See more regional focus issues in the Regional Summary series at www.appinsys.com/GlobalWarming
The IPCC calculates average temperatures based on the average temperatures in 5x5 degree grid “squares”. The IPCC AR4 (Figure 9.6, 2007) shows the following trend maps. The following temperature charts are from the GHCN database.
Left: 1901 – 2005 Right: 1979 – 2005
The following page shows the temperature stations in the two 5x5 degree grids (white rectangles indicate the grids). The problem observed for [50-55 lat, 100-105 long] (above-left) is that there is only one station – Irkutsk – an urban station, which shows continuous warming. The [50-55 lat, 105-110 long] (above-right) grid has more stations, which show no warming until the 1990’s – this is when all but one station stop. The only one (Ust Barguzin) is actually a combination of multiple sites. These two grids illustrate the problem of having only one station in a grid.
The following figure shows monthly averages for Irkutsk (red) with the annual average (blue). Most of this urban area warming is occurring in the winter months.