The Physical Basis for Global Warming

» Historical background
» Definition of climate change
» The relationship between greenhouse gas and global warming
» Different sources of greenhouse gas and evidence for their increase
» The evidence for global warming and how it is measured (» proxy data » climate and CO₂ variability » temperature records)

 

Historical Notes

The following quotations are taken from a detailed article with extensive references by Spencer Weart » [1]. They give some historical background and I found it helpful to realise that the ideas behind global warming had developed over so long a period.

Fourier 1824
“What determines the average temperature of a planet like the Earth? When light from the Sun strikes the Earth's surface and warms it up, why doesn't the planet keep heating up until it is as hot as the Sun itself? Fourier's answer was that the heated surface emits invisible infrared radiation, which carries the heat energy away into space. But when he calculated the effect with his new theoretical tools, he got a temperature well below freezing, much colder than the actual Earth.  The difference, Fourier recognized, was due to the Earth's atmosphere. Somehow it kept part of the heat radiation in.”» [1]

Tyndall 1863
"As a dam built across a river causes a local deepening of the stream, so our atmosphere, thrown as a barrier across the terrestrial rays, produces a local heightening of the temperature at the Earth's surface."» [1]

James Croll 1875
“James Croll worked as a janitor and clerk in institutions where he could be near the books he needed to develop his influential theory of the ice ages. Croll noted how the ice sheets themselves would influence climate. When snow and ice had covered a region, they would reflect most of the sunlight back into space. The Sun would warm bare, dark soil and trees, but a snowy region would tend to remain cool.”» [1]

Arrhenius 1896
“Svante Arrhenius, in his pioneering 1896 study of how changes in the amount of CO₂ may affect climate. Following the same line of reasoning as Tyndall, Arrhenius pointed out that an increase in the blocking of heat radiation would make for a smaller temperature difference between summer and winter and between the tropics and the poles. He also calculated that the consequences of adding CO₂ and warming the planet a bit would indeed be amplified because warmer air held more water vapor. In a sense, raising or lowering CO₂ acted mainly as a throttle to raise or lower the really important greenhouse gas, H₂O. He further estimated what might happen if the amount of gas in the atmosphere, at some distant time in the past or future, was double its present value. He computed that this would bring roughly 5 or 6 °C of global warming.” » [1]

References & Links

1. Spencer Weart “The Discovery of Global Warming” » [home page]; American Institute of Physics » [home page]
   » Available: http://www.aip.org/history/climate/simple.htm [accessed 2007, April. 29]

» Back to top

What is meant by climate change

Climate – “ The statistical description in terms of the mean and variability of relevant quantities eg temperature, precipitation and wind over a period of time ranging from months to thousands or millions of years. The classical period is 30 years” IPCC» [1]

Climate change (modified from UNFCCC)
“A change of climate caused by human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability” UNFCCC» [2]

Climate Change ( modified from IPCC 2001).
“A statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period (typically decades or longer). It may be due to natural internal processes or external forces, or to persistent anthropogenic changes in the composition of the atmosphere or in land use” IPCC» [1]

» Read more here . . .

References & Links

1. “IPCC 3 rd Assessment Report: “Climate Change 2001: The Scientific Basis ” Appendix I: Glossary » [home page]
   » Available: http://www.grida.no/climate/ipcc_tar/wg1/518.htm [accessed 2007, May. 19]
   
   
2. “United Nations Framework Convention on Climate Change” Article 1: Definitions » [home page]
   » Available: http://unfccc.int/essential_background/convention/background/items/2536.php [accessed 2007, May. 19]
   
   
3. “National Biodiversity and Climate Change Action Plan 2004 – 2007” Australian Government – DEH » [home page]
   » Available: http://www.environment.gov.au/biodiversity/publications/nbccap/glossary.html [accessed 2007, May. 19]

» Back to top

Greenhouse gases and their effect on Earth’s temperature

Greenhouse gases are gases in the atmosphere which help to maintain the Earth’s temperature. “Carbon dioxide, water vapour, methane, nitrous oxide, and a few other gases are greenhouse gases. They are each composed of more than two component atoms, bound loosely enough together to be able to vibrate with the absorption of heat. The major components of the atmosphere, nitrogen and oxygen, are two-atom molecules too tightly bound together to vibrate and thus they do not absorb heat and contribute to the greenhouse effect.” NCAR » [1]

The chart below describes how the suns radiation consists of Xrays, ultraviolet, visible light, infrared, microwaves and radio waves. It also shows that most of the radiation is contained as UV, visible light or infrared » [1]

» Read more here . . .

