National Climatic Data Center
15 May 2008
The data presented in this report are preliminary. Ranks and anomalies may change as more complete data are received and processed. The most current data may be accessed via the Global Surface Temperature Anomalies page.
Temperature anomalies for April 2008 are shown on the dot maps below. The dot map, below left, provides a spatial representation of anomalies calculated from the Global Historical Climatology Network (GHCN) data set of land surface stations using a 1961-1990 base period. The dot map, below right, is a product of a merged land surface and sea surface temperature anomaly analysis developed by Smith and Reynolds (2005). Temperature anomalies with respect to the 1961-1990 mean for land and ocean are analyzed separately and then merged to form the global analysis. Additional information on this product is available.
The January-April 2008 map shows anomalous warm conditions over much of the world's land surface, especially across Europe and northern Asia where temperatures were 2°-4°C (4°-7°F) above average. Elsewhere, cooler-than-average conditions were observed in parts of the western and north-central states of the contiguous U.S., central Africa, eastern Australia, and parts of Colombia. As for sea surface temperatures (SST), warmer-than-average conditions were present in the Atlantic and Indian oceans, the Niño 1+2 region, and parts of the northwest Pacific Ocean. Cooler-than-average conditions were observed in all of the Niño regions (with the exception of Niño 1+2 region), parts of the northeastern Pacific and some areas in the southern oceans.
During April, above average temperatures were observed across Europe, Mexico, eastern Brazil, northwestern Alaska, northern Africa, most of Asia, the northeastern and parts of the southwestern states of the contiguous U.S. As shown in the April 2008 map, temperatures across Europe and most of Asia were 1°-4°C (2°-7°F) above the 1961-1990 mean. The warm conditions in April over Europe and Asia were associated with the least snow cover extent on record for the Eurasian continent. Meanwhile, cooler-than-average conditions were present across the central and western U.S., eastern Australia, central Russia, and parts of India and South Africa.
SSTs during April 2008 were warmer than average in the Atlantic, northwestern Pacific, eastern equatorial Pacific, and parts of the south Indian and south Pacific oceans. Cooler-than-average conditions were present in parts of the southern oceans, parts of the North Indian Ocean, and in the Niño regions, with the exception of the Niño 1+2 region where the monthly temperature anomaly cooled slightly to +0.41°C (+0.74°F). Temperatures across the Niño 3.4 and Niño 4 regions warmed but the anomalies remained below average. Please see the latest ENSO discussion for additional information.
The mean position of the upper level ridges of high pressure and troughs of low pressure (depicted by positive and negative 500-millibar height anomalies on the April map) are generally reflected by areas of positive and negative temperature anomalies at the surface, respectively. For other Global products, please see the Climate Monitoring Global Products page.
Images of sea surface temperature conditions are available for all weeks during 2008 at the weekly SST page.
Effective with the February 2006 report, NCDC transitioned from the use of the Operational Global Surface Temperature Index (Quayle et al. 1999) to the blended land and ocean dataset developed by Smith and Reynolds (2005). The differences between the two methods are discussed in Smith et al. (2005).
The combined global land and ocean surface temperature was the thirteenth warmest on record in April and the twelfth warmest on record for January-April year-to-date period. La Niña, the cold phase of the El Niño-Southern Oscillation, persisted in the equatorial Pacific, damping ocean surface temperatures. The global average ocean sea surface temperature (SST) in April was the 9th warmest on record.
