Weatherdem's Weblog

Bridging climate science, citizens, and policy

Ocean Acidification: 100X Faster Than Last Similar Event

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Last week, I wrote about a study that had found warmer waters reaching the glaciers of Greenland, helping to melt those glaciers from below while warm temperatures melt them from above.  This scenario presents numerous dangers for societies around the world.  Faster melting glaciers means faster rising sea levels, which means more impacts sooner.

Today, I will write about a scenario that is potentially more threatening than glaciers melting faster than expected.  New research demonstrates that the oceans are acidifying more quickly than has happened naturally for tens of millions of years.  The threat that presents is when the last similar acidification event occurred, upwards of 50% of marine life went extinct.  It took hundreds of thousands to millions of years to recover from this catastrophe.  It is known as the Paleocene–Eocene Thermal Maximum, or PETM, and it happened 55 million years ago.  The event saw global temperatures rise by around 6°C (11°F) over 20,000 years, with a corresponding rise in sea level as the whole of the oceans warmed.  To put that warming in context, climatologists are warning that global temperatures could rise by a similar amount over ~200 years.  That’s 100 times faster than the last rapid global warming event of similar magnitude.

Under natural conditions, CO2 is removed from the atmosphere by being absorbed into the oceans.  This occurs chemically: hydrogen ions are generated as carbon dioxide dissolves in water.  The more hydrogen ions there are, the more acidic the water becomes.  This process is regulated by minerals being carried from land to the ocean.    One mineral in particular is critical for small kinds of marine life: calcium carbonate.  Marine organisms, mollusks and arthropods for example, use calcium carbonate in the water to build their shells.  When the concentration of hydrogen ions increase, shelled animals in the ocean have a harder time building their shells.  At first, shells get thinner.  Eventually, the shells cost too much to make and the animal dies.  On a large enough scale, this means the extinction of those animals.  Again, under natural conditions, increased CO2 in the atmosphere occurs over a long enough time period that the warming it causes also causes increased precipitation over land.  That increased precipitation offsets the acidifying ocean by transporting more calcium carbonate to the oceans.  Marine life is largely able to make it through the warmer, more acidified oceans.

Since the beginning of the Industrial Revolution, the acidity of the ocean, as measured by the pH scale, has increased for surface water by 30%; from 8.179 to 8.104.  Now, that might not seem like much.  But it’s a large enough change over a short enough time period that serious concern about the future acidity of the ocean exists.  That’s because by 2050, the pH could be 7.949 and by 2100, it could be 7.824.  I’ll remind the reader that these estimates are based on slightly older research and that more rapid changes aren’t unrealistic.  Even so, such an increase is 10 times faster than the PETM event.

It should be obvious that marine life isn’t used to these potentially rapid shifts in ocean acidity.  Evolution of these complex life forms takes place over millenia, not decades.  Even if oceans acidify at rates that are ‘only’ a fraction of what they have exhibited in the past 300 years, enormous pressure will still be placed on untold numbers of oceanic animals.  We simply don’t have any event in Earth’s history that comes close to the forcing that we’re exerting on the planet’s systems.  Similar but slower events in the geologic past all point to massive changes in ecosystems in response to rapid climate forcings.

We can choose to either slow down and halt our forcing by reducing greenhouse gas pollution and minimize the effects on ecosystems or we can choose to keep polluting and see how far we can push natural systems before they break.

Cross-posted at SquareState.


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