How Does Global Warming Affect the Coral Reefs?

Coral reefs do much more than exude beauty. They provide a perfect biome for numerous undersea flora and fauna. They serve as barriers to protect shorelines from the ravages of hurricanes and other tempests. As a refuge for spawning fish, they also attract tourists and sightseers interested in the multiple species that visit these ridges. Distressingly, the health and survival of coral reefs is threatened by the adverse effects of climate change. The good news is that things can improve. But how does global warming affect the coral reefs?

1. Higher Ocean Temperatures

surface water temperatures

Image Source: NASA Visible Earth

Although such polyp ridges do best in warmer waters, there is such a thing as too warm. Under normal conditions, 84˚F is the high end of their comfort zone. Granted, they can endure for a season in higher temperatures but – over time – their endurance will run out.

Due to global warming, the seas covering the Great Barrier Reef off of Australia are so consistently heated as to cause coral bleaching. This occurs when the specific algae upon which the coral depends for life is expelled from the heated reef. Before it dies, the coral loses its color, hence the “bleaching.”While it might recover from this condition, continued high temperatures make that unlikely.

2. Rising Sea Levels

The answer to “How does global warming affect the coral reefs?” is vividly demonstrated by rising sea levels. As they ascend, tides encroach deeper into the coastline. In so doing they draw sand and other sediment back into the ocean. The first recipients of this action are coral reefs.

For one thing, suspended sediment obstructs light required for photosynthesis. Once settled, these dregs can bury coral, which must then exhaust energy to cleanse its surfaces. In this way, sediment is dangerous to the reefs and climate change promotes more sediment. Scientists have discovered that this trend is prominent among the reefs off the coast of Maui, Hawai’i. Even nominal sea level rises produce this effect.

3. Longer Growing Seasons

Change in the Growing Season

Image Source: Climate Central

Many among those who see less danger in climate change celebrate the prospect of longer growing seasons. More abundant food means less expensive food. That should boost the quality of life. What, though, are the unseen consequences of something so seemingly beneficial? Again, we will see an increase in sediment.

The United Nations Food and Agriculture Organization (FAO) determines that eroded farm soil (plus any chemicals it contains) can travel over 100 miles as runoff. It further contends that nearly all the reefs off Asia and Central America suffer from excess sediment. In fact, the FAO estimates that up to 70 percent of fringing reefs globally have this affliction. Longer seasons and higher yields suggest more plowing and soil impaction. More sediment will be the inevitable result.

4. Increased Storm Activity

As noted, coral reefs are a natural barricade between beaches and the violence of storms. This, however, does not imply that they are storm-proof. The third largest barrier reef in the world sits off of the coast of Florida. Some category four and five tropical storms have pulverized coral reefs, particularly those closest to the shore. Others farther out lose significant amounts of hard coral cover from their ridges.

The unhappy consequence is that the reefs lose their ability to lessen shore damage and flooding. As climate scientists find greater correlation between climate change and storm intensity, the question of “How does global warming affect the coral reefs?” becomes ever more urgent.

5. Greater Precipitation

Greater precipitation now compared to 1958.

Increases in the amount falling in the heaviest 1% of daily precipitation events (1958 to 2012).
Image Source: GLISA – University of Michigan

Coral reefs form because of a perfect confluence of factors. One such variable is salinity, i.e. the amount of salt in a measure of water. Coral generally needs a salinity range between 32 and 40 practical salinity units. Trouble arises when precipitation increases because the salt is further diluted, making the environment less suitable for healthy polyps.

How does global warming affect the coral reefs? According to the National Aeronautic and Space Administration (NASA), global warming causes a higher degree of evaporation. This, in turn, ups the amount of precipitation where it is common, as in tropical areas where coral reefs live. The salinity can then drop to unhealthy concentrations.

6. Volatile Ocean Currents

Of course, coral lacks the power of locomotion, and must therefore depend on ocean currents to deliver its nutrients and distribute its larvae to other places. Needing just the right nutrition to build its constituent calcium carbonate, coral receives its food when tides and currents are optimal, never exposing it to air. Yet climate change can throw a wrench into the tidal works.

How does global warming affect the coral reefs? Freshwater runoff from melting ice and snow can interrupt the oceanic “conveyor belt” that distributes heat from the equator to the poles. Should the normal pace of circulation slow, the coral reefs may be deprived of their building blocks.

7. Higher Acidity

Coral reef affected by global warming

Image Source: Shutterstock

Among the most serious answers to the question, “How does global warming affect the coral reefs?”, is the acidification of the seawater. The chemical yield from carbon dioxide (CO2) and the ocean is carbonic acid. This compound impedes the production of calcium carbonate – the very building block of the coral exoskeleton. Decay can then set in.

If the tempo of erosion outpaces that of its accretion, the protective shell of the coral is compromised and it becomes more subject to damage. As CO2 builds in the atmosphere, a corresponding acidification of the oceans follows. This is how climate change poses a serious hazard to the well-being and benefits of coral reefs.

Summing Up

Why are coral reefs dying? Is it all about global warming? Clearly, reducing the presence of greenhouse gases in the atmosphere will ultimately aid in the recovery of coral reefs. Energy conservation, renewable fuels and clean-burning technologies are a positive start.

While some threats to the reefs are unrelated to climate change, those that are rooted in global warming should be treated with the utmost urgency. The climate-induced weakness of these ecosystems makes them vulnerable to other dangers.

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