[♪ INTRO] All over the planet, plants and animals are migrating to more suitable habitats as global climate patterns shift.

They’re all seeking the same thing: a climate closer to the one they evolved in. But as Earth gets warmer, some plants and animals might not have as far to go, thanks to a weird phenomenon that creates pockets of land sheltered from climate change.

These climate change - proofed bubbles manage to stay cool even when things are heating up just a few kilometers away, and the shelter these cool zones provide could end up a key adaptive strategy for species looking to beat climate change. Now to be clear, we aren’t talking about like, huge regions being shielded from the effects of our rapidly warming planet. The vast, vast majority of habitats and ecosystems are going to see these upheavals.

That’s one big reason the climate crisis is a crisis. But on small scales, there are some places that end up being cut off from the weather patterns around them. Like, in Utah, there’s a basin in the mountains that’s often the coldest place in the United States, even when the temperatures just outside the basin are pretty average.

And in the Cascade Mountains, the valleys can stay cool for days no matter what’s going on over and around them. Many of these sheltered places have one thing in common: They’re found on uneven terrain, where there’s a low-lying region surrounded by higher land. And that’s not a coincidence.

On an average day in most parts of Earth, the temperature is warmest near the surface and cooler at higher altitudes, forming a heat gradient. That’s partly because heat radiating off Earth’s surface warms lower levels of the atmosphere more than higher ones. Solid ground is a better conductor of heat than air, so the Earth’s surface holds onto the heat from the sun better than air can.

However, the ground will cool off pretty quickly at night, since it’s no longer absorbing energy from the sun. Usually, cloud cover will trap that heat and keep it in the lower layers of the atmosphere, close to the ground. But if it’s a clear, cloudless night, that heat is able to dissipate out into space, creating a layer of chilly air over the ground and warmer air higher above it.

That cold air is too dense to circulate with the warmer air above it, so it gets cut off from the rest of the mixing of air that makes the heat gradient effect happen. This scenario, where cold air sits below warmer air, is called a temperature inversion. So that cold air just sits there until the Sun rises and heats it up again, or the wind pushes it somewhere else… as long as the ground is flat.

But if the ground is sloped, this layer of cool air will start sliding downhill. And as it falls, it can get stuck in valleys and other dips in the land, creating what are called cold air pools. These pools can be a few meters or even hundreds of meters deep.

And they can form all over the world, even in hot places like the tropics and in regions that are not super mountainous, since all you need is some air that’s cooler than the rest, and a slope leading to a dip in the land, like a basin or valley. Since all that cold air is denser than the air above it, it doesn’t really mix with other air, meaning it's essentially cut off from the rest of the atmosphere. This creates cool areas, called microrefugia, that are sheltered from the weather patterns around them, where some species can go to beat the heat.

There are other forms of microrefugia, too. Cool air under forest cover, on shady mountain slopes, or along certain shorelines can also act as microrefugia. And as the climate crisis worsens, these microrefugia might help some life forms survive when they die out everywhere else.

Which could be hugely important for preserving biodiversity. We know this is a possibility because it’s happened before. Close to 3 million years ago, temperatures on Earth were pretty moderate, and Europe was covered with forests.

Then, Earth entered a period of ice ages and thaws. For tens of thousands of years at a time, huge ice sheets covered the Northern Hemisphere. Eventually, things would warm up for a few thousand years, before cooling down and freezing over again.

These temperature seesaws were rough for the species living in these places. And when things first froze over, lots of trees died. But… not all of them.

When temperatures dropped, some species of warm-adapted trees managed to survive in pockets of land near the Mediterranean that stayed warmer than their surroundings. Then when everything else warmed up between ice ages, trees that had been thriving during cold times survived in chilly microrefugia where the air stayed relatively cool. Researchers managed to trace these shifting tree populations by comparing the abundance of different kinds of pollen in ancient rock layers.

Their findings show that microrefugia have helped plant species make it through climate fluctuations more than once in the past. And some scientists think they could help again during the climate change that’s happening now. In fact, some species around the world already seem to be hunkering down in microrefugia.

For instance, in southern France, there’s an herb called wood sorrel that grows better in cool microrefugia than it does in surrounding areas that are more affected by climate change. Over in Nevada, sections of the Wassuk Mountains seem to be acting as microrefugia for conifer trees adapted to cold climates. It’s hard to see this kind of shift in action, but scientists are working on identifying microrefugia around the world and figuring out what species may be retreating into them.

Once we know where microrefugia exist and what kinds of living things are thriving there, we can work on preserving these natural shelters to protect the species living in them. Take the monkey puzzle tree. This tree species is beloved in its native home of southern Brazil, but thanks to logging and climate change, it’s nearly extinct.

Today, small populations of monkey puzzle trees are surviving in microrefugia in the highlands, but only a tiny fraction of these lands are protected under conservation laws. Unfortunately, if these trees don’t manage to survive in microrefugia, climate models suggest the species will soon die out altogether. So, it’s up to people to protect the small ranges where this tree can still live.

This could be true for many species whose future depends on microrefugia. That’s not to say this type of solution can save every species that’s being affected by climate change. A large animal that’s used to roaming far and wide might not be able to make itself at home in a cramped mountain valley.

Some things need macro-habitats, not micro- ones. But as our planet warms and more living things need to escape the heat, microrefugia could shelter at least some of the species that are threatened. All the research into microrefugia isn’t just about documenting what’s already happening.

Some researchers even hope that if we understand exactly how they work, we might be able to create them to protect certain species. And while this isn’t anywhere near a reality just yet, it’s just another compelling reason why these tiny, isolated habitats are so important for the entire world. This video was made possible thanks to our supporters on Patreon.

It takes a lot of people to make these videos, and we couldn’t do it without our community’s support. If you’d like to become a patron, you can go to Patreon.com/SciShow to join, and as always, thanks for watching. [♪ OUTRO]