Climate of 2003 Preliminary Annual Review

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National Climatic Data Center Edited: December 16, 2003 Published: Wednesday, 17-Dec-2003 04:43:55 EST

GLOBAL TEMPERATURES

Global temperatures in 2003 will likely be 0.55°C (1.00°F)* above the long-term (1880-2002) average**, which will make 2003 the third warmest year on record. The warmest and second warmest years on record are 1998 and 2002, respectively. Land temperatures are on track to be 0.81°C (1.46°F)* above average, ranking third in the period of record while ocean temperatures will likely rank as second warmest with 0.44°C (0.79°F)* above the 1880-2002 mean. The Northern Hemisphere temperature averaged near record levels in 2003 at 0.63°C (1.13°F)* above the long-term average. The Southern Hemisphere temperature also reflected the globally warmer conditions, with a positive anomaly near 0.45°C (0.81°F)*.

In 2003, warmer temperatures and shifts in atmospheric circulation patterns contributed to a second straight year of extremely low Arctic sea ice extent in September. Northern Hemisphere sea ice extent was almost as low as that observed in September 2002, the lowest since satellite monitoring began in 1978.

TEMPERATURE TRENDS

During the past century, global surface temperatures have increased at a rate near 0.6°C/century (1.1°F/century) but this trend has increased to a rate approaching 2°C/century (3.6°F/century) during the past 25 to 30 years. There have been two sustained periods of warming, one beginning around 1910 and ending around 1945, and the most recent beginning about 1976. Temperatures during the latter period of warming have increased at a rate comparable to the rates of warming projected to occur during the next century with continued increases of anthropogenic greenhouse gases.

Data collected by NOAA’s polar orbiting satellites and analyzed for NOAA by the University of Alabama in Huntsville (UAH) and Remote Sensing Systems (RSS, Santa Rosa, California) indicate that temperatures in the lower troposphere from the surface to an altitude of five miles are on track to make 2003 the third warmest year for the globe. The average middle troposphere temperature for 2003 (the layer which is centered in the mid-troposphere at an altitude of 2 to 6 miles, but which includes the lower stratosphere) is also on track as the third warmest year on record.

Analysis of the satellite record that began in 1979 shows that the global average temperature in the middle troposphere has increased, but differing analysis techniques have yielded different trends. While trends are positive in both cases, the increase in the UAH time series is
0.04°C/decade (0.08°F/decade), while the trend in the RSS series is larger;
0.12°C/decade (0.22°F/decade). Trends in both cases are less than the trend in global surface temperatures, which increased at a rate near
0.17°C/decade (0.30°F/decade) during the same 25 year period. Research toward reconciling differences in trends between surface and troposphere temperatures has been undertaken by the National Academy of Sciences.

While lower tropospheric temperatures as measured by the MSU indicate increasing temperatures over the last 2 decades, stratospheric (14 to 22 km /


9 to 14 miles) temperatures have been decreasing. This is consistent with the depletion of ozone in the lower stratosphere. The large increase in 1982 was caused by the volcanic eruption of El Chichon, and the increase in 1991 was caused by the eruption of Mt. Pinatubo in the Philippines.

REGIONAL TEMPERATURES

Annual temperatures through the first 11 months of the year were above average across most land areas. Temperatures in regions of the contiguous United States and Alaska, as well as most of Europe and Asia, were 2-5°C (3.6-9.0°F)* above the 1961-1990 average. The global analysis was performed using data from the Global Historical Climatology Network, a network of more than 7,000 land surface observing stations. The only widespread areas of negative anomalies were across parts of the eastern U.S., coastal areas of Australia and far western Asia where temperatures were between 1 and 3°C (1.8-5.4°F)* cooler than average. Notable temperature extremes during 2003 included a severe heatwave during summer of 2003 across Europe. Daily maximum temperatures ranged from 30-37°C (90-99°F) across France, Switzerland and the Mediterranean region, killing approximately 25,000 people. France had its warmest summer on record, and according to news reports, more than 14,000 people died of heat-related causes during the peak of the heat wave in late July and August. In North America, extreme cold winter temperatures resulted in an unusually high ice concentration across the Great Lakes. More than 90 percent of lakes Superior, Erie and Huron were frozen by March 10th, the most ice cover since February 1994. Unseasonably cold weather affected Bangladesh, India and much of Asia in January, leading to the deaths of more than 1,000 people. Average minimum temperatures were as low as 2-4°C (36-39°F), in a region where minimum temperatures are usually 12-14°C (54-57°F). In the Peruvian highlands, temperatures dropped below -20°C (-5°F) during the Southern Hemisphere winter month of July, which led to the reported deaths of more than 200 people.

