Having said I do not trust predictions made by climate models, I have tried looking at the data to see if global warming is happening. In principle this ought to be quite simple, but what I found was a morass of bad and missing data that makes it extremely difficult if not impossible.
My first attempt was a simple one: I would get the raw station data from NASA’s GIS for only those rural stations that had full data for 1901 to 1910, and also for 2001 to 2010. That would only be a few, but with thousands of stations around the world I should be able to get at least a representative sample. In addition I would look at some decades in between to see if there was a consistent trend (rather than just an isolated warm or cold decade)
If there were too little data then I could loosen my criteria by using a later starting date when necessary.
The first disappointment was that I could not get a single download of raw data. You can download data a station at a time, but this has an unexplained correction applied to it.
I did email and ask, and was told I could get a complete data download, but this is gridded data, not raw station data. I anyone knows how I can get raw station data please let me know! What I really need is a single download in an easy to parse format.
I subsequently found some worrying criticism of the corrections, and even of the raw data. The most important are Surface Temperature Records – Policy-driven Deception? and surfacestations.org.
What really convinced me of the validity of these criticisms was how difficultly I had in finding any complete records on the NASA GIS site. Lots of station records stopped (i.e. stations were closed or moved) in the 1980s ad 1990s: stations were being closed, especially most of the old stations that give us an invaluable long term record at a single location. Why was this happening just as global warming was becoming an important issue? I suspect the people in charge of the funding were more concerned about the politics of global warming than the science.
Essentially the temperature data is too suspect to be of much use in proving anything.
There is one more thing I noticed while looking for this data. Those who claim that global warming is proven often spin a romantic tail of brave scientists trying to establish proof of global warming in the face of a well funded sceptical lobby. It is apparent that this is the exact opposite of the truth. There is a huge amount of funding for those pushing the global warming claim. Government funds run sophisticated websites, such as the two NASA climate change sites. There are plenty of research grants (because it is now an important issues). There are plenty of big money vested interests in carbon trading and renewable energy. On the other hand surfacestations.org relies on volunteers to carry out the work, and many of the sceptical websites and organisations are obviously run by very small teams, not often even full time.
As far as temperature rises go, the evidence is inconclusive. We are back to relying on models, and I do not trust complex models.
I plan to look at sea level rises next. That is the most important claimed consequence of global warning, and firm evidence of a sea level rise large enough to be problematic will show that we have a serious problem.