FY 2005

State of the climate in 2004

Levinson (ed.), D.H., P. Ambenje, O. Baddour, G.I. Belchansky, G.D. Bell, M. Chelliah, M.S. Halpert, K. Mo, W.M. Thiaw, M.A. Bell, S.J. Camargo, E.K. Grover-Kopec, E. Blake, R. Pasch, J.E. Box, O.N. Bulygina, N.N. Korshunova, V. Razuvaev, J.C. Christy, E.R. Cook, M.C. Váquez, B.C. Douglas, D.C. Douglas, S.D. Drobot, C.M. Eakin, C. Woodhouse, R.A. Feely, M.J. McPhaden, M.A. Fortune, B. Garanganga, K.L. Gleason, J.H. Lawrence, D.H. Levinson, M.J. Menne, R.W. Reynolds, S.E. Stephens, A.M. Waple, S. Goldenberg, C. Landsea, J. Kennedy, C. Kocot, D. Phillips, R. Whitewood, K.R. Kumar, W. Landman, N. Maximenko, L. Miller, P. Niiler, L. Talley, A.K. Njogu, F. Rahimzadeh, M. Rajeevan, J. Richter-Menge, E. Rignot, I.G. Rigor, D.A. Robinson, M. Rusticucci, M.J. Salinger, R.C. Schnell, R.S. Stone, D. Stanitski, A. Taghipour, R. Wanninkhof, A.B. Watkins, B. Trewin, P. Zhai, and X. Zou

Bull. Am. Meteorol. Soc., 86(6), S1–S86, doi: 10.1175/BAMS-86-6-Levinson (2005)

From a global perspective, the annual average surface temperature in 2004 was the fourth highest value observed since regular instrumental records began in 1880. Global surface air temperatures in 2004 were 0.44°C (0.79°F) above the 1961-90 mean, according to both the U.S. and U.K. archives. Observations of the global annual mean temperature in 2004 from the combined lower and middle troposphere was 0.38°C (0.68°F)--the fourth warmest year in the 47-yr archive of worldwide radiosonde observations, and the ninth warmest year out of the past 26 based on satellite measurements.

The average precipitation anomaly over global land areas in 2004 was 10.7 mm above average, which was ~1% above the 1961-90 mean, and the first year since 2000 that the global mean value was wetter than average. Northern Hemisphere sea ice extent was the third lowest on record for the year, dating back to 1973. The annual snow cover extent over Northern Hemisphere land areas was 25.1 million km, which was the 25th most extensive snow cover during the period of record.

Levels of carbon dioxide (CO) continue to increase in the atmosphere at the NOAA/Climate Modeling and Diagnostics Laboratory (CMDL) Mauna Loa Observatory on the Big Island of Hawaii; CO₂ rose approximately 1.3 parts per million (ppm) in 2004, to reach a preliminary value of 377.6 ppm. However, the 2004 increase was below the long-term average increase of 1.5 ppm yr. A minimum ozone concentration of 138 Dobson units (DU) was measured on 4 October 2004 at South Pole station, which was above the 1986-2004 average minimum value of 117 ± 26 DU.

Sea levels continued to rise globally, increasing at a rate of 2.8 ± 0.4 mm yr based on satellite altimeter measurements. The satellite measurements since 1993 have recorded a significantly higher rise in sea level than the overall twentieth-century rate of 1.8 ± 0.3 mm yr, determined from tide gauge observations during the past century.

The climate of 2004 was influenced by the development of a weak El Niño (i.e., ENSO warm event) in the western and central equatorial Pacific Ocean during the second half of the year. A series of westerly wind bursts during July-October, which were initiated by Madden-Julian oscillation activity in the tropical western Pacific, generated several Kelvin waves in the oceanic mixed layer that aided in the formation of the warm event. Only limited regional-scale impacts associated with El Niño occurred during the boreal autumn, because the event did not develop basinwide.

Tropical cyclone activity was above average in the North Atlantic, west North Pacific, and South Indian Ocean basins in 2004. The hurricane season was extremely active in the North Atlantic basin, with a total of 15 named storms, nine hurricanes, and six major hurricanes in 2004. Nine of these tropical cyclones struck the Atlantic and Gulf of Mexico coasts of the United States, with three of these landfalling as major hurricanes. The first documented hurricane developed in the South Atlantic Ocean (cyclone "Catarina"), which made landfall along the southern coast of Brazil in late March. The west North Pacific typhoon season was also very active, with 10 tropical systems making landfall in Japan, breaking the previous record of 6 during a single season. In the South Indian Ocean, Tropical Cyclone Gafilo devastated Madagascar, making landfall as a category 5 supercyclone.

From a regional perspective, the annual mean temperature across Europe as a whole in 2004 was 0.98°C above the 1961-90 base period average, with temperature anomalies in excess of 1°C measured across parts of northwest Europe and Scandinavia. Temperatures were also warm across South America and parts of Asia. The annual average temperature in Russia was 0.8°C above the long term mean, but temperatures in 2004 were anomalously cold in Asian Russia.

Drought conditions continued across western North America, although conditions improved in the southwest United States and California late in the year, while the multiyear drought persisted in parts of the Pacific Northwest and Northern Rockies. Drought conditions also persisted across a majority of the Greater Horn and southern Africa. Monsoonal rains were deficient across the Indian subcontinent in 2004; only 87% of the long period average rainfall was recorded. In contrast, above-normal rainfall across parts of Southwest Asia helped ease some of the long-running drought conditions in the region.