Under the Microscope/Prof William Reville: Looking back over the years, I recall giving my garden grass its first annual cut in the first or second week of March.
This year I cut the grass on February 21st because it was growing so strong. I have also noticed that birds are nesting earlier and, in Cork, winter snow and ice are becoming increasingly rare.
Casual observation indicates that the world is warming and climate is changing. Scientific results confirm casual observations. The changing climate is placing a range of biological species under stress, and many may become extinct, as explained by Daniel Grossman in the January 2004 edition of Scientific American.
Alistair and Richard Fitter are British naturalists who recorded the first flowering dates of plant species, the spring arrival of birds and other seasonal signs around Oxford, England, over the past 50 years. Their records show that, during the 1990s, 385 plants flowered an average of 4.5 days earlier than in the previous 4 decades. Sixty plant species flowered 2 weeks earlier. This data correlates with the rising world temperature. Near-surface Earth temperature has risen by 0.6 degrees Celsius in the last 100 years and the warmest decade on record was the 1990s.
Many changes in life patterns in plants and animals around the world have also been recorded. Some 80 per cent of the more than 500 organisms studied have changed the time of migration or reproduction, the length of the growing season, or the population size or distribution in ways consistent with warming temperatures. Alistair Fitter believes that many of these changes are stressful and will lead to biological extinctions.
Studies now show that global warming damages relations among plants and animals within ecosystems by eroding links in food chains and challenging the fitness of some creatures to live in their habitats. The Netherlands Institute of Ecology has been studying great tits in the De Hoge Veluwe National Park since the 1950s. Since 1985, the tits have laid their eggs each year at the same time.
However, over this same period local spring temperatures have warmed by two degrees Celsius and winter moth caterpillar numbers, on which the tits feed their chicks, now peak a fortnight earlier than in 1985. In 1985, the caterpillar peak matched the greatest need of the tit hatchlings, but now the caterpillar season is well on the wane by the time most of the chicks have hatched. Birds and moths are growing out of synchrony - and are becoming "decoupled".
Decoupling is also seen further down the food chain in the link between the moth and its food - young oak leaves. The moth caterpillar must hatch almost exactly when the oak leaves open. The insects will starve if they hatch more than about 5 days before the leaves open and also if they hatch more than 2 weeks after the leaves open because by then the leaves have filled up with inedible tannin.
The oak leaves now open 10 days earlier than they did 20 years ago. Caterpillars overcompensate for this by now hatching 15 days earlier, and so they must now wait at least 5 days for food. Because critical links in the food chain of this ecosystem are stretched to the limit it is only a matter of time before the tit population goes into serious decline.
The component parts of an ecosystem, under constant climatic conditions, evolve to live together in synchrony so that the system is stable.
Thus, the tits, oaks and moths each respond to temperature change in a different way. The tit egg hatch date is determined by the early spring temperature when the eggs are laid a month before hatching. Early spring temperatures have not changed in the past 30 years. Moth egg hatch date is partly determined by the temperature in late winter and early spring, which has increased in recent decades. The time of oak leaves opening is affected by late spring temperature which has risen by two degrees Celsius since 1980. Thousands of years of evolution synchronised the life cycles of these three organisms, but the recent global warming is throwing things into disarray.
Migrating birds are also affected by climate change. Global climate is not changing uniformly - temperate regions are warming much more than the tropics. Many birds decide on when to depart tropical wintering sites by using the length of day as a cue. Global warming has no influence on the length of day and therefore migrating birds are in danger of finding completely unsuitable conditions when they arrive at their temperate breeding grounds.
Changing climate conditions will disrupt ecosystems and put many species at risk, as apparently happened at the end of the last ice age. Some species are nimble enough to adapt to changing climate conditions but the less nimble species, such as many plants, are more at risk.
Pollen studies of the end of the last ice age are suggestive of what might happen. Forests moved in as the ice sheet retreated. However, complete forest communities did not move north en block as temperatures rose. The mix of animals and plants changed as the forest moved. Global warming could have a similar effect, discarding species that cannot adapt and creating new ecosystems that are unknown today. We are aboard a moving train travelling to an unknown destination.
William Reville is associate professor of biochemistry and director of microscopy at University College Cork