Two Bits of Good News on the Climate Front

by Bill Chameides | May 27th, 2009
posted by Erica Rowell (Editor)

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Coral reefs, an important part of the ocean’s ecosystem and regional economies, provide food and shelter to millions of species, including some 4,000 kinds of fish. Coral reefs face a number of threats, including global warming. But some can maybe adapt.

Some encouraging developments: lower carbon dioxide (CO2) emissions and a chance for coral reefs.

U.S. Emissions Decline in 2008

They say that every cloud has a silver lining. If true, then the bright spot for the economic downturn may prove to be a decline in emissions of greenhouse gases, the pollutants causing global warming. In a preliminary “flash estimate,” the U.S. Energy Information Administration reports that U.S. CO2 emissions did indeed fall in 2008 — by 2.8 percent, in large part as a result of a 6 percent drop in our petroleum use.

In the final analysis the severity of global warming will be determined not by the rate at which these gases are emitted but by the extra amount of pollution we add to the atmosphere. Emitting more now will mean having to emit less later on to avoid dangerous anthropogenic interference in the climate, and this in turn would mean having to cut emissions that much more quickly and radically later. On the other hand, emitting less now allows a little more wiggle room down the road, a little more time to get our act together and rein in greenhouse gas emissions.

How much extra wiggle room will the economic slowdown buy us? To begin to answer that, first we’ll need estimates for global emissions from last year, due out in November. And then of course there’s the emissions for 2009. So stay tuned.

Coral Reefs in American Samoa: Adaptive Little Critters

Coral reefs, a fundamental constituent of the ocean biota, are a complex ecosystem that serves as habitat and food for a wide array of marine life — some nine million species, to put a number on it. Unfortunately, a number of threats, from dredging and habitat loss to pollution and global warming, are putting these so-called rain forests of the seas at risk.

The past few decades have seen a collapse of one-fifth of the world’s coral reefs, and now scientists estimate 50-60 percent of those remaining are under threat.

Global warming is especially worrisome when it comes to the survival of coral reefs because it is, well… global. Plus, it packs a double-barreled threat:

Today we focus on coral bleaching.

High Temperatures Bleach Corals

Coral reefs are a microcosm of interdependent life forms, sometimes representing millennia of very slow growth (a width of a dime per year). Corals can live centuries on end. But despite such longevity, they are also extremely vulnerable to certain events.

The existence of a coral reef depends upon a symbiotic relationship between the reef and an algae called zooxanthella that lives on the reef’s surface. These algae give corals their coloring and provide their food. They use sunlight for photosynthesis and much of the biomass produced from the photosynthesis is transferred to the reef. However, the algae are highly sensitive to temperature; even a small rise in temperatures can kill the zooxanthelae, causing the coral to bleach and ultimately leading to the reef’s death.

Coral bleaching has become a major problem for much of the world’s oceans. For example, in 2005 unusually warm waters in the Caribbean (which is home to 10 some percent of the world’s reefs) resulted in an unprecedented level of bleaching events. Some 28 percent of observed coral cover in the U.S. Caribbean were at least partially bleached, a government-led study in December 2005 found. (Read more on the 2005 Caribbean bleaching event in this report [pdf]. See’s database of global bleaching events.)

Will Rising Temperatures Destroy All Coral Reefs?

There is some hope that at least some coral reefs may be able to survive rising temperatures. It turns out that certain reefs have a specific type of zooxanthella — Clade D Symbiodinium — which scientists call a “temperature specialist,” meaning that it is able to survive or adapt to varying temperatures.

In a new paper published in Marine Ecology Progress Series researchers Thomas A. Oliver and Stephen R. Palumbi of Stanford University confirm that coral reefs with these types of symbionts are anomalously plentiful in American Samoa. Ocean waters in Fiji, Palmyra Atoll, and the Philippines — the other areas the authors studied — were virtually bereft of the Clade D Symbiodinium. Why? We don’t yet know.

If the reasons for the coral-Clade D Symbiodinium pair prevalence in American Samoa can be elucidated, perhaps this strain can be propagated to other regions of the ocean. Or, if such “engineering” is deemed inadvisable, the Oliver-Palumbi study suggests that we have identified a marine area that can serve “as resilient ‘fortresses of diversity’ around which to build [a] conservation strategy.” And, in a perhaps prescient moment, Congress has already helped in constructing such a fortress: in 1988 it established the National Park of American Samoa.

Will this temperature resistance prove to be enough to keep coral reefs alive in the face of the twin threats of global warming and ocean acidification? Stay tuned.

filed under: carbon dioxide emissions, climate change, coral reefs, faculty, global warming, oceans, science
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