AP®︎/College Environmental science
Climate emergency: feedback loops - permafrost
Global warming is causing the thawing of permafrost, the icy expanse of frozen ground covering one-quarter of the Northern Hemisphere. As it melts, previously frozen carbon stored in plant and animal remains is released into the atmosphere as heat-trapping greenhouse gases, warming the climate further, and melting more permafrost in a dangerous feedback loop. Created by Khan Academy.
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[Narrator] In the Northern Hemisphere, nearly one-quarter of the land is covered by an icy expanse called permafrost. Extending from the surface down thousands of feet, its soil contains billions of tons of carbon-rich plant and animal remains suspended in a perpetually frozen state. But now, with human activity warming the Arctic two to three times faster than the rest of the globe, this permafrost is starting to thaw. And, alarmingly, it contains twice as much carbon as in the atmosphere today, and three times as much as in all the world's forests combined. As it thaws, microscopic animals called microbes that have been frozen for up to tens of thousands of years are waking up and feeding on the newly thawed carbon remains, emitting dangerous heat-trapping gases. [Tanentzap] If we were to take all of the microbes on Earth, we'd find that they'd weigh probably 50 times more than all of the animals on Earth. Now, these microbes need to eat and what they eat are the dead remains of plants and animals. And, as a byproduct of feeding on that material, they produce carbon dioxide and methane. [Narrator] To understand how warming temperatures accelerate microbial activity, you need to look no further than your own kitchen. [Natali] It's like having a chicken in your freezer. You take the chicken out, you put it on the counter and it starts to thaw, and then you go away for the weekend, you forgot about the chicken that's on the counter and you come back and the house smells and the chicken's decomposed. That's what happens to the carbon that's in permafrost. It's fuel for microbes. As they're breaking it down and using that fuel, they're releasing greenhouse gases– carbon dioxide and methane– into the atmosphere. [Narrator] Driven by fossil fuel emissions raising the temperature in the Arctic, these microbes are amplifying the warming as the permafrost thaws by releasing more carbon dioxide and methane into the atmosphere and warming the climate even more, in a self-perpetuating loop. Which of these heat-trapping gases is released depends on the environment in which microbes digest the carbon. In oxygen-rich conditions, like soil and lake surfaces, microbes produce carbon dioxide as a byproduct. But in environments lacking oxygen, like bogs and muddy lake bottoms, they produce methane, which is nearly 30 times more potent at trapping heat than carbon dioxide. Scientists predict the impact of both methane and CO2 added to the atmosphere from permafrost thaw will be staggering. [Natali] The amount of carbon that could be released from thawing permafrost by the end of the century has been estimated to be up to 150 billion tons of carbon. So, to put that in context, the U.S. is currently the second largest greenhouse gas emitting country in the world. If we took our current U.S. emissions and added that up through 2100, this is on par with the amount of carbon that might be released from thawing permafrost. [Narrator] Last summer, while working in her usual field location in Alaska, Natali witnessed a remarkable acceleration of permafrost melting. [Natali] First of all, it was very, very warm, it was 90 degrees Fahrenheit in the tundra. There were places where we walked, where my foot fell into the ground because there was no longer any ground structure because the permafrost was thawing. I've never seen change happening that quickly from one year to the next. [Narrator] To understand how this thawing will impact the global climate, Natali and her team collect permafrost cores from different locations across the Arctic. In the lab, she analyzes their carbon content and composition to determine how much gas will be released when the permafrost thaws. [Natali] These cores were taken from a location that has really organic-rich, deep, peaty soils, and you can tell that when you look at this core because it's really dark brown, and that dark brown color means that it holds a lot of carbon. [Narrator] The thawing permafrost not only impacts the climate through the release of greenhouse gases, it can entirely transform the landscape, as Natali has seen in Duvanny Yar, Russia. [Natali] I had never seen permafrost thaw and ground collapse of that magnitude. I remembered driving up to it on the boat and it was like, wow, this huge cliff, many, many stories high. You see these really, really fine roots that have been frozen for 40,000 years. Once they're thawed, they'll decompose in a year. [Narrator] And something else is having a dramatic effect on the landscape in Siberia: crater-like holes which are thought to be the result of a build-up of methane under a thick layer of ice. When the ice melts, the pressure gives way, causing an explosion. A year or two later, the craters form lakes that release the previously buried methane into the atmosphere. Sometimes lakes that form from shifts in the landscape emit so much methane, you can light them on fire. As the permafrost thaws and the Arctic heats up faster than the rest of the planet, that blanket of warming mixes into the atmosphere, encircles the globe, and it leads to all kinds of global disasters: crop failure in the Midwest, droughts and flooding in Africa, record heat waves in India. And in the Northern Hemisphere, home to most of the world's lakes, the warming is having an impact similar to the permafrost thaw by bringing new food sources to the microbes that live there. Plant species from south of this region are migrating north, setting off another feedback loop. [Tanentzap] Traditionally, the pine needles that the microbes would be digesting would have provided quite a limited diversity of food sources. But now, with deciduous broadleaf species, like maple and oak, that's bringing a much greater diversity of organic matter and carbon for microbes to digest. [Narrator] More food choices means an increase in microbial activity, which in muddy lake bottoms lacking oxygen leads to methane production, a warmer climate, and more greening of lakes in an ever-amplifying loop. And the geographical range where this dynamic is happening is expanding. [Tanentzap] That northward shift isn't just happening in northern latitudes where most of the world's lakes are found, but also elsewhere, like New England, like the Great Lakes area. [Narrator] Deciduous trees aren't the only species drawn to the warmer climate. [Tanentzap] Another major change that we're seeing happening around lakes is that cattails are moving northwards into the lakes, where they previously didn't grow. And where we compared the effect of cattails versus pines and oaks and maples on the amount of methane released from lake sediments, what we found was that there was at least 400 times more methane produced when we added the cattail litter than any of the tree litter. [Narrator] Models show that in the next 50 years cattails around lakes will double. And since more cattails means more methane, methane production is predicted to increase by 70% across all northern lakes. [Tanentzap] From the global climate perspective, this is something that we really need to be worrying about and thinking about how to actually mitigate and offset. [Narrator] And the problem is only going to get worse as the amount of heat-trapping gases microbes produce increases. Today, we have a choice: we can continue with business as usual and let these warming feedback loops spin out of control, or we can choose another way of living. We can implement policies that support a sustainable future, we can curb fossil fuel use, and regreen the Earth. This would slow down and eventually reverse the feedback loops to restore the planet. For permafrost, the less warming we create, the less carbon dioxide and methane will be released into the atmosphere, the more temperatures will drop, and the more permafrost will stay frozen. [Natali] Once carbon is emitted from permafrost, it will take a very long time for it to build back up. There are some places where the physical effects of permafrost thaw may be permanent. But in other cases, when you're having permafrost thaw, you can have permafrost refreeze. [Narrator] Since greenhouse gases mix throughout the global atmosphere, action everywhere in the world will reduce permafrost thaw, and reduced permafrost thaw will decrease warming everywhere in the world. [Natali] Communicating with our policymakers that this is important to us, that this is impacting each one of us, that this is important for human health, for human well-being, is the most important action that each one of us can take. [Duffy] To successfully address climate change requires an unprecedented level of societal cooperation, cooperation across nations, cooperation within nations, across multiple sectors. And that could happen; it does require leadership. Ideally, what science can do for us in this conversation is illustrate different possible futures.