Anyone who has followed the evolution of global warming as a media topic over the past two decades is familiar with the story of low-lying island nations as being the most vulnerable to the anticipated sea-level rise and stormy weather predicted to accompany the "greenhouse effect." It makes a good story – island nations, with their small populations and low emissions of greenhouse gases, are the least at fault for global warming and the least able to do anything about it. Yet, they are the nations most at risk, with the fewest options for mitigation.
The First National Communication on Climate Change, submitted to the UN by the BEST Commission, describes the Bahamas as lacking "any real adaptation options other than abandonment, retreat, or accommodation to climate change." The document drives home its woe-is-us view with pictures of beached boats, ruined houses, and eroded shorelines. The BEST Commission avoids making the obvious recommendation, which is that the Bahamas should use moral suasion to shame industrial nations into reducing their greenhouse gas emissions, since the nation can't really do anything else. Instead the Commission recommends more scientific studies, and better computers for its staff.
But what if the Bahamas could significantly impact global warming? What if, better yet, it could be paid to do so? This article examines the possibilities.
The Global Carbon Cycle
First, a brief overview of the global carbon cycle, which controls atmospheric carbon dioxide (CO2), a major greenhouse gas. CO2 occurs naturally in the atmosphere and is essential to life. It is absorbed by plant photosynthesis, and emitted by animal respiration. As a greenhouse gas it traps heat from the sun. In the last 300 years atmospheric CO2 concentrations have increased from 278 to 381 parts per million due to human activity. This is projected to increase global temperatures, raising sea levels as polar ice caps melt and perhaps spawning more intense hurricanes.
The amounts of carbon involved are not small – the usual unit of measure is the gigatonne, one billion metric tonnes of carbon or GtC. Human activity releases about 8.5GtC into the atmosphere each year. About 75% of this is due to burning of fossil fuels – oil, coal, and natural gas. Most of the rest comes from CO2 released as land is cleared for agriculture or settlement. These "sources" of carbon are partly offset by natural "sinks" which increase their uptake of CO2 in response to higher atmospheric CO2 levels. Due to these sinks, only 3.2GtC of the total 8.5GtC human emissions accumulates in the atmosphere each year. The most important carbon sink is the ocean, absorbing 2.4GtC annually above its pre-industrial amount. Another 2.9GtC is absorbed annually by "missing sinks" which are thought to be natural biologic and geologic processes that help keep the earth's carbon budget in balance.
The Bahamas may contain one of these "missing sinks."
The Bahama Banks as a Carbon Sink
The Bahama Banks are a unique geologic formation, comprised of a thick layer of calcium carbonate (CaCO3) deposited by marine animals, algae, and corals growing in shallow water. They have accumulated over 25 million years as glaciers have recurrently raised and lowered sea levels. During the 90,000-year glaciations, the banks are large plateaus with steep cliffs rising from the sea. During the 10,000-year interglacial periods, the banks are mostly covered with shallow water as we see them today. All of the carbonate accumulation on the banks occurs during the interglacial periods.
The banks, including the islands, cover an area of 131,900 square kilometers. Average depth of marine deposited sediment is 4.5 kilometers, yielding a volume of 593,550 cubic kilometers of more or less pure calcium carbonate. Making the calculation simple, 1 cubic kilometer of water weighs 1 gigatonne. Assuming a specific gravity of 1.8 for the sediments (this includes pores and gaps) and a 12% carbon content, 593,550 x 1.8 x 0.12 = 128,206 GtC beneath the banks! All of this carbon was removed from the atmosphere, one shell and sand grain at a time.
Calculating the present-day carbon sink potential of the banks requires some guesswork because no complete study of the banks has been done with this objective. One study in Belize suggests a highstand accumulation rate of 0.24 to 0.46 cm/yr; another in the Bahamas suggests a rate of 0.28 cm/yr on the bank margins. Let us assume an average rate of 0.30 cm/yr over the 118,500 square kilometers of the banks not including the islands. There are 100,000 centimeters in a kilometer. Using our previous calculation, (118,500 x 1.8 x 0.12)/100,000 = 0.256 GtC per year, or about 3% of the 8.5GtC annual human emissions.
Not bad for a nation with 0.006% of the human population!
Carbon Sinks as a Revenue Source
How much are carbon sinks worth? Potentially, quite an enormous sum, but getting an exact answer is tricky. Various technical methods are under research and development to "sequester" or capture carbon emissions and bury them underground or deep in the ocean. The US Department of Energy estimates these technologies to cost in the range of $100 to $300 per tonne of carbon, and has a project underway which hopes to reduce this cost to $15 per tonne by 2015. The US Forest Service points out that growing more trees might capture carbon at a cost of $30 to $90 per tonne.
The 25 nations of the European Union currently operate greenhouse gas emissions trading scheme for CO2 under the framework of the Kyoto Protocol which currently governs carbon emissions. This is a "cap and trade" market similar to those employed in the US for sulfur dioxide and other pollutants. These trading schemes, if implemented properly, use market forces to find the lowest overall cost of limiting emissions to a specific level. European prices recently collapsed from E30 to E10 per tonne of CO2 when it became clear that many countries had given their industries such generous emission caps that there was no need for them to reduce emissions. Since CO2 is 27% carbon, this would imply a carbon reduction cost of E37 per tonne or about $48 at current exchange rates.
Regardless of which valuation you choose, it is clear that if all of the carbon currently captured by the Bahama Banks were valued on a market basis, it would be a sum in the billions of dollars per year! What would it take for the Bahamas to turn some of this into real money?
