For tens of millions of years, Earth’s oceans have maintained a relatively stable acidity level. It’s within this steady environment that the rich and varied web of life in today’s seas has arisen and flourished. But research shows that this ancient balance is being undone by a recent and rapid drop in surface pH that could have devastating global consequences.
Since the beginning of the industrial revolution in the early 1800s, fossil fuel-powered machines have driven an unprecedented burst of human industry and advancement. The unfortunate consequence, however, has been the emission of billions of tons of carbon dioxide (CO2) and other greenhouse gases into Earth’s atmosphere.
Scientists now know that about half of this anthropogenic, or man-made, CO2 has been absorbed over time by the oceans. This has benefited us by slowing the climate change these emissions would have instigated if they had remained in the air. But relatively new research is finding that the introduction of massive amounts of CO2 into the seas is altering water chemistry and affecting the life cycles of many marine organisms, particularly those at the lower end of the food chain.
When carbon dioxide dissolves in this ocean, carbonic acid is formed. This leads to higher acidity, mainly near the surface, which has been proven to inhibit shell growth in marine animals and is suspected as a cause of reproductive disorders in some fish.
On the pH scale, which runs from 0 to 14, solutions with low numbers are considered acidic and those with higher numbers are basic. Seven is neutral. Over the past 300 million years, ocean pH has been slightly basic, averaging about 8.2. Today, it is around 8.1, a drop of 0.1 pH units, representing a 25-percent increase in acidity over the past two centuries.
Since the start of the industrial revolution, enough fossil fuels—coal, oil, and natural gas—have been burned and enough forests cut down to emit more than 500 billion tons of CO2. As is well known, the atmosphere has a higher concentration of CO2 today than at any point in the past 800,000 years and probably a lot longer.
What is less well known is how carbon emissions are changing the oceans too. The air and the water constantly exchange gases, so a portion of anything emitted into the atmosphere eventually ends up in the sea. Winds quickly mix it into the top few hundred feet, and over centuries currents spread it through the ocean depths. In the 1990s an international team of scientists undertook a massive research project that involved collecting and analyzing more than 77,000 seawater samples from different depths and locations around the world. The work took 15 years. It showed that the oceans have absorbed 30 percent of the CO2 released by humans over the past two centuries. They continue to absorb roughly a million tons every hour.
For life on land this process is a boon; every ton of CO2 the oceans remove from the atmosphere is a ton that’s not contributing to global warming. But for life in the sea the picture looks different. The head of the National Oceanic and Atmospheric Administration, Jane Lubchenco, a marine ecologist, has called ocean acidification global warming’s “equally evil twin.”
The pH scale, which measures acidity in terms of the concentration of hydrogen ions, runs from zero to 14. At the low end of the scale are strong acids, such as hydrochloric acid, that release hydrogen readily (more readily than carbonic acid does). At the high end are strong bases such as lye. Pure, distilled water has a pH of 7, which is neutral. Seawater should be slightly basic, with a pH around 8.2 near the sea surface. So far CO2 emissions have reduced the pH there by about 0.1. Like the Richter scale, the pH scale is logarithmic, so even small numerical changes represent large effects. A pH drop of 0.1 means the water has become 30 percent more acidic. If present trends continue, surface pH will drop to around 7.8 by 2100. At that point the water will be 150 percent more acidic than it was in 1800.
The acidification that has occurred so far is probably irreversible. Although in theory it’s possible to add chemicals to the sea to counter the effects of the extra CO2, as a practical matter, the volumes involved would be staggering; it would take at least two tons of lime, for example, to offset a single ton of carbon dioxide, and the world now emits more than 30 billion tons of CO2 each year. Meanwhile, natural processes that could counter acidification—such as the weathering of rocks on land—operate far too slowly to make a difference on a human time-scale. Even if CO2 emissions were somehow to cease today, it would take tens of thousands of years for ocean chemistry to return to its pre-industrial condition.
Acidification has myriad effects. By favoring some marine microbes over others, it is likely to alter the availability of key nutrients like iron and nitrogen. For similar reasons it may let more sunlight penetrate the sea surface. By changing the basic chemistry of seawater, acidification is also expected to reduce the water’s ability to absorb and muffle low-frequency sound by up to 40 percent, making some parts of the ocean noisier. Finally, acidification interferes with reproduction in some species and with the ability of others—the so-called calcifiers—to form shells and stony skeletons of calcium carbonate. These last effects are the best documented ones, but whether they will prove the most significant in the long run is unclear.
In 2008 a group of more than 150 leading researchers issued a declaration stating that they were “deeply concerned by recent, rapid changes in ocean chemistry,” which could within decades “severely affect marine organisms, food webs, biodiversity, and fisheries.” Warm-water coral reefs are the prime worry. But because carbon dioxide dissolves more readily in cold water, the impact may actually show up first closer to the Poles. Scientists have already documented significant effects on pteropods—tiny swimming snails that are an important food for fish, whales, and birds in both the Arctic and the Antarctic. Experiments show that pteropod shells grow more slowly in acidified seawater.
Will organisms be able to adapt to the new ocean chemistry? The evidence from Castello Aragonese is not encouraging. The volcanic vents have been pouring CO2 into the water for at least a thousand years, Hall-Spencer told me when I visited. But the area where the pH is 7.8—the level that may be reached oceanwide by the end of the century—is missing nearly a third of the species that live nearby, outside the vent system. Those species have had “generations on generations to adapt to these conditions,” Hall-Spencer said, “yet they’re not there.
“Because it’s so important, we humans put a lot of energy into making sure that the pH of our blood is constant,” he went on. “But some of these lower organisms, they don’t have the physiology to do that. They’ve just got to tolerate what’s happening outside. And so they get pushed beyond their limits.”
The oceans currently absorb about a third of human-created CO2 emissions, roughly 22 million tons a day. Projections based on these numbers show that by the end of this century, continued emissions could reduce ocean pH by another 0.5 units. Shell-forming animals including corals, oysters, shrimp, lobster, many planktonic organisms, and even some fish species could be gravely affected.
Equally worrisome is the fact that as the oceans continue to absorb more CO2, their capacity as a carbon storehouse could diminish. That means more of the carbon dioxide we emit will remain in the atmosphere, further aggravating global climate change.
Scientific awareness of ocean acidification is relatively recent, and researchers are just beginning to study its effects on marine ecosystems. But all signs indicate that unless humans are able to control and eventually eliminate our fossil fuel emissions, ocean organisms will find themselves under increasing pressure to adapt to their habitat’s changing chemistry or perish
We the human made those mistakes..as this day is INTERNATIONAL COASTAL CLEANUP DAY
we may wake and have our sorounding clean and responsible for our ,other organisms livees too…..
Save The Sea Save The Life