 The two effects of climate change that I think we can be absolutely certain about, beyond any question, is that the temperature of the ocean is rising, and the acidity of the ocean is rising, and work that's been done here in Heron Island and elsewhere makes it absolutely clear as to what the effect of those two factors will be upon coral growth. So I still remember in the early 80s, for example, when the lab that I was in at UCLA in California, Los Angeles, the first bleach samples coming out of the Caribbean and being sent to my professor, and people going, we don't know why this has happened, but large amounts of coral have gone white. We're calling it bleaching. I've worked on every major coral reef region in the world now with very few exceptions, and that's a lot, that's 66 expeditions, that's 6,000 hours of scuba diving, and working on corals, not playing, and I've come back to the same place sometimes 20 years later, and I've seen this drastic deterioration in coral reefs. As we've pumped more CO2 into the atmosphere from the burning of fossil fuels, about 30% of it has actually been absorbed by the ocean. Now in one sense, that's been quite good because we've had less greenhouse gases, so less of a warming effect, but that CO2 going to the ocean has had its own chemical impact on the ocean. It wasn't until the early 1980s that I really got alarmed about what was happening to coral reefs, and then I realised it was happening to oceans everywhere. We've not only stressed these systems from a temperature point of view, we've also imposed a rapidly changing chemistry, and that chemistry is, well I think it's fundamental to their biology, biology of most organisms. Something like a third of all marine species have some part of their life cycle in coral reefs. It's a huge proportion, and so when coral reefs go down, it's not just the extinction of corals, that's almost trivial in this thing, it's the entire ecosystem goes down and takes with it, it'll take with it a third of all marine species. The other horrible thing about corals is they commonly grow best right at the tolerance of the temperature that will inevitably kill them. They like to live on the edge, thrill seekers in so many ways, and so if you make it a little bit warmer and they don't have time to adapt, then you get the coral bleaching issues. We're really in the early stages of changes that are probably happening, or they are according to the IPCC, at a rate that's the highest in 65 million years, and so much slower and less significant changes have had huge impacts on life and ecosystems. We can look at what happened in the past, were mass extinctions happened because of rapid climate change or because of habitat loss. And I think what we generally see, I'm no expert in this, but I think we generally see is similar types of organisms go extinct as those organisms which we now see on red lists that are very sort of critically endangered. Well the mass extinction events I think show us what's possible with actually a lot slower change, which is pretty frightening. When you think about the rates of change we're seeing, apart from the Cretaceous Boundary event when you had an asteroid hit the Gulf of Mexico or made the Gulf of Mexico, it's hard to think that a lot of these other ones happened over thousands of years, yet we're doing equivalent changes over a few decades. So I suppose these mass extinction events tell us that we can have some major effects with even a lot lower rates of change. It's not the amount of carbon dioxide, it's the rate at which it's building up, and for so much of the animal life and the oceans, they're not genetically equipped to accommodate such rapid change. Coral cover on the Great Barrier Reef has dropped by about a half since the early 1980s, so in a way that's really like demonstrating that adaptation isn't effective enough to drop that decline. If evolution was working to give them the tools to adapt to changing climatic conditions, they wouldn't be disappearing from hot places, and they are. I can't see a grain of evidence to tell me that we are not launching into the sixth mass extinction. There's never been an increase in carbon dioxide like we've seen. So observed extinction rates around the world right now have reached what I think most biologists would call a mass extinction level, so we are about, I mean the exact rates are not precisely known, so we normally speak about extinction rates in terms of orders of magnitude relative to what would happen in the absence of human activity. So what the geological record indicates is a normal baseline rate of extinctions. Right now we are at about one thousand times the natural rate of extinction, which puts us more or less in the middle of the end of the age of the dinosaurs in terms of how fast species are disappearing from the world. The increasing, the time passing and increasing of those figures will lead to disaster unless something is done, and there are those who say that there's almost nothing that can be done, except, and my response to that is that it'll be worse if we do nothing. There's not an excuse for doing nothing, saying you can't stem it. You can slow it down, that's for sure. And it'd be really culpable if we don't.