A story of ice and fire

Around the planet, temperature plays a hidden part in the symphony of life. Helen Czerski’s new programme reveals just how surprising its effects can be

There’s a lot more to temperature than feeling hot or cold.

BLACK OR WHITE?

On a hot day, we tend to think that white clothes will reflect sunlight and therefore keep us cool. Yet while black absorbs more heat, it also radiates it away more quickly. A famous paper in 1980 noted that the Bedouin wear black robes in astonishingly hot desert conditions, but found that the advantages and disadvantages pretty much cancelled each other out. It turns out that other factors matter much more than clothing colour: for example, loose garments are helpful for heat loss because the air that flows between you and the clothes will cool you down, and a breeze will help too. So wear whatever colour you like!

INVERSE FREEZING

We all know that freezing is the process of cooling down a liquid until it solidifies. But scientists have also discovered a process called ‘inverse freezing’, where it happens backwards. A solution of two chemicals (alpha-cyclodextrin and 4-methylpyridine) in water starts off as a transparent liquid at room temperature and then becomes a milky white solid once it’s heated. When cooled, it returns to a liquid. It’s thought that at lower temperatures, the two chemicals cluster together, making the solution liquid. When the temperature rises, the bonds joining them to each other break, and then the whole mixture can crystallise to form a solid.

Dr Helen Czerski is a physicist, oceanographer and broadcaster. Her latest BBC series is From Ice To Fire: The Incredible Science Of Temperature. Catch up on iPlayer. bit.ly/ice_fire

The Bedouin provide proof that you can wear whatever colour you like in scorching conditions

Most liquids, like water, become solid when they cool down. But some chemicals seemingly defy the laws of physics