In the previous video, I introduced the science of paleoclimatology, climates of the past, and reviewed there some of the big changes in climate that have occurred throughout Earth's history, going back even billions of years. I mean, the Earth is very ancient. I made the point there, I'm going to just re-emphasize that again, that all climate change has a reason, it doesn't just happen by itself. In terms of what's been going on over the past 100 years or so, that's clearly us loading the atmosphere with greenhouse gases. But past climate changes before then had some different reasons, but that doesn't mean there was no reason, right? Climate change always has a reason. Now, what I'd like to do now is turn the page a bit and speak about the data sources that we use to get this paleoclimate information to understand these past climates. The key point is that there's many sources of paleoclimate information. The Arctic is a rich store of paleoclimate data, and many past climate changes turns out to intimately involve the Arctic. Now, what's one source of paleoclimate information? Ocean cores. Ocean cores are very important. They can provide us records going back several million years. This is a picture of part of the core repository at The Lamont-Doherty Ecological Observatory, the LADES. This is actually where I met my wife many, many years ago. She was the Assistant Curator of the Core lab we used to make out down in the lab sometimes. But these are records going back several million years. Basically, you've got ship. The ship has a drill rig, and it gets these cores. From the sediments, you can analyze things like oxygen isotope ratios and really get information on what was going on in the past. We have these from all over the world. They've been drilled all over oceans all through the world, including the Arctic. Now, of course, getting ocean cores in the Arctic waters is not an easy task because we've got all that sea ice in the way and things like that, but we have some from the Arctic. We really have them from all over the world. Now, another source of information is ice cores from Greenland and Antarctica. We have ice cores that have been drilled all the way through the ice sheet. Again, from all kinds of information, like oxygen isotope analysis, dust layers, all sorts of things, we can understand past climates. So here's just a picture here of someone holding a bit of an ice core. I'm not sure where this one is from. Here's a question. How far back in time do cores from the Greenland ice sheet provide climate records? The answer is almost 125,000 years ago. That's back to almost the previous interglacial. We're in an interglacial now, the past interglacial was called the Eemian. The Greenland ice core had to go back almost that far. Now, it turns out that ice cores from Antarctica go back almost 750,000 years. They go back much further. So these really provide some very detailed records of climates in the past. Lake cores. Lake cores, there's another source of paleoclimate information. Here's some people drilling a lake core in Svalbard. But again, the idea is that you lower down something. You have a drill rig, it's basically a piston core, and you get these sediment cores. Again, you can tell all kinds of things about past climates from them. Now, here's another question. How far back in time can lake cores provide paleoclimate records? The answer is up to 3 million years. Now, some of them, shallow ones, several thousand years. But there are some, notably this one over here from lake Lake Elgygtgyn in Siberia, that goes back basically 3 million years. Lake E, as it called, is actually formed by a meteorite impact 3.6 million years ago. But since then, sediments have collected in it. We can go back, and we can core that, and we can get records of past Arctic climate going back 3 million years. Pretty remarkable from lake cores. Here, you see on the left, there's lake E, a nice blue lake. On the right is a satellite image showing what that meteorite impact is. That's the lake. It was actually a meteorite impact, which itself may have had some climate effects, at least maybe in the immediate region. Radiocarbon dating, carbon-14. There's different isotopes of carbon. Carbon-12 is what most things are. It's the most common isotopes with this carbon-14 and it's radioactive. What happens is that carbon-14 is assimilated into tissues of living organisms, whether they be trees, people, mastodons, whatever. But as soon as they die, something dies, that assimilation stops and a clock starts, and the radiocarbon decays, and it decays at a known rate. So we can use that to date objects. It goes back to maybe 40,000 years, something like that, where we can date objects. But it's a very, very valuable source of paleoclimate information. So we can take old stumps, or not even old stumps, old pieces of wood or bones, anything like that, and we can date them and see how old they are. Now, dendrochronology, something you may have heard of, the analysis of tree rings. We can use tree-ring information. We can go back several thousand years this way to understand past climate information. Basically, it refers to the thickness of the rings. It's not nearly that simple, but basically that's the idea. You can assess what was going on in terms of things like precipitation stresses and things like that. So there's all information. One of them, also, interestingly, is art. This is a figure here by Avercamp. This is a picture. It was a photograph of a picture, The Pleasures of Winter. This was something that he painted back during the Little Ice Age showing people skating in England. Well, you don't see that anymore. But it turns out painters, artists will tend to draw what they see. Well, this is what was happening back then. It turns out that art may itself be a useful source of paleoclimate information. So what I've hope I've gotten through in this short video is that there are many, many different sources of paleoclimate information. You can get entire degrees in paleoclimatology to study these things. It's a fascinating field. I've been on the side of it a bit. I work with and know many paleoclimate scientists. But it is very important to understand paleoclimatology and the science of paleoclimatology because I've said before, a lot of understanding the future of where we're going to go, is to understand what was going on in the past. Thank you.