In an astonishing announcement on global warming and extreme weather, the World Meteorological Organisation signalled last night that the world's weather is going haywire.

In a startling report, the WMO, which normally produces detailed scientific reports and staid statistics at the year's end, highlighted record extremes in weather and climate occurring all over the world in recent weeks, from Switzerland's hottest-ever June to a record month for tornadoes in the United States - and linked them to climate change.

The unprecedented warning takes its force and significance from the fact that it is not coming from Greenpeace or Friends of the Earth, but from an impeccably respected UN organisation that is not given to hyperbole (though environmentalists will seize on it to claim that the direst warnings of climate change are being borne out).

The Geneva-based body, to which the weather services of 185 countries contribute, takes the view that events this year in Europe, America and Asia are so remarkable that the world needs to be made aware of it immediately.

The extreme weather it documents, such as record high and low temperatures, record rainfall and record storms in different parts of the world, is consistent with predictions of global warming. Supercomputer models show that, as the atmosphere warms, the climate not only becomes hotter but much more unstable. "Recent scientific assessments indicate that, as the global temperatures continue to warm due to climate change, the number and intensity of extreme events might increase," the WMO said, giving a striking series of examples.

In southern France, record temperatures were recorded in June, rising above 40C in places - temperatures of 5C to 7C above the average.

In Switzerland, it was the hottest June in at least 250 years, environmental historians said. In Geneva, since 29 May, daytime temperatures have not fallen below 25C, making it the hottest June recorded.

In the United States, there were 562 May tornadoes, which caused 41 deaths. This set a record for any month. The previous record was 399 in June 1992.

In India, this year's pre-monsoon heatwave brought peak temperatures of 45C - 2C to 5C above the norm. At least 1,400 people died in India due to the hot weather. In Sri Lanka, heavy rainfall from Tropical Cyclone 01B exacerbated wet conditions, resulting in flooding and landslides and killing at least 300 people. The infrastructure and economy of south-west Sri Lanka was heavily damaged. A reduction of 20-30 per cent is expected in the output of low-grown tea in the next three months.

Last month was also the hottest in England and Wales since 1976, with average temperatures of 16C. The WMO said: "These record extreme events (high temperatures, low temperatures and high rainfall amounts and droughts) all go into calculating the monthly and annual averages, which, for temperatures, have been gradually increasing over the past 100 years.

"New record extreme events occur every year somewhere in the globe, but in recent years the number of such extremes have been increasing.

"According to recent climate-change scientific assessment reports of the joint WMO/United Nations Environmental Programme Intergovernmental Panel on Climate Change, the global average surface temperature has increased since 1861. Over the 20th century the increase has been around 0.6C.

"New analyses of proxy data for the northern hemisphere indicate that the increase in temperature in the 20th century is likely to have been the largest in any century during the past 1,000 years."

While the trend towards warmer temperatures has been uneven over the past century, the trend since 1976 is roughly three times that for the whole period.

Global average land and sea surface temperatures in May 2003 were the second highest since records began in 1880. Considering land temperatures only, last May was the warmest on record.

It is possible that 2003 will be the hottest year ever recorded. The 10 hottest years in the 143-year-old global temperature record have now all been since 1990, with the three hottest being 1998, 2002 and 2001.

The unstable world of climate change has long been a prediction. Now, the WMO says, it is a reality.