The Earths climate is projected to change because human activities are altering the chemical composition of the atmosphere through the build-up of greenhouse gases- primarily carbon dioxide, methane and nitrous oxide. These gases trap heat and create a rise in global temperature.
The effect of the potential rise in surface temperature would be to speed up the hydrological cycle. Increases of 4 to 7 percent in the global mean evaporation and precipitation rates might occur for a doubling of the carbon dioxide level and a few degrees rise in global mean temperature. The effect on the water balance would be regional in nature, with some places becoming wetter and others drier. In general, there would be a trend toward greater and longer periods of summer dryness induced by lower soil moisture content and higher evaporation rates in the mid-latitudes of the Northern Hemisphere.
The potential changes in the hydrologic cycle do not seem great. However, their consequences could be severe for ecosystems and human populations, notably since the latter are so sensitive to and dependent on such changes.
On the other hand, there could be benefits and opportunities in some regions as the climate changes. In the Arctic, for example, as warming occurs, there will be more running and standing water, along with a thinner and reduced ice cover. Coastal navigation will increase with new opportunities for water transport, tourism and trade. The Arctic Ocean could become a major global trade route. Also, some northern extension of farming may be possible, and in general, marine ecological activity should rise.