Rod Fujita, Ph.D., is a scientist in the Oceans program at Environmental Defense Fund.

Coral reefs aren't just pretty places for scuba divers (although they do bring in billions of tourist dollars). These rich ecosystems supply the inhabitants of coral reef countries with the fish that they depend on as their main source of protein. Coral reefs, like rainforests, are also treasure troves of biodiversity that may hold the keys to fighting diseases like cancer and arthritis. Human wellbeing is tightly bound to the health of coral reefs.

Unfortunately, coral reefs are in trouble, and climate change plays a major role.

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If you're an avid follower of the news, you may have heard of a company called Planktos that's trying to fight global warming and make a profit at the same time through a process called "ocean fertilization".

The concept is simple: phytoplankton (tiny one-celled algae) take up carbon dioxide (CO₂) during photosynthesis. Fertilizing the ocean encourages growth of phytoplankton, and increases the rate at which CO₂ is consumed - presumably leading to less CO₂ in the atmosphere. Since ocean photosynthesis is often limited by lack of iron, the idea is to dump iron into the ocean and watch the phytoplankton bloom. Planktos sees this as an economic opportunity: Increase CO₂ uptake in the ocean, and sell it as an offset to carbon emitters. (I talked more about how offsets work in a previous post on land-based offsets.)

Ocean fertilization may sound like a good idea, but it has some very serious problems. Here's why.

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The second installment of the IPCC's 4th Assessment on Climate Change, titled "Impacts, Adaptation and Vulnerability", will be released on April 6, 2007. In recognition of this report, I'm doing a weekly series called "Climate Dangers You May Not Know About".

1. More Acidic Oceans
2. Drinking Water and Disease
3. Shifts in Lifecycle Timing
4. Drought and Violence
5. Melting of the North Pole

Everyone knows that carbon dioxide (CO₂) warms the globe. But many people don't know about its other dangerous effect. The build-up of CO₂ is undermining ocean life through "ocean acidification". I'll start by explaining why our oceans are becoming more acidic, and then illustrate why this is so dangerous to ocean life and our entire food chain.

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Coral reef brilliance
Bleached white by loss of algae,
Killed by warming sea.

Left: Healthy corals (iStockphoto). Right: bleached corals (Ray Berkelsman, CRCReef, Townsville).