Global change refers to the consequences of natural processes and human activities that affect the global environment directly and cumulatively. Some forms of global environmental change, such as deforestation, urbanization and the loss of wetlands, can be measured over a matter of weeks or months. Others, such as changes in our climate and oceans, and the thinning of the atmosphere's stratospheric ozone layer, are detectable only over a span of decades or centuries.

The consequences of global environmental changes cut across the entire face of our planet from the outer reaches of the atmosphere to the depths of the oceans, from human health to the productivity of the world's food crops, fish stocks and forests.

Major global environmental changes affecting our planet today include:

climate change
In the past 200 years, the rapid increases in human population and industrialization have led to significant increases in the concentrations of carbon dioxide (CO2) and other so-called greenhouse gases in the atmosphere. Researchers are now detecting climate changes consistent with computer-based modelling of the effects of greenhouse gases. The gradual warming of the planet's climate could have serious consequences around the world rising sea levels, with serious consequences for low-lying countries and regions; changes in growing seasons, affecting the security of world food supplies; and increases in the frequency and severity of extreme weather events such as droughts, heat waves, floods and hurricanes.

stratospheric ozone loss
A layer of ozone (O3) high in the stratosphere acts as a natural shield protecting the earth's surface from the harmful effects of ultraviolet rays emitted by the sun. Researchers have determined that the use of certain chemicals, including chlorofluorocarbons (CFCs) and halons, is leading to the depletion of this ozone layer. Decreases in stratospheric ozone concentrations will allow more of the sun's harmful UVB radiation to strike the earth, resulting in increases in skin cancers and eye problems in humans and affecting the productivity of ecosystems, including phytoplankton, the base of the ocean's food web.

air pollution
Once considered a local problem, air pollution is now recognized as a global change issue. Air contaminants such as chemicals and fine particles can be carried in the atmosphere great distances from their sources, affecting the air quality in every corner of the planet. Air pollutants are known to affect human health, particularly the respiratory system, as well as the build-up of toxic chemicals in the food chain.

biodiversity loss
Much of the world's richest natural habitat is being converted to agriculture, urbanization and other human uses or is being degraded through overuse and pollution. These changes can lead to soil degradation and the loss of plant and animal species. Biodiversity loss, in turn, undermines the ability of ecosystems to adapt to change. It also limits the availability of the world's genetic resources to serve as future sources of medicines and specialized strains of food crops.

soil degradation
The world's soils provide the foundation for all life on land. Soil degradation the loss of its productive capacity can be caused by a variety of natural forces and human activities, such as overcultivation, water and wind erosion, deforestation, salinization and changing land uses. Over the past 45 years, an estimated 11% of the earth's vegetated land surface has experienced moderate to extreme soil degradation. Loss of soil productivity threatens our capacity to feed a growing world population.

fresh water issues
A growing world population, with its industrialization, agriculture, forestry and urbanization is depleting the world's fresh water resources. The demands and wastes generated from these human activities have put at risk the quality and quantity of this resource.

ocean pollution
For most of human history, the world's oceans have been able to supply an important source of food and absorb pollution from human settlements and activities. Today, climate change, pollution and resource exploitation are reducing the capacity of the world's oceans to sustain life and provide food.