State of the Climate
Global Analysis
May 2007

National Oceanic and Atmospheric Administration

National Climatic Data Center

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Global Highlights:

Based on preliminary data, globally averaged combined land and sea surface temperature was the third warmest on record for boreal spring (March - May 2007) and the fourth warmest for May.
March - May 2007 temperatures were above average in Europe, Asia, western Africa, eastern Brazil, and most of the contiguous U.S. Cooler-than-average conditions occurred in southern Alaska and parts of Argentina and Chile.
Precipitation during March - May 2007 was above average in Uruguay, the central and northeastern region of the contiguous U.S., northwestern Australia, southern Brazil, and most of Europe. Drier than average conditions were observed in the southeastern and western U.S., the eastern coast of Australia, and parts of Asia.
ENSO conditions remained in a neutral phase during May.

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.

Introduction

Temperature anomalies for March - May 2007 and May 2007 are shown on the dot maps below. The dot maps, below left, provide 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 maps, below right, are 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.

Anomalously warm temperatures covered much of the globe throughout the first few months of the year. The January-May 2007 year-to-date map of temperature anomalies shows the presence of warmer than average temperatures across all land areas with the exception of cooler than average temperatures in Alaska and Argentina. Warmer than average Sea Surface Temperatures (SSTs) occured in the northwestern Pacific, North Atlantic and the North Indian Ocean. Cooler than average conditions were observed in the northeastern Pacific and some areas in the South Atlantic, South Indian, and South Pacific oceans.

During boreal spring, temperatures were above average in Europe, Asia, western Africa, eastern Brazil, and most of the contiguous U.S. Cooler than average conditions occurred in southern Alaska and parts of Argentina and Chile. Warmer than average SSTs were observed across the North Atlantic, North Indian, and northwestern Pacific oceans. Cooler than average SSTs were observed in areas of the eastern equatorial and northeastern Pacific Ocean and parts of the South Pacific and South Indian oceans.

Current season's Land Surface Temperature Dot map

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Current season's blended Land and sea surface Temperature Dot map

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During May, there were above average temperatures across the contiguous U.S., Europe, Asia, and western Africa. Cooler than average temperatures were observed in Finland and southern areas of South America. Warmer than average SSTs occurred in the North Atlantic, North Indian, and northwestern Pacific oceans. In the Niño regions, SST anomalies were near or slightly below average, indicative of a neutral ENSO phase. Please see the latest ENSO discussion for additional information.

Current month's Land SurfaceTemperature Dot map

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Current month's blended Land and sea surface Temperature Dot map

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The mean position of upper level ridges of high pressure and troughs of low pressure (depicted by positive and negative 500-millibar height anomalies on the March - May 2007 and the May map) are generally reflected by areas of positive and negative temperature anomalies at the surface, respectively. For other Global products see the Climate Monitoring Global Products page.

Images of sea surface temperature conditions are available for all weeks during 2007 at the weekly SST page.

Temperature Rankings and Graphics

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 for May was the fourth warmest on record. The global surface temperature for the combined January-May period tied with 1998 as the warmest January-May on record. Separately, the global land-surface temperature was the warmest on record for boreal spring (March-May), as well as for the year-to-date period and second warmest for May. The May ocean-surface temperature was the 9th warmest in the 128-year period of record as near average to cooler than average conditions were present across the equatorial Pacific.

Current Month / Seasonal / Year-to-date

May	Anomaly	Rank	Ties	Warmest (or Next Warmest)Year on Record
Global Land Ocean Land and Ocean	+0.93°C (+1.67°F) +0.37°C (+0.67°F) +0.52°C (+0.94°F)	2nd warmest 9th warmest 4th warmest	2001 2003	2005 (+0.94°C/1.69°F) 1998 (+0.54°C/0.97°F) 1998 (+0.62°C/1.12°F)
Northern Hemisphere Land Ocean Land and Ocean	+1.15°C (+2.07°F) +0.38°C (+0.68°F) +0.67°C (+1.21°F)	2nd warmest 8th warmest 2nd warmest		2001 (+1.17°C/2.11°F) 2005 (+0.60°C/1.08°F) 2005 (+0.73°C/1.31°F)
Southern Hemisphere Land Ocean Land and Ocean	+0.30°C (+0.54°F) +0.36°C (+0.65°F) +0.36°C (+0.65°F)	25th warmest 10th warmest 11th warmest	1990,1991	1981 (+1.11°C/2.00°F) 1998 (+0.58°C/1.04°F) 1998 (+0.61°C/1.10°F)

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March-May	Anomaly	Rank	Ties	Warmest (or Next Warmest) Year on Record
Global Land Ocean Land and Ocean	+1.15°C (+2.07°F) +0.40°C (+0.72°F) +0.60°C (+1.08°F)	warmest 8th warmest 3rd warmest		2005 (+1.13°C/2.03°F) 1998 (+0.53°C/0.95°F) 2005 (+0.65°C/1.17°F)
Northern Hemisphere Land Ocean Land and Ocean	+1.33°C (+2.39°F) +0.42°C (+0.76°F) +0.76°C (+1.37°F)	2nd warmest 5th warmest 2nd warmest	2003	2000 (+1.35°C/2.43°F) 2005 (+0.52°C/0.94°F) 2005 (+0.77°C/1.39°F)
Southern Hemisphere Land Ocean Land and Ocean	+0.61°C (+1.10°F) +0.38°C (+0.68°F) +0.42°C (+0.76°F)	8th warmest 9th warmest 8th warmest		2005 (+0.95°C/1.71°F) 1998 (+0.57°C/1.03°F) 1998 (+0.62°C/1.12°F)

