Here is a cookie for you. From Have's link:
The Sceptic:
Instruments show there has been some warming of the Earth's surface since 1979, but the actual value is subject to large errors. Most long-term data comes from surface weather stations. Many of these are in urban centres which have expanded in both size and energy use. When these stations observe a temperature rise, they are simply measuring the "urban heat island effect". In addition, coverage is patchy, with some regions of the world almost devoid of instruments. Data going back further than a century or two is derived from "proxy" indicators such as tree-rings and stalactites which, again, are subject to large errors.
Answer:
"Warming is unequivocal. Weather stations, ocean measurements, decreases in snow cover, reductions in Arctic sea ice, longer growing seasons, balloon measurements, boreholes and satellites all show results consistent with the surface record of warming. The urban heat island effect is real but small; and it has been studied and corrected for. Analyses by Nasa for example use only rural stations to calculate trends. Recently, work has shown that if you analyse long-term global temperature rise for windy days and calm days separately, there is no difference. If the urban heat island effect were large, you would expect to see a bigger trend for calm days when more of the heat stays in the city. Furthermore, the pattern of warming globally doesn't resemble the pattern of urbanisation, with the greatest warming seen in the Arctic and northern high latitudes. Globally, there is a warming trend of about 0.8C since 1900, more than half of which has occurred since 1979. "
One can easily add to this.
1- Moving migrations currently happening. Be it birds, insects, fish or plants
2- Changes in agriculture, where plants for warmer climate can suddenly be grown successfully in what were cooler regions.
3- Tree rings. Yes, they were mentioned, but going back for quite some time, they give an interesting datapool.
4- Seeds. If you excavate some good deep soil, it is possible to determine the flora in ancient times.
5- History. One of the reasons we know that much about both the medieval warming period, and the little Ice age. In my area the MWP is supported with History, archeological remains, and seeds.
6- Glacial scratches and Glacial landscaping. It does not have to be entire valleys, but since glaciers advance and as mostly today, - retreat, - this helps to tell where the glaciers were at best in ancient (but historic) times.
Anyway, all point the finger more or less in the same direction. A warming trend. BTW, do not confuse climate with weather, - if I recall right, the climate is measured in a min. 30 years span.
Have a nice day
