<p>NASA’s Goddard Institute for Space Studies has revised its Surface Air Temperature Anomaly record for the continental United States after Stephen McIntyre,mining businessman now blogger at climateaudit.com, discovered an error which made post-2000 data significantly warmer.</p>
<p>The correction means 1934 has been rediscovered as the hottest year in American history with 1998 and 2006, previously the hottest two years, relegated to second and fourth respectively. 1921 and 1931 completed the top 5 warmest years since records began. The <a href="http://data.giss.nasa.gov/gistemp/">new data</a> is available on NASA’s <a href="http://data.giss.nasa.gov/gistemp/graphs/Fig.D.txt">website</a>.</p>
<p>To date the only known official statement NASA has released on the change, posted to its website, read: <span style="font-style: italic;">"the USHCN station records up to 1999 were replaced by a version of USHCN data with further corrections after an adjustment computed by comparing the common 1990-1999 period of the two data sets. (We wish to thank Stephen McIntyre for bringing to our attention that such an adjustment is nec</span>essary to prevent creating an artificial jump in year 2000.)"</p>
<p>While the effect on measured global warming is said to be a minor but not insignificant minus 1-2 per cent of warming the adjustment at a stroke reveals the heat of the <a href="http://en.wikipedia.org/wiki/Dust_Bowl">"dustbowl"</a> 1930s and makes contemporary runaway global warming vanish from US-based temperature history.</p>
<p>After the change to trace the <a href="http://data.giss.nasa.gov/gistemp/graphs/Fig.D_lrg.gif">US chart</a> (pictured) is to find what look like cycles of warming of equal potency between 25 years of cooling rather than continuous, runaway global warming.</p>
<p>That does not mean our current period of global warming is not historically exceptional: the equivalent <a href="http://data.giss.nasa.gov/gistemp/graphs/Fig.A2_lrg.gif">global chart</a>, which includes data from weather stations outside the United States, still shows recent temperature history as a huge mountain compared what has gone before.</p>
<p>Yet, the continental United States, as the largest area in the world subject to rigorous continous climatic measurement, has been seen as the "gold standard" of temperature records and the change is likely to attract attention.</p>
<p>The new disparity between US and world temperature records will be an inconvenient truth both to politicians who believe in human-driven global warming and those who don’t and mean increased division rather than concensus among climate scientists.</p>