In 2017, storms, floods, and droughts displaced 18 million people from their homes worldwide.

And by some estimates, over the next three decades, 200 million people may need to leave their homes to escape the same kind of disasters, made worse by climate change.

That's basically like moving the entire population of Brazil or Pakistan.

Where in the world will all these people go?

[OPEN] The human story is, in many ways, a story of climate migration.

To make a REALLY long story short, modern humans evolved in eastern Africa around 200,000 years ago, but dry conditions kept us from successfully moving elsewhere until around 60,000 years ago, when a wetter climate opened the door to our global expansion.

We don't know exactly what motivated our ancestors, but they probably went in search of food, moderate weather, and an easier life.

Although a few important details have changed in the years since then, people who move today move for the same general reasons - better conditions, and a better life.

Sometimes we move to communities nearby, and sometimes we move across borders, a recent invention our ancient relatives didn't have to deal with.

And as the climate changes - this time from human activities - between 25 million and 1 billion people might get displaced by its impacts before the year 2050.

The predictions vary because we don't know exactly how bad the impacts will be or exactly why people move from one place to another.

But the most common estimate is around 200 million people.

Lots of these people will be displaced by sudden disasters [pulse disturbance] - like hurricanes, fires, and extreme temperatures.

For example, nearly 400 million people live less than 10 feet above sea level, in places like Bangladesh, making them susceptible to storm surges that are getting taller.

Others will leave because of slower-moving changes.

In Miami, the gradual rise of the sea will eventually put some homes under water, even on calm days.

And in the North Atlantic the warming of the oceans could mean there are fewer fish to catch.

Communities may also face an increasing number of hot days, and less predictable rainfall, like in Ethiopia, which can make it harder to keep crops and livestock healthy.

Wealthy countries like the United States have more resources to deal with the impacts of climate change, but some of their citizens will likely have to migrate too.

As Americans flee sea level rise, many of them will probably leave major coastal cities like Miami, New Orleans, and Los Angeles and move inland, because you can only put so many buildings on stilts.

And sometimes, you have to move an entire community.

Or... 30 communities.

That's the number of Alaskan villages and cities at risk of flooding or falling into the ocean due to erosion of their coastlines.

A few of these communities have already begun the expensive process of preparing to move.

In the island nation of Fiji, one village, also threatened by erosion and flooding, has already moved.

They worked with the national government to decide where they would move to and what their new village would look like.

As a whole, Fiji is also studying which communities are most vulnerable to the impacts of climate change, and drafting guidelines for handling future relocations.

But Fiji has it a bit easier than their almost-neighbors on the Marshall Islands, who may have to move their entire population to a different country.

We really don't know how that's going to work.

It's complicated even for individuals who have to move to a new country, because you currently can't cite climate as a reason you are seeking asylum or refugee status.

And for the communities where climate migrants end up, the influx of people can stress local infrastructure, and expose or trigger human prejudices.

Overall, the migration of people as a result of our changing climate will change the makeup of neighborhoods, cities and entire countries, and may even challenge our ideas of nationhood itself.

This is a lot to digest, but... remember where we came from.

If the earliest humans hadn't ventured to new lands, we might not have ever populated your city, your country, or even your continent.

We wouldn't have built the Great Wall of China, experienced the Northern Lights, or caught all the Pokémon.

(We also probably wouldn't have gotten ourselves into this climate mess, but that's another story.)

The point is, if we could successfully migrate across a changing planet tens of thousands of years ago, we can do it again today.

We just have to get ready for it.