Professor Ian Plimer

They don't learn about the past, so they can't ask the right questions.

And that's why we geologists are never regarded seriously when it comes to climate change, because the same processes that operated 100 years ago or a billion years ago, they're still here.

You have to change the laws of physics and chemistry if you're going to say, well, the geology's wrong.

It doesn't work.

So when we look in the past, we look at the six great ice ages.

We look at the five great extinctions of complex life.

But we also integrate that with history.

We integrate it with what has been lived.

So I used the example before when someone might say, oh, it's the hottest time we've had ever.

You say, well, no, we've cooled down since the time of Jesus.

It was much hotter then.

It was much hotter in the medieval times.

It was much hotter in the 1930s.

So how far do you want to go back?

You don't have to go back very far to show that we're not living in unusual times.

We are actually living in an ice age because we've got polar ice.

Ice is a rare rock.

for less than 20% of time we've had ice on Earth.

So we're living in an unusual time, but when you look at the temperature over time, and you don't need to go back very far, the temperature doesn't change very much at all in our lifetime compared with the past.

So we had a period after the last glaciation, which ended 14,400 years ago, where the ice sheets broke up and dropped huge amounts of ice into the Atlantic Ocean.