World Weather Report

1999 closes the warmest decade and warmest century of the last millennium according to WMO annual statement on the global climate

provided by the World Meteorological Organization


he 1990s were, globally, the warmest decade since instrumental measure started in the 1860s. Recent scientific evidence based on pre-instrumental proxy climate data, mostly from sites in the northern hemisphere, indicates that the 1990s were the warmest decade and the 1900s the warmest century during the last 1,000 years. The seven warmest years globally in the instrumental record have occurred this decade, with the warmest being 1998. The 1999 global mean combined land-surface air and sea surface temperature is estimated to be in the order of 0.3 to 0.4 ºC above the 1961-1990 normal, which will be the 5th warmest in the 140-year record, according to the World Meteorological Organization (WMO).

1999 will have been the 21st consecutive year with an above normal global surface temperature, and the ten warmest years have all occurred since 1983. The four warmest years were 1998 (0.58 ºC above normal), 1997 (+0.44), 1995 (+0.38) and 1990 (+0.35). The high temperature of 1999 is remarkable because it occurred despite the typical cooling influence of the tropical Pacific La Niña, which persisted throughout the year. The global mean annual temperatures at the end of the 20th century are almost 0.7 ºC above those recorded at the end of the 19th century.

The regional temperature patterns (January through October) show most of the globe with above average temperatures, except for the Northeast Pacific, equatorial east and central Pacific, western South America and northernmost parts of Eurasia. In central England, where the instrumental record extends back 341 years, it is likely that 1999 will be the warmest year ever. Records in Japan indicate that 1999 will be the 3rd warmest year in their 102-year record. In Canada, 1999 will likely be the second warmest since 1948 (1998 was the warmest). In June/July, Russia experienced one of its longest heat waves of the century, with record temperature departures from normal exceeding 5 °C in June in central and northwestern regions. Drought and heat led to the outbreak of numerous forest fires. In parts of northern and central Europe, September was the warmest in this century. Northern Germany recorded departures from normal of up to 4.5 °C. In September, Norway had departures from normal up to 5 ºC and, in November, up to 6-7 ºC. By contrast, a cold snap in late January of this year brought some of the coldest temperatures experienced in Norway and Western Russia since the late 1800s.

The major 1997/98 El Niño gave way to La Niña conditions (colder than average equatorial Pacific sea surface temperatures) by mid-1998, which continued through late 1999. The La Niña is expected to continue well into 2000 according to most climate models. Such long-lived cold episodes don't occur often but this La Niña is not unique. Extended cold episodes characterized the periods 1954 to 1957, 1973 to early 1976 and late 1983 to early 1986. The evolution of the 1998/99 La Niña has been similar to, but much stronger than, the 1983 to 1986 cold episode, which followed the extremely strong El Niño in 1982/83.

The ozone depletion over Antarctica during the austral spring was again very strong last year. This was only the second season in the last 20 years that ozone-hole values (<220 m atm. cm) covered an area greater than 10 million km2 for more than 93 consecutive days (compared to 100 days in the record year, 1998). Over northern middle latitudes, ozone values were 4 - 8% lower than the pre-1976 averages. Above the Arctic, the lower stratosphere was unusually warm with no ozone destruction during the northern winter-spring season of 1999.

Extremely heavy precipitation had devastating consequences in many parts of the world. A severe super-cyclonic storm with winds of up to 250 km/h crossed the coast in Orissa, India on October 29, 1999. This may prove to have been the worst cyclone of the century in the Orissa region, and is responsible for as many as 10,000 deaths, for rendering millions homeless, and for extensive property damage. Scores of people in Japan and China have been killed this year by floods, landslides and storm surges caused by tropical cyclones. Two serious flooding events following torrential rains late this year have rendered hundreds of thousands of people in Vietnam homeless, and hundreds dead.

In February, heavy snowfall occurred across Central Europe disrupting traffic connections and cutting off roads and villages, especially in Hungary, Slovakia, Bulgaria, Ukraine, Austria, Switzerland and France. Regionally, the heaviest snowfall in decades was recorded. Destructive avalanches occurred across the Alps; in western Austria, southern Switzerland and eastern France, at least 50 people lost their lives. In May, heavy rain and thawing of the extreme deep snow cover in the higher parts of the Alps caused extreme flooding of the river Danube and Lake Constance. Losses amounted to one billion German Marks.

