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Climate Change: Evidence 

The Earth’s climate has changed throughout history.   Just in the last  650,000 years there have been seven cycles of glacial advance and  retreat, with the abrupt end of the last ice age about 7,000 years ago   marking the beginning of the modern climate era — and of human  civilization.  Most of these climate changes are attributed to  very  small variations in Earth’s orbit that change the amount of solar energy  our planet receives.
The current warming trend is of particular significance because most of  it is very likely human-induced and  proceeding at a rate that is  unprecedented in the past 1,300 years.1
Earth-orbiting satellites and other technological advances have enabled  scientists to see the big picture, collecting many different types of  information about our planet and its climate on a global scale.   Studying these climate data collected over many years reveal the signals  of a changing climate.
Certain facts about Earth’s climate are not in dispute:
The heat-trapping nature of carbon dioxide and other gases was demonstrated in the mid-19th century.2 Their ability to affect the transfer of infrared energy through the  atmosphere is the scientific basis of many JPL-designed instruments,  such as AIRS.  Increased levels of greenhouse gases must cause the Earth  to warm in response.
Ice cores drawn from Greenland, Antarctica, and tropical  mountain glaciers show that the Earth’s climate responds to changes in  solar output, in the Earth’s orbit, and in greenhouse gas levels.  They  also show that in the past, large changes in climate have happened very  quickly, geologically-speaking: in tens of years, not in millions or  even thousands.3
The evidence for rapid climate change is compelling:

Sea level rise
Global sea level rose about 17 centimeters (6.7 inches) in the last  century. The rate in the last decade, however, is nearly double that of  the last century.4

Global temperature rise
All three major global surface temperature reconstructions show that Earth has warmed since 1880. 5 Most of this warming has occurred since the 1970s, with the 20 warmest  years having occurred since 1981 and with all 10 of the warmest years  occurring in the past 12 years. 6 Even though the 2000s witnessed a solar output decline resulting in an  unusually deep solar minimum in 2007-2009, surface temperatures  continue to increase. 7

Warming oceans
The oceans have absorbed much of this increased heat, with the top 700  meters (about 2,300 feet) of ocean showing warming of 0.302 degrees  Fahrenheit since 1969.8

Shrinking ice sheets
The Greenland and Antarctic ice sheets have decreased in mass. Data from  NASA’s Gravity Recovery and Climate Experiment show Greenland lost 150  to 250 cubic kilometers (36 to 60 cubic miles) of ice per year between  2002 and 2006, while Antarctica lost about 152 cubic kilometers (36  cubic miles) of ice between 2002 and 2005.

Declining Arctic sea ice
Both the extent and thickness of Arctic sea ice has declined rapidly over the last several decades. 9

Glacial retreat
Glaciers are retreating almost everywhere around the world — including  in the Alps, Himalayas, Andes, Rockies, Alaska and Africa.10

Extreme events
The number of record high  temperature events in the United States has been increasing, while the  number of record low temperature events has been decreasing, since 1950.   The U.S. has also witnessed increasing numbers of intense rainfall  events.11

Ocean acidification
Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30 percent.12,13 This increase is the result of humans emitting more carbon dioxide into  the atmosphere and hence more being absorbed into the oceans. The  amount of carbon dioxide absorbed by the upper layer of the oceans is  increasing by about 2 billion tons per year.14,15

