The decade of 1998-2007 is the warmest on record, according to data sources obtained by the World Meteorological Organization (WMO). The global mean surface temperature for 2007 is currently estimated at 0.41°C/0.74°F above the 1961-1990 annual average of 14.00°C/57.20°F.

The University of East Anglia and the Met Office's Hadley Centre have released preliminary global temperature figures for 2007, which show the top 11 warmest years all occurring in the last 13 years. The provisional global figure for 2007 using data from January to November, currently places the year as the seventh warmest on records dating back to 1850.

Other remarkable global climatic events recorded so far in 2007 include record-low Arctic sea ice extent, which led to first recorded opening of the Canadian Northwest Passage; the relatively small Antarctic Ozone Hole; development of La Niña in the central and eastern Equatorial Pacific; and devastating floods, drought and storms in many places around the world.

The preliminary information for 2007 is based on climate data up to the end of November from networks of land-based weather stations, ships and buoys, as well as satellites. The data are continually collected and disseminated by the National Meteorological and Hydrological Services (NMHS) of WMO’s 188 Members and several collaborating research institutions. Final updates and figures for 2007 will be published in March 2008 in the annual WMO brochure for the Statement on the Status of the Global Climate.

WMO’s global temperature analyses are based on two different sources. One is the combined dataset maintained by both the Hadley Centre of the UK Meteorological Office, and the Climatic Research Unit, University of East Anglia, UK, which at this stage ranked 2007 as the seventh warmest on record. The other dataset is maintained by the US Department of Commerce’s National Oceanic and Atmospheric Administration (NOAA), which indicated that 2007 is likely to be the fifth warmest on record.

Since the start of the 20th century, the global average surface temperature has risen by 0.74°C. But this rise has not been continuous. The linear warming trend over the last 50 years (0.13°C per decade) is nearly twice that for the last 100 years.

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According to the Intergovernmental Panel on Climate Change’s 4th Assessment (Synthesis) Report, 2007, “warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.”

2007 global temperatures have been averaged separately for both hemispheres. Surface temperatures for the northern hemisphere are likely to be the second warmest on record, at 0.63°C above the 30-year mean (1961-90) of 14.6°C/58.3°F. The southern hemisphere temperature is 0.20°C higher than the 30-year average of 13.4°C/56.1°F, making it the ninth warmest in the instrumental record since 1850.

January 2007 was the warmest January in the global average temperature record at 12.7°C/54.9°F, compared to the 1961-1990 January long-term average of 12.1°C/53.8°F.

Regional temperature anomalies

2007 started with record breaking temperature anomalies throughout the world. In parts of Europe, winter and spring ranked amongst the warmest ever recorded, with anomalies of more than 4°C above the long-term monthly averages for January and April.

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Extreme high temperatures occurred in much of Western Australia from early January to early March, with February temperatures more than 5°C above average.

Two extreme heat waves affected south-eastern Europe in June and July, breaking previous records with daily maximum temperatures exceeding 40°C/104°F in some locations, including up to 45°C/113°F in Bulgaria. Dozens of people died and fire-fighters battled blazes devastating thousands of hectares of land. A severe heat wave occurred across the southern United States of America during much of August with more than 50 deaths attributed to excessive heat. August to September 2007 was extremely warm in parts of Japan, setting a new national record of absolute maximum temperature of 40.9°/105.6°F on 16 August.

In contrast, Australia recorded its coldest ever June with the mean temperature dropping to 1.5°C below normal. South America experienced an unusually cold winter (June-August), bringing winds, blizzards and rare snowfall to various provinces with temperatures falling to -22°C/-7.6°F in Argentina and -18°C/-0.4°F in Chile in early July.

Prolonged drought

Across North America, severe to extreme drought was present across large parts of the western U.S. and Upper Midwest, including southern Ontario/Canada, for much of 2007. More than three-quarters of the Southeast U.S. was in drought from mid-summer into December, but heavy rainfall led to an end of drought in the southern Plains.

In Australia, while conditions were not as severely dry as in 2006, long term drought meant water resources remained extremely low in many areas. Below average rainfall over the densely populated and agricultural regions resulted in significant crop and stock losses, as well as water restrictions in most major cities.

China experienced its worst drought in a decade, affecting nearly 40 million hectares of farmland. Tens of millions of people suffered from water restrictions.

Flooding and intense storms

Flooding affected many African countries in 2007. In February, Mozambique experienced its worst flooding in six years, killing dozens, destroying thousands of homes and flooding 80,000 hectares of crops in the Zambezi valley.

In Sudan, torrential rains caused flash floods in many areas in June/July, affecting over 410,000 people, including 200,000 left homeless. The strong southwesterly monsoon resulted in one of the heaviest July-September rainfall periods, triggering widespread flash floods affecting several countries in West Africa, Central Africa and parts of the Greater Horn of Africa. Some 1.5 million people were affected and hundreds of thousands homes destroyed.

