On July 6th, Dr Roy Spencer released the University of Alabama-Huntsville (UAH) global average lower tropospheric temperature anomaly as measured by satellite for June 2015 (here). The anomaly refers to the difference between the current temperature reading and the average reading for the period 1981 to 2010 as per satellite measurements.
June 2015: Anomaly +0.33 degrees Celsius This is the 3rd warmest June temperature recorded since the satellite record was started in December 1978 (36 June observations). The warmest June to date over this period was in 1998, with an anomaly of +0.56 degrees Celsius. Full data set available here (click for larger image).
The El Nino Southern Oscillation (ENSO) cycle is the main determinant of new temperature records over the medium term (up to 30 years) . The U.S. government’s Climate Prediction Centre currently has an El Nino advisory in effect and is forecasting that the current El Nino event is set to continue through into 2016 (update 9 July 2015 here):
Overall, there is a greater than 90% chance that El Niño will continue through Northern Hemisphere winter 2015-16, and around an 80% chance it will last into early spring 2016.
Given this background, I would expect the UAH anomalies to remain elevated for some time.
As background, five major global temperature time series are collated by different international agencies: three land-based and two satellite-based. The terrestrial readings are from NASA GISS (Goddard Institute for Space Studies), HadCRU (Hadley Centre/Climate Research Unit in the U.K.), and NCDC (National Climate Data Center). The lower-troposphere temperature satellite readings are from RSS (Remote Sensing Systems, data not released to the general public) and UAH (Univ. of Alabama at Huntsville).
The most high profile satellite-based series is put together by UAH and covers the period from December 1978 to the present. Like all these time series, the data is presented as an anomaly (difference) from the average, with the average in this case being the 30-year period from 1981 to 2010. UAH data is the earliest to be released each month.
One of the initial reasons for publicising this satellite-based data series was due to concerns over the accuracy of terrestrial-based measurements (worries over the urban heat island effect and other factors). The satellite data series have now been going long enough to compare the output directly with the surface-based measurements. All the time series are now accepted as telling the same story (for a fuller mathematical treatment of this, see Tamino’s post at the Open Mind blog here). Note that the anomalies produced by different organisations are not directly comparable since they have different base periods. Accordingly, to compare them directly, you need to normalise each one by adjustment to a common base period.
I mentioned it before, be carefull with those UAH data… I don’t think that it is just ‘bad luck’ that data from Spencer and Christy differ from the other data sets… Several months ago a very interesting article in the Journal of Climate was published and a guardian article covers it quite well