is Global Warming?
To raise the earth's temperature requires adding energy in the form of heat. Where can such energy come from? A build up of certain gases that do not allow heat from the sun to leave the Earth's atmosphere would certainly raise the earth's temperature. These heat trapping gases are called "greenhouse gases," and are the chief cause for the increase in heat retention of the atmosphere. Most scientists believe that human activity is the cause of increasing gases, resulting from burning of fossil fuels.
However, a few scientists say that warming could be due to natural causes. Still other scientists claim that the evidence for warming is not convincing. The temperature sampling around the world is incomplete, especially in very cold areas that are inaccessible. For every iceberg that melts, new ones are forming. How can we know for sure just what is the average temperature of the earth?
Natural Causes of Global Warming
In short, we know from studying the earth's history that there have been Ice Ages and global warming periods long before humans existed. Scientists do not know why these major climate changes have occurred, but there are some possibilities:
As the world evolves, changes in the earth's environment affect the climate in various ways. For example, explosions on the sun generate even more heat than the sun normally gives off and some of this heat makes it to the earth causing rising temperatures. Volcanic eruptions on Earth can cause temperatures to decrease, because the smoke and gases given off can act like an umbrella shade and prevent sunlight from passing through the atmosphere. Any slight change in the earth's orbit could cause the earth to move closer or farther away from the sun. This could radically change temperatures, because the earth would be closer or farther away from its principle source of heat.
Human Contributions to Global Warming
Why do they call these "fossil" fuels? Scientists believe that oil (which is the source of gasoline), coal, and natural gas are made from decaying animal and plant life. In fact, the presence of fossils deep within the earth often helps oil drillers to locate oil and gas. But you say, "Oil can be found miles deep in the earth's crust. How could animals and plants be buried so deep?" The answer seems to be that the oil and gas were created closer to the surface but seeped deeper through cracks in the earth's crust.
So, are humans causing global warming? We do not know. We do know that burning fossil fuels adds to the heat given off into the atmosphere, and that certainly can't help.
is happening now?
Warmer air will mean more frequent and more severe storms (thunderstorms, hurricanes, tornados). Rainfall has gradually increased over the last hundred years, as temperature has risen. Rising temperatures may also make some areas more arid than they already are because of the increased heat. It is hard to say what will happen to specific regions.
But there is conflicting evidence. Consider the following facts:
A review of the evidence, published in The Journal of American Physicians and Surgeons 12 (2007) 79-90, cites published papers showing that::
1. glacier shrinkage started increasing around 1825 (before fossil fuels had any impact) and has increased with a steady slope that has not been affected by increasing use of fossils fuels. Similarly, sea level rise began around 1850, and its slope of increase is not changed by increasing use of fossil fuels.
2. Arctic air temperature correlates with solar activity, not use of fossil fuels. the same is true for U.S.surface temperatures.
3. number of severe tornados in U.S. over the last 50 years is decreasing and number of hurricanes making landfall in U.S. has not increased during the last 100 years.
4. long-lived trees are growing faster in correlation with the increase in atmospheric CO2.
5. increased CO2 accelerates growth of plants tested (wheat, orange trees, young pine trees)
6. the earth has had much warmer weather in the past and warmer weather increases the growing season, makes plants grow faster, 