Melbourne has just endured its hottest September on record. Sydney is predicted to set an October temperature record on Thursday.

But when do we stop talking about breaking records and admit we've got a radically different climate?

In Melbourne, a new study suggests, it will be 2045. In Sydney that time will come in 2038.

Climate scientists have created an index of the year when the average climate of any given region on earth will likely push outside the extreme records experienced in the past 150 years should greenhouse gas emissions continue unabated.