Adjusting the figures

Watts Up With That reports on a fascinating temperature measurement oddity:

'UAH, RSS and HadCrut show 1998 to be the hottest year, while GISS shows 2010 and 2005 to be hotter.

But it wasn’t always like that. GISS used to show 1998 as 0.64 anomaly, which is higher than their current 2005 record of 0.61.'

Read the whole article but here are a couple of other extracts:

'Note that not only was 1998 demoted, but also many other years since 1975 – the start of Tamino’s “modern warming period.” By demoting 1998, they are now able to show a continuous warming trend from 1975 to the present – which RSS, UAH and Had Crut do not show.

...

Note that without the post-1999 gymnastics, GISS and Had Crut match quite closely, with warming ending in 1998.'

The conclusion is even more fascinating:

'Conclusion : GISS recently modified their pre-2000 historical data, and is now inconsistent with other temperature sets. GISS data now shows a steady warming from 1975-2010, which other data sets do not show. Had GISS not modified their historic data, they would still be consistent with other data sets and would not show warming post-1998.'

Why is data being adjusted to fit the pattern desired?