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| Global temperatures in 2004 were 0.54°C (0.97°F) above the long-term (1880-2003) average**, ranking 2004 the fourth warmest year on record. The warmest year on record is 1998, having an anomaly of 0.63°C (1.13°F), followed by 2002 and 2003 both having an anomaly of 0.56°C (1.01°F). Land temperatures in 2004 were 0.83°C (1.50°F) above average, ranking fourth in the period of record while ocean temperatures were third warmest with 0.42°C (0.76°F) above the 1880-2003 mean. |  |
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The map of temperature anomalies (above right) contains data
from an in-situ
and satellite blended data set of land and ocean temperatures.
The period of record for this data set is 1988-2004, a relatively
warm period compared to the base period used in the creation of the
land only
map of temperature anomalies. Some minor differences in the
land surface anomalies between these two maps result from the
differences in base periods and data that are used to construct the
two maps. **The 1880-2003 average combined land and ocean annual temperature is 13.9°C (56.9°F), the annually averaged land temperature for the same period is 8.6°C (47.4°F), and the long-term annually averaged sea surface temperature is 16.1°C (60.9°F). |
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| 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 of 1.7°C/century (3.1°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) for the period that began in 1979, shows that the global average temperature in the middle troposphere (the layer which is centered in the mid-troposphere at an altitude of 2 to 6 miles, but which includes the lower stratosphere) 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 0.08°C/decade (0.15°F/decade), while the trend in the RSS series is larger: 0.13°C/decade (0.23°F/decade). Trends in UAH and RSS data are less than the trend in global surface temperatures, which increased at a rate near 0.17°C/decade (0.31°F/decade) during the same 26 year period. |  |
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However, recent
research at the University of Washington and NOAA’s Air
Resources Laboratory (Fu et al. 2004) suggests
the smaller increase in tropospheric temperatures reflected in the
MSU measurements may be caused by the partial measurement of
stratospheric temperatures, whose large cooling trend offsets the
more significant contributions of tropospheric warming. Fu et al. (2004) developed a method for quantifying the
stratospheric contribution to the satellite record of tropospheric
temperatures and applied an adjustment to both the UAH and RSS
temperature record for the middle troposphere. This adjustment,
which aims to remove the stratospheric influence on the middle
troposphere record, results in trends that are closer to
+0.17°C/decade (0.31°F/decade) increase observed at the
surface. When adjusted by Fu et al. (2004), the
middle troposphere 1979-2004 trend for the UAH data is
+0.11C/decade (+0.20F/decade) and the trend for the RSS data is
+0.19C/decade (+0.34F/decade) as seen in the graphic to the
left. Research toward reconciling differences in trends between surface and troposphere temperatures has been undertaken by the National Academy of Sciences and continues to be addressed by the world's leading climate change scientists. |
| While middle 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 below average. This is consistent with the depletion of ozone in the lower stratosphere. The large temperature 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. |  |
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Annual temperatures were above average across most land areas. The adjacent figure depicts warmer than average temperatures (for a 1961-1990 base period) that were widespread across much of the contiguous United States and Alaska, as well as most of Europe and Asia. Temperatures in these regions were 2-4°C (3.6-7.2°F) above the 1961-1990 average. This map was created 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 western coastal areas of Australia, central Canada and north-central Siberia where temperatures were between 1 and 2°C (1.8-3.6°F) cooler than average. |
| Notable temperature extremes in 2004 included a severe heat
wave that affected much of eastern Australia from February until
the end of March. Many city and state temperature records were set
as maximum temperatures reached 45°C (113°F). According to
the Australian Bureau of Meteorology, the spatial and temporal
extent of the heat wave was greater than that of any other February
heat wave in the Australian meteorological record, and ranked
amongst the top five Australian heat waves in any month, just short
of the January 1939 event but comparable with those of January
2001, January 1982 and December 1972/January 1973. In Spain, during
June and July, 73-year records were broken when maximum
temperatures reached between 39-42°C (104-108°F). In Japan,
a heat wave during mid-July produced a record temperature of
39°C (103°F) in Tokyo's financial district, the hottest
temperature recorded since records began in 1923. Early in the year, extreme cold temperatures as low as 0-5°C (32-41°F) in South Asia contributed to as many as 600 deaths from late December 2003 into January 2004. In July, cold temperatures were responsible for deaths of forty six children in Peru, along with more than 100,000 farm animals and 300,000 hectares (741,000 acres) of cropland destroyed. For more information on temperature extremes during 2004 see the annual report of Significant Events |
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For the third straight
year, Arctic sea ice extent was extremely low, ranking as the
second lowest extent since reliable records began in the 1950s.
