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Nature and Environment

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How Bad Is Climate Change for Coral Reefs?

coral reef

As ocean temperatures rise, coral reefs are vulnerable to bleaching: a whitening process brought on by the loss of algae in coral tissue. The relationship between the two is vital, because coral gets its nutrients from algae. Without algae, the coral loses its greenness and health, which leaves it vulnerable to diseases that could ultimately cause mass outbreaks among marine life.

Most of this is due to dropping pH, informally known as ocean acidification, which is caused by carbon dioxide — brought on by pollution and industrial waste in the atmosphere. As acidification takes its toll, calcification rates drop around coral environments.

The Effects of Emissions and Acidification

Since 1800, one-third of all CO2 emissions have been absorbed by ocean waters. A large percentage of this has stemmed from burning fossil fuel, of which half the emissions have dissolved into the sea. As the ocean's CO2 levels rise, its pH drops, which leads to acidification. When the water becomes acidified, corals are deprived of calcium carbonate, which is vital to their skeletons; without calcium, the skeletons dissolve.

Thus far, emissions have lowered the ocean's pH from 8.179 to 8.069 units. This marks a 30 percent jump in acidification since the mid-18th century. If emissions aren't drastically reduced, it's only a matter of time before the ocean's pH drops to devastating lows for all of the world's coral ecosystems.

Declining calcification levels not only impact corals but also clams, snails and urchins, who form cells via calcium carbonate. Acidification deprives these organisms of essential, shell-building calcium supplies.

Emissions at their current rate could spawn enough CO2 to lower the sea to a pH of 7.8 by the end of this century. At that level, the ocean might lose its coral reefs entirely, which would have a devastating impact on many surrounding organisms.

Severe Events of Coral Reef Bleaching

Throughout Polynesia, moderate bleaching is typical during warmer months. But over the last two decades, the problem has been on the rise. In the National Park of American Samoa, abnormal spikes in bleaching rates were observed during 1994, 2002 and 2004.   

In 2005, an unprecedented bleaching event devastated the reefs of the Caribbean. It all started with rising temperatures around the Antilles, which drifted south and turned half the coral white within a single year. Based on year-by-year satellite imagery from the preceding two decades, scientists determined that the damage from this event exceeded all that had occurred in the prior 20 years put together.

However, warm water isn't always the culprit. During the winter of 2010, an uncharacteristically low drop in ocean temperatures around the Florida Keys resulted in a major loss of coral life. Since then, researchers have studied the impacts of unusually cold, La Niña-like ocean temperatures on the accretion of reef layers.

In the Panama Pacific, researchers gathered 6,750-year old coral to determine whether past changes in climate were responsible for a 2,500-year halt in reef accretion. Extracting the oldest core corals within the reefs, they determined cooler oceans, stronger downpour, and greater upwelling were all factors in the region some 4,100 years ago, around the time when reef growth went into hiatus.

What Humans Can Do to Stop Warming Sea Temperatures

From now to the end of this century, emission levels could largely depend on population numbers, energy consumption, energy sources and the types of industries that humans rely on for products and transportation.

It starts with each individual, where the amount of energy that's used to heat a home or fuel a car will ultimately contribute to CO2 levels in the air. By driving fewer vehicles, using green energy, and keeping homes better insulated for less heating/cooling consumption, we as humans can do our part to halt global warming trends before they make our world an unlivable place for flora and fauna alike. 

Image by stevebidmead.

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