Excessive precipitation fell in the USA's Pacific Northwest during the November 1998-March 1999 period, which resulted in a very deep snowpack in many of the mountainous areas in the region. Many areas reported 150% to 200% of their normal seasonal precipitation totals, with Mt. Baker in Washington State setting a new record of 28.96 m for the most snowfall ever measured in the United States in a single season. In western Canada, at Tahsta Lake, British Columbia, Canada's greatest one-day accumulation of snow ever, reaching 145 cm, was recorded this year. Parts of the central and eastern Canadian Prairies received more then half of their normal yearly rainfall in May alone, submerging some of the country's most productive farmland.

In the July to October period, heavy rains and flash floods wreaked havoc in parts of western Africa. Thousands were left homeless, hundreds dead, and there was extensive property damage across large areas. Also in October, torrential rains, landslides and flooding devastated parts of Mexico, leaving hundreds dead. New Cale-donia has reported a warm and wet year, thanks to the relatively strong La Niña influence early in the year. Finally a rare snow event occurred in and around Buenos Aires in August.

Overall, the 1999 Atlantic hurricane season was very active with 12 named storms, 8 of which became hurricanes and 5 of which became intense hurricanes. Only one of these twelve storms formed prior to 19 August. The Atlantic hurricane seasons in 1995, 1996 and 1998 were also very active. During each of these periods, the regional circulation features known to be conducive to increased tropical storm and hurricane activity were strongly linked to a much larger scale climate signal associated with La Niña conditions.

A number of areas were plagued by drought conditions. One of the worst droughts in eastern US history intensified during spring and peaked in late summer before increasing rainfall, aided by three tropical cyclones, significantly eased conditions later in the year. Lack of precipitation damaged crops and forced the imposition of substantial water use restrictions. In parts of eastern United States, April - July 1999 was the driest such period since records began in 1895 and the July 1998 - July 1999 period was among the driest 3% of all 13-month periods on record. At the end of 1999, the Great Lakes water levels are below the 80-year average, and for Lakes Michigan and Huron, the drop in water levels was the largest year-to-year decline since record-keeping began in 1860. Nova Scotia, in Eastern Canada, is experiencing drought for the third successive year. In Hawaii, rainfall amounts have been below normal for well over a year in most areas.

In Australia, there was well below average precipitation over central and southeastern areas and record drought over the last three years in parts of southeastern Australia. In Argentina, precipitation has been less than normal in eastern coastal regions. Drought and heat led to the outbreak of numerous forest fires early in 1999, and in October. Serious droughts were reported this year in the Middle East as well.


Information sources

This preliminary information for 1999 is based on observations up to mid-December from a network of ships, buoys and land-based weather stations. The data are collected and disseminated on a continuing basis by the national Meteorological and Hydrological Services of the WMO Member countries.

It should be noted that following established practice, WMO's global temperature analyses are based on a data set maintained by the Hadley Centre of the UK Meteorological Office and the Climatic Research Unit, University of East Anglia, UK. In this data set, departures from normal are based on the most recent WMO climatological standard normals period 1961-1990. Another authoritative global surface temperature data set is maintained by the USA Commerce Department's National Oceanic and Atmospheric Administration (NOAA) in which departures from normal are based on the full period record dating back to 1880. Results from these two data sets are comparable, both projecting (from data up to the end of November) that 1999 will be the fifth warmest year globally.

More extensive information will be made available in the annual WMO booklet statement on the status of the global climate, to be published in time for WMO's 50th anniversary celebrations on WMO Day, 23 March, 2000.

This information is from a joint press release issued in collaboration with the Hadley Centre of the UK Meteorological Office, the Climatic Research Unit at the University of East Anglia, UK and in the USA: the National Climatic Data Center in Asheville; the Climate Prediction Center in Washington; and the International Research Institute in New York. Other contributing WMO Member countries were Argentina, Australia, Canada, Germany, India, Japan, Norway and the Russian Federation.