Scientists at two of the world’s leading climate centres – NASA and NOAA – have been caught out manipulating temperature data to overstate the extent of the 20th century “global warming”.

The evidence of their tinkering can clearly be seen at Real Science, where blogger Steven Goddard has posted a series of graphs which show “climate change” before and after the adjustments.

When the raw data is used, there is little if any evidence of global warming and some evidence of global cooling. However, once the data has been adjusted – ie fabricated by computer models – 20th century ‘global warming’ suddenly looks much more dramatic.

This is especially noticeable on the US temperature records. Before 2000, it was generally accepted – even by climate activists like NASA’s James Hansen – that the hottest decade in the US was the 1930s.

As Hansen himself said in a 1989 report:

In the U.S. there has been little temperature change in the past 50 years, the time of rapidly increasing greenhouse gases — in fact, there was a slight cooling throughout much of the country.

However, Hansen subsequently changed his tune when, sometime after 2000, the temperatures were adjusted to accord with the climate alarmists’ fashionable “global warming” narrative. By cooling the record-breaking year of 1934, and promoting 1998 as the hottest year in US history, the scientists who made the adjustments were able suddenly to show 20th century temperatures shooting up – where before they looked either flat or declining.

But as Goddard notes, the Environmental Protection Agency’s heatwave record makes a mockery of these adjustments. It quite clearly shows that the US heat waves of the 1930s were of an order of magnitude greater than anything experienced at any other time during the century – far more severe than those in the 1980s or 1990s which were no worse than those in the 1950s.

These adjustments, however, are not limited to the US temperature data sets. Similar fabrications have taken place everywhere from Iceland to Australia.

The fact that supposedly reputable scientists can make these dishonest adjustments and get away with it is, notes long-time sceptic Christopher Booker, one of the more remarkable anomalies of the great climate change scam.