The year 2008 is likely to rank as the 10th warmest year on record since the beginning of the instrumental climate records in 1850, although the global average temperature was slightly lower than previous years of the 21st century, according to the United Nations meteorological agency.
The combined sea-surface and land-surface air temperature for 2008 is estimated at 0.31 degrees Celsius (C) or 0.56 Fahrenheit (F), above the 1961-1990 annual average of 14C, or 57.2F, while the Arctic Sea ice volume during the melt season was its lowest since satellite measurements began in 1979, the UN World Meteorological Organization (WMO) said.
The average temperature of 2008 was moderated by La Niña, a weather phenomenon that shrinks the warm pool water in the central and western Pacific, which developed in the latter half of 2007.
Climate extremes, including devastating floods, severe and persistent droughts, snowstorms, and heat and cold waves, were recorded in many parts of the world, with above-average temperatures all over Europe and a remarkably cold winter over Eurasia stretching from Turkey to China, causing hundreds of casualties in Afghanistan and China.
In North America, February was a cold month with average daily temperatures in the Midwest of the United States ranging from 4C to 5C below normal in some areas, while in South America a very cold episode due to an early Antarctic air mass saw minimum temperature drop below –6C in May in central Argentina breaking annual absolute minimum records.
Conversely, mean July temperatures were more than 3C above average in large parts of Argentina, Paraguay, southeast Bolivia and southern Brazil, making it the warmest July in the last 50 years for many locations, while November broke historical records with central Argentina, including Buenos Aires city, experiencing its warmest November in 50 years.
In southern Australia, March brought a record heat wave with Adelaide experiencing its longest heat wave on record – 15 consecutive days of maximum temperatures above 35°C. Several heat waves also occurred in south-eastern Europe and the Middle East during April, with a very warm spring also observed in a large part of the rest of Europe and Asia.
Prolonged drought hit most parts of the southeast of North America at the end of July and hindered efforts to contain numerous large wildfires in California, while southern British Columbia in Canada experienced its fifth driest period in 61 years. In Europe, Portugal and Spain had their worst drought winter in decades, while in South America, a large part of Argentina, Uruguay and Paraguay an intense drought which caused severe damage to agriculture.
Dry conditions in south-eastern Australia reinforced long-term drought, exacerbating severe water shortages in the agriculturally important Murray-Darling Basin and causing widespread crop failures in the area.
Heavy snow with subsequent melt, flooding and intense storms were experienced in many regions. The US experienced 1,489 tornadoes, the most since reliable records began in 1953, and the year was one of the top 10 for tornado-related fatalities at 123. Sub-Saharan Africa was hit by heavy rains, which caused the worst-ever recorded flooding in Zimbabwe. Extreme rainfall was recorded in northern Morocco with up to 200 millimetres (mm) in less than six hours.
In southern Asia, including India, Pakistan and Viet Nam, heavy monsoon rains and torrential downpours produced flash floods, killing more than 2,600 people, and displacing 10 million people in India. Meanwhile in South America, continuous above-normal rainfall in western Colombia and southern Brazil caused severe flooding affecting some 2 million people.
The most deadly tropical cyclone of the year was Cyclone Nargis, which killed nearly 78,000 people and destroying thousands of homes in Myanmar. Sixteen tropical storms formed in the Atlantic including eight hurricanes, five of which were major at Category 3 or higher (averages are eleven, six and two, respectively), causing many casualties and widespread destruction.
For the first time on record, six consecutive cyclones made landfall in the US and a record three major hurricanes hit Cuba. In the East Pacific, 17 tropical storms were recorded, of which 7 evolved into hurricanes, 2 of them major (averages are 16, 9 and 4, respectively).
In the western North Pacific, 22 tropical storms were recorded, 10 of them typhoons, compared to the long-term average of 27 and 14, respectively.
In the Antarctic, the ozone hole reached a maximum of 27 million square kilometres, less than the record of more than 29 million square kilometres in 2006, but larger than the 25 million square kilometres of last year.
In the Arctic, the average sea ice extent over the month of September was 4.67 million square kilometres, the second lowest on record after last year’s low of 4.3 million square kilometres. Because ice was thinner in 2008, overall ice volume was less than that in any other year.
A remarkable occurrence in 2008 was the dramatic disappearance of nearly one-quarter of the massive ancient ice shelves on Ellesmere Island in the Canadian Arctic. Ice 70 metres thick, which a century ago covered 9,000 square kilometres, has shrunk to just 1,000 square kilometres today, underscoring the 30-year downward trend in Artic sea ice.