Emissions of greenhouses 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 consequences for 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 biomass for energy use is a major contributor to the enhanced greenhouse effect. It makes up the largest share of greenhouse gases and is a key factor in countries’ ability to deal with climate change.

Atmospheric pollutants from energy transformation and energy consumption, but also from industrial processes, are the main contributors to regional and local air pollution. Major concerns relate to their effects on human health and ecosystems.

Degraded air quality can have substantial economic and social consequences, from health costs and building restoration needs to reduced agricultural output, forest damage and a generally lower quality of life.

Freshwater resources are of major environmental, economic and social importance. Their distribution varies widely among and within countries. 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.

Pricing of water and water-related services is an important mechanism for managing demand and promoting efficient use of water, for allocating water among competing uses and for generating finance to invest in water-related infrastructure and services. When consumers do not pay the full cost of water, they tend to use it inefficiently. At the same time, when the price levels are high, this may pose problems of continued access to water for poorer consumers, and the affordability of the water bill for low income households needs to be taken into account.

Water quality (physical, chemical, microbial, biological) is affected by water abstraction, by pollution loads from human activities (agriculture, industry, households) and by climate and weather.

Biological resources are essential elements of ecosystems and of natural capital; they provide the raw materials of production and growth in many sectors of the economy and their diversity plays an essential role in maintaining life-support systems and quality of life.

Forests are among the most diverse and widespread ecosystems on earth, and have many functions: they provide timber and other forest products; have cultural values; deliver recreation benefits and ecosystem services, including regulation of soil, air and water; are reservoirs for biodiversity; and act as carbon sinks.

Fish resources play key roles for human food supply and aquatic ecosystems. Fish is among the most traded food commodities, and in many countries fisheries make an important contribution to sustainable incomes and employment opportunities. Fish represents around 20% of the animal protein consumed worldwide. In certain countries, including at least two OECD countries – Iceland and Japan – fish is the main source of animal protein intake.

Waste is generated at all stages of human activities. Its composition and amounts depend largely on consumption and production patterns.