Hank Green: Alright. Today, I'm gonna give it to you straight about climate change. [SciShow intro] Perhaps you've heard of it, like, on TV or something. At this point, I think we're all pretty much at saturation on climate change. For the past ten years, it's been all day and all night on the news. Several TV news clips: "Climate changes..." "Global warming trend..." "Climate change..." "Global warming..." "Climatic changes..." "Climate change..." "Climate change is real." Hank: Climate change is coming to blow up your house and eat your dog! So basically, [takes off jacket] I'm not gonna be needing that anymore [takes off hat] and I'm not gonna be needing that. But what does it even mean? And what does what it means mean? And should you even care? Uh, yeah. You should care. I realize that climate change is one of those things that some people don't "believe in." Specifically, there are people who challenge the widely-held belief that it's gettin' hot in here, which I think was firmly established by Nelly in 2002, just before he requested that we take off all our clothes. And that, unfortunately, turns out to not be a particularly effective strategy to combat global warming. Fun though! Actually, some of the deniers agree that it's getting warmer, they just disagree that the cause is the way that we, as humans, live our lives. Which is understandable, I guess, because who want's to believe that their actions are hurting other people in the world and other generations as well? You know, besides rational, responsible, adult people who want to do the right thing, if at all possible. And what are we doing that's so wrong? Well, in the immortal words of one of my heroes, Nancy Sinatra, "We've been messin' where we shouldn't've been a-messin'." So, we release, uh, massive amounts of carbon dioxide into the atmosphere by burning coal and gas and oil and jet fuel, and we also really like to destroy natural carbon sinks like the Amazon Rainforest. And then in the place of those rainforests, we like to put other things that produce greenhouse gases, like cattle. And here's the kicker: the Earth has seen these massive increases in carbon dioxide concentrations in our atmosphere in the past, and, every time, it's been a complete disaster. What scientists can't completely agree on is what nightmare apocalypse scenario is going to get to us first. Or, you know, I guess they could all... all of them happen all at once. There's always that. One thing they are agreeing on: Not zombies. So we're safe from that. So, here are the five scariest things that could happen, or probably are already happening, because of climate change: So, the number five scariest thing about climate change: everything is just getting so confused up in here. So, when people talk about global warming, they're basically talking about the fact that over the last hundred years or so, the average temperature of the Earth has increased by about a degree-and-a-half Fahrenheit. And most of that increase has happened in the last thirty years or so. So, here's how you should be thinking of the Earth: it's a beautiful, precisely-calibrated and self-regulating machine. And it's more complex and amazing than we will ever be able to understand. Seriously guys, it's a friggin' masterpiece. But let's say that a terribly intelligent group of animals on its surface starts to drastically alter the composition of its atmosphere. In that case, all of those elegant and beautiful self-regulating systems start to go all screwy. Stuff that seems totally inconsequential, like rain falling a few weeks later than it otherwise would, can affect when the streams are full, which changes when the plants bloom, which changes when the insects hatch, and that can affect historically synchronized pollination of crops and fish spawns and bird migrations and water supplies for drinking and irrigation. What we're seeing now, with just over a degree difference in the temperature of the Earth, is significantly affecting our weather already. Some places are flooding, some places are experiencing record droughts, we're seeing ice caps melting and the historic ranges of animals and plants either shrinking or expanding. I mean, check it out: in the past ten years, they've actually had to change the little maps on the backs of seed packets to tell you when to plant your cucumbers. The worldwide redistribution of growing conditions and fresh water. 'Cause you know, you have air conditioning and so it's not too big of a deal if the world gets super hot. But you know who doesn't have air conditioning? Cucumbers and cows and other stuff that we like to eat. Those things have to be outside, that's how they work, and so they care if suddenly everything gets super hot and dry. And right now a lot of the wealth and a lot of the people in the world are distributed in the places where there's really good growing conditions. And as the Earth continues to warm, places with historically really amazing growing conditions, like central California, could become lifeless hellscapes. And that'll be a perfect habitat for zombies, but not so good for cabbages and strawberries. And by the time we reach something as subtle as a three degree increase in global temperatures, which scientists say could happen as soon as 2100, Saskatchewan could be the next central California. And all of the fertile crescents of the world may stop bringing forth their marvelous bounty. And what always comes along with poor growing conditions and drought? Well, you get famine, and you also get his brother horseman, war. In case you didn't hear, back in October the human population hit 7 billion people, and every single one of them wants to eat food. And when people get really hungry, they start to hurl little hunks of metal through each other's bodies, which is one of my least favorite recreational activities of humans. So famine's pretty scary, and so is number three, which is displacement and mass extinctions due to sea level rise. So you've probably heard of this one, because it effects all the cool kids like polar bears and people who live in Brooklyn. So it's gettin' hotter, right? And all that precious fresh water