The 5 greenest countries in the world

Finland took the top spot on the index, scoring 90.68. It ranks fourth in health impacts, eighth in fisheries, and top 20 in climate and energy, biodiversity and habitat, water resources, and air quality.

Though Finland is one of Europe's most forested countries, it didn't score well on the agriculture and forests categories coming in at 87th and 106th respectively. 

According to the EPI, Finland has made a "societal commitment to achieve a carbon-neutral society that does not exceed nature's carrying capacity by 2050." 

Iceland came in a close second on the index, scoring 90.51. It ranks third in health impacts, as well as climate and energy, and fourth for air quality.

Iceland's top performance is a function of its unique geology — around 25% of its power is produced geothermally, more than anywhere else on Earth, according to the EPI. 

And 100% of Iceland's electricity comes from renewable sources, like wind, and hydro-power, according to Iceland's National Energy Authority. 

Sweden came in a close third, scoring 90.43. It ranks fifth in health impacts, tenth in climate and energy, and top 20 for both water and sanitation, and water resources. 

Across the board, Sweden earned almost perfect scores on drinking water quality and wastewater treatment, according to the EPI. 

Like Finland, Sweden performed poorly on forests — largely due to unsustainable logging practices. 

Denmark came in fourth, scoring 89.21 overall. Denmark ranked in the top 20 for health impacts, water and sanitation, water resources, and biodiversity and habitat.

Denmark ranked a lowly 128 on fish stocks, meaning that its fisheries have much to improve upon.

Denmark also pledged 13.5 billion DKK (approximately $1.9 billion USD) to its "Green Growth Initiative" which is designed to support environmental protection along with economic growth. 

Slovenia came in fifth, scoring 88.98 overall. It took the eighth spot for biodiversity and habitat, and 15th for forests. 

Air quality hurt Slovenia's rankings, as nitrogen dioxide and PM2.5, common airborne pollutants, continues to pose problems for Slovenia's residents.

But Slovenia is also the global leader for habitat protection — it received perfect scores for terrestrial protected areas and species protection. 

Overall, the EPI's findings present a mixed bag: in some ways the world has vastly improved since the EPI started ranking countries in 2000. Health effects, like access to clean drinking water, and access to sanitation, have made huge gains.

Marine protected areas have also increased due in part to international agreements and strong grassroots advocacy.

But in other categories, like fish stocks, and air pollution, things have gotten much worse in the past 15 years. 

Economic development helps in some respects, as many newly-wealthy countries will spend heavily to create sanitation infrastructure and provide their citizens with clean drinking water.

But these countries often create this wealth by relying on industrial production, so air quality — as evidenced by Beijing — suffers.