Update: Warwick Hughes has reminded me of his post on 5 December at http://www.warwickhughes.com/blog/?p=2496 where he shows a distinct drift in UAH data compared with RSS, and in later posts he confirms this in southern Africa and the USA. Warwick says:
"I have checked UAH against CRUT4 and GHCN CAMS for all Australia and it looks like there was a drift in UAH 2005-2006. Until UAH resolves the issue, I think their ranking of Australian hot years is not worth repeating."
That may help explain the large divergence in recent years.
I will leave this post as is, with the caveat that it is based on available UAH and Acorn data.
On Friday, 2 January, the BOM released its Climate Statement claiming 2013 as the hottest year on record.
The UAH dataset for lower troposphere temperatures has also been just released.
I have compared BOM monthly data with UAH by converting the BOM anomalies to the same reference period as UAH (1981-2010).
It is plain to see that in the satellite era, Australian surface temperatures (as calculated by the BOM) reached a record last year.
For the 12 month periods to December, UAH agrees that 2013 was the hottest, just ahead of 1998 and 2009.
According to UAH, the 12 months period to October 2013 was just edged out by the 12 months to June 2010.
So, the BOM is right in saying 2013 was the hottest on their 104 year (and very much adjusted) record.
While the two datasets match reasonably well in most years, especially 1996-1999, they diverge markedly in recent extreme years. It appears that the BOM area averaging algorithm accentuates extremes, probably because of the scarcity of observing sites in the remote inland, where warming and cooling are much greater. Alice Springs, for example, being hundreds of kilometres from the nearest neighbouring site, contributes 7 – 10% of the national warming signal.
As well, the satellites’ remote sensors do not necessarily match the atmospheric conditions at ground level, depending on different seasonal conditions. However, to quote Dr John Christy, “the temperature of the lower troposphere (TLT) more accurately represents what the bulk atmosphere is doing – which is the quantity that is most directly related to greenhouse gas impacts.”
So- if you are interested in the weather, how hot it is locally, consult the BOM- the old Weather Bureau. If you are interested in whether the climate is changing due to greenhouses gases, consult the satellite data.
And yes, the weather has been hot (and still is where I live).