Humans rely heavily on fossil fuels in this industrial age.

In a similar fashion, humans now live upon the resource of dead organic matter. We've found our dead whale below ground, in the form of oil, gas and coal -- the fossil remains of plants that lived long ago.

Our atmosphere is small in mass, so changes to it are serious.

• Prior to the advent of the industrial age, the concentration of CO₂ in the atmosphere was about 280 ppm (parts per million).
• Today it's over 360 ppm. That's an increase of about 30% in less than 300 years.

• Coming to earth from the sun, visible radiation passes through the clear atmosphere and hits the earth.
• A portion of it is absorbed and re-radiated back to space as IR.
• CO₂ traps this IR and reflects it back to the earth's surface, causing further warming. 

The heat on Earth would be unbearable with too much greenhouse effect.

To illustrate the greenhouse effect, consider a car with the windows rolled up:

• The sun's rays pass through the car's windows (visible light), and hit the car's seats.
• There the visible light is absorbed, and re-radiated to the interior of the car as IR.
• But the car's glass windows, while transparent to visible light, are opaque to IR, so the heat is trapped within the car, and the car's interior temperature becomes unbearable. 

So that's why many scientists think that increasing the amount of CO₂ in the air may well cause the earth to get warmer.

Global sea level rise is caused by two factors. One is the delivery of water to the ocean as land ice melts, such as mountain glaciers and polar icecaps. Current evidence of global warming includes the widespread retreat of glaciers on 5 continents. For example:

• The ice cap on Mount Kilimanjaro may be gone in 20 years. About 1/3 of Kilimanjaro's ice field has disappeared in the last 12 years and 82% of it has vanished since it was first mapped in 1912.
• Sea ice in the Arctic Ocean is thinning.
• Massive Antarctic ice sheets have collapsed into the sea with alarming rapidity.

The 20th century has seen a dramatic rise in sea levels.

Since the end of the last ice age, 18,000 years ago, sea level has risen by over 120 meters.

• Geological data suggests that global average sea level may have risen at an average rate of 0.1 to 0.2 mm/yr over the last 3000 years.
• However, tide gauge data indicate that the global rate of sea level rise during the 20th century was 1 to 2 mm/yr.

• Along the marshy Gulf Coast of Florida, the effects of sea level rise can be observed in the number of dead cabbage palms at the seaward edge of the salt marsh.
• Along the Atlantic Coast of the USA, erosion is narrowing beaches and washing out vacation houses. As sea level rises and coastal communities continue to grow and pump water from aquifers, salt water intrusion into groundwater will become a greater problem.

• Tuvalu comprises nine coral atolls between Australia and Hawaii. Their highest point is 5 meters (15 feet) above seal level. As sea level has risen, Tuvalu has experienced lowland flooding. Saltwater intrusion is adversely affecting drinking water and food production. Tuvalu's leaders predict that the nation will be submerged in 50 years. In March 2002, the country's prime minister appealed to Australia and New Zealand to provide homes for his people if his country is washed away, but the plight of this nation is being ignored.
• Other threatened island nations include the Cook Islands and the Marshall Islands. During the last decade, the island of Majuro (Marshall Islands) has lost up to 20 per cent of its beachfront.

Current rate of fossil fuel consumption indicates that the carbon dioxide content of the air will double by 2100.

• This doubling will enhance the greenhouse effect and result in a 1 to 5 degree Centigrade increase in global temperature. 
• Land areas will warm more rapidly than the global average as the temperature of oceanic areas will be moderated by the heat capacity of water. 
• Warming will also be greatest at higher latitudes, for in the past, climate change has affected the earth's polar regions to the greatest extent. 
• Humidity effects, included in the heat index, will exacerbate warming effects.

Ecosystems
Warming trends will change the distribution of trees and other native plants, altering animal habitat. Models predict the northward retreat of temperate tree species and the northward advancement of tropical and subtropical species. But individual species will respond differently to climate change. Communities of species will not simply march back and forth, chasing the ice caps. Normal associations of plants and animals may be disrupted. Human barriers such as motorway corridors may present significant obstacles for migrating native species to jump, allowing the spread and dominance of weedy and exotic plants.

There is no immediate fix to the problem other than to curtail our use of fossil energy. As individuals we can help in the short term:

• We need to drive smaller vehicles and heat and cool our buildings more moderately.
• Carbon dioxide emissions can be reduced if consumers purchase more energy-efficient appliances, such as new refrigerators.
• Compact fluorescent light bulbs save tremendous amounts of fuel.

But in the long term, we need to extract energy more efficiently from fossil fuels and to develop alternative energy sources that do not lead to the production of greenhouse gases. By doubling the concentration of atmospheric CO₂, we are conducting a planetary wager -- one we can't afford to lose.

A view of the Earth from space. What shape does it look like to you? Click on image for full size ( 378K GIF) Image courtesy of NASA

Earth may look perfectly spherical from space, like a giant marble, but it actually isn't! Since the first satellites were launched, scientists realized that Earth is not a sphere. Instead, our planet is wider around the equator because matter is forced out as Earth spins (just as you feel you are pushed right when your car turns fast to the left). However, Earth doesn't stay the same, and scientists have been tracking some interesting changes in our planet's shape.

Standing on Earth's surface can not see the small changes in Earth's shape but researchers have been watching the equator shrink slowly over the past few decades with satellites, a process that they believe has been going on since the last ice age 18,000 years ago. Since the ice age, glaciers at the poles have been melting slowly as global temperatures warm, allowing magma under Earth's crust to move towards the poles once the heavy weight of ice was no longer squashing them. This allowed the equator to shrink as the molten rock (magma) moved away.

For the past four years, however, Earth has been doing something quite different. Researchers at Raytheon and NASA's Goddard Space Flight Center have been watching the equator grow larger. Since we know that glaciers are still melting at the poles, scientists are puzzled why the process would change.

For Earth's equator to increase in size, material must have been moved from somewhere else on the planet. One hypothesis is that molten rock has been moving within the Earth to below the equator. This may have been caused by the brief reversal of the Earth's magnetic field that occurred in 1999, which happens about once every 10 years. One of these reversals may have caused changes in the circulation of magma in the Earth's interior.

Another hypothesis is that there is more ocean water piling up at the equator. As the polar ice caps melt, they add more water into the oceans, which will move with the ocean currents towards the equator.

Whatever the reason, the researchers believe that this change in the shape of Earth is the result of long-term natural variations, and is not anything that humans have done to the planet.