Here is a project that I hope some will find interesting. I am assuming, incidentally, that most on this forum are not skeptical about the reality of climate change (in common with 97% of scientific researchers!).
Have a look at the first picture below, which was provided by Professor Tim Sparks, with whom I have worked on this. It shows two views of the same scene, importantly taken on the same date. And the key point is that it shows different levels of foliage. The progress of the seasons was obviously different in the two years.
This led us to look for other photos taken on the same day in different years. For the comparison to be really useful they have to be either in the autumn or spring so you can see fairly easily how much foliage there is - there is not much variation in the summer! And this turns out to be quite tricky - all those photos in the album you inherited from your mum don't tend to be of the same view, and very rarely have accurate dates on them - 'Easter 1934' if you are lucky! Tim and I cast about, and we came up with Armistice Day (Nov 11) in Whitehall, May Day in Moscow (though some suspicion as to whether the trees had been trucked in to look impressive!) and, bizarrely enough, Queen Beatrice' birthday in Holland, officially on April 30. But Armistice Day was the winner, with quite a lot of newspaper and archive photos and videos. See the next pic for some examples; we managed to find a good 60 or so from different years.
Tim did some work with classes full of students, inviting them to judge, on a 5 point scale, whether the trees were in full leaf or leafless. There were surprising levels of disagreement, and also some inconsistencies in the same year. See the third image, a graph, in which the vertical lines connect photos of the same year with trees in different states of leaf.
Obviously there are very big variations from year to year, as would be expected, so one has to concentrate on the long term trends. The overall message is pretty clear, though, from the line on the graph. London Plane trees, Platanus × acerifolia, have clearly tended to lose their leaves later on as the twentieth century passed. Very similar things happened in Paris, and this correlates very well with the temperature record for the period - next graph.
This provides a rather different perspective on the overall subject of climate change, though we haven't yet published it - you heard it here first! One of the complications is the 'urban heat island effect' - cities are warmer than the country, and that may have influenced the result; also, the causes of leaf fall are more complex than just temperature. But to find that trees - when their foliage is captured in a photo - are telling the story of climate change, is I think moving, powerful and somewhat poetic.
We'd love to get more data on this. Does anyone have any other photos to contribute, ideally a lot of them? The criteria are hard to meet:
- photographic views of the same foliage
- with trustworthy, identical dates in different years
- during the period when foliage either develops or leaves fall.