| April | Anomaly | Rank | Warmest (or Next Warmest) Year on Record |
|---|---|---|---|
GlobalLandOcean Land and Ocean |
+0.64°C (+1.15°F) +0.33°C (+0.59°F) +0.41°C (+0.74°F) |
12th warmest 9th warmest 13th warmest |
2007 (+1.40°C/2.52°F) 1998 (+0.53°C/0.95°F) 1998 (+0.70°C/1.26°F) |
Northern HemisphereLandOcean Land and Ocean |
+0.81°C (+1.46°F) +0.33°C (+0.59°F) +0.51°C (+0.92°F) |
9th warmest 8th warmest 7th warmest |
2000 (+1.66°C/2.99°F) 2004 (+0.53°C/0.95°F) 2007 (+0.84°C/1.51°F) |
Southern HemisphereLandOcean Land and Ocean |
+0.08°C (+0.14°F) +0.33°C (+0.59°F) +0.29°C (+0.52°F) |
49th warmest 19th warmest 22nd warmest |
2005 (+1.09°C/1.96°F) 1998 (+0.59°C/1.06°F) 1998 (+0.63°C/1.13°F) |
| January-April | Anomaly | Rank | Warmest (or Next Warmest) Year on Record |
|---|---|---|---|
GlobalLandOcean Land and Ocean |
+0.77°C (+1.39°F) +0.29°C (+0.52°F) +0.42°C (+0.76°F) |
11th warmest 13th warmest 12th warmest |
2007 (+1.36°C/2.45°F) 1998 (+0.53°C/0.95°F) 2007 (+0.68°C/1.22°F) |
Northern HemisphereLandOcean Land and Ocean |
+0.91°C (+1.64°F) +0.29°C (+0.52°F) +0.52°C (+0.94°F) |
11th warmest 8th warmest 9th warmest |
2002 (+1.56°C/2.81°F) 2004 (+0.50°C/0.90°F) 2007 (+0.87°C/1.57°F) |
Southern HemisphereLandOcean Land and Ocean |
+0.31°C (+0.56°F) +0.30°C (+0.54°F) +0.30°C (+0.54°F) |
20th warmest 23rd warmest 22nd warmest |
2005 (+0.88°C/1.58°F) 1998 (+0.56°C/1.01°F) 1998 (+0.61°C/1.10°F) |
The most current data may be accessed via the Global Surface Temperature Anomalies page.
The maps below represent anomaly values based on the GHCN data set of land surface stations using a base period of 1961-1990. During April 2008, above average precipitation fell over areas that include the Philippines Islands, central and midwestern contiguous U.S., and parts of Europe, southeastern Asia, and South America. Drier-than-average conditions were observed across the Hawaiian Islands, eastern and northern Australia, and southeastern China, western U.S. and parts of the South America and Africa.
In the U.S., rainfall during April led to improving drought conditions in much of the Southeast, but at month's end, moderate to extreme drought remained over 43% of the region. Torrential rains on April 30 affected parts of the northeastern U.S. and southeastern Canada, prompting the overflow of rivers and causing record breaking floods. In Brazil, heavy rainfall caused widespread floods that destroyed crops, killed 15 people, and affected more than 30,000 across the northeast part of the country. In Haiti, heavy rain prompted a deadly mudslide on the 24th that killed three children and injured 2 people. Additional details on flooding and drought can also be found on the April Global Hazards page.
According to the Australian Bureau of Meteorology (BoM), Western Australia's capital, Perth, had the wettest April since records began in 1876, with a total of 152.4 mm (6 inches) of rain as of April 29. The previous record was set in 1926 when a total of 148.8 mm (5.9 inches) of rain fell. Perth also had the second wettest January-April period on record with a total of 214.2 mm (8.4 inches) of rainfall, behind 1955 which had a total of 296.9 mm (11.7 inches) of rain. A complete summary is available courtesy of the Australian BoM.
Sea surface temperature (SST) anomalies in the equatorial Pacific Ocean warmed, but remained below average. SST anomalies in the Niño 3.4 region rose to -0.75°C (-1.35°F), a warming of +0.28°C (0.50°F) compared to March's anomaly. These conditions indicate that some weakening of La Niña (ENSO cold phase) occurred during April, but cold phase (La Niña) conditions remained across the tropical Pacific Ocean (shown in the adjacent animation of weekly sea surface temperature anomalies). A comprehensive summary of April 2008 ENSO conditions can be found on the ENSO monitoring page. For the latest advisory on ENSO conditions go to NOAA's Climate Prediction center (CPC) and the CPC ENSO Diagnostic Discussion.
