Defining the 'pre-industrial' climate

Scientists are seeking to define a new baseline from which to measure global temperatures - a time when fossil-fuel burning had yet to change the climate.

At the moment, researchers tend to use the period 1850-1900, and this will often be described as "pre-industrial".

But the reality is that this date range came after industry really got going.

Ed Hawkins from Reading University explained to our correspondent Jonathan Amos why 1720-1800 might make a better "starting line".