Global Warming Trends

Charlie Nelson
director foreseechange
April 2003

Global temperatures have increased significantly over the past 100 years and particularly rapidly over the past 25 years.

The Jones et al temperature data set contains annual temperature time series data at a grid-box resolution of 5 degrees latitude by 5 degrees longitude.  It is a product of the Climate Research Unit of the University of East Anglia and the Hadley Centre of the UK Meteorological office1.



Over the entire period, there is a statistically significant upward trend of 0.6 degrees Celsius per century.  For the period from 1975, the upward trend is a statistically significant 2.0 degrees per century.

There was a period of cooling between the mid-1940s and the mid-1970s.  The more rapid rate of increase since the mid-1970s has been observed in Australia, USA and elsewhere and is probably due to reduced concentrations of sulphur dioxide in the atmosphere.  Sulphur dioxide is emitted by coal fired power stations and has a cooling effect.  Clean air initiatives resulted in reduced emissions since the 1970s.

The future rate of temperature increase will be influenced by natural factors as well as the rate of increase in greenhouse gasses.  But the conclusion from this data set is clear there has been statistically significant global warming over the past century and this appears likely to continue.


  1. Jones, P. D., Parker, D. E., Osborn, T. J. and Briffa, K. R. 1999.  Global and hemispheric temperature anomalies land and marine instrument records.  In Trends: A Compendium of Data on Global Change.  Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Ok Ridge, TN, USA.