Images of sea surface temperature conditions are available for all weeks since 2003 at the weekly SST page.
As shown in the time series to the right, the mean Northern Hemisphere snow cover extent during April 2008 was below average. Similar to the month of March, snowfall across the Northern Hemisphere was variable during April. The Northern Hemisphere had the 8th least snow cover extent on record. The mean Northern Hemisphere April snow cover extent for the 1967-2008 period of record was 31.3 million square kilometers.
Across North America, snow cover for April 2008 was above average, the 9th largest April extent since satellite records began in 1967. This was the first time in April with substantially above average snow cover extent across the North America since 1997. The mean North America April snow cover extent was 13.3 million square kilometers for the 1967-2008 period of record. In North America, multiple snow storms swept across the continent prompting numerous daily and seasonal records of snowfall. On April 11, a winter storm brought heavy snow accumulations across southern Canada. Calgary, the largest city in the province of Alberta, saw a new daily snowfall record when the storm left more than 23 cm (9 inches) of snow, surpassing the 88-year-old previous record of 15 cm (6 inches). Across the U.S., April 2008 had a total of 530 new daily snowfall records.
As depicted in the time series to the right, Eurasia's snow cover extent during April 2008 was below average. This was the least snow cover extent over the 41-year historical period for April, surpassing the previous least snow cover extent set in 1990. Much of this can be attributed to the above normal temperatures that covered most of the Asian continent. On average, the Eurasian snow cover extent in April was 17.9 million square kilometers for the 1967-2008 period of record.
Data were provided by the Global Snow Laboratory, Rutgers University.
According to the National Snow and Ice Data Center, the April 2008 Northern Hemisphere sea ice extent, which is measured from passive microwave instruments onboard NOAA satellites, was below the 1979-2000 mean, but greater than the previous four years. This was the eighth least April sea ice extent on record. The past four years had the least April sea ice extent since records began in 1979, with 2007 having the least April sea ice extent on record. Sea ice extent for April has decreased at a rate of 3 percent per decade (since satellite records began in 1979) as temperatures in the high latitude Northern Hemisphere have risen at a rate of approximately 0.37°C per decade over the same period.
Meanwhile, the April 2008 Southern Hemisphere sea ice extent was much above the 1979-2000 mean. This was the largest sea ice extent in April (17.5 percent above the 1979-2000 mean) over the 30-year historical period, surpassing the previous record set in 1982 by 4.1 percent. Sea ice extent for April has increased at a rate of 2.5 percent per decade.
For further information on the Northern and Southern Hemisphere snow and ice conditions, please visit the NSIDC News page, provided by the NOAA's National Snow and Ice Data center (NSIDC).
Temperatures above the Earth's surface are measured within the lower troposphere, middle troposphere, and stratosphere using in-situ balloon-borne instruments (radiosondes) and polar-orbiting satellites (NOAA's TIROS-N). The radiosonde and satellite records have been adjusted to remove time-dependent biases (artificialities caused by changes in radiosonde instruments and measurement practices as well as changes in satellite instruments and orbital features through time).
These temperatures are for the lowest 8 km (5 miles) of the atmosphere. Information on the UAH and RSS sources of troposphere data is available.
