Letter: A week of extreme heat raises a crucial question (2)

From Leslie King, Basingstoke, Hampshire, UK

In your article “A week of record-breaking heat”, you present a graph showing the rise of global temperatures over the past few decades. But why is there such a seasonal effect if the temperatures really are global?

To put it another way, why are temperatures during summer in the southern hemisphere so much lower than during summer in the northern hemisphere?

The editor writes:

Thanks for raising this. It is to do with there being more land in the northern hemisphere, which boosts the average temperatures there.