Are the data and methods that provide evidence of global warming valid?
A small number of sites demonstrate a clear urban heat island (UHI) effect. Dark tarmac absorbs sunlight and radiates heat in the immediate vicinity; windows and bright concrete surfaces of buildings reflect sunlight towards the ground; and industrial and urban effluent from external air conditioning units, generators and vehicles send hot air flow into the surrounds. Influences such as these can cause the temperature within parts or all of a city or urban area to be significantly higher than would otherwise occur in that geographic location. Studies that look at hemispheric and global temperature trends, however, conclude that any UHI trend is less than one tenth smaller than decadal and longer term trends that are evident in the data. In addition, other studies have corrected for this effect and demonstrated that the warming trend is still clearly evident. There has been much debate over the ‘hockey stick’ graph of increasing northern hemisphere temperature anomalies (departures from