According to the National Snow and
Ice Data Center, Northern Hemisphere sea ice extent was almost
as low as September 2002, which is the lowest on record. Arctic sea ice conditions are inherently variable from year to year in response to wind, temperature and oceanic forcings. Quite often, a "low" ice year is followed by recovery the next year. But increasing surface temperatures in high latitudes have contributed to progressively more summer melt and less ice growth in the fall and winter. While natural variability is responsible for year-to-year variations in sea ice extent, three extreme minimum extent years along with evidence of thinning of the ice pack suggest that the sea ice system is experiencing changes not solely related to natural variability. |
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| As shown in the time series to the right, mean Northern Hemisphere snow cover extent during winter (December-February) was slightly above average. Mean Northern Hemisphere winter snow cover extent for the 1967-2004 period of record is 45 million square kilometers. (Blue bars indicate seasons with below average snow cover and red bars indicate seasons with above average snow cover. Data were provided by David Robinson, Global Snow Lab, Rutgers University). |  |
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Snow cover for the winter season across North America and Greenland was above average for only the 4th time in 16 years. Mean North American winter snow cover extent is 17 million square kilometers for the 1967-2004 period of record. |
| Northern Hemisphere snow cover extent was significantly below average during the March-May spring season. As shown in the time series graph to the right, spring snow cover extent in the Northern Hemisphere has been below average in 15 of the past 17 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 31 million square kilometers for the 1967-2004 period of record. |  |
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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 2004 season, the 15th below average year since 1985. Mean North America spring snow cover extent is 13 million square kilometers for the 1967-2004 period of record. |
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Global precipitation was above the 1961-1990 average in 2004, the first time in 4 years. Regionally drier than average conditions were widespread across the western U.S. where the multi-year drought continued to ravage the region. India monsoon rainfall was 87 percent of normal, with the worst regional deficit being in northwest India with 22 percent less than average precipitation. The March-May rainy season was shorter and drier than normal across parts of the Greater Horn of Africa, resulting in a continuation of multi-season drought in this region. In Kenya only 50 percent of normal rainfall has fallen in the past two years. In Somalia, more than 600,000 people were directly affected by the current drought and in need of food aid. |
| There were also areas of above average
precipitation in 2004. A winter storm brought heavy snowfall to
much of the Mediterranean and Middle East regions in January. The
storm blanketed areas with more than 61cm (2 feet) of snow causing
the closing of local airports, an avalanche and three deaths. In
Brazil, heavy rains that began in December and continued into
February caused floods and mudslides, leaving tens of thousands of
people homeless and killing at least 56 people. In April, a strong
storm system brought 127-178mm (5-7 inches) of rain to the
southwestern U.S. and adjacent areas in Mexico. Flash flooding of
the Escondido River in Piedras Negras caused 36 deaths and damaged
hundreds of homes. This event was characterized as some of the
worst flooding on record along the U.S.-Mexico border. For more
information about precipitation extremes during 2004, see the
annual report of Significant Events.
Additional information on other notable weather events can be found in the Significant Events section of this report. |
| NOAA's National
Climatic Data Center is the world's largest active archive of
weather data. The preliminary temperature and precipitation
rankings are available from the center by calling: 828-271-4800.
NOAA works closely with the academic and science communities on climate-related research projects to increase the understanding of El Niño and improve forecasting techniques. NOAA's Climate Prediction Center monitors, analyzes and predicts climate events ranging from weeks to seasons for the nation. NOAA also operates the network of data buoys and satellites that provide vital information about the ocean waters, and initiates research projects to improve future climate forecasts.
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