Copenhagen, Denmark. Wow! What a whirlwind couple of days here in Copenhagen. COS participated in the COP-15 “Oceans Day” events and I spoke to the assembled group about ocean acidification as part of a panel of international scientists and policy experts. One issue at hand is “what should the target limit be?”. For the atmosphere, people talk about 450 ppm greenhouse gas equivalents as a target maximum. The term “equivalents” is a nod to the fact that other gases have much greater specific greenhouse effects that carbon dioxide. Methane is a good example of this. So in fact, if we add up the effects of the other gases, we are now at an equivalent CO2 level in the atmosphere of about 420 ppm. So, 450 ppm isn’t very far away – less than 10 years in fact. Can we stay below 450 ppm? Doesn’t seem likely. Should we strive to do so? Absolutely.
But does this work for the ocean? Not at all. We have good reason to believe that the oceans and life in the sea will suffer serious and negative consequences if carbon dioxide levels are maintained above 350 ppm. In fact, modern marine life has evolved and adapted to natural levels of average CO2 in the ocean’s surface waters that range from 180 ppm to 280 ppm, so even 350 ppm represents an adaption challenge. The challenge comes from ocean acidification –the changing pH and carbonate saturation state of the sea as a result of the uptake of excess CO2 from the atmosphere. So even though there is much focus here at COP-15 on specifying a maximum permissible rise in temperature (some say 2 degrees; others, like small island states, argue for 1.5 degrees C), a better metric to use for the future of the ocean and all people that depend on it is the actual concentration of carbon dioxide. 350 ppm actual CO2 is a good clear target and we are already way beyond it. Nevertheless we should aspire to bring the ocean back down to 350 ppm as soon as possible. And this is just for CO2. The concept of greenhouse gas equivalents doesn’t easily apply here, at least insofar as ocean acidification is concerned. We need to sort out a way of getting this target inserted into the negotiation process.
We ran into Holmes Hummel today, a former Stanford ES and IPER student, now a lead negotiator for the US Department of Energy. She pointed out that unless we have a way to scrub CO2 out of the atmosphere, it will be a long time before we can get back to 350 ppm. Models support her view. It could take over 100 years for oceanic CO2 levels to drop back to 350 ppm, even if we do embark on dramatic emissions reductions today. This means that mitigation against most ocean acidification effects is an intergenerational issue, a point made eloquently by Professor Ove Hoegh-Guldberg in our conversation with Holmes. Can we get people behind the notion that they must act now in order to save the oceans 50 years or 100 years out? It seems like we should be able too but it’s a tough sell in fact, and again, the community here is mostly focused on temperature rise targets on land. The ocean must play a more prominent role in future climate change meetings.
- posted by Dr. Rob Dunbar, Professor of Earth Sciences at Stanford University