The International Surface Temperature Initiative
My name is MIchael de Podesta andI am a metrologist - actually the person who has made the most accurate temperature measurements in human history - and I sit on the steering for the International Surface Temperature Initiative.
Point 1. All the data is available on line if you want it.
Point 2. The dataset is difficult and the main problems using it are clearing through erroneous files - station records that are duplicated or misidentified. Only after this process can one begin 'homogenising' the data. This is the process of adjusting older data FROM A PARTICULAR WEATHER STATION so that it is fairly comparable with recent data FROM THAT SAME WEATHER STATION. This keeps as many things as possible the same
Point 3. You might think that weather data is very variable - but the statistics deal with the 'monthly means' - the average of 60 max/min readings which reduces the noise by square root 60 and actually data is not too noisy. By averaging these data over a decade or two trends of a small fraction of degree can be clearly seen.
Point 4 The homogenisation process looks for statistically significant 'odd' events. Originally this was done by hand and was very time consuming. Now the Pair-Wise Homogenisation Algorithm (PHA) is used. PHA takes the difference between two nearby (<~100 km) stations - with the expectation that a climate trend will be the same in both stations. By searching through many pairs it is possible to identify and locate anomalies in a particular station. Very great care is taken not to over adjust and PHA has been demonstrated to be conservative - it deliberately doesn't remove the full non-climate effect but it does very reliable detect urban heat islands.
Other teams use other techniques to detect UHIs e.g. - satellite maps of night time illumination.
Point 4. All the analyses - including that from Berkeley Earth Sciences which set out to show how bad the other analyses were - agree with other.
Point 5. The recent readjustment from NOAA NCDC Karl et al resulted in miniscule changes to the modern record but eliminated the hiatus because 10-year trens in climate data are statistically fragile.
Summary: The fact is the data tells us the Earth is warming - and the warming the oceans which cover 2/3 of the planet is very important for the temperature and rainfall for the land. I ask you all to please not impugn scientists who are just doing their best to get at the truth.