What is dangerous?

Last week, I referenced a figure from a recent Science review that brilliantly illustrates the current predicament for the planet and, in particular, the planet's coral reefs.

Those of you who have been following climate science and policy for a while will remember that Article Two of the 1992 UN Framework Convention on Climate Change (UNFCCC) - the godfather of all climate policy, the precursor to Kyoto, all the COPs, and to Bali, the document that was signed by pretty much every country on the planet even the US - famously called for the:

" stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system."

A central challenge of climate change science and policy research since 1992 has been defining dangerous . Not just because the word appears in some international agreement, but because it is a useful way for us to determine allowable levels and trajectory of greenhouse gas emissions.

Notice the important use of term "climate system" rather than climate. This recognizes that the issue is not just the weather and the climate; changes in the oceans, in the planet's ice sheets or in the terrestrial biosphere could be dangerous to the planet and humanity.

Adjectives, of course, are difficult to clearly define. The Merriam-Webster Dictionary takes a big whiff on dangerous with "exposing to or involving danger". The UNFCCC text is more helpful in providing the following as a benchmark:

"such a level [of atmospheric greenhouse gas concentrations] should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner."

So, most scientific efforts to define "dangerous anthropogenic interference" have focussed on the collapse of major ice sheets (which would presumably threaten the economy), shifts in ocean circulation causing abrupt climate change (ditto), and sometimes debilitating tropical droughts (threatening food production).

What about coral reefs? The UNFCCC text states that an ecosystem not being able to adapt naturally to climate change is dangerous. As the figure illustrates, corals reefs will be in imminent danger if greenhouse gas concentrations are not stabilized around or below 500 ppm CO2-equivalent because of increased frequency and severity of coral bleaching events and the consequences of CO2-driven changes in ocean chemistry. As it, ocean warming due to climate change has already dramatically increased the likelihood of coral bleaching.

Yet the predicted demise of the world's coral reefs has only been included as an example of dangerous anthropogenic interference in a few studies (e.g., Harvey, 2007; O'Neill and Oppenheimer, 2004).

Why? Pardon the building of a straw man... I can only presume that people think coral reefs are not that vital to humanity. Sure, losing Nemo would be a shame, but it wouldn't be a disaster, like all of Greenland melting into the ocean.

That argument is not only wrong, it betrays a very northern, developed bias in our thinking. Coral reefs provide food, income and shoreline protection to hundreds of millions of people, almost all of whom live in developing countries. For those people, degradation of coral reefs surely would be dangerous.