Because most global warming emissions remain in the atmosphere

for decades or centuries, the energy choices we make today greatly influence the climate our children and grandchildren inherit. We have

the technology to increase energy efficiency, significantly reduce

these emissions from our energy and land use, and secure a high

quality of life for future generations. We must act now to avoid dangerous consequences.

The year 2005 exceeded previous global annual average temper-

atures despite having weak El Niño conditions at the beginning

of the year and normal conditions for the rest of the year. (

El Niño is a period of warmer-than-average sea surface temper-

atures in the east-central Pacific Ocean that influences weather conditions across much of the globe.) In contrast, the record-

breaking temperatures of 1998 were boosted by a particularly

strong El Niño.

The record heat of 2005 is part of a longer-term warming trend exacerbated by the rise of heat-trapping gases in our atmosphere

that is due primarily to our burning fossil fuels and clearing forests. Nineteen of the hottest 20 years on record have occurred since

1980 (See photo at right).

Fact Sheet (low resolution) (Go to URL at top and click

on "Fact Sheet")

The record surface temperatures of the past 20 years reinforce

other indications that global warming is under way. For example,

the observed rise in average surface temperatures has been accompanied by warming of the atmosphere and oceans, and

increased melting of ice and snow. These observations,

summarized briefly below, paint a consistent picture of widespread

and significant changes in global climate over the past several decades.

Evidence of Twentieth Century Global Warming

Warming of the Troposphere

The latest report on U.S. emissions found that 2004 marked

the highest annual total of heat-trapping gases released since

record keeping began in 1990

A 2005 re-analysis of satellite observations of temperature trends

in the troposphere—the layer of atmosphere extending about five

miles up from Earth's surface—uncovered errors in previous

studies. The updated studies show that air temperatures have

increased in the past 20 years or so, consistent with the funda-

mental understanding that increases in surface temperatures are accompanied by increases in air temperatures above the surface.

The new results are also consistent with recent increases in

tropospheric water vapor, which would be expected when rising temperatures accelerate ocean evaporation.

By comparing several sets of data from satellites and weather

balloons, these new atmospheric analyses account for drifts in

satellite orbits and changes in instrumentation over the measure-

ment period. While the corrected results represent only one of

several pieces of global warming evidence, they are important

in part because the earlier flawed analysis has often been cited.

Melting of Snow and Ice

Further evidence of widespread warming comes from observations of seasonal snow and frozen ground coverage.

The extent and duration of frozen ground have declined in most

locations. Snow cover in the Northern Hemisphere has declined

about five percent over the past 30 years, particularly in late

winter and spring, and the freezing altitude has risen in every

major mountain chain. Alpine and polar glaciers have retreated

since 1961, and the amount of ice melting in Greenland has i

ncreased since 1979. Over the past 25 years, the average

annual Arctic sea ice area has decreased by almost five percent

and summer sea ice area has decreased by almost 15 percent.

The collapse of the Larsen Ice Shelf off the Antarctic Peninsula

appears to have no precedent in the last 11,000 years.

Melting of the Greenland Ice Sheet

Figure courtesy of NOAA and CIRES

Satellites are used to map the extent and duration of snowmelt

on the Greenland ice sheet. The dark red area represents the

extent of snowmelt in 2005—the most extensive in the 27-year

history of data collection. ( See photo at right)

Warming of the Oceans

Oceans comprise 97 percent of Earth's water. They have an

average depth of approximately 13,000 feet (4 kilometers). It

takes a great deal of heat to raise the temperature of this huge

body of water, and the oceans have absorbed the bulk of Earth's

excess heat over the past several decades. (See figure,

"Estimates of Earth's Heat Balance.") From 1955 to 1998,

the upper ~9,800 feet (3,000 meters) of the ocean have warmed

by an average 0.067 degrees Fahrenheit (0.037 degrees Celsius).

