We're Frying Now!

You can expect the media to be shouting over the next few days that the last October was the hottest October ever. It was,except for parts of Asia where October was the hottest September ever.

It turns out that the data is skewed by heat-wave conditions in Siberia (normally called "summer"). A close examination of the raw data shows that several cities in that region had identical temperatures, right down to 0.1 deg, for October and September. It's possible that in a region where temperatures vary from +40 C in summer to -40C in winter, and hence you expect monthly trends to show several degreeds difference, it is possible that a heatwave led to pretty much the same conditions in two consecutive months-- but 5 cities in a region showing identical temperatures in two consecutive months is a data error not a heat-wave!

There are two broad groups of data used to estimate temperatures. The first is using land based measurements in various towns and cities. This is the method referred to above. The problem with this is that there is a huge urban heat island effect which causes large cities to warm up far more than rural areas- you can see that by the fact that on several days each year many parts of Sydney have hotter summer days than Narrabri for example, something that never happened when I was young. Another problem with this methodology is that it only measures the temperature where there are stations to measure them which might be 20 km or up to 1000 km apart.

The other method uses satellite data to measure temperatures in the lower atmosphere. It can cover areas not monitored by land-based stations, such as the ocean and the poles and other uninhabited areas. It avoids the heat island effect, and gives a more complete coverage, but on the other hand is dependent on satellites actually tracking over a particular region. Whereas the land-based system goes back up to 100 years, the satellite figures only go back 40 years.

The land-based system shows a greater amount of warming than the satellite system. The managers of both systems both have their own presuppositions... the man in charge of the land system is a global warming alarmist, while the guy in charge of the satellite system is a global warming sceptic. In both cases it is hard to say whether they have a bias before they started collecting the data or whether their conclusions come from the data.

Here are a couple of links:

Climate Skeptic

Andrew Bolt