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January-May	Anomaly	Rank	Ties	Warmest (or Next Warmest) Year on Record
Global Land Ocean Land and Ocean	+1.26°C (+2.27°F) +0.43°C (+0.77°F) +0.65°C (+1.17°F)	warmest 6th warmest warmest	1998	2002 (+1.15°C/2.07°F) 1998 (+0.53°C/0.95°F) 2002 (+0.64°C/1.15°F)
Northern Hemisphere Land Ocean Land and Ocean	+1.47°C (+2.65°F) +0.44°C (+0.79°F) +0.83°C (+1.49°F)	warmest 4th warmest warmest		2002 (+1.34°C/2.41°F) 1998 (+0.50°C/0.90°F) 2002 (+0.76°C/1.37°F)
Southern Hemisphere Land Ocean Land and Ocean	+0.63°C (+1.13°F) +0.42°C (+0.76°F) +0.45°C (+0.81°F)	4th warmest 8th warmest 6th warmest		2005 (+0.88°C/1.58°F) 1998 (+0.57°C/1.03°F) 1998 (+0.61°C/1.10°F)

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The most current data may be accessed via the Global Surface Temperature Anomalies page.

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Precipitation

The maps below represent anomaly values based on the GHCN data set of land surface stations using a base period of 1961-1990. During boreal spring, above average precipitation fell over areas that include Uruguay, the central and the northeastern region of the contiguous U.S., northwestern Australia, southern Brazil, and most of Europe. Drier than average conditions were observed in the southeastern and western U.S., the eastern coast of Australia, and parts of Asia.

During May 2007, above average precipitation fell over areas that include the central U.S. and most of Europe and Asia. Below average precipitation was observed in the Middle East, the eastern U.S., and parts of South America and Australia. Additional details on flooding and drought can also be found on the May Global Hazards page.

Precipitation Dot map in Millimeters for March-May

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Precipitation Dot map in Millimeters for May

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ENSO SST Analysis

Last week of the month's ENSO condtions Map

Click here for animated loop

Sea Surface Temperature anomalies were near average or slightly cooler than average across the equatorial Pacific, indicative of a neutral ENSO phase (shown in the adjacent animation of weekly sea surface temperature anomalies). A comprehensive summary of May 2007 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.

Northern Hemisphere Snow Cover Extent

As shown in the time series to the right, mean Northern Hemisphere snow cover extent during boreal spring (March-May) 2007 was below average. Much of this was due to anomalously warm conditions across Asia, Europe, and most of the contiguous U.S. Spring 2007 snow cover extent on the Northern Hemisphere was the 3rd lowest extent on record. Mean Northern Hemisphere spring snow cover extent for the 1967-2007 period of record is 92.6 million square kilometers.

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Current season's North America Snow Cover extent

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Snow cover for boreal Spring across North America was below average, giving March-May 2007 a rank of 8th lowest extent on record. Mean North America boreal spring snow cover extent is 38.7 million square kilometers for the 1967-2007 period of record.

As depicted in the time series to the right, Eurasia's snow cover extent this spring was below average and was the 4th lowest extent over the 41-year historical period. The low snow cover extent during March-May 2007 can be attributed to the anomalous warmth that covered much of Europe and Asia. For example, during the month of May, much of Russia suffered a record breaking heatwave which prompted temperatures to rise to 30°C (86°F) or higher. On average, Eurasian spring snow cover extent is 53.9 million square kilometers for the 1967-2007 period of record.

Current season's Eurasia Snow Cover extent

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(Data were provided by Global Snow Laboratory, Rutgers University).

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Northern Hemisphere Sea Ice Extent

According to the National Snow and Ice Data Center, the Northern Hemisphere sea ice extent, which is measured from passive microwave instruments onboard NOAA satellites, was below the 1979-2000 mean. Sea ice extent for the month of May has decreased at a rate of 2.8%/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/decade over the same period. For further information on the Northern Hemisphere snow and ice conditions, please visit the NSIDC News page, provided by the NOAA's National Snow and Ice Data Center (NSIDC).

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Troposphere

Temperatures above the Earth's surface are measured using in-situ balloon-borne instruments (radiosondes) and polar-orbiting satellites (NOAA's TIROS-N). The radiosonde and the 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).

Lower Troposphere
Current Month / Seasonal / Year-to-date

These temperatures are for the lowest 8km (5 miles) of the atmosphere. Information on the UAH and RSS sources of troposphere data is available.