that's locked up in the polar ice caps is melting. So like right now, as I'm eating this hot pocket -- I love hot pockets, have I told you I love hot pockets? -- there's some polar ice cap melting. And now, it just keeps happening -- oh thank God, that's good. That's why they fake eat in television shows. Screw that! So there's enough water locked up in the ice on our planet that, if it all melted, we'd pretty much would all be in some serious trouble. Here in the U.S. we could expect to see New Orleans under water, parts of the Bay Area, a lot of New York City. But worldwide, it's actually looking a lot worse than that. Entire island nations like the Philippines and Indonesia would lose all of their fresh water supplies. And it's possible they would need to be entirely evacuated within this century. Many of the largest countries in the world, like Bangladesh, Vietnam, India, and China, all have very high populations living in very low-lying urban areas. And all of that is to say nothing of the diverse and vital ecosystems that could be completely destroyed in the event of a large magnitude sea level rise. Though I think Miami would make a sweet artificial reef, I'm sure the octopi would love it. The acidification of the world's oceans. Basically, carbon dioxide is water soluble, which means that as the concentration in our atmosphere goes up, so goes up the concentration in the ocean. So, the oceans have a deal with the atmosphere, which is that all the carbon dioxide that the plants on the Earth don't want, the ocean will suck it up, for plants and animals in the ocean to use. And the animals in the ocean use that carbon dioxide to create their bones and their shells and their pearls and whatever, and then when they die all that stuff falls to the bottom of the ocean and becomes rock. This is great, we're getting rid of carbon dioxide. However, when carbon dioxide dissolves into water, there's a chemical reaction, which slightly lowers the pH of that water. And a lower pH means it's more acidic. And it's not a super huge change, but it turns out that a lot of the animals in the ocean, especially the ones at the bottom of the food chain, really require a very specific pH. So the carbon dioxide gets dissolved in the water, the pH goes down just a little bit and guess what? It's mass extinction time again! Which is like a party! Except with 70-90% fewer species on the planet. I'm sorry, are you doing ok? I know this episode has been kind of a downer, but we've only got one more horrible scary thing to go, and that's shutdown of the global conveyor belt. So, unfortunately I don't have time to get into this topic in all of the detail that it deserves, but if you want to Google it, just look up thermohaline circulation. Thermohaline circulation is awesome, and it's a huge reason why our planet cannot only support so much life, but also such complexity of life. Basically, all of the ocean's in the world are connected together through this giant conveyor belt. And it's driven by winds, and the rotation of the Earth, and the different salinities of the ocean. But, most of all, it's driven by the difference in temperature between the equator and the poles. It's impossible to talk about climate without talking about the thermohaline circulation because it affects everything. For instance, this conveyor belt brings water up from the Caribbean, along the eastern coast of America, and then across to England, which is why England turns out to be so balmy even though its latitude would suggest that it would have a climate more like Canada. It also, and this is very important, delivers oxygen from the surface of the Earth down to the watery depths, where all of those extra weird organisms, like anglerfish, live, that we don't know very much about. In the history of our planet, when carbon dioxide levels get above a thousand parts per million, this thermohaline circulation has shut down, which is leading scientists to wonder if this could happen again. And if it does, what could happen? Oh my God, so many bad things would happen! First, all of the weather in the world would change, or stop, or something. It's unclear exactly what would happen because all of the models go totally screwy when you shut down the thermohaline circulation. But, basically it would be dramatic and probably catastrophic. Secondly, the oceans of the world would become a big stagnant puddle. Except for some of the stuff that's living on the very surface. But most of the ocean would become a freezing, black, dark, deep, oxygen-less place, like space. And third, this massive lack of oxygen, at pretty much every strata of the ocean, would lead to a huge explosion of the population of anaerobic bacteria. And anaerobic bacteria, ah, they like to produce this compound called hydrogen sulfide, which, if you've ever smelled rotting eggs, you are aware of what it smells like. But, in a full thermohaline shutdown it would become a much more familiar smell because everything would smell like it. The reason why we think it smells so bad is because hydrogen sulfide is extremely poisonous. It's one of the most toxic chemicals that we know of. There would be so much of it that pretty much all of the animals near the coast would die. And you and your friends and family would have to put on gas masks before you go outside. So I can't talk about this anymore because I don't have time, and also because it freaks me out. It is impossible to stress how * * * * * this would be. So if you're here for a worst case scenario, there it is: everything dies, and the entire Earth smells like twenty billion rotten eggs. And guess what? That is still not enough to convince me to stop eating meat, and driving to work, and flying to the east coast to see my family. And I have no idea why that is. But I bet that there's a very smart social scientist working on that issue right now, trying to figure out why we are all so stupid. And, hopefully, they'll figure it out soon. Thank you for joining us here on SciShow. You can connect with us on Twitter or Facebook, or right down below in the comments. Right here in my pants area. Am I pointing in the right place? Yep? OK, good.