GLOBAL SNOW COVER EXTENT

As shown in the time series, mean Northern Hemisphere snow cover extent during the winter season (December-February) was the second highest since records began in 1967. Mean Northern Hemisphere winter snow cover extent for the 1967-2003 period of record is 4.6 million square kilometers. Colder than normal conditions contributed to greater than average snow cover across large parts of western and southern Asia as well as Eastern Europe. Measurements from the Special Sensor Microwave Imager (SSM/I) indicate the presence of higher than average snow cover in these regions during December, January, and February. However, higher than average temperatures in northern and western regions of North America, and below average precipitation in some regions led to below average winter season snow cover extent for the continent. This is seen in the time series of winter snow cover extent anomalies for North America. Mean North America winter snow cover extent for the 1967-2003 period of record is 1.7 million square kilometers. Northern Hemisphere snow cover extent was


also above average during the March-May spring season, but only marginally so. Spring snow cover extent in the Northern Hemisphere has been below average in 14 of the past 16 years as a trend to warmer spring temperatures has led to more rapid loss of snow cover during the transition season between winter and summer. Mean Northern Hemisphere spring snow cover extent is 3.1 million square kilometers for the 1967-2003 period of record. Spring snow cover extent has also been below average across North America in much of the past two decades. Snow cover extent was below average for the spring 2003 season, the 14th below average year since 1985. Mean North America spring snow cover extent is 1.3 million square kilometers for the 1967-2003 period of record.

GLOBAL PRECIPITATION

Global precipitation was below the 1961-1990 average in 2003 for the third year in a row. Drought was widespread across much of eastern Australia during the first half of the year. India monsoon rainfall was 102 percent above normal, bringing relief to areas that were plagued with drought for much of 2002. Western Asia’s rainfall was 80 percent above than average, alleviating long-term drought conditions. In Zimbabwe, severe drought affected 900,000 people, one of Zimbabwe’s worst droughts in 50 years. Other drought-affected areas included the western United States where the multi-year drought continued to ravage the region. In contrast to drought conditions, Denver, CO had it’s second biggest snowstorm on record when 31.80 inches of snow fell in March. In February, a snowstorm hit the northeastern U.S., breaking numerous 24-hour snowfall records. Heavy rainfall in mountainous regions of southwest Asia’s mountain region ameliorated long-term drought conditions but caused a landslide in the village of Kara-Taryk, Kyrgyzstan killing 38 people. In Sante Fe, Argentina the reported worst flooding to occur since 1573 occurred in April of 2003. Several days of heavy rainfall caused local rivers to rise as much as 20 inches in one hour, killing 23 people and forcing the evacuation of
45,000. By early May, flooding was so severe, Sante Fe was characterized as an island.

ENSO CONDITIONS

The year began with the equatorial Pacific Ocean in an El Niño/Southern Oscillation (ENSO) warm event. This El Niño warming began in mid-2002, and reached its maturity in November 2002 when the sea-surface temperature (SST) anomalies in the Niño region reached their warmest condition with a +1.54°C (+2.77°F) SST anomaly.

Beginning in January of 2003, the anomalously warm waters in the oceanic mixed-layer in the eastern equatorial Pacific began to slowly cool. Between December 2002 and January 2003, the SST anomaly in the Niño region decreased from +1.42°C (+2.55°F) to +0.66°C (+1.18°F). This cooling spread westward, and had affected the ocean conditions basin-wide in the February monthly mean ocean temperatures. The trend in SST anomalies was also evident in the western Pacific Ocean. The observed cooling trend in basin-wide SSTs continued through March. The dissipation of the warm event and


the transition to near-neutral ENSO conditions occurred in April, when the SST anomalies cooled to near-normal across the equatorial Pacific basin. After the El Niño event had dissipated in April, ocean surface and sub-surface temperatures began to rapidly cool. This cooling suggested the development of a La Niña cold event in the eastern and central equatorial Pacific. By the end of May, SST anomalies in the eastern and central equatorial Pacific had cooled to below -1.5 °C adjacent to the South American coast. The cold anomaly in the Niño region was -0.63°C (-1.13°F) in May. The rapid cooling was generated by the return of easterly trade winds across the near-equatorial region, which increased equatorial upwelling in the eastern Pacific in April and May. The colder than normal SST anomalies extended into the middle of June, but were abruptly halted when a strong westerly wind event propagated across the equatorial Pacific basin. Since the cessation of the cold SST anomalies in June, the equatorial Pacific region has slowly warmed. This observed warming has not yet developed into an El Niño (as of the end of November), but the SST anomalies have been consistently warm since July in both Niño regions (map of Niño regions). The warm oceanic conditions were also present in the sub-surface measurements from NOAA’s array of moored buoys. Warmer than normal conditions were evident in the mixed-layer during November across the entire Pacific basin, although the observed ocean temperatures were well below the peak warmth observed during the 2002-2003 El Niño event.