After Hurricane Katrina devastated New Orleans, the US Army Corps of Engineers got to work on a huge network of levees and flood walls to protect against future catastrophes. Finally completed in 2012, the project ended up costing $14.5 billion and that figure does not include the upkeep these defences will require, not to mention the cost of someday replacing them altogether.
But levees are not the only things that protect coasts. Nature offers protection, too. Coastal marshes absorb the wind energy and waves of storms, weakening their impact inland. And while it is expensive to maintain constructed defences, wetlands rebuild themselves.
Protection from storms is just one of many services that ecosystems provide us services we would otherwise have to pay for. In 1997, a team of scientists decided to estimate how much they are actually worth. Worldwide, the team concluded, the price tag was $33 trillion equivalent to $48.7 trillion in todays dollars. Put another way, the services ecosystems provide us whether shielding us from storms, preventing soil erosion or soaking up the greenhouse gases that lead to global warming were twice as valuable as the sum of the gross national product of every country on Earth in 1997.
We basically said, Its an imprecise estimate, but its almost definitely a pretty big number, and weve got to start paying attention, said Robert Costanza, a professor at Australian National University who led the study.
That study proved hugely influential. Many governments large and small started to take the value of ecosystem services into account when they planned environmental policies. But the study also set off a lot of debate. Some economists argued that it was based on bad economics, and some conservation biologists said that calculating price tags was the wrong approach to saving ecosystems.
Seventeen years later, the debate is being re-energised, just as the US becomes immersed in an intense fight over the Obama administrations effort to tackle the emissions that scientists say could threaten many of these ecosystems. Costanza and his colleagues have updated the 1997 estimate in a new study, published in the May issue of the journal Global Environmental Change, and concluded that the original estimate was far too low. The true value of the services of the worlds ecosystems is at least three times as high, they said.
Coral reefs, for instance, have proved to be much more important for storm protection than