Clear indications that global warming is affecting Ireland's climate have been found in changes to living organisms. Swallows are arriving earlier and the growing period for trees is increasing.
Scientists from Trinity College Dublin and NUI Maynooth carried out a project to identify biological indicators which could be used to detect climate change in Ireland. In particular they were looking for a response to changes in temperature.
Scientists believe air temperature in the State will increase in line with the average global increase of at least 0.3 degrees Celsius per decade over the next 50 years. Yet finding a reliable indicator of global warming is difficult, says Dr Alison Donnelly of the Climate Change Research Centre, School of Botany, TCD, who is leading the project.
She says the environment is a complex system with various interacting factors, all of which can influence the behaviour of organisms. The project, which is currently in its final stages, first looked at a number of possible indicators.
Tree rings are excellent indicators of abrupt climate changes, but are not suitable for noting the gradual increase in temperatures, as they did not suffer a concentrated period of stress, says Dr Donnelly. And Ireland's climate, unlike that of other countries, doesn't have the more extreme climactic conditions which may be reflected in tree rings.
Dr Donnelly said crops were also considered as possible indicators, but were not very reliable, as their growth and development is influenced by several other factors. So it is not a scientifically valid assumption to say an increasing temperature and the emergence of a specific type of crop definitely indicates climate change. Dr Donnelly says the crop's growth could also be influenced by, for example, more advanced agricultural techniques, or increased subsidies for farmers to grow a specific crop.
Reliable indicators for global warming need several essential characteristics, Dr Donnelly explains. They need a historical record to show how the indicator responds over time to a change. They need to be sensitive to a change in temperature, and they need a baseline against which the change in the indicator's behaviour can be measured.
Even so, "it is difficult to say, with absolute, 100 per cent certainty" that something is a reliable indicator, she says.
The researchers found the growing cycle of trees showed evidence of influence of climate change. The scientists discovered that the beginning of the growing season, defined by the unfolding of leaves, was occurring earlier in the spring.
And they also noted that the end of the growing season, the time when the leaves fall, occurred later in autumn, both of which point to an influence of rising global temperatures.
The current growth cycle of trees could be compared with previous cycles, using data collected since 1966 from four gardens located in the State: the National Botanical Gardens, Dublin; Johnstown Castle, Co Wexford; the JFK Arboretum, Co Wexford; and on Valentia Island.
The four are special phenology gardens where the relationship between the growth cycles of trees and climate change can be studied scientifically. Native Irish trees studied included the birch, poplar, cherry, rowan and willow.
Introduced species, including beech, lime and robinia, were also examined. The same trends - earlier blooming, leaves falling later - emerged in both types of trees.
Historical records do not extend as far back for the migratory patterns of birds. Dr Donnelly said records of when swallows arrive on the east coast only extend back to the 1980s, but provided some evidence to reveal the swallows' changing patterns of migration.
The study "gives us a reasonably good proof that we need long-term monitoring programmes in the State", she said.
The research is part of a larger project, funded by the Environmental Protection Agency (EPA), on impacts and indicators of climate change in the State. This project is due to finish in October.