In Bolivia, flooding in January-February affected nearly 200,000 people and 70,000 hectares of cropland. Strong storms brought heavy rain that caused extreme flooding in the littoral region of Argentina in late March/early April. In early May, Uruguay was hit by its worst flooding since 1959, with heavy rain producing floods that affected more than 110,000 people and severely damaged crops and buildings. Triggered by storms, massive flooding in Mexico in early November destroyed the homes of half a million people and seriously affected the country’s oil industry.

In Indonesia, massive flooding on Java in early February killed dozens and covered half of the city of Jakarta by up to 3.7 metres of water. Heavy rains in June ravaged areas across southern China, with flooding and landslides affecting over 13.5 million people and killing more than 120. Monsoon-related extreme rainfall events caused the worst flooding in years in parts of South Asia. About 25 million people were affected in the region, especially in India, Pakistan, Bangladesh and Nepal. Thousands lost their lives. However, rainfall during the Indian summer monsoon season (June-September) for India was, generally, near normal (105% of the long-term average), but with marked differences in the distribution of rainfall in space and time.

A powerful storm system, Kyrill, affected much of northern Europe during 17-18 January 2007 with torrential rains and winds gusting up to 170km/h. There were at least 47 deaths across the region, with disruptions in electric supply affecting tens of thousands during the storm.

England and Wales recorded its wettest May-July period since records began in 1766, receiving 406 mm of rain compared to the previous record of 349 mm in 1789. Extensive flooding in the region killed nine and caused more than US$6 billion in damages.

Development of La Niña

The brief El Niño event of late 2006 quickly dissipated in January 2007, and La Niña conditions became well established across the central and eastern Equatorial Pacific in the latter half of 2007.

In addition to La Niña, unusual sea surface temperature patterns with cooler than normal values across the north of Australia to the Indian Ocean, and warmer than normal values in the Western Indian Ocean, were recorded. These are believed to have modified the usual La Niña impacts in certain regions around the world.

The current La Niña is expected to continue into the first quarter of 2008 at least.

Devastating tropical cyclones

Twenty-four named tropical storms developed in the North-West Pacific during 2007, below the annual average of 27. Fourteen storms were classified as typhoons, equalling the annual average. Tropical cyclones affected millions in south-east Asia, with typhoons Pabuk, Krosa, Lekima and tropical storms like Peipah among the severest.

During the 2007 Atlantic Hurricane season, 14 named storms occurred, compared to the annual average of 12, with 6 being classified as hurricanes, equalling the average. For the first time since 1886, two category 5 hurricanes (Dean and Felix) made landfall in the same season.

In February, due to tropical cyclone Gamède, a new worldwide rainfall record was set in French La Reunion with 3,929 mm measured within three days.

In June, cyclone Gonu made landfall in Oman, affecting more than 20,000 people and killing 50, before reaching the Islamic Republic of Iran. There is no record of a tropical cyclone hitting Iran since 1945.

On 15 November, tropical cyclone Sidr made landfall in Bangladesh, generating winds of up to 240 km/h and torrential rains. More than 8.5 million people were affected and over 3,000 died. Nearly 1.5 million houses were damaged or destroyed. Often hit by cyclones, Bangladesh has developed a network of cyclone shelters and a storm early-warning system, which significantly reduced casualties.

Australia’s 2006/2007 tropical season was unusually quiet, with only five tropical cyclones recorded, equalling the lowest number observed since at least 1943-44.

Relatively small Antarctic ozone hole

The 2007 Antarctic ozone hole was relatively small due to mild stratosphere winter temperatures. Since 1998, only the 2002 and 2004 ozone holes were smaller. In 2007, the ozone hole reached a maximum of 25 million square kms in mid-September, compared to 29 million square kms in the record years of 2000 and 2006. The ozone mass deficit reached 28 megatonnes on 23 September, compared to more than 40 megatonnes in the record year of 2006.

Record-low Arctic sea ice extent opened the Northwest Passage

Following the Arctic sea ice melt season, which ends annually in September at the end of the northern summer, the average “sea ice extent” was 4.28 million square kms, the lowest on record. The “sea ice extent” at September 2007 was 39% below the long-term 1979-2000 average, and 23% below the previous record set just two years ago in September 2005.For the first time in recorded history, the disappearance of ice across parts of the Arctic opened the Canadian Northwest Passage for about five weeks starting 11 August. Nearly 100 voyages in normally ice-blocked waters sailed without the threat of ice. The September rate of sea ice decline since 1979 is now approximately 10% per decade, or 72,000 square kms per year.

Sea level rise continues

The sea level continued to rise at rates substantially above the average for the 20th century of about 1.7 mm per year. Measurements show that the 2007 global averaged sea level is about 20 cm higher than the 1870 estimate. Modern satellite measurements show that since 1993 global averaged sea level has been rising at about 3 mm per year.

Global 10 Warmest Years Mean Global temperature (°C) (anomaly with respect to 1961-1990)

1998 0.52 2005 0.48 2003 0.46 2002 0.46 2004 0.43 2006 0.42 2007(Jan-Nov) 0.41 2001 0.40 1997 0.36 1995 0.28

UK 10 Warmest Years Mean UK Temperature (°C) (anomaly with respect to 1971-2000)