There has been quite a debate over at WUWT regarding temperature measurements and temperature anomalies. The AGW crew argue that only anomalies can be relied on to track global warming. These anomalies calculated at each individual weather station are the deltas between the measured temperatures and the mean temperatures over a fixed period – just for that station. The anomalies from ~4000 stations all over the globe are then combined to give one global anomaly, yielding the familiar graph we know and love which shows ~0.6 deg.C rise since 1850. Looking in more detail however we discover that some parts of the world are not warming at all and some are even cooling. Thus motivated I went off in search of the “hot stations” and the “cold stations” from the Hadley/CRU provided station data. Here we define “hot stations” as those yielding an average anomaly increase since 1990 > 0.4 degrees. “Cold stations” are defined as those with an average anomaly < 0.1 degrees. since 1990. Had/CRU anomalies are relative to the period 1960-1989 so they all measure warming/cooling relative to that baseline.
The map above shows in red the “hot stations” and in blue the “cold stations”. In both cases the larger the point the stronger the warming/cooling. This is an active flash map so you can zoom in by dragging a rectangle, and view the data by clicking on any station, (zoom out by clicking anywhere else).
It immediately becomes obvious that the bulk of observed warming is concentrated in the Northern Hemisphere : Eastern Europe, Russia, central Asia, India, China, Japan, Middle East, North Africa. These are all areas of rapid population increase, development and industrialisation. There is essentially no warming at all in the Southern Hemisphere. Bolivia, Peru, Paraguay and Argentina all appear to be cooling. Even Australia and Zealand are static or cooling. The US is evenly divided and the UK shows essentially no signal at all.
The US actually has hundreds of stations used for the anomaly calculations – so most of them show little (<0.4deg.C) or no warming since before 1960 – see figure 1.
Could much of the observed temperature rise over the last 6 decades be simply due to increasing urbanisation and development since ~1960 ? We know that many of the weather stations are close to urban areas, so let’s do a back of the envelope calculation to see if this is a realistic possibility.
Estimates of the total urban land cover globally from satellites are about 2% of total land surfaces – approximately 3,000,000 km2 . Total average world energy consumption rate ( fossil, nuclear,hydro etc.) is about 15 TW ( see: wikipedia), and increasing by ~ 5%/year. My guess is that 80% of this energy ends up as heat (2nd law thermodynamics). Assuming that energy consumption is concentrated mostly in urban areas then the net “anthropogenic” heating in those areas works out at around 5 watts/m2. This then leads to an average 1.4 degreeC. rise in temperature for urban areas. Anyone who has lived in the city knows from experience that the surrounding countryside is indeed some 1-2 degrees colder.
This expansion in urbanisation is accelerating and by 2030 global urban land cover will increase by between “430,000 km2 and 12,568,000 km2, with an estimate of 1,527,000 km2 more likely”.[quoted from ref: 1]. The main growth areas are in China, India, South West Asia and Africa, which is also where the station data show most warming. Those stations appear to be experiencing anthropogenic warming of a rather more direct kind than that proposed by IPCC. They are likely warming due to increasing urban heating.
Another result of the debate on WUWT was the conclusion that there are actually 2 different ways to determine global temperatures. The first is to simply average the measured temperatures within a lat,lon grid and then weight the result according to the surface area on the Earth. The second method is to average instead the black body equivalent energy flux (T^4) to derive an equivalent “radiative” temperature. The averaged T^4 term is then converted back to a single “radiative” temperature by taking the 4th root. This would be interpreted as the black body temperature of the Earth. This new second method however has the effect of biasing the contribution of places with higher than average temperatures. I used both methods to calculate global temperatures from 1950 to 2011. A comparison of the two results for the period 1950-2011 is shown below.
The conclusions from this study are:
1) There has been no warming in the Southern Hemisphere since 1950. Radiative and measured temperature averages also agree.
2) Warming is observed in the Northern Hemisphere since 1950. This is concentrated in regions where rapid development and urbanisation are also occurring. It is therefore probable that some of these “hot stations” are affected by urbanisation warming rather than AGW. Discrepancies between the radiative and measured temperatures also imply that a few main Hot Spots are responsible.