In my last column, I discussed the confusion around the terms "global warming" and "climate change:" Global warming, the change in average surface temperature, is just one aspect of the major change in Earth's climate caused (according to the best science available) by our reckless burning of fossil fuels.

When coal, natural gas and oil burn, carbon dioxide is the major by-product. The level of CO2 in the atmosphere increased by 24 percent from 1958 to 2013, when it hit 400 parts per million for the first time in recorded history. Although global warming is stressing Earth's terrestrial flora and fauna, ocean acidification, its "evil twin," may have even direr consequences. See the PBS documentary Lethal Seas for a harrowing look.

About 60 percent of fossil-fuel emissions stay in the atmosphere, while the planet's oceans absorb most of the rest — about 30 million metric tons every day — creating weak carbonic acid in the process. Average ocean acidity is currently increasing by about 5 percent every decade, with potentially catastrophic results for sea life. Particularly hard hit are marine ecosystems in the chilly waters of the Arctic and Antarctic oceans, because cold water absorbs more CO2 than warm water.

Pteropod, or "winged-foot," is the rather imprecise name given to a group of marine animals, one clade of which (commonly called the "sea butterfly") is a tiny shelled creature living at the bottom of the food chain in the polar oceans. Like all shelled animals (including our local oysters), sea butterflies manufacture their shells by calcification, combining natural calcium and carbonate ions to form calcium carbonate in the form of aragonite or calcite.

Due to increasing ocean acidity, the future of these pteropods is under threat: The more acidic the water, the fewer carbonate ions are available. A recent survey in Antarctica found a 35-percent loss in pteropod shell thickness compared to just a decade ago. As a result, pteropod populations are starting to fall, with consequent effects up the food chain. Marine scientists worry that we may soon be faced with a massive decline in the numbers of cold water fish and marine mammals in high latitudes.

We have at least one precedent for rapid acidification of our oceans. Some 250 million years ago, the end of the Permian era arrived suddenly and decisively in what geologists sometimes call "The Great Dying," when more than 90 percent of marine life disappeared from the fossil record. Most researchers put the blame for this mass extinction on a spike in volcanic activity which sent vast clouds of acidic dust and aerosols in the atmosphere. Falling into the oceans, the debris would have raised the acidity of the water, resulting in global extinctions of sea life. Sound familiar?

Even if all nations, particularly the ones like ours that are most responsible for CO2 emissions, were to take immediate draconian steps to reduce them, the long-term effects are irreversible. If tomorrow we completely stopped venting greenhouse gases into the atmosphere, Earth would continue to warm (another one degree F by 2100). While we can never completely undo the damage already done, a critical first step would be to take the consensus scientific predictions seriously and act decisively so that our children aren't left wondering how we could have been so willfully blind for so long.

Barry Evans ([email protected]) believes that, long term, acidification of Earth's oceans will be a greater catastrophe than global warming.