Professor Ian Plimer

we suddenly became cool.

And this is a period called the Younger Dryas.

And we had temperature drops that were very, very large, like 10 and 15 degrees Celsius drops.

And it took about 10 years to have a 15 degree Celsius rise after the Younger Dryas.

Now that's global warming.

What happened in the Younger Dryas?

We actually huddled into villages.

We fortified those villages.

We invented animal husbandry.

We invented, for survival, we invented agriculture where we collected grass seeds and actually grew them.

We've got extremely good evidence of that.

So in these times of hardship, we humans thrived.

And once it became warm, and history shows us this, then we get the populations expanding, we have less war, the economy thrives.

For example, in the medieval warming, Europe had two harvests a year.

That gave an enormous amount of wealth.

That wealth was spent on the universities, the cathedrals, the monasteries.

We see evidence.

You've only got to travel through Europe and see this.

So over time, we can see that temperature has changed a lot.

Now we also have cycles of climate.