Evidence for Global Warming:
Degradation of Earth's Atmosphere; Sealevel Rise; Ozone Holes; Vegetation Response

"Global change". "Greenhouse effect". "Global warming". The media are full of statements, concerns, guesses, and speculation about these phenomena, as scientists and policy-makers around the world struggle to address recent scientific observations that indicate human activities impact our environment. And yet, each of these is a "natural" phenomenon, as are many others. Hurricanes, droughts, and monsoons all occur without any control by humans, to initiate, forestall or moderate them.

We can learn about our planet's interacting physical systems by observing the results of such natural phenomena, and use our knowledge to explore human-induced changes. Consider, for example, the eruption of a volcano, such as Mount Pinatubo in the Philippine Islands in 1991, that happened without human intervention. This volcano had been dormant for more than 600 years.

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Remember, people in 1900 didn't know what an atom was. They didn't know its structure. They also didn't know what a radio was, or an airport, or a movie, or a television, or a computer, or a cell phone, or a jet, an antibiotic, a rocket, a satellite, an MRI, ICU, IUD, IBM, IRA, ERA, EEG, EPA, IRS, DOD, PCP, HTML, internet. interferon, instant replay, remote sensing, remote control, speed dialing, gene therapy, gene splicing, genes, spot welding, heat-seeking, bipolar, prozac, leotards, lap dancing, email, tape recorder, CDs, airbags, plastic explosive, plastic, robots, cars, liposuction, transduction, superconduction, dish antennas, step aerobics, smoothies, twelve-step, ultrasound, nylon, rayon, teflon, fiber optics, carpal tunnel, laser surgery, laparoscopy, corneal transplant, kidney transplant, AIDS\ufffd None of this would have meant anything to a person in the year 1900. They wouldn't know what you are talking about.

Global warming 101

PAUL SOLMAN: Now, Wally Broecker could be wrong, but given the costs if he's right, let's suspend skepticism for the next 10 minutes or so and consider the origin of the greenhouse gases that may be warming the globe and what we might do about them.

First, where do the gases come from? Mainly, it turns out, from the carbon stored up in plants long, long ago.

You may or may not remember from high school biology that plants are fueled by photosynthesis, combining water and carbon dioxide with the help of sunlight.

ROBERT ELDE, University of Minnesota: It's a mixture of coal from Wyoming...

PAUL SOLMAN: So says Professor Bob Elde at the University of Minnesota's power plant.

ROBERT ELDE: The carbon that was captured by photosynthesis and is included in the coal was carbon that was in the atmosphere 100, 200 million years ago.

PAUL SOLMAN: So this is former plants?

ROBERT ELDE: Plant material, that's right.

PAUL SOLMAN: Compressed over the eons, fossilized into coal or oil. That's the simple chemistry behind global warming.

There's no more carbon on Earth than ever before; it's just that much of the carbon absorbed by plants over those eons was easy for humans to dig up and burn above ground to produce energy.

Unfortunately, the burning of carbon, C, combines it with oxygen, O, which resulted in, yes, CO-2, the greenhouse gas carbon dioxide. So, the carbon that it took nature millions of years to bury is resurfacing a lot faster.

Volcanoes release more than 130 million tonnes of CO2 into the atmosphere every year.