Estimates of Earth's Heat Balance

The oceans have absorbed the bulk of Earth's excess heat over

the past several decades. (See photo at right)

If only a small fraction of the heat currently stored in the

oceans were released, it would significantly warm the atmos-

phere and melt the world's glaciers. For a hypothetical example,

if the average temperature of the world's oceans increased by

0.18 degree Fahrenheit (0.1 degree Celsius) and this heat was transferred instantly to the atmosphere, the air temperature

would increase by about 180 degrees Fahrenheit (100 degrees

Celsius). In reality, the circulation and redistribution of this

excess

heat is a slow process. Even if we could maintain atmospheric

CO2 concentrations at today's level, stored heat released by the

oceans will cause Earth's average surface temperature to continue

rising approximately one degree Fahrenheit (half a degree Celsius)

in the coming decades. To put this into perspective, this is the

same as the global average temperature rise that occurred over

the last century. The warming of the oceans and the melting of

glaciers worldwide have already caused sea levels to rise during

the twentieth century, and most of this rise has come in the past

few decades.

The Role of Natural Variability

Human-induced warming is superimposed on natural processes

to produce the observed climate. Because these natural

fluctuations (which are always present) play a role in deter

mining the precise magnitude and distribution of temperature

in a particular year, record warmth in any one year is not in

itself highly significant. What is noteworthy, however, is that

global average temperatures experienced a net rise over the

twentieth century, and the average rate of this rise has been

increasing. When scientists attempt to reproduce these twentieth

century trends in their climate models, they are only able to do

so when including human-produced heat-trapping emissions in

addition to natural causes.

[1] The years 1998 and 2005 are so similar (i.e., within the error

range of the different analysis methods or a few hundredths of

a degree Celsius) that independent groups (e.g., NOAA, NASA,

and the United Kingdom Meteorological Office) calculating these

rankings basedbased on reports from the same data-collecting

stations around the world disagree on which year should be ranked

first. Annual global rankings are based on combined land-air

surface temperature and sea surface temperature since 1880.

Dr. Marcia Baker (professor emeritus in Earth and Space

Sciences and Atmospheric Sciences at the University of Washing-

ton) prepared this summary with input from Dr. Brenda Ekwurzel

(climate scientist at the Union of Concerned Scientists).

References

Arctic Climate Impact Assessment. 2004. Impacts of a Warming

Arctic. Cambridge, UK: Cambridge University Press. Available at http://www.acia.uaf.edu.

Arrenhius, S. 1896. On the influence of carbonic acid in the air

upon the temperature of the ground. Philosophical Magazine

41:237-276.

Barnett, T.P., D.W. Pierce, and R. Schnur. 2001. Detection of anthropogenic climate change in the world's oceans. Science

292:270-274.

Domack, E., D. Duran, A. Leventer, S. Ishman, S. Doane, S.

McCallum, D. Amblas, J. Ring, R. Gilbert and M. Prentice. 2005.

Stability of the Larsen B Ice Shelf on the Antarctic Peninsula

during the Holocene Epoch. Nature 436:681-685.

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.

Hansen, J., L. Nazarenko, R. Ruedy, M. Sato, J. Willis, A.

Del Genio, D. Koch, A. Lacis, K. Lo, S. Menon, T. Novakov, J.

Perlwitz, G. Russell, G. A. Schmidt, N. Tausnev. 2005. Earth's

energy imbalance: Confirmation and implications. Science

308:1431-1435.

Intergovernmental Panel on Climate Change. 2001. Climate

Change 2001: The Scientific Basis. Cambridge, U.K.:

Cambridge University Press.

Krabill, W., E. Hanna, P. Huybrechts, W. Abdalati, J. Cappelen,

B. Csatho, E. Frederick, S. Manizade, C. Martin, J. Sonntag, R.

Swift, R. Thomas and J. Yungel. 2004. Greenland Ice Sheet:

Increased coastal thinning. Geophysical Research Letters 31.

Levitus, S., J. Antonov, and T. Boyer. 2005. Warming of the

world ocean, 1955-2003. Geophysical Research Letters 32.

Mears, C.A., and F.J. Wentz. 2005. The effect of diurnal

corrections on satellite-derived lower tropospheric temperatures.

