 When the scientists did a survey of azurella macquarieensis in April 2008 there was no recorded evidence of these cushions showing decline. They all seemed to tick the healthy box. When the scientists went back out into the bush after the winter, so this was December 2008, there was major dieback. Major, major dieback. And by 2010 the plant was listed as critically endangered. Now it's an important plant. Firstly, it's endemic to macquarie island. Even though azurella as a genus exists widely around the world, azurella macquarieensis specifically just found on macquarie island. And secondly, it's a dominant species in the felt mark which is sort of a barren part of the island. So it plays a really important architectural role in solar erosion and providing an environment for other species to grow. So the loss of these cushions is really important. These are not little cushions. I mean a lot of them are small, but they can grow to a couple of metres across and half a metre, maybe even three-quarter of a metre tall. So the million dollar question, why did they suddenly die between April and December? If it was this gradual drying of the atmosphere, which we know is a phenomenon in the Southern Ocean at high latitude, but if it was that we would have expected to see some evidence, at least of sensitive cushions somewhere on the island exhibiting a decline, but we didn't. This was just a crash. When we started working on this project, we did the usual, we looked at the temperature and the rainfall and the this and the that, and we really concentrated on drying. And then one day we were talking to Professor Marilyn Ball about what kills plants. And we started talking about unseasonal extreme events. Now you're starting to hear a pattern here. Extreme events that are occurring at uncharacteristic times. And so we went back into the data and instead of looking for drying seasons, we looked for an unseasonal frost. Just like an unseasonal frost here in Canberra will kill all the tomato plants, the same happens with plants around the world. Frost is well known when it occurs just after the new foliage has budded to cause permanent damage. And we found November 2008, a very cold frost that extended for several days with nice, sunny, dry conditions, so perfect for the formation of what we call black frost. And it had only occurred once before in 1952.