One of the lesser known and potentially catastrophic consequences of global warming is something called ocean acidification. Since the onset of the industrial revolution, acidity in the ocean has increased by about 30 percent. The problem is even more evident in some coastal areas. A researcher at St. Joseph's College in Standish is on the front lines of demonstrating how shellfish and other ocean life are being threatened.

Picture the ocean as a giant sponge that's been absorbing carbon dioxide from the burning of fossil fuels for more than 200 years. For a while, scientists thought it was a good thing that about half of all the world's CO2 was going into the ocean. They thought it might slow the rate of global warming. But there was another more menacing side effect.

"I think the changes are so clear and the evidence is so robust," says Dr. Mark Green. "I mean when you look at a photograph of a dissolving clam, it's hard to argue."

Dr. Green has been researching the effects of ocean acidification on oysters, soft and hard shell clams, bay scallops and mussels for the past 15 years. The problem for creatures with calcium carbonate shells is that CO2 is a soluable gas that produces carbonic acid when it mixes with water.

It's the reason mothers everywhere warn kids that drinking too much soda will dissolve their teeth. And now the ocean is having the same effect on clams because of a lower ph level. "We put about 21 million metric tons of CO2 into the ocean everyday," Green says. "One metric ton is equivalent to the weight of a small automobile so we're putting the weight of approximately 21 million small automobiles worth of CO2 into the ocean everyday."

Susan Sharon: "How do we know this? How do we measure it?"

Dr. Mark Green: "It's as simple as putting a ph electrode into the water. That's the thing. There's no real elaborate mathematical models. And we've lowered the ph on average globally less in some places, much more in others, but globally on average by about 0.1 ph units."

What does that mean to clams, mussels and oysters and the other sea creatures that depend on them for food?

"Essentially, right now we're trying to induce these oysters to spawn so we can grow the larvae." In a laboratory at St. Joseph's College in Standish, research assistant Lane Hubacz is helping Dr. Green study the effects of different ph levels on the larvae of shellfish -- how it affects their fertility and ultimately their survivorship.

"What we're mimicking are the ph's that we've seen in Casco Bay and some other places: Long Island Sound, Chesapeake Bay, Narragansett Bay, Boston Harbor. I've seen some ph's in Boston Harbor in the low sevens. At the end of the day it's all acid. In this particular case it's coming from decomposition of phytoplankton as opposed to fossil fuel burning."

Susan Sharon: "So when you say Boston Harbor has a seven what does that mean?"

Dr. Mark Green: "Well, I'll give you an example. There was a recent study -- someone looked at Sydney rock oysters and it had a ph of 7.6. They saw a 75 percent mortality relative to the control ph of 7.8 or 7.9, so huge increases in mortality with relatively small changes in ph."

As ph levels continue to drop, Dr. Green says there is the potential to lose shellfish species across the globe. In Maine, the clamming industry alone is worth about $21 million a year. But Dr. Green says the threat goes well beyond that when you consider that one-third of the world's fish live on or in coral reefs, which are already being threatened by ocean acidification.

"You want a sea full of jelly fish and it's green and soupy and it's not a very pleasant place to swim? That's what we're going to get and we're going get it sooner rather than later," Dr. Green says.

Lisa Suatoni, a senior scientist at the Natural Resources Defense Council agrees that time is running out. "Oceanographers have observed that the ocean is 30 percent more acidic now than it was during pre-industrial times, and the acidity is going to more than double by the end of the century if we continue to pollute as we are now."

Suatoni, who has been working on ocean acidification and climate change for two years, says capping CO2 emissions is the only way to curb the effects of ocean acidification. But she says reversing the damage that's already been done is another story.

"The changes in ocean acidification that we've already observed are going be here for thousands of years. It's reversible but only on time scales that humans don't really care about."

Suatoni says the high rate of acidity occurring in the ocean is greater than anything that's been seen in the last 65 million years. That gives plants and animals little time to adapt and evolve, which is one reason Dr. Green and his assistant will be experimenting with ways to buffer surface mud in Boston Harbor this summer to see if clams can survive acidity longer under certain conditions.