Science 309:1548-1551.

Mote, P. W., A..F. Hamlet, M.P. Clark and D. P. Lettenmaier

2005. Declining mountain snowpack in western North America.

Bulletin of the American Meteorological Society 86:39-49.

Rodhe, H., and R.J. Charlson, eds. 1998. The Legacy of Svante Arrhenius: Understanding the Greenhouse Effect. Royal Swedish Academy of Sciences, Stockholm University.

Santer, B.D., T.M.L. Wigley, C. Mears, F.J. Wentz, S.A. Klein,

D.J. Seidel, K.E. Taylor, P.W. Thorne, M.F. Wehner, P.-J.

Gleckler, J.S. Boyle, W.D. Collins, K.W. Dixon, C. Doutriaux, M.

Free, Q. Fu, J.E. Hansen, G.S. Jones, R. Ruedy, T.R. Karl, J.R.

Lanzante, G.A. Meehl, V. Ramaswamy, G. Russell, and G.A.

Schmidt. 2005. Amplification of surface temperature trends and

variability in the tropical atmosphere. Science 309:1551-1556.

Sherwood, S., J. Lanzante, and C. Meyer. 2005. Radiosonde

daytime biases and late-20th century warming. Science 309:

1556-1559.

Siegenthaler, U., T.F. Stocker, E. Monnin, D. Lüthi, J.

Schwander, B. Stauffer, D. Raynaud, J.-M. Barnola, H. Fischer,

V. Masson-Delmotte and J. Jouzel. 2005. Stable carbon cycle-

climate relationship during the late Pleistocene. Science 310:

1313-1316.

Steffen, K., and R. Huff. 2005. Greenland Melt Extent, 2005.

Cooperative Institute for Research in Environmental Sciences

(CIRES), University of Colorado at Boulder and National Oceanic

and Atmospheric Administration (NOAA). Available at http://cires.colorado.edu/science/groups/steffen/greenland/

melt2005.

United Kingdom Climate Research Unit (CRU). 2005. Global

Temperature for 2005: Second warmest year on record.

Norwich U.K. Available at http://www.cru.uea.ac.uk/cru/press

/2005-12-WMO.pdf

U.S. Department of Energy (DOE). 2005. Emissions of Greenhouse

Gases in the United States 2004. DOE/EIA-0573(2004). Washing-

ton DC. Available at ftp://ftp.eia.doe.gov/pub/oiaf/1605/cdrom/pdf/ggrpt/057304.pdf.

U.S. National Aeronautics and Space Administration (NASA). 2005.

Global Temperature Trends: 2005 Summation. NASA Goddard

Institute for Space Studies (GISS). New York, NY. Available at http://data.giss.nasa.gov/gistemp/2005/.

U.S. National Oceanic and Atmospheric Administration (NOAA).

2006. Climate of 2005 –Annual Report. National Climate Data

Center (NOAA) Asheville, NC. Available at http://www.ncdc.noaa.gov/oa/climate/research/2005/ann/

global.html

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Global Warming Science

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Contents

Global Warming 101

Global Warming Human Fingerprints

Record Temperatures 2005

Global Warming FAQ

Science of Global Warming

Past, Present, and Future Temperatures: the Hockeystick FAQ

Abrupt Climate Change FAQ

Hurricanes and Climate Change

Recognizing Forests' Role in Climate Change

Climate Change in Key Regions

California Global Warming Impacts

Global Warming in New Hampshire

Gulf Coast Ecological Heritage at Risk

Great Lakes Communities and Ecosystems at Risk

Arctic Climate Impact Assessment

Climate Change in the Hawkeye State

Early Warning Signs of Global Warming

Causes

Each Country's Share of CO2 Emissions

The impacts of land use on climate change

Recognizing Forests' Role in Climate Change

Resources

Sound Science Initiative

Global Warming Materials for Educators

Crichton Thriller State of Fear

The Intergovernmental Panel on Climate Change

Skeptic Organizations

Global Warming FAQ