Changed interpretations?

This commentary is not about the science of climate change, though it is about change of a sort – change in how historical temperature information is being presented.

1999

An August 1999 Science Brief  from Goddard Institute for Space Studies stated, “The U.S. has warmed during the past century, but the warming hardly exceeds year-to-year variability. Indeed, in the U.S. the warmest decade was the 1930s and the warmest year was 1934.”1

The figure on the right, a trace of U.S. mean surface temperature anomaly2 for the contiguous 48 United States from 1880 to 1999 was included in the brief.  It clearly shows 1934 almost half a degree Celsius warmer than any other temperature in the figure and 0.6°C  (1.1°F) warmer than 1998.

2012Over the last 12.5 years, adjustments have been made such that the current version of the NASA GISS figure is different than that provided in the 1999 science brief.  When queried about the adjustments, NASA officials claim that the adjustments are small and not significant.  However, 1998 is now shown as higher than 1934 with a 0.7°C change relative to each other.  That’s equivalent to 23% of the total anomaly scale being used.

Below the two figures is a “blink comparator” images that shows, in animated form, how the information has been altered.  To me, it appears that the values have been changed from showing an overall average lowering of temperature in the 48 contiguous states since about 1934 to an overall rise in temperature since 1880.

1998changesannotatedNASA’s Goddard Institute for Space Studies (GISS) climate dataset is one of the world’s major climate sources of information for current and past climate information.  Policies and decision making related to climate are based on it.

Almost 30% of the world’s historic climate stations are in the United States – and almost 50% since 1990 –, yet the U.S. comprises only 2% of the earth’s surface.

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1 Whither U.S. Climate? by James Hansen, Reto Ruedy, Jay Glascoe and Makiko Sato — August 1999 (Note: This document no longer appears to be available on the NASA GISS website, but can be found on Internet Archive.  The GISS website is currently down and from what I can tell from reading other online sources, it’s been down for at least a couple of days.)
2 Temperature anomaly – a departure from a reference value or long term value.  The 1935 annual temperature was 1.5°C above the average long-term temperature.

Sunday Commentary for January 13, 2013.

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