References1 IPCC Fourth Assessment Report, Summary for Policymakers, p. 5

B.D. Santer et.al., “A search for human influences on the thermal  structure of the atmosphere,” Nature vol 382, 4 July 1996, 39-46
Gabriele C. Hegerl, “Detecting Greenhouse-Gas-Induced Climate Change  with an Optimal Fingerprint Method,” Journal of Climate, v. 9, October  1996, 2281-2306
V. Ramaswamy et.al., “Anthropogenic and Natural Influences in the  Evolution of Lower Stratospheric Cooling,” Science 311 (24 February  2006), 1138-1141
B.D. Santer et.al., “Contributions of Anthropogenic and Natural  Forcing to Recent Tropopause Height Changes,” Science vol. 301 (25 July  2003), 479-483.
2 In the 1860s, physicist John  Tyndall recognized the Earth’s natural greenhouse effect and suggested  that slight changes in the atmospheric composition could bring about  climatic variations.  In 1896, a seminal paper by Swedish scientist  Svante Arrhenius first speculated that changes in the levels of carbon  dioxide in the atmosphere could substantially alter the surface  temperature through the greenhouse effect.
3 National Research Council  (NRC), 2006. Surface Temperature Reconstructions For the Last 2,000  Years.   National Academy Press, Washington, DC.
4 Church, J. A. and N.J. White  (2006), A 20th century acceleration in global sea level rise,  Geophysical Research Letters, 33, L01602, doi:10.1029/2005GL024826.
The global sea level estimate described in this work can be downloaded from the CSIRO website.
5http://www.ncdc.noaa.gov/oa/climate/research/ anomalies/index.html
http://www.cru.uea.ac.uk/cru/data/temperature
http://data.giss.nasa.gov/gistemp
6 T.C. Peterson et.al., “State of  the Climate in 2008,” Special Supplement to the Bulletin of the  American Meteorological Society, v. 90, no. 8, August 2009, pp. S17-S18.
7 I. Allison et.al., The  Copenhagen Diagnosis: Updating the World on the Latest Climate Science,  UNSW Climate Change Research Center, Sydney, Australia, 2009, p. 11
http://www.giss.nasa.gov/research/news/20100121/
http://science.nasa.gov/headlines/y2009/ 01apr_deepsolarminimum.htm
8 Levitus, et al, “Global ocean  heat content 1955–2008 in light of recently revealed instrumentation  problems,” Geophys. Res. Lett. 36, L07608 (2009).
9 L. Polyak, et.al., “History of  Sea Ice in the Arctic,” in Past Climate Variability and Change in the  Arctic and at High Latitudes, U.S. Geological Survey, Climate Change  Science Program Synthesis and Assessment Product 1.2, January 2009,  chapter 7
R. Kwok and D. A. Rothrock, “Decline in Arctic sea ice thickness from  submarine and ICESAT records: 1958-2008,” Geophysical Research Letters,  v. 36, paper no. L15501, 2009
http://nsidc.org/sotc/sea_ice.html
10 National Snow and Ice Data Center
 World Glacier Monitoring Service
11 http://lwf.ncdc.noaa.gov/extremes/cei.html

12 http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F (Note: The pH of surface ocean waters has fallen by 0.1 pH units. Since  the pH scale is logarithmic, this change represents approximately a 30  percent increase in acidity.)

13 http://www.pmel.noaa.gov/co2/story/Ocean+Acidification
14 C. L. Sabine et.al., “The Oceanic Sink for Anthropogenic CO2,” Science vol. 305 (16 July 2004), 367-371
15 Copenhagen Diagnosis, p. 36.

Climate Change: Evidence

The Earth’s climate has changed throughout history. Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era — and of human civilization. Most of these climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives.

The current warming trend is of particular significance because most of it is very likely human-induced and proceeding at a rate that is unprecedented in the past 1,300 years.1

Earth-orbiting satellites and other technological advances have enabled scientists to see the big picture, collecting many different types of information about our planet and its climate on a global scale. Studying these climate data collected over many years reveal the signals of a changing climate.

Certain facts about Earth’s climate are not in dispute:

  • The heat-trapping nature of carbon dioxide and other gases was demonstrated in the mid-19th century.2 Their ability to affect the transfer of infrared energy through the atmosphere is the scientific basis of many JPL-designed instruments, such as AIRS. Increased levels of greenhouse gases must cause the Earth to warm in response.
  • Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that the Earth’s climate responds to changes in solar output, in the Earth’s orbit, and in greenhouse gas levels. They also show that in the past, large changes in climate have happened very quickly, geologically-speaking: in tens of years, not in millions or even thousands.3

The evidence for rapid climate change is compelling:

  • Sea level rise

    Global sea level rose about 17 centimeters (6.7 inches) in the last century. The rate in the last decade, however, is nearly double that of the last century.4
  • Global temperature rise

    All three major global surface temperature reconstructions show that Earth has warmed since 1880. 5 Most of this warming has occurred since the 1970s, with the 20 warmest years having occurred since 1981 and with all 10 of the warmest years occurring in the past 12 years. 6 Even though the 2000s witnessed a solar output decline resulting in an unusually deep solar minimum in 2007-2009, surface temperatures continue to increase. 7
  • Warming oceans

    The oceans have absorbed much of this increased heat, with the top 700 meters (about 2,300 feet) of ocean showing warming of 0.302 degrees Fahrenheit since 1969.8
  • Shrinking ice sheets

