THE Earth’s temperature has risen by 1 °C over the past 500 years and
half of the warming took place in the 20th century.
Harry Pollack of the University of Michigan in Ann Arbor collected data from
more than 600 boreholes around the world. He estimated past climate by analysing
the temperatures at different depths. Shallow boreholes reflect recent climates,
while deeper boreholes record more distant times. He found increases of 0.3
°C in the 19th century and 0.5 °C in the 20th century (Nature,
vol 403, p 756).
