Figure 2. Comparison of three annual instrumental temperature series from the West Qinling Mountains, in China.

A) The three annual instrumental temperature series (CRUTEM3v, CRUTS3.1, and the annual mean instrumental temperature anomalies, averaged from measurements at 12 local meteorological stations) for the period AD 1901–2006. B) The three instrumental series for the period AD 1951–1995, after low-pass filtering with a Butterworth IIR filter with a cut-off frequency of 0.1 cycles per year.