Earth's average global surface temperature is increasing. It has risen about 1ºF in the last century, and is expected to go up another 3 -11ºF in the next 100 years. This climate change has been dubbed "Global Warming". Although the magnitude of warming may seem insignificant, many natural processes have been profoundly affected. For example, a number of changes in the water cycle have been documented, and many more are under investigation. Global warming intensifies the movement of water through the cycle, because many of the processes involved are temperature-dependent.
The images and questions below address some of the interdependent relationships between global warming and the water cycle. These include the long-term redistribution of water, accelerated water movement between reservoirs, and shifting weather and climate patterns. Study the images and read the information below, then answer the questions. If you want more information, many web sites contain more detailed data on global warming and the water cycle. These two are good places to begin:
Study the images and read the information below. Then click on the Question and Answer button to answer the questions that correspond to each section. [In order to view all of the images, you may need to maximize the activity window.]
Scientists would like to be able to pinpoint the magnitude and consequences of global warming in the years to come, but they cannot. Precise forecasts are impossible because global warming depends partially on future human behavior, which is uncertain, and partially on the response of planetary climate, which is not completely understood. The tangled interrelationship between climate and the water cycle is just one example of the complexity of the systems involved.
You have seen how global warming can influence the water cycle. Describe ways in which you think the water cycle could affect global warming, and reinforce or diminish temperature change.
Scientists seek to understand and explain how the natural world works. Many of the questions raised in this endeavor have no absolute answers.
There are several ways that the water cycle could accelerate
global warming. For example, snow and ice have a cooling effect, because their
white and shiny surfaces reflect sunlight away from the surface. If global
warming reduces the amount of ice, more solar energy will hit the ground and
warm the surface up even more.
Also, if extended droughts decrease the water flowing through rivers, less
electricity will be generated hydroelectrically. If this "clean" power source
is replaced by sources that emit more of the gases that contribute to global
warming, then there will be more warming.
On the other hand, warmer temperatures dry out soils and kill plants. That
could cause more dust and dirt to blow into the air, once the plant cover is
gone. All those particulates could cool the surface by shielding the ground
from sunlight.
And transpiration and evaporation increase when temperature rises. These processes
absorb heat, and cool the surface.