The Protocol includes the Clean Development Mechanism (CDM) which allows developed nations to purchase emission credits from developing nations in lieu of reducing their own carbon emissions. Both parties benefit from the transactions – developed nations meet their carbon reduction goals at a lower cost; developing nations modernize their infrastructure, reduce ancillary pollution, and increase local employment. Natural carbon sinks were problematic to include in the CDM due to disagreements about the permanence of the carbon stored in them, their environmental worth, and whether they would have happened regardless. As a result, reforestation projects are the only natural carbon sinks currently approved under the CDM.
The CDM expires in 2012, with the expectation that it will be replaced by a more comprehensive emissions trading scheme. If the Bahama Banks are to qualify as a CDM-approved carbon sink in the next protocol, Bahamians must begin lobbying for inclusion now. The process will be both scientific and political. Additional studies will be needed to establish the existing baseline for carbonate accumulation, estimate future growth, and determine which methods are best to increase accumulation while protecting the environment. Politically, the Bahamas will need to ally itself with other nations that have similar coastal geology – coral reefs, mangrove shorelines, and/or carbonate platforms. The effort is much more likely to succeed if many nations could qualify, rather than CDM approval being a special case for the Bahamas.
Realistically, the Bahamas should expect to get CDM credits only for the amount of carbon it can capture above the amount that would have happened naturally, without any human action. It will also need to show that the carbon is captured for the long term, and not released back into the atmosphere in a few decades or centuries. In essence, the Bahamas is likely to get credits only for its incremental carbon capture, not its total carbon capture. As a result, actual revenues will probably be in the millions, not billions.
Still, that is more than pocket change. What could the Bahamas do to maximize this revenue?
Enhancing Carbon Sink Potential
There are a number of possible actions the Bahamas could take to improve the carbon capture of the banks. Any discussion, of course, is purely speculative in the absence of scientific studies to validate them. These studies should also consider the impact on the nation's greatest natural assets – the marine environment and scenic beauty of the islands. Fortunately, these kinds of studies are of great interest to universities, international organizations, and non-profits. It should be possible to fund all of the necessary research without spending a dime of Bahamian money.
Increasing coral reef growth would benefit the Bahamas in several ways. The reefs are composed of carbonate, so they capture carbon directly. As sea levels rise, healthy rapid-growing corals are critical for the edges of the banks to keep pace with the rising waters. The fringing reefs form a barrier that allows algae and marine animals to deposit carbonate sand in the calm waters of the banks. Healthy reefs also protect beaches and settled areas from storms. Current efforts in the Bahamas to protect reefs focus on limiting human pollution and physical damage. The Reef Ball Foundation has successfully used artificial structures in more than 50 countries to encourage formation of new coral structures. With funding from CDM credits, these projects could be greatly increased in scale.
Widening the mangrove fringe on the west side of Andros, north side of Grand Bahama, and other shallow areas of the banks would build up a significant layer of carbonate sediment as the bottom converted from seagrass to mangrove. These are areas which are naturally transitioning to mangrove. Properly designed barriers could speed this process up, while creating additional tidal habitat necessary as a nursery for many marine animals. It would also provide additional protection from storm damage for the inhabited areas of these islands.
Increasing sand deposition over the interior of the banks could result in a great deal of carbon capture given their vast area. Accomplishing this would require a much more detailed knowledge of the chemistry, currents, and biology of carbonate-capturing organisms on the banks. Presently it appears that most carbonate sand is formed at the margins of the banks and carried to the interior by currents. The interiors produce little carbonate sand of their own. Whether this could be increased without negative environmental consequences is unknown. Possibilities include dredging channels to improve water flow to stagnant areas, or to increase the occurrence of "whiting" where carbonates condense directly out of seawater.
Moving sand to deeper water might be a good method of keeping the sand level at the margins of the banks optimal for production, while moving the carbon in the sand to more-or-less permanent storage in the depths. Tongue of the Ocean and Exuma Sound appear especially well-suited for this. They are deep enough to hold all the sand that the banks could produce for thousands of years, but not so deep that water pressure would dissolve the carbonate sand dumped into them. They are "dead end" basins without deep currents that could carry the sand to undesired locations. The sand might be moved over the edge using a system of pipes and pumps, or it might be possible to dredge the sand banks in a pattern that caused tidal action to transport the sand over the edge. Again, any such scheme would have to consider adverse environmental impacts.
Environmentally friendly Bahamian cement might even be a possibility! One enterprise that has been moving sand off the banks for many years is the mine at Ocean Cay south of Bimini. Recent production has averaged 1.2 million tons per year, exported primarily for cement production. Heating CaCO3 for cement releases CO2, making this the largest industrial process contributing to CO2 emissions. Most cement is made from limestone deposited eons ago, so the CO2 released from it is additive to the environment in the same way that CO2 from fossil fuel is. But since the cement made from Bahamian sand comes from recently and actively deposited carbonates, its CO2 emissions are part of a closed cycle. As fast as the Ocean Cay dredges load up sand, more is deposited on the banks. If this cycle were properly documented and approved, Bahamian sand could be marketed as a "green" ingredient for construction materials, potentially increasing its value and rate of production.
Conclusions
An article such as this can only serve as the starting point for discussion and action. Clearly, if these ideas are practical, they would bring real benefits to the Bahamian ecology and economy, and would help preserve the islands for future generations. Making it happen will require a positive answer to the following questions:
