Extreme conditions: What's happening to our weather?

Britain is just a few showers away from recording a record wet summer, at the climax of the most remarkable period of broken weather records in the country's history. All of the smashed records are to do with temperature and rainfall - the two aspects of the climate most likely to be intensified by the advent of global warming.

While no specific event can be ascribed directly to climate change, the sequence of events is strongly suggestive of a climate that is now unmistakably altering before our eyes.

Furthermore, the pattern of increasing heat and wet weather has been visible in the same period all around the globe, with temperature and rainfall records broken in many other countries, from Australia (record drought) and India (record monsoon rains) to Greece (record forest fires).

Yet in the UK alone, in the past 14 months we have experienced the hottest July, the hottest April and the wettest June since records began. We have seen the hottest autumn and the hottest spring, and the second-hottest winter. We have also seen the hottest single month, and - by a considerable margin - the hottest single 12-month period.

Now we are on the brink of seeing the soggiest British summer as a whole - defined as June, July and August - since records were first kept for the United Kingdom in 1914. By Friday morning of last week, the average rainfall in Britain since the beginning of June was 356.6mm - just over 14 inches - and nudging up to the record of 358.4mm, set in 1956. It is increasingly likely a new record will be set if there is any significant rainfall between now and Saturday.

Even if there is none, summer 2007 has already passed the second-wettest summer mark (which previously was 1985, with a rainfall of 342.7mm). And the three months from May to July have easily broken the record for rainfall for that period.

The significance of these records is that they are actually occurring in the real world - rather than in the forecasts generated by computer mathematical models of the global climate.

That marks a major shift. For the initial decade of the climate change problem (from the first report of the UN's Intergovernmental Panel on Climate Change in 1990), the effects of global warming, such as extreme heatwaves and downpours, were seen as future events which the climate models predicted. They were thus much easier for sceptics to dismiss.

But, in recent years, extreme and record-breaking real events, entirely consistent with global warming predictions, have started to mount up - beginning with the remarkable heatwave of August 2003, which caused 35,000 excess deaths in France and northern central Europe.

That episode, the first event whose severity was ascribed by scientists directly to climate change, only just caught Britain with its edge.

But even so, it broke the UK's air temperature record on 10 August 2003, pushing it for the first-time ever over 100F, to 101.3F, or 38.5C. The previous record (set in 1990) was 98.8F or 37.1C. Thus the jump to the new record was 2.5F, or 1.4C - an absolutely enormous leap.

Some of the records of the past 14 months which we detail today are of similar astonishing dimensions. In particular, April 2007 and the summer just ended produced quite unprecedented weather for Britain - with quite unprecedented effects.

April was so warm (contributing to the warmest spring on record) that the natural world was put completely out of sync: swifts arrived (from Africa) a month early, as did the hawthorn flowers - known as May - which prompted suggestions they should be renamed April blossom.

And summer was so wet that it produced the worst flooding Britain has ever seen - with the two catastrophic "extreme rainfall events" of 24 June and 24 and 20 July, which did the damage, each being of a severity likely only once in 200 years, or even longer.

The climate has a natural variability which means that extreme weather has always occurred throughout the years. But the occurrence of all these extremes together, in such a short period, suggests that we are witnessing something quite new in the climate of Britain.

The 2nd hottest winter

The winter of 2006-07 (counted as December, January and February) was the warmest on record in the northern hemisphere since records began in 1860, according to US scientists; in Britain it was the second-warmest since records for the whole country began in 1914. It had some perverse effects, especially on the UK's hedgehogs, which were fooled by the warmth into having extra litters, thinking it was still early autumn; the young then died when the cold finally did arrive because they had had insufficient time to put on weight for hibernation, said the British Hedgehog Preservation Society.

The hottest April

The creamy-white flowers of the hawthorn bush have, for centuries, been an infallible sign in England that the month of May has arrived - the average date was about 11 May - but in April 2007, such were the astonishingly high temperatures, they came out three weeks early. April this year became - in effect - the new May. Swifts arrived back from Africa in the middle of the month, when they would normally get here at about the end of May's first week. The month was also the hottest April ever recorded in Britain.

(Almost) the wettest summer

The rainfall of this summer has been unprecedented. We are a few millimetres away from a record, taking summer as June, July and August, but the record for the period May, June and July has already been smashed. The floods that this summer's rain caused were the worst in recorded British history and caused perhaps £3bn worth of damage, leaving more than a third of a million people without drinking water, nearly 50,000 people without power and thousands more homeless. At the height of the flooding, scientists announced that a link between global warming and rainfall patterns in recent decades had been established for the first time.

April's scarcely-believable warmth turned spring 2007 (defined as March, April, and May) into the hottest on record. Perhaps the most remarkable visible effect of this in the natural world was the emergence of British butterflies: no fewer than 11 species broke their records for early appearances. The chalkhill blue, for example, was seen in Sussex on 16 May; normally it would appear in the first week of July. The speckled wood, normally visible at the end of March, was seen in Cornwall on 16 January, seven weeks early.

The wettest June

It started to rain heavily in the second half of May but, in June, the downpours really got into their stride, culminating in the "extreme rainfall event" of 24 June, which was so heavy in parts of the North of England that it brought catastrophic flooding to places where they were entirely unexpected, such as Doncaster and Hull, and began the disturbing flood summer (counties bordering the river Severn had their turn in July). With rainfall in some areas more than 250 per cent above normal, it was the wettest June in UK Met Office records.

The hottest month

July 2006 gave us a heatwave that produced temperatures not seen since August 2003, when the UK's air temperature record was broken. It reached a peak on 19 July when the temperature at Wisley, Surrey, hit 36.5C, or 97.7F, beating a record that had lasted since 1911; some thought the all-time record would be broken. But even though the peak of 10 August, 2003, was not reached (101. 3F, or 38.5C) the month taken as a whole was the hottest ever recorded in Britain.

The hottest autumn

Autumn in 2006 was a golden time, with its astonishing warmth extending through September and October into late November, when cherry trees were in blossom in Devon, and raspberries were fruiting in Northumberland. It broke the seasonal record for Britain with its mean temperature for the three months of 12.6C (or 54.6F). Perhaps the most remarkable example of the exceptional season was that holly berries were fruiting in mid-October, six weeks early- prompting fears there would be none left for Christmas.

The hottest single 12 months

At the end of April this year, the Met Office announced the previous 12 months, taken together (the end of April 2006 to the end of April 2007), had been the hottest 12 months ever to have occurred in Britain, with a provisional mean temperature of 10.4C. The previous record (March 1997 to April 1998) was 9.7C. That leap of nearly three-quarters of a degree is huge and should make everybody consider whether a major shift in Britain's climate is now becoming visible. It is by no means unreasonable to answer that question with a "yes".