It's my impression that most people, even those fully convinced by the science of global climate change, picture the changes that are coming as being pretty gradual, and being such that we (even if only the "we" in high-tech Western countries that don't share borders with low-lying poor countries) will be able to adapt to them to some degree, whatever (nasty) pain they inflict. I've pretty much been thinking that way.
That is: we'll see hotter summers, changing rainfall patterns, more and more powerful storms (Minnesota beat Texas this year in number of tornadoes), beach erosion, and so on. Not to mention the social and political and military implications of climate refugees (the Pentagon is taking this very seriously). But, we think, life will go on, and the human race will survive -- even if life is a lot harder and there's a lot of suffering.
I am no longer so sanguine.
This Scientific American article, How Acidification Threatens Oceans from the Inside Out, is one of the scariest things I've ever read. (The full article is not available online; it's in the August 2010 issue.)
The oceans are getting more acidic due to dissolved carbon dioxide, which forms carbonic acid. (Dissolved carbon dioxide one of the main reasons that Coca-Cola has a pH around 3 in the can.) Not coincidentally, the oceans have been absorbing huge amounts of carbon dioxide from the air -- keeping the atmospheric CO2 levels from increasing even faster than they already are.
Ocean acidification is seriously problematic because most plants and animals in the ocean have evolved to live in a given range of acidity -- and changing that acidity can seriously mess up body chemistry. We're already seeing corals damaged by it, and experiments have shown that small shifts in acidity levels can have big effects on ocean life — reducing reproduction rates, impairing immune system function, and so on: even before acidity gets to the point of simply destroying life, cells and systems in oceanic life forms have to work harder to maintain their internal acidity levels, which takes more resources and impairs their ability to reproduce and thrive.
We're nearing the acidity range where we'll see serious impairment for a large range of sea life — and it might happen quickly, rather than gradually.
The REALLY scary thing about this is that if the acidity messes with phytoplankton (the source of half our atmospheric oxygen), then it's quite simply game over. We're not just talking about a lot of pain and suffering. We're not talking about merely the end of human civilization, or even the end of the human species: we're talking about the end of the biosphere as we know it. Game over, we took off and nuked it from orbit — but we forgot to take off first.
The thing about ocean acidification is that there's no wiggle room at all for global warming denialists. We've got the data on ocean acidity. We've got the experiments on various sea life and the effects of acidity change. There's no remediation possible — no giant space mirror or sulfur in the stratosphere is going to help this. (Sorry, Space Cadets.)
We simply have to lower (or eliminate) our carbon dioxide output. End of story — or end of us.