May	Anomaly	Rank	Warmest (or Next Warmest) Year on Record	Trend
UAH low-trop	+0.19°C/0.34°F	6th warmest	1998 (+0.66°C/1.19°F)	+0.10°C/decade
*RSS low-trop	+0.09°C/0.16°F	13th warmest	1998 (+0.70°C/1.26°F)	+0.16°C/decade

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March- May	Anomaly	Rank	Warmest (or Next Warmest) Year on Record	Trend
UAH low-trop	+0.27°C/0.49°F	4th warmest	1998 (+0.64°C/1.15°F)	+0.13°C/decade
*RSS low-trop	+0.18°C/0.32°F	9th warmest	1998 (+0.73°C/1.31°F)	+0.18°C/decade

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January- May	Anomaly	Rank	Warmest (or Next Warmest) Year on Record	Trend
UAH low-trop	+0.35°C/0.63°F	2nd warmest	1998 (+0.63°C/1.13°F)	+0.14°C/decade
*RSS low-trop	+0.24°C/0.43°F	7th warmest	1998 (+0.71°C/1.28°F)	+0.18°C/decade

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Mid-Troposphere
Current Month / Seasonal / Year-to-date

These temperatures are for the atmospheric layer centered in the mid-troposphere (approximately 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 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). 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 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.

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Radiosonde measurements indicate that for the January-May year-to-date period, temperatures in the mid-troposphere were 0.68°C (1.22°F) above average, resulting in the 2nd warmest January-May since global measurements began in 1958. However, as shown in the table below, satellite measurements of the January-May 2007 year-to-date period for the middle troposphere varied from 3rd to 6th warmest on record, depending on the analysis method.

During the boreal spring, radiosonde measurements indicate that temperatures in the mid-troposphere were 0.67°C (1.21°F) above average, giving March-May a rank of 2nd warmest on record. The table below shows that satellite measurements for the boreal spring varied from 6th to 8th warmest on record depending on the analysis method.

The global mid-troposphere temperatures were warmer than average in May 2007, as shown in the table below. Satellite measurements for May 2007 varied from 7th to 9th warmest on record depending on the analysis method.

May	Anomaly	Rank	Warmest (or Next Warmest) Year on Record	Trend
UAH mid-trop	+0.10°C/0.18°F	9th warmest	1998 (+0.59°C/1.06°F)	+0.03°C/decade
*RSS mid-trop	+0.17°C/0.31°F	9th warmest	1998 (+0.65°C/1.17°F)	+0.10°C/decade
**UW-UAH mid-trop	+0.23°C/0.41°F	7th warmest	1998 (+0.76°C/1.37°F)	+0.09°C/decade
*UW-RSS mid-trop	+0.25°C/0.45°F	7th warmest	1998 (+0.77°C/1.39°F)	+0.16°C/decade

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March- May	Anomaly	Rank	Warmest (or Next Warmest)Year on Record	Trend
UAH mid-trop	+0.14°C/+0.25°F	8th warmest	1998 (+0.59°C/1.06°F)	+0.05°C/decade
*RSS mid-trop	+0.21°C/0.38°F	7th warmest	1998 (+0.65°C/1.17°F)	+0.12°C/decade
**UW-UAH mid-trop	+0.24°C/+0.43°F	6th warmest	1998 (+0.71°C/1.28°F)	+0.11°C/decade
*UW-RSS mid-trop	+0.30°C/+0.54°F	6th warmest	1998 (+0.77°C/1.39°F)	+0.17°C/decade
RATPAC	+0.67°C/1.21°F	2nd warmest	1998 (+0.86°C/1.55°F)	+0.15°C/decade

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January- May	Anomaly	Rank	Warmest (or Next Warmest) Year on Record	Trend
UAH mid-trop	+0.19°C/+0.34°F	5th warmest	1998 (+0.57°C/1.03°F)	+0.05°C/decade
*RSS mid-trop	+0.26°C/0.47°F	6th warmest	1998 (+0.64°C/1.15°F)	+0.12°C/decade
**UW-UAH mid-trop	+0.30°C/+0.54°F	3rd warmest	1998 (+0.71°C/1.28°F)	+0.12°C/decade
*UW-RSS mid-trop	+0.36°C/+0.65°F	6th warmest	1998 (+0.76°C/1.37°F)	+0.18°C/decade
RATPAC	+0.68°C/1.22°F	2nd warmest	1998 (+0.80°C/1.44°F)	+0.15°C/decade

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Stratosphere

Current Month / Seasonal

The table below summarizes stratospheric conditions for May 2007. On average, the stratosphere is located approximately between 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.

May	Anomaly	Rank	Coolest Year on Record
UAH stratosphere	-0.51°C (-0.92°F)	5th coolest	1996 (-0.63°C/-1.13°F)
*RSS stratosphere	-0.34°C (-0.61°F)	6th coolest	1996 (-0.53°C/-0.95°F)

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March- May	Anomaly	Rank	Coolest Year on Record
UAH stratosphere	-0.48°C (-0.86°F)	4th coolest	1999 (-0.62°C/-1.12°F)
*RSS stratosphere	-0.39°C (-0.70°F)	6th coolest	1999 (-0.56°C/-1.01°F)

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For additional details on precipitation and temperatures in May, see the Global Hazards page.

References

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.