    The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA’s Gravity Recovery and Climate Experiment show Greenland lost 150 to 250 cubic kilometers (36 to 60 cubic miles) of ice per year between 2002 and 2006, while Antarctica lost about 152 cubic kilometers (36 cubic miles) of ice between 2002 and 2005.
  • Declining Arctic sea ice

    Both the extent and thickness of Arctic sea ice has declined rapidly over the last several decades. 9
  • Glacial retreat

    Glaciers are retreating almost everywhere around the world — including in the Alps, Himalayas, Andes, Rockies, Alaska and Africa.10
  • Extreme events

    The number of record high temperature events in the United States has been increasing, while the number of record low temperature events has been decreasing, since 1950. The U.S. has also witnessed increasing numbers of intense rainfall events.11
  • Ocean acidification

    Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30 percent.12,13 This increase is the result of humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the oceans. The amount of carbon dioxide absorbed by the upper layer of the oceans is increasing by about 2 billion tons per year.14,15

References

1 IPCC Fourth Assessment Report, Summary for Policymakers, p. 5

B.D. Santer et.al., “A search for human influences on the thermal structure of the atmosphere,” Nature vol 382, 4 July 1996, 39-46

Gabriele C. Hegerl, “Detecting Greenhouse-Gas-Induced Climate Change with an Optimal Fingerprint Method,” Journal of Climate, v. 9, October 1996, 2281-2306

V. Ramaswamy et.al., “Anthropogenic and Natural Influences in the Evolution of Lower Stratospheric Cooling,” Science 311 (24 February 2006), 1138-1141

B.D. Santer et.al., “Contributions of Anthropogenic and Natural Forcing to Recent Tropopause Height Changes,” Science vol. 301 (25 July 2003), 479-483.

2 In the 1860s, physicist John Tyndall recognized the Earth’s natural greenhouse effect and suggested that slight changes in the atmospheric composition could bring about climatic variations. In 1896, a seminal paper by Swedish scientist Svante Arrhenius first speculated that changes in the levels of carbon dioxide in the atmosphere could substantially alter the surface temperature through the greenhouse effect.

3 National Research Council (NRC), 2006. Surface Temperature Reconstructions For the Last 2,000 Years. National Academy Press, Washington, DC.

4 Church, J. A. and N.J. White (2006), A 20th century acceleration in global sea level rise, Geophysical Research Letters, 33, L01602, doi:10.1029/2005GL024826.

The global sea level estimate described in this work can be downloaded
from the CSIRO website.

5http://www.ncdc.noaa.gov/oa/climate/research/ anomalies/index.html

http://www.cru.uea.ac.uk/cru/data/temperature

http://data.giss.nasa.gov/gistemp

6 T.C. Peterson et.al., “State of the Climate in 2008,” Special Supplement to the Bulletin of the American Meteorological Society, v. 90, no. 8, August 2009, pp. S17-S18.

7 I. Allison et.al., The Copenhagen Diagnosis: Updating the World on the Latest Climate Science, UNSW Climate Change Research Center, Sydney, Australia, 2009, p. 11

http://www.giss.nasa.gov/research/news/20100121/

http://science.nasa.gov/headlines/y2009/ 01apr_deepsolarminimum.htm

8 Levitus, et al, “Global ocean heat content 1955–2008 in light of recently revealed instrumentation problems,” Geophys. Res. Lett. 36, L07608 (2009).

9 L. Polyak, et.al., “History of Sea Ice in the Arctic,” in Past Climate Variability and Change in the Arctic and at High Latitudes, U.S. Geological Survey, Climate Change Science Program Synthesis and Assessment Product 1.2, January 2009, chapter 7

R. Kwok and D. A. Rothrock, “Decline in Arctic sea ice thickness from submarine and ICESAT records: 1958-2008,” Geophysical Research Letters, v. 36, paper no. L15501, 2009

http://nsidc.org/sotc/sea_ice.html

10 National Snow and Ice Data Center

World Glacier Monitoring Service

11 http://lwf.ncdc.noaa.gov/extremes/cei.html

12 http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F (Note: The pH of surface ocean waters has fallen by 0.1 pH units. Since the pH scale is logarithmic, this change represents approximately a 30 percent increase in acidity.)

13 http://www.pmel.noaa.gov/co2/story/Ocean+Acidification

14 C. L. Sabine et.al., “The Oceanic Sink for Anthropogenic CO2,” Science vol. 305 (16 July 2004), 367-371

15 Copenhagen Diagnosis, p. 36.