A few minutes after arriving at my hotel in New Orleans, I was struck by a disquieting thought: I was probably standing underwater. Curious, I double-checked with the great god Google (‘the All Knowing’) as soon as I reached my room. I was right. Street-level in this part of New Orleans was six feet below sea level!
Six feet under. I live at 7000 feet above sea level, so this fact took a minute to sink in. Still curious, I asked the great Google what New Orleans’ fate might be under climate change, which will cause sea levels to rise steadily. I found a recent study which said that between 10,000 and 13,500 square kilometers of coastal lands surrounding New Orleans will “drown” due to rising sea levels and land subsidence by 2100, a far greater amount than previous estimates. Yikes!
As for New Orleans itself – its fate wasn’t clear. In the short run, engineers will keep raising the height of the levees that surround the city, which should keep it ‘high and dry’ for a while. As for the medium term, it depends on what happens to the Mississippi River. If sediment from the Great River can be used to create a buffer between the city and the sea, then the Mardi Gras partying can continue for years. However, that’s a Big “If” – it depends on a lot of the political stars lining up just right. As for the long-term, well, if all the ice sheets and glaciers around the world melt, the picture is not so cheery.
Thinking about sea levels while strolling down Bourbon Street, as I did on my first evening in town, tempted me to try a local alcoholic concoction called a ‘Hand Grenade,’ which was billed as “the strongest drink in Louisiana.” I passed. Still, who wants to think about the future in a town known for good times? Not me.
Besides, I was here for the good news about blue carbon. That’s the non-technical term for biological carbon captured and stored in coastal wetlands, seagrasses, salt marshes, cypress and mangrove swamps – pretty much anything connected to seawater.
I had learned recently that of all the carbon captured annually in the world by photosynthesis, more than half is caught by marine organisms. Even more remarkably, even though plant biomass in the ocean is only a fraction of that on land, it cycles almost the same amount of carbon each year, representing an extremely efficient carbon sink. Scientists say the total carbon deposits per square kilometer in coastal ecosystems may be up to five times the carbon stored in tropical forests!
Here’s a photo of seagrass:
However, I also learned that blue carbon is an underappreciated player in the planet’s vast carbon cycle, mostly because humans have focused so much on role of forests and rangelands in climate mitigation and adaptation planning. In fact, the United Nations Convention on Climate Change (think: Copenhagen in 2009) largely ignores the role of coastal ecosystems and ocean plants in greenhouse gas emissions or sequestering carbon dioxide in its soils.
In an attempt to remedy this situation, an International Working Group on Coastal “Blue” Carbon formed in 2011. Composed mainly of scientists, its goal is to raise the awareness of blue carbon among researchers, policy-makers, and the public. Here’s a summary statement from their first publication:
“The natural coastal ecosystems sequester and store large quantities of carbon in both the plants and in the sediment below them. If destroyed, degraded or lost, these coastal ecosystems become sources of carbon dioxide emitted into the ocean and atmosphere. Much of this emitted carbon is thousands of years old and other processes in the ecosystem do not balance its rapid release. Given the large quantity of carbon in coastal ecosystems relative to their area, these emissions are likely of global significance.”
The problem is, as I learned during my visit, the rate of wetland destruction in Louisiana is equivalent to a football field disappearing every hour! Globally, coastal systems are being lost at an alarming rate of 2% per year, which is four times the rate of annual tropical forest loss. That’s why the Working Group says there is a critical need for effective measures to protect vulnerable carbon pools stored in coastal systems and to restore their carbon sequestration capacity.
The simplest way to maintain coastal wetland carbon pools is to block their degradation or development through protection and sustainable management. Restoration of wetlands is also an important strategy, though given the high cost and substantial bureaucratic and political obstacles involved, success is slower to achieve. Still, some management activities, such as rewetting of drained soils or replanting of mangroves can slow or halt carbon loss.
Blue carbon is important and complex part of the global carbon situation. Right now, however, it involves a lot of crossed fingers especially around New Orleans, which is Ground Zero in the effort to save and restore the nation’s blue carbon stocks, as I’ll describe in the next post.
In the meantime, here’s a photo of a cypress swamp: