In 2007 the Intergovernmental Panel on Climate Change (IPCC) – a collection of the world’s top climate change experts – concluded that not only is global warming “unequivocal”, but that it has accelerated over the last 50 years (IPCC 2007). This conclusion is based on data collected at the Earth’s surface and by satellites, which show that average global temperatures increased by 0.74^oC during last century.

This warming trend can be seen in Figure 1, below, which charts the variation in average global surface temperatures since instrumental records began in 1850.

^{Photo Attribution}

Figure 1: Global surface temperature trends over the period 1850 to 2008. (Data source: UK Metrological Office, 2008a)

The IPCC also concluded that there was a greater than 90 per cent certainty that increases in global temperatures since the mid-20th century was caused by a build up of greenhouse gases generated by human activities, especially burning of fossil fuels and land clearing (Hegerl et al 2007).

The climate does not change magically and must be driven by either internal changes or external forcing. While sun spots, solar activity and other factors do affect the Earth’s temperature, the most recent analysis from the IPCC concludes that global warming is overwhelmingly driven by the build up of greenhouse gases in the atmosphere (see Figure 5 in Myth 5).

UK Meteorology Office (2008a), HadCRUT3: Global surface temperatures, http://www.metoffice.gov.uk/research/hadleycentre/obsdata/HadCRUT3.html

Hegerl, G.C., F. W. Zwiers, P. Braconnot, N.P. Gillett, Y. Luo, J.A. Marengo Orsini, N. Nicholls, J.E. Penner and P.A. Stott, 2007: Understanding and Attributing Climate Change. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

http://www.flickr.com/photos/benpiper/ / CC BY-NC-SA 2.0