Why is UV so high in Australia?

A high sun

The closer the sun is to directly overhead, the less atmosphere its light passes through and the stronger the UV. Much of Australia lies between the tropics and the mid-latitudes, so the summer sun climbs very high at midday. In the north it stays high for most of the year.

Clear, dry air

Large parts of the country have long runs of cloudless days and low humidity. With little cloud or haze to scatter it, more UV reaches the ground.

A closer sun in summer

The Earth’s orbit isn’t a perfect circle. It’s closest to the sun in early January, right in the middle of the southern summer. That adds around 7% more UV than the northern hemisphere gets in its summer, at the same latitude.

Ozone

The ozone layer absorbs much of the sun’s most damaging UV. Levels over Australia are a little lower than over Europe and North America at similar latitudes, and the ozone hole over Antarctica occasionally lowers levels over southern Australia in spring.

What it means day to day

Summer UV of 11 or more is routine in every capital except Hobart, and the north sees Extreme readings for much of the year. That’s why Australian sun protection advice starts at 3, and why it’s worth checking the index rather than the temperature.

What UV 11 means