Global warming, or climate change, is a subject that shows no signs of cooling down.

Here's the scoop on why it's happening, what's causing it, and how it might change our planet.

Is it happening?

Yes! The earth is already showing many signs of worldwide climate change:

• Average temperatures around the world have climbed 1.4 degrees Fahrenheit (0.8 degree Celsius) since 1880.
• The 80s and 90s were the hottest in 400 years, and 11 of the past 12 years are among the dozen warmest since 1850.
• Arctic ice is rapidly disappearing, and glaciers and mountain snows are quickly melting. For example, Montana's Glacier National Park now has only 27 glaciers, compared to 150 in 1910, only 98 years ago.
• Coral reefs, which are highly sensitive to small changes in water temperature, suffered the worst die-off in response to stress ever recorded in 1998. Experts expect these sorts of events to increase in frequency and intensity in the next 50 years as sea temperatures rise.
• A dramatic upsurge in the amount of extreme weather events, such as wildfires, heat waves, and strong tropical storms (remember Katrina?), is attributed in part to climate change.

Are humans causing it?

"Very likely," said the UN Intergovernmental Panel on Climate Change (IPCC) in a February 2007 report based on the work of 2500 scientists in more than 130 countries.

• Industrialization, deforestation, and pollution have greatly increased atmospheric concentrations of water vapor, carbon dioxide, methane and nitrous oxide, all greenhouse gases that help trap heat near the Earth's surface.
• Some point out that the earth naturally experiences warming and cooling cycles, but such changes occur over the span of several centuries. What's worrisome now is that today's changes have taken place ove rthe past hundred years of less!

What's going to happen?

A follow-up report by the IPCC released in April 2007 warned that global warming could lead to large-scale food and water shortages and have catastrophic effects on wildlife.

• The sea level could rise between 7 and 23 inches by the end of the century. This would effect most of us since much of the world's population is concentrated in vulerable coastal cities. In the United States, Lousiana and Florida are especially at risk.
• Glaciers around the world could melt, causing sea levels to rise while creating water shortages in regions that depend on runoff for fresh water.
• Strong hurricanes, droughts, heat waves, wildfires, and other natural disasters may become commonplace in many parts of the world. The growth of deserts may also cause food shortages and famine in many places.
• More than a million species face extinction from disappearing habitat, changing ecosystems, and acidifying oceans.
• The ocean's circulation system, known as the ocean conveyor belt, could be permanently altered. This could cause rapid changes around the world, including a mini-ice age in Western Europe.
• At some point in the future, warming could become uncontrollable. Rising temperatures could release additional greenhouse gases by unlocking methane in permafrost (soil at or below the freezing point of water) and undersea deposits, freeing carbon trapped in sea ice, and causing increased evaporation of water.

Sources:
National Geographic
Environmental Defense Fund
Stop Global Warming