intensity and volcanic activity are relevant to current century
time scales.
To understand climate change and the controversy
surrounding this issue, we need to distinguish between climate
change and global warming trends brought on by the
greenhouse effect. Climate change refers to a long-term shift in
weather conditions, and includes average and extreme
conditions that can be the result of natural or human activity.
Global warming is attributed to the intensifying natural
greenhouse effect. The greenhouse effect is naturally
occurring, where certain gases in the atmosphere allow
sunlight to enter while absorbing heat to keep the Earth’s
temperature at approximately 15 degrees Celsius (59 degrees
F). The main greenhouse gases consist of water vapor, carbon
dioxide, methane, nitrous oxide and chlorofluorocarbons.
Without the natural greenhouse effect, the earth’s temperature
would be at about -18 degrees Celsius (0 degrees F). This
would be a far more extreme environment for many species to
survive on earth. However, what scientists have found over the
past several decades concerning climate change is that it is a
warming trend, and not just a warming cycle, which varies
from year to year and decade to decade. Natural climate