Edwin Latimer

When we take a temperature reading we use a thermometer and this would be what we call dry bulb temperature.

And it's an indication of how much moisture the air can hold, but also our ability to lose heat through sweating.

In usual circumstances, even if the normal temperature is high... When the relative humidity, so the amount of moisture in the air, is lower, the wet bulb temperature is lower because it can pass that energy into the surrounding air.

So if the amount of moisture in the air reaches 100%, then the dry bulb temperature and the wet bulb temperature would be the same because you would no longer be able to lose any heat.

You would no longer be able to cool down that thermometer through the moisture from the muslin cloth.

Yes, you would not be able to cool your body down anymore through sweating.

The temperature of wet bulb is likely to be around 25 degrees Celsius in the UK this week so already for Monday there are observations of 22 degrees Celsius in the wet bulb temperature for the UK so we are likely to reach that however that is not a critical threshold for wet bulb temperatures.

So a dangerous wet bulb temperature threshold is about 35 degrees Celsius.

However, there's a range depending on the type of person.

So those that are most vulnerable to heat, so these would be people that we've heard of that are like the elderly or those who are children under the age of five.

This could be as low as sort of 30 to 32 degrees Celsius.

But the one that people quote is 35 degrees Celsius.

And this is not being seen in Europe.

It's not likely to be seen.

We're reaching that threshold in parts of the world like Pakistan and India.

And this is where, you know, temperatures in the sort of hottest season regularly reach 50 degrees Celsius or above.