Ocean patterns resistant to global warming

Another Life:A still October morning; an overnight raindrop pendant from every berry. Mooching out to measure what fell, a different sound catches my ear, a snatch of football rattle. A different bird flies up from the ruby platters of the guelder rose and perches on the wire: a big, long thrush bibbed with dark spots like a chest of medals; an upright, military bearing. One brief bugle of song, then it spots me and is gone.

A mistle thrush, as you knew. Plenty everywhere else, just not here at Thallabawn - our first, in fact. But we have berries and to spare: not only hawthorn and guelder rose, but firethorn brandishing wands across my window, bush roses smothered with hips, the apple trees bowed down. No mistletoe, of course, so stick with the mistle thrush's older name, the stormcock.

But that could lead us off to reveries quite disallowed by climate change: the stormcock perched on a bare branch in the bleak mid-winter etc, the first bird to sing in January, stuff borrowed from bards in the island next door. Will it still need to commandeer a loaded holly tree and bully all the other birds away? Without winter, what's a stormcock for? News of frost the other morning was marvellous: we haven't quite lost the seasons after all. I'm at an age to trot out talk of exquisite frost ferns on the inside of my bedroom window (I was 11) and frost still does beautiful things for hedgerows and trees. So long, of course, as we don't have to drive anywhere, and our water pipe from the hill stream doesn't freeze.

But I was also thinking of nature's own needs, for a spell of rest or even death: a cleansing interval. In Ireland's ecological scheme of things, plants and insects have been chosen over centuries to fit certain rhythms of senescence and growth, of seasonal extinction and renewal. Yes, our species will all "move north", very slowly and sequentially, to make way for unguessable successions. But when change overtakes nature's pace of selection, the prospect is a sort of tumbling anarchy. Midges bearing bluetongue - who'd have thought? Even the cold was a bit odd, after all those weeks of pampering warmth.

In Monkstown, Co Dublin, a butterfly-watcher spotted third-generation holly blues mating optimistically. Then brrr! and our first autumn logs in the stove. But this could, apparently, be that sort of winter - colder and drier than average - for the North Atlantic Oscillation (NAO) is in a weakly negative phase.

Given that the NAO is one of the oldest weather patterns on record, and that its influence seems, for the moment, well able to hold its own with the impact of global warming, it really is surprising how little we know about it.

What oscillates in the NAO is sea-level pressure of the atmospheric mass between Iceland and the Azores - islands on the same line of longitude, but with two very different climates. In winter, the mass swings between Iceland's low-pressure centre that generates so many Atlantic storms, and a high-pressure centre on warm, sub-tropical waters between the Azores and Iberia.

When there is a very large and consistent difference between barometer readings in the Azores and Iceland, the NAO is said to be "positive", with "a high seasonal index". In this state, there are more and stronger winter storms travelling northeast across the Atlantic, bringing warm, wet air to Ireland but giving cold, dry winters to the Mediterranean.

In a "negative" NAO winter, the difference in pressure is small. There are fewer and weaker storms, which bring warm, moist air to the Mediterranean and cold, dry, polar air from the north and east blowing into northern Europe.

Knowing that this happens is one thing: predicting it, quite another. UK meteorologists plumped for a statistical method using the slow variations in Atlantic sea-surface temperature. Clinching evidence for a link with the winter NAO did not come until 1999. Even now, for all the ocean's supposed inertia, big changes in the NAO can happen from one winter to the next and even within the winter months.

The recent run of dry, sunny days and cool nights should reward us with brilliant autumn colours in the trees. It is just the weather to promote the annual death of chlorophyll, leaving other pigments - yellow carotenes, red and purple anthocyanins - to blaze out in a brief biochemical glory before the fall of leaves.

Our native trees are already yielding a little to climate change in the timing of spring budburst, but are slower, supposedly, to move their autumn rhythm. Nature watchers might like to track their progress by sending records of colour change and leaf fall to www.biology.ie

Eye on Nature

On October 7th, I counted 12 pairs of jackdaws sitting on the high roof of a farm building. There were none sitting alone or in larger groups.

Christine Walker, Co Roscommon

Jackdaws start forming pairs in autumn. They sit closely together and fly to feeding grounds and roosts.

I found large numbers of sea snails (Janthine globosa) on a beach at Carrickfin, Co Donegal. I noticed a red string or worm running inside the floater foam. Could it have been the snail itself?

Peter Carr, Maynooth, Co Kildare

Dr Don Cotton tells me that it is the egg mass. The snails are dark blue/black .

A cheeky mouse regularly appears to feed on the nuts in our bird-feeder. Is this a field mouse?

Phil Brophy, Rathfarnham, Dublin 14

If it has dark-brown or chestnut fur, large ears and a yellow patch on he throat, it is a field or wood mouse.

Is it climatic warming or inversion that accounts for our cowslips flowering?

Paul Mohr, Corrandulla, Co Galway

The rhododendron is flowering again in October.