter or smaller — roughly the size of a single bacterium. Such pollution, as Business Insider's Lydia Ramsey explained in 2016, "is especially dangerous because it can get lodged in the lungs and cause long-term health problems like asthma and chronic lung disease."
When PM 2.5 levels go above roughly 35 micrograms per cubic meter of air, it can become a major health problem. The WHO recommends keeping PM 2.5 levels to about 10 micrograms per cubic meter.
Air pollution levels are one thing, but deaths attributed to them are another.
Take China, for instance. The country isn't in the top 10 for highest average levels of air pollution, in terms of PM 2.5 (Saudi Arabia wins that contest, thanks in part to its oil industry). However, it ranks fifth for having the most deaths per capita due to air pollution, in part because if its high population density.
The US currently has one of the lowest death rates attributed to air pollution.
Decades of scientific work across multiple lines of evidence corroborate a powerful yet inconvenient truth: Human-caused global warming and climate change is real, and it's briskly accelerating as we dump more carbon emissions into the atmosphere.
Looking at per-person average emissions of carbon dioxide, a persistent greenhouse gas emitted by burning fossil fuels, the US ranks as the eighth-highest contributor in the world.
Less developed nations, which lack robust and power-hungry infrastructure, rank among the lowest contributors to carbon dioxide emissions.
The main reason the US ranks so poorly on carbon dioxide emissions is because its per-person consumption rate of electricity is so high; all of that energy comes primarily from fossil fuels.
As with carbon dioxide emission rankings, less developed nations tend to score better on electricity consumption because access to electrical power is not as widely available.
Despite their poor rankings in air pollution and electricity consumption categories, China, India, and the US are the top-three contributors to renewable energy.
The ranking here is in "tonnes of oil equivalent" or TOE — meaning renewable energy sources generated (and presumably replaced) the energy created by burning that many metric tons of oil in a year.
Four Middle Eastern nations — Qatar, Kuwait, Bahrain, and Oman — are tied for "worst" in this category, since each had a "0" in TOE contributed by renewables. However, they are not shown in our graphics because this may be due to a lack of available data (all four nations are actively pushing growth in renewable energy sources).
