Evidence for climate change - Climate Change: A Very Short Introduction - page 37

tinuous record of global surface temperature from 1880 to 2012, which shows a global
warming of 0.85°C over this period. These observations are supported by 50 years of bal-
loon and satellite data. For example there are over 800 stations that twice a day release
rawinsondes (meteorological instruments), or balloons, to measure temperature, relative
humidity, and pressure through the atmosphere to a height of about 20 km, where they
burst.
7. Northern Hemisphere temperature reconstruction for the last 1,300 years
Global temperatures have also been reconstructed for periods of time pre-dating instru-
mental or thermometer records. This is has been achieved by using palaeoclimate proxies
such as the thickness of tree rings and the isotopic composition of ice cores or cave depos-
its to estimate local temperatures. The global warming 'hockey stick' term, which was
discussed in Chapter 2 , came about when the global mean temperature instrumental record
was combined with palaeoclimate reconstructions of the last 2,000 years (see Figure 7 ). In
this context it is clear that the last 50 years have been very different and much warmer
than the previous 2,000 years.