This week, a study of mere cats and their growth spurts with some unusual ingredients.

There's always like boiled eggs boiling in the kitchen, and thousands of boiled eggs every week, that's for sure.

And how forests make it rain.

Trees can't run for shade when there's a lot of sun, But what they can do is emit vapours and become

seeds for cloud droplets. Plus a Neanderthal construction project deep inside a French cave. This is

the nature podcast for time the question is,

how are clouds made? The basics are already nailed. Water droplets start to gather around tiny aerosol particles, anything small enough to be

floating through the air. Enough of that happens and you get a cloud. But physicists want to know where

the aerosol particles come from. And it's an important question for climate scientists too,

who find clouds hard to model, but know they can have important effects on global warming.

Scientists thought that man-made emissions, particularly sulphur dioxide, were keyed to the

formation of aerosols and therefore increased the amount of clouds. But a set of new papers

question whether sulphur dioxide is really the only player. They find a much more natural process

might be conjuring up clouds. Jasper Kirkby has been creating clouds in a special chamber at CERN.

Davidei Castelvechi called him to learn more. If you were to go up into a cloud and pick out

a droplet, first of all, it would be very small. But if you evaporated it, you'd find that there was a little seed inside, and that's known as a cloud and pick out a droplet, first of all, it would be very small. But if you evaporated

it, you'd find that there was a little seed inside, and that's known as a cloud condensation

nucleus. It's a small suspended liquid or solid particle in the air, and all air on Earth has

hundreds, if not thousands of these in every cubic centimeter.

But without them, there would be no clouds in the sky.

How do you go about studying clouds in the lab?

What we have at CERN is we've built the cloud chamber.

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