- There is wide agreement that human activity is changing the Earth's climate.
- The wide variety of human activity means there are many effects.
- Some of activities have confounding results.
Global Warming (greenhouse effect)
- An increase in a natural warming process caused by the atmosphere absorbing heat from the Earth's surface.
- An analogy is drawn to the warming of a greenhouse in sunlight.
- Gases that create this effect include H2O vapor, CO2, and methane (CH4).
- Human activity will double CO2 by 2060 due to burning of fossil fuels and deforestation.
- Humans also are increasing the levels of other greenhouse gases.
- The anticipated effect will be warmer global temperatures.
- Climate models and evidence from earlier shifts in the planet's climate suggest that a wide range of possibilities exist (including episodes of widespread cooling and glaciation).
- Ocean temperatures are also rising.
- Dust from desertification and SO2 reduce the amount of sunlight hitting the Earth's surface. This may reduce global warming.
Ozone is a form of oxygen (O3)
- O3 absorbs dangerous ultraviolet (UV) rays from the sun.
- UV can break the bonds in DNA. O3 protects life on Earth.
- There is a thin layer of ozone in the lower stratosphere (17 km - 25 km).
- At ground level, ozone is a pollutant that causes lung irritation.
- Were used in refrigerators, air conditioning, aerosol propellants, plastic foam packing materials and a variety of industrial applications.
- Released at the Earth's surface, CFCs migrate to the stratosphere where UV light releases the chlorine atoms.
- Chlorine acts as a catalyst that turns O3 back into O2. One chlorine atom can destroy over 100,000 ozone molecules.
- CFCs released already will continue to act on the ozone levels for approx. 50 years.
- There has been a 50% thinning of the ozone layer in the stratosphere around the poles.
- Over the U.S., ozone levels have fallen 5-10%.
- The Montreal Protocol of 1989 was a treaty to eliminate the use of CFCs by 1996.
Evidence from glacial ice cores indicate that the climate of the last 10,000 years has been more moderate than previous millennia.