It involves going out to your nearest green space and looking for snails and cataloging them for colour and banding. The hypotheses being tested are these:
(i) the proportion of lighter coloured snails have increased due to global warming;
(ii) there are generally more snails because their arch enemy (or main predator), the thrush, have declined in number over the last thirty years.
(It is my impression that thrushes are coming back again - I often hear them tapping away on snail shells. It is the sparrows that have declined. I used to see a flock of them descend onto the grass, but nowadays there seem to be very few).
With thanks to Eric-the-blogless for pointing out my typos.