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Comment by skh | Hacker News Reader

The evidence is that the Earth is warming so it's not odd that there aren't any dire warnings about it cooling. When it cools suddenly then I'm certain there would be dire warnings.

It seems to me that the dire consequences are about the ability of nations to deal with relatively sudden changes. We are no longer at the point where populations can shift easily on a grand scale. Four thousand years ago it was much easier for humanity to shift production of food and seek out new places to live. Today not so much. This is especially so since almost no one knows how to live off the land anymore and the even if we did know this it isn't possible due to the massive decline in animal populations and habitat.

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"We are no longer at the point where populations can shift easily on a grand scale." We can more easily now than ever before and don't need to be near food. We have trucks for that.

Four thousand years ago, just a two year drought and 1/3 of your village would die of starvation. Few people could move anywhere. Pastoral peoples moved around but during times of scare resources, like a drought, multiple groups moving to the last remaining pasture would result in a battle with mass killing.

Are you saying that when the going got tough, the tough got going?

If Bangladesh becomes uninhabitable those 150 million or so people will need to move. Four thousand years ago there weren't anywhere near that number of people in the area that is now called Bangladesh. The scale has drastically changed.

It's easier for an individual to move now than in the past. This is clear. But if an entire high population region becomes uninhabitable in a short period of time then it's difficult for that population to shift. The neighboring countries generally won't want to accept the incoming people and often times can't sustain the incoming population.

Look at the problems with a few million people suddenly going to Europe has caused. Imagine if it were 150 million people trying to get into Europe.

Like you mentioned, the thing that causes millions of people needing to move in a short timescale these days is caused by humans, ie. wars. Even if sea-level rise is as bad as the most dire predictions and the Bangladeshis can't find a way to build some dikes, it will still take many multiple decades for parts of Bangladesh to become "uninhabitable".

I mentioned relatively short time scales. I'm thinking multi decade time scales and not something like wars. If the predictions of sea level rise are correct then the problem won't be to just one region. It will be world wide and the resulting migrations/chaos will be catastrophic for nations and people. I was just giving an example of how the scale has changed now versus 5000 years ago.

I was about to say. Individuals didn't move, its just that the centre of mass of living humans shifted when people died off somewhere and prospered elsewhere.

Quite right. I find it amusing to read dire concerns about how N million people are going to have to move N miles. Especially when the posts are written by people who, far more often than not, live thousands of miles (and sometimes entire continents) away from where they were born.

If a region becomes unproductive, the kids will move. The parents will stay. And populations will shift as they always have.

An individual moving is not a problem. Entire nations needing to move is.

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