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Dr Christian Hance lives in Sussex but was able to join us online. He is Chair of the Chichester Natural History Society. He was awarded his PhD by the University of Sussex for his work on the IT modelling of flowering, although he was quick to tell us he is not a botanist. His father, our founder Dennis Hance, made brief appearances before and after his talk.

Christian explained that there are natural cycles in the Earth’s temperature. It has been cooling for the last three million years, with ice ages occurring at intervals of 41,000 and 22,000 years. We should be entering an ice age about now, so global warming isn’t entirely bad news.

During internment in Austria at the beginning of the First World War, the Serbian scientist Milutin Milankovitch researched the cyclical changes in sunlight reaching the Earth. He concluded that they were due to:

• the regular change in the eccentricity of the Earth’s orbit around the sun, ie the extent to which it differs from a perfect circle, which cycles roughly every 413,000 years,
• the degree of tilt of the Earth’s axis, which cycles between 22.1° and 24.5° about every 41,000 years,
• the precession of the equinoxes, ie the continual change in the direction in which the Earth’s north pole points, which cycles every 25,771½ years. [An incredibly precise figure compared with the others but the phenomenon has been known about for a long time. Webmaster]

These are known as the “Milankovitch cycles”.

The human race has been impacting on our weather for a very long time. An increase in CO₂ in the atmosphere around 8000 BC has been put down to farmers adopting “slash and burn” tactics to clear land. An increase in methane in the atmosphere about 5000 BC is thought to have been caused by an increase in rice farming, methane being given off by the discarded parts of the crop. There is a theory that the decimation of the population of America because of diseases brought by Europeans in the 16th century led to a reduction of farming there and a consequent increase in carbon-capturing plants, leading in turn to a reduction in CO₂ in the atmosphere and the mini ice age in Europe in the 17th century.

Here in the UK there was a period of around 500 years when the temperature was warm enough to allow vines to be grown as far north as Cheshire. This ended some 700 years ago.

Christian showed us a coloured “bar code” with the various colours indicating the changes in temperature since 1850. There was a considerable amount of red as it got nearer the current day. However, the average UK temperature did not start to increase until 1940. The summer temperatures in the UK are now 5% higher than they used to be, with temperatures in other seasons being a staggering 11% higher than they were.

The changes in the seasons are causing problems for wildlife because particular species have evolved to occupy particular niches. This has led some species, for example, to move their ranges northward as temperatures rise.

There are particular problems for animals which turn white in the winter either to protect themselves from predators or to hide themselves from prey. They are now turning white before the snow arrives, and in some cases remaining white after it goes, making it much easier for other creatures to spot them.

Some flowering species are now flowering earlier. This can cause problems if they then flower before the emergence of the insects which feed on them or which they need for pollination. In some cases the interdependent species have themselves adapted. For example, caterpillars are now hatching earlier in sync with the earlier availability of the plants they feed on. This has led tits to hatch earlier to coincide with the greater abundance of the caterpillars on which they feed.

Christian mentioned that newts are now appearing earlier than they did but frogs aren’t. This results in newts eating the frogspawn, leading to a reduction in frog numbers.

He also told us about a 14-year study conducted by the Chichester Natural History Society, during which members were asked to record the first dates on which they saw various indicator species. Originally there were 27 species on the list but the chiff-chaff had to be withdrawn because it is becoming a year-round resident. Christian averages the results for each species each year. Three species now regularly appear 26 days earlier than they did 14 years ago and one species 30 days earlier.

Christian had started his talk by promising that he would address the question “Why are some bees getting more sex?” He ended his talk with this.

The answer comes from the interrelationship between the Miner Bee and the Early Spider Orchid. To a male Miner Bee the orchid looks, feels and smells like a female Miner Bee. The male bee emerges before the female but is preoccupied with sex and therefore seeks to mate with the orchids, pollinating them in the process. When the females emerge it loses interest in the orchid and goes after them instead. The changing seasons have led the male Miner Bees, the Early Spider Orchid and the female Miner Bees all to emerge or flower earlier than they did. The problem for the orchid is that the gap between the emergence of the male and female bees is now shorter than it was, giving a shorter time for the orchids to be pollinated. They could disappear completely.

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