| April | Anomaly | Rank | Warmest (or Next Warmest) Year on Record | Trend |
|---|---|---|---|---|
| UAH low-trop | +0.02°C/0.04°F | 17th warmest | 1998 (+0.76°C/1.37°F) | +0.12°C/decade |
| *RSS low-trop | +0.08°C/0.14°F | 15th warmest | 1998 (+0.90°C/1.62°F) | +0.18°C/decade |
*Version 03_0
| January- April |
Anomaly | Rank | Warmest (or Next Warmest) Year on Record | Trend |
|---|---|---|---|---|
| UAH low-trop | +0.02°C/0.04°F | 17th warmest | 1998 (+0.66°C/1.18°F) | +0.15°C/decade |
| *RSS low-trop | +0.02°C/0.04°F | 19th warmest | 1998 (+0.71°C/1.28°F) | +0.18°C/decade |
*Version 03_0
These temperatures are for the atmospheric layer centered in the mid-troposphere (approximately 3-10 km (2-6 miles) above the Earth's surface), which also includes a portion of the lower stratosphere. (The MSU channel used to measure mid-tropospheric temperatures receives about 25 percent of its signal above 10 km (6 miles).) Because the stratosphere has cooled due to increasing greenhouse gases in the troposphere and losses of ozone in the stratosphere, the stratospheric contribution to the tropospheric average, as measured from satellites, may create an artificial component of cooling to the mid-troposphere temperatures. The University of Washington (UW) versions of the UAH and RSS analyses attempt to remove the stratospheric influence from the mid-troposphere measurements, and as a result the UW versions tend to have a larger warming trend than either the UAH or RSS versions. For additional information, please see NCDC's Microwave Sounding Unit page.
The radiosonde data used in this global analysis were developed using the Lanzante, Klein, Seidel (2003) ("LKS") bias-adjusted dataset and the First Difference Method (Free et al. 2004) (RATPAC). Additional details are available. Satellite data have been adjusted by the Global Hydrology and Climate Center at the University of Alabama in Huntsville (UAH). An independent analysis is also performed by Remote Sensing Systems (RSS) and a third analysis has been performed by Dr. Qiang Fu of the University of Washington (UW) (Fu et al. 2004)** to remove the influence of the stratosphere on the mid-troposphere value. Global averages from radiosonde data are available from 1958 to present, while satellite measurements began in 1979.
Radiosonde measurements indicate that for the January-April year-to-date period, temperatures in the mid-troposphere were 0.16°C (0.29°F) above average, resulting in the twentieth warmest January-April since global measurements began in 1958. However, as shown in the table below, satellite measurement of the January-April year-to-date period for the middle troposphere varied from twentieth to twenty-sixth warmest (fifth to eleventh coolest) on record.
The global mid-troposphere temperatures were slightly cooler than average in April 2008. As shown in the table below, satellite measurement for April 2008 ranked from eighteenth to twenty-seventh warmest (fourth to thirteenth coolest) on record.
| April | Anomaly | Rank | Warmest (or Next Warmest) Year on Record | Trend |
|---|---|---|---|---|
| UAH mid-trop | -0.20°C/-0.36°F | 27th warmest (4th coolest) |
1998 (+0.71°C/1.28°F) | +0.03°C/decade |
| *RSS mid-trop | -0.07°C/-0.12°F | 21st warmest (10th coolest) |
1998 (+0.77°C/1.38°F) | +0.10°C/decade |
| **UW-UAH mid-trop | -0.13°C/-0.23°F | 22nd warmest (9th coolest) |
1998 (+0.83°C/1.49°F) | +0.10°C/decade |
| **UW-*RSS mid-trop | +0.02°C/+0.04°F | 18th warmest (13th coolest) |
1998 (+0.90°C/1.62°F) | +0.16°C/decade |
*Version 03_0
| January- April |
Anomaly | Rank | Warmest (or Next Warmest) Year on Record | Trend |
|---|---|---|---|---|
| UAH mid-trop | -0.14°C/-0.26°F | 26th warmest (5th coolest) |
1998 (+0.60°C/1.07°F) | +0.05°C/decade |
| *RSS mid-trop | -0.08°C/-0.14°F | 23rd warmest (8th coolest) |
1998 (+0.64°C/1.15°F) | +0.11°C/decade |
| **UW-UAH mid-trop | -0.06°C/-0.10°F | 21st warmest (10th coolest) |
1998 (+0.72°C/1.30°F) | +0.12°C/decade |
| **UW-*RSS mid-trop | 0.00°C/0.00°F | 20th warmest (11th coolest) |
1998 (+0.76°C/1.37°F) | +0.17°C/decade |
| RATPAC | +0.16°C/0.29°F | 20th warmest | 1998 (+0.75°C/1.34°F) | +0.14°C/decade |
*Version 03_0
The table below summarizes stratospheric conditions for April 2008. On average, the stratosphere is located approximately between 16-23 km (10-14 miles) above the Earth's surface. Over the last decade, stratospheric temperatures have been below average in part due to the depletion of ozone. The large positive anomaly in 1982 was caused by the volcanic eruption of El Chichon in Mexico, and the sharp jump in temperature in 1991 was a result of the eruption of Mt. Pinatubo in the Philippines. In both cases the temperatures returned to pre-eruption levels within two years.
