Climate and Environment

More than any other substance on Earth, water, with its unique properties, affects and is affected by changes in climate or the environment. Water acts like a climatic thermostat-it can absorb more heat than most other substances. Holding this heat rather than releasing it, large bodies of water, like oceans and lakes, will maintain more constant temperatures. Water also acts as a heat exchanger. When temperatures rise, it stores the heat, becoming a vapour; when temperatures drop, it releases the heat and freezes. In this way, both heat from the sun and water - in the form of vapour, rain, snow, or ice-are redistributed. This cycle of change of water is referred to as the hydrological cycle.

Changes in Climate

Water not only drives the hydrological cycle, but can also drive the cycle of change we see in our climate. Evaporated by the sun from oceans, lakes, and rivers, water vapour collects in the atmosphere, some of which will be returned to the Earth as precipitation. But some will remain in the atmosphere. Here the water vapour has a greenhouse effect, trapping heat from the inner Earth in the atmosphere. Greenhouse gases, like water vapour, contribute to global warming-the gradual warming of global temperatures. Rising temperatures increase the rate of water evaporation creating yet more vapour in the atmosphere. Rising temperatures also increase melting of glaciers and polar ice caps, which can cause sea levels to rise. Higher temperatures also cause more water to be lost from soil, which in turn will become drier and need more irrigation. Increased water vapour in the atmosphere not only has a greenhouse effect, but also can change precipitation patterns causing flooding and monsoons in some regions, while others face drought.

Dams, reservoirs, irrigation and drainage systems, and waterways, all change how much and where water flows. Removal of trees and vegetation, changes of land uses, and expansion of paved areas, not only affect soil ecology, but also the water balance. Without cover, more soil moisture is lost to the atmosphere. Drier soils are more at risk of erosion and further water loss. Similarly, changes in land use from agriculture to urban can dramatically change surface water distribution, blocking routes that once drained into natural reservoirs. Increased urbanization also requires more water to feed the city's population and industry, often requiring deeper and deeper wells to be drilled or water to be moved from even more distant locations. Expansion of paved areas reduces the amount of vegetation available to transpire water back into the atmosphere. It also affects the drainage of surface water, and in northern latitudes, contributes to groundwater pollution should salt used to melt road ice be allowed to runoff into the natural drainage system.

Changes in the Environment

Changes in the environment can have a dramatic effect on the quality and availability of water.

Much of the water used in human activities is returned to the environment, but in a polluted form. Around the world, millions lack access to proper sanitation systems, which means that used water is returned to the environment without any treatment for bacteria or other hazards. Phosphate residues from fertilizers and pesticides used in intensive agriculture, untreated manure from pig and cattle farming, and hazardous chemicals from industry, all threaten the quality of groundwater and ultimately the health of those who use it.

Problems with water contaminated by bacteria and parasites are not restricted to developing countries. Ineffective water treatment systems have caused serious outbreaks, for example of the parasite cryptosporidium in the United States or the bacteria E. coli in Canada. During an outbreak of the cholera in South America in the early 1990's, Peru was most affected because of the poor state of its water sanitation systems.

Agricultural irrigation, if not properly managed, can leach the salt out from the soil into the water table, causing once fertile soil to become saline. Not only does this affect the quality of the water, but also starts a dangerous cycle, where the saline soil requires more and more irrigation, and which, if not broken, can make soil a virtual wasteland.

Airborne pollution, particularly sulfur dioxide, causes water vapour in the atmosphere to become more acidic. This so-called acid rain then passes on this increased acidity further along the hydrological cycle-to surface water, groundwater, lakes, and rivers. The increased acidity not only affects the water itself, but all life that relies on it.

Since the earliest known times, humans have been modifying where and how water flows, by diverting, damming, or drilling for water. Advances in technology have provided the means to improve how we harness water and, more importantly, how we can reduce the potential adverse consequences of development. The challenge for the future will be to meet our global need for water, but not at the expense of the climate or environment.