On May 6th, Dr Roy Spencer released the University of Alabama-Huntsville (UAH) global average lower tropospheric temperature anomaly as measured by satellite for April 2014.
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.
April 2014: Anomaly +0.19 degrees Celsius
This is the 6th warmest April temperature recorded since the satellite record was started in December 1978 (35 April observations). The warmest April to date over this period was in 1998, with an anomaly of +0.66 degrees Celsius. Incidentally, April 1998 was also the warmest month ever recorded for this time series.
The El Nino Southern Oscillation (ENSO) cycle is the main determinant of when global mean temperature hits a new record over the medium term (up to 30 years). In this connection, the U.S. government’s Climate Prediction Center is now giving a 65% chance of an El Nino developing this summer or fall (here). Should this happen, I would expect the UAH anomalies to head back up into the 0.5s, 0.6s or higher.
As background, five major global temperature time series are collated: 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.
The official link to the data at UAH can be found here, but most months we get a sneak preview of the release via the climatologist Dr Roy Spencer at his blog.
Spencer, and his colleague John Christy at UAH, are noted climate skeptics. They are also highly qualified climate scientists, who believe that natural climate variability accounts for most of recent warming. If they are correct, then we should see some flattening or even reversal of the upward trend within the UAH temperature time series over a long time period. To date, we haven’t (click for larger image).
That said, we also haven’t seen an exponential increase in temperature either, which would be required for us to reach the more pessimistic temperature projections for end of century. However, the data series is currently too short to rule out such rises in the future. The Economist magazine published a very succinct summary of the main factors likely accounting for the recent hiatus in temperature rise (here).
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 adjusting them to a common base period.
Risk and Well-Being 
I frequently get skeptic community comments when I post on climate-related topics. There is a high bar for approval. For example, if the comment contains any derogatory terms, then it goes straight into the trash can. For example, if a post has wording such as “climate models are crap”, then into the bin it goes. Life is too short to deal with such low level discourse.
I wonder why you use the premature data Roy Spencer is publishing every month. Why not wait till NOAA or some other official organisation release their data? I agree that Roy Spencer has been a respect climate scientist long time ago but the papers he is publishing last years are often providing more rebuttals than readers (or even the editor in chief resigning, see Remote Sens. 2011, 3, 2002-2004; doi:10.3390/rs3092002).
Stefaan. I wouldn’t say the data is premature since it is the same data released by UAH, just a couple of days early. Further, the UAH data is official and recognised within the scientific community. It is different from NOAA or GISS to the extent that it is satellite data as opposed to terrestrial. You are right though that Roy Spencer has many detractors and is certainly viewed with suspicion by the wider climate scientist community. His blog is also very libertarian in tone. Why I track this data is because it is the most timely of the main global temperature data series and because it is quite useful from a Popperian falsificationist perspective. In short, if the temperature anomaly starts to move up again significantly for an extended period of time, which I expect it will in due course, it negates the idea that warming has ceased or sensitivity is very low. Note, it is possible that climate sensitivity is quite low; I think few mainstream climate scientists would deny that; they just assign it a very low probability while Spencer assigns this a very high probability. The UAH data will, in time, show who is right. Of course, so will GISS, but the satellite data has always been the series most advocated by the climate skeptic community.
I admit that falsification can be a strong tool when Christy and Spencer are involved… On the other hand, I can imagine that people not following the climate debate, again will have the impression that there is still a huge controversy about AGW in the scientific world when they use their names as the main stream climatologists.
I think that ultimately the data will speak. That’s why I believe that those who advocate aggressive mitigation measures to tackle climate change are on the right side of history. Whether to engage with climate change skeptics or ignore them is irrelevant.
Are you OK Justin? It’s been a while since your last post.
Hi Joe. My mother, who is 88, recently had a fall and I’ve been trying to sort things out for her, which has rather upended a lot of things for me. This has also come on top of a variety of other personal stuff I have been dealing with. I’ve also been involved in a variety of what I would call ‘micro’ type community sustainability projects, which have absorbed huge amounts of my time (often, unfortunately, for very little result – a source of future posts in and of itself). The blog has suffered a lot on account of all this, which is unfortunate, given it is one of the things which gives me most pleasure in life. I will endeavour to carve out some sacrosanct blog time, but please bear with me for a little while.
Sorry to hear about your Mother’s misfortune. I will patiently await your next post.