Emissions of greenhouse gases (GHGs) from human activities disturb the radiative energy balance of the earth-atmosphere system. They exacerbate the natural greenhouse effect, leading to temperature changes and other disruption of the earth's climate. Land use changes and forestry also play a role by altering the amount of greenhouse gases captured or released by carbon sinks. Carbon dioxide (CO2) from the combustion of fossil fuels and deforestation is a major contributor to greenhouse gases. CO2 makes up the largest share of greenhouse gases and is a key factor in countries’ ability to mitigate climate change. National emissions are also affected by changes in global demand and supply patterns with increasing trade flows and the displacement of carbon-intensive production abroad. Reductions in domestic emissions can thus be partially or wholly offset elsewhere in the world.

Air pollution is the world’s leading environmental health risk and a major cause of environmental degradation. Atmospheric pollutants from energy transformation andenergy consumption, and from industrialprocesses,are the main contributors to regional and local air pollution.Major concerns relate to theireffects on humanhealth and ecosystems.Human exposure is particularly high in urban areas where economic activities are concentrated and where demand for mobility is highest. Degraded air quality can have substantial economic and social consequences, from health costs and a lower quality of life to infrastructure maintenance, reduced agricultural output and forest damage. Some population groups are especially vulnerable to air pollution. The very young and the very old are the most at risk.

Freshwater resources are of major environmental, economic and social importance. Their distribution varies widely among and within countries. Their availability and their quality are affected by water abstractions such as for public supply irrigation, industrial processes or cooling of electric power plants, pollution loads from agriculture, industry and households, changes in climate and weather conditions. Infrastructure developments can also affect the natural integrity of rivers, lake, aquifers and wetlands. If a significant share of a country’s water comes from transboundary rivers, tensions between countries can arise. In arid regions, freshwater resources may, at times, be limited to the extent that demand for water can be met only by going beyond sustainable use.

Material resources form the physical foundation of the economy and are an important source of income and jobs. They differ in their physical and chemical characteristics, their abundance and their value to countries. Economic growth generally implies growing demand for raw materials, energy and other natural resources, and growing amounts of materials that end up as waste if not properly managed.

Biodiversity and ecosystem services are integral elements of natural capital. Biodiversity, which encompasses species, ecosystems, and genetic diversity, provides invaluable ecosystem services (including raw materials for many sectors of the economy) and plays an essential role in maintaining life-support systems and quality of life.

The ocean may be a new economic frontier (OECD, 2016) but foremost it is a shared global resource. Ocean-related industries in many countries have expanded with insufficient consideration for the environment, risking the natural resources and essential marine ecosystem services on which economies and the well-being of people depend.