The Earth's climate is changing because of man's interference with the environment and if you don't believe the scientists, believe the butterflies.
New research published last week shows that a whole range of non-migratory butterfly species are gradually drifting northwards, relocating to cooler climes. And a separate research study of all those factors capable of influencing climate indicates that when all others are factored out, human activity is having an impact.
Both papers appear as letters in the current edition of the science journal Nature. Together they provide compelling evidence that our climate is slowly changing as a result of the discharge of greenhouse gases. The greenhouse scenario states that as levels of gases such as carbon dioxide and methane build up in the upper atmosphere, they will serve to heat up the atmosphere by trapping energy reaching us from the sun.
Researchers from Sweden, the US, Spain, Britain, France, Finland and Estonia joined forces to study over 50 species of migratory and non-migratory butterflies. They studied changes in their respective ranges, looking for shifts either north or south.
They note that some migratory species will respond rapidly to yearly climate variation by altering the timing or destination of migration. It is more difficult to assess whether a given year or decade represents a response to variability in weather or to true climate change.
The non-migratory species are easier to track however, as they tend to remain in a given area, and are unable to respond rapidly to change. They can be measured, however, by the ratios of extinctions to colonisations at the northern and southern boundaries of their respective ranges.
The researchers looked at species right across Europe and north Africa, and tried to avoid any effects that might have been due to non-climatic factors such as changes in agricultural practice.
They found, when looking at the whole range of their sample of 35 non-migratory butterfly species, that 63 per cent had ranges that have shifted to the north by between 35km and 240km during this century. Another 29 per cent were stable at both their northern and southern boundaries and only 3 per cent of species shifted both north and south.
They looked at the northern boundaries of 52 species and found that 65 per cent of these had moved northward over the past 30 to 100 years, 34 per cent were stable and 2 per cent had moved southwards. Looking at southern boundaries of 40 species they reported that 22 per cent of species had moved northward, 72 per cent had remained stable and five per cent had extended southward.
The researchers pointed out that Europe has warmed by about 0.8 C this century, shifting the climatic average northwards by about 120km. They could only conclude that the northward shift was a response to increased temperatures. "Given the relatively slight warming in this century compared with predicted increases of 2.1C to 4.6C for the next century, our data indicate that future climate warming could become a major force in shifting species' distributions," they conclude.
Things don't look much better when looking at all possible causes for this rise in temperatures. Researchers at the Hadley Centre for Climate Prediction and Research at Bracknell, at the Space Science Department at the Rutherford Appleton Laboratory in Chilton and at the University of Oxford's Department of Physics looked at warming trends over this century.
While it is difficult to pin down causes for warming up to 1940, they suggest that warming over the past 30 to 50 years "is unlikely to be entirely due to internal climate variability".