| April | Anomaly | Rank | Coolest Year on Record |
|---|---|---|---|
| UAH stratosphere | -0.66°C (-1.19°F) | 2nd coolest | 1999 (-0.72°C/-1.30°F) |
| *RSS stratosphere | -0.52°C (-0.94°F) | 3rd coolest | 1999 (-0.60°C/-1.09°F) |
*Version 03_0
For additional details on precipitation and temperatures in April, see the Global Hazards page.
Christy, John R., R.W. Spencer, and W.D. Braswell, 2000: MSU tropospheric Temperatures: Dataset Construction and Radiosonde Comparisons. J. of Atmos. and Oceanic Technology, 17, 1153-1170.
Free, M., D.J. Seidel, J.K. Angell, J. Lanzante, I. Durre and T.C. Peterson (2005) Radiosonde Atmospheric Temperature Products for Assessing Climate (RATPAC): A new dataset of large-area anomaly time series, J. Geophys. Res., 10.1029/2005JD006169.
Free, M., J.K. Angell, I. Durre, J. Lanzante, T.C. Peterson and D.J. Seidel(2004), Using first differences to reduce inhomogeneity in radiosonde temperature datasets, J. Climate, 21, 4171-4179.
Fu, Q., C.M. Johanson, S.G. Warren, and D.J. Seidel, 2004: Contribution of stratospheric cooling to satellite-inferred tropospheric temperature trends. Nature, 429, 55-58.
Lanzante, J.R., S.A. Klein, and D.J. Seidel (2003a), Temporal homogenization of monthly radiosonde temperature data. Part I: Methodology, J. Climate, 16, 224-240.
Lanzante, J.R., S.A. Klein, and D.J. Seidel (2003b), Temporal homogenization of monthly radiosonde temperature data. Part II: trends, sensitivities, and MSU comparison, J. Climate, 16, 241 262.
Mears, Carl A., M.C. Schabel, F.J. Wentz, 2003: A Reanalysis of the MSU Channel 2 tropospheric Temperature Record. J. Clim, 16, 3650-3664.
Peterson, T.C. and R.S. Vose, 1997: An Overview of the Global Historical Climatology Network Database. Bull. Amer. Meteorol. Soc., 78, 2837-2849.
Quayle, R.G., T.C. Peterson, A.N. Basist, and C. S. Godfrey, 1999: An operational near-real-time global temperature index. Geophys. Res. Lett., 26, 333-335.
Smith, T.M., and R.W. Reynolds (2005), A global merged land air and sea surface temperature reconstruction based on historical observations (1880-1997), J. Clim., 18, 2021-2036.
For all climate questions, other than questions concerning this report, please contact the National Climatic Data center's Climate Services Division:
Climate Services DivisionFor questions about this report, please contact:
Ahira Sánchez-Lugo-or-
Richard Heim
http://www.ncdc.noaa.gov/oa/climate/research/2008/apr/global.html 