The following three images are reproduced from the
NCAR & UCAR/Comet program » [1]

This figure gives approximate percentages for solar radiation absorbed and reflected by the earth » [1]

Below is an illustration of how some radiation is reflected from the earth but infrared is absorbed and then reemitted. The infrared radiation is then reflected back to earth by the atmosphere. » [1]

References & Links

1. “ The Greenhouse Effect” National Centre for Atmospheric Research & UCAR/Comet » [home page]
   » Available: http://www.ucar.edu/learn/1_3_1.htm [accessed 2007, May. 19]

» Back to top

Climate Variability and Change

This section gives references describing a few of the interactions between events happening on the earth, CO₂, water vapour, and the temperature of the earth's atmosphere. It gives a fair impression of the complexity of the system.

Extracts from “Sources and Losses of Greenhouse Gases” NASA Athena Program » [1]

“The amount of greenhouse gas [in the Earth’s atmosphere] is a balance between how fast the gas is put into the atmosphere (source) and how rapidly it is lost”……”Major sources of CO₂ include fossil fuel burning and biomass (plants) burning, both natural and by humans. Volcanic gases are another source of carbon dioxide. Sources of methane include rice fields, digestive waste from ruminant animals (cattle, sheep, wild animals), coal mining, wetlands and natural gas venting, and biomass burning (incomplete combustion). Industrial processes are the only source of CFC's.” » [1]

“Natural processes also remove CO₂ from the atmosphere. Plants absorb the gas as they grow, trapping it until they die and decay. So reduction of forests and other agricultural practices by humans may change the absorption of carbon dioxide. The ocean absorbs large amounts of CO₂ from the atmosphere. After absorption the CO₂ ultimately converts to calcium carbonate, or is re-emitted to the atmosphere. Human activity doesn't change absorption by the ocean. There are almost no processes that remove CFC's from the atmosphere. They have a long lifetime - possibly more than a century.” » [1]

“In the absence of other effects the global average temperature is related to the amount of CO₂and CH4 in the atmosphere. Hence human activities, which have likely increased the levels of CO₂ and CH 4 in the atmosphere, may very well result in an increase in the mean global temperature. Large-scale computer models developed to study the Earth's climate predict this effect.” » [1]

“The situation is not simple since there are other factors involved. For example, water vapour is a powerful greenhouse gas. You might think that if it is warmer the ocean would evaporate more, putting more vapour into the air, which would make it still warmer. However, a warmer and moister climate might make more plants grow, and these tend to remove carbon dioxide. Moreover, if the water vapour condenses into clouds (which are not vapour but liquid water drops of ice crystals) the white clouds reflect sunlight back into space (an effect called albedo) before it can warm the Earth. You can see that the Earth's atmosphere is part of a complicated system” » [1]

"Processes and Interactions in the Global Climate System" NIWA [2]

References & Links

1. H.Anderson, B.Walter, E.Sparrow.“Atmospheric Greenhouse Gases” NASA Athena Program » [home page]
   » Available: http://vathena.arc.nasa.gov/curric/land/global/greenhou.html [accessed 2007, Feb. 24]
   
   
2. Wratt D and Mullan B “A schematic view of many of the processes and interactions in the global climate system
   (based on fig 1.1 of the 1995 IPCC Science Assessment)” NIWA » [home page]
   » Available: http://www.niwascience.co.nz/ncc/clivar/models [accessed 2007, Feb. 24]

» Back to top

Enhanced Greenhouse Effects

Increases in the earth's temperature can occur naturally for example, by solar cycles and changes in the sun's radiation. Human activities however, are increasing the concentration of greenhouse gases in the atmosphere. Australian Greenhouse Office » [1]

» Read more here . . .

References & Links

1. "Comparison of Global Warming Potentials from the second and third Assessment Reports of the (IPCC)" » [home page]
   » Available: http://www.eia.doe.gov/oiaf/1605/gwp.html » [home page]
   
   
2. “Greenhouse? What's that?” Education Fact sheet. Australian Greenhouse Office » [home page]
   » Available: http://www.greenhouse.gov.au/education/factsheets/what.html#what [accessed 2007, Feb. 24]

» Back to top

Anthropogenic Greenhouse Gases

Green house gases measured at Cape Grim
CSIRO [1]

Graphs A, B, C & D show data from a CSIRO measuring station at Cape Grim in Tasmania Australia » [1]. They relate to greenhouse gases which have entered the atmosphere through human activities, i.e. anthropogenic greenhouse gas. The Cape Grim station is one of a group of international stations. An information sheet on these graphs has been written by Paul Holper of CSIRO » [1]

             Figure A                                                                  Figure B

           Figure C                                                                     Figure D

The following notes represent my understanding of the graphs.

Figure A – The increase shown here contributes to the evidence for anthropogenic CO₂

Figure B – Evidence for fossil fuel contribution to atmospheric CO₂. The ¹³C/ ¹²C ratio in CO₂is written as d¹³C. Fossil fuel CO₂ has a much lower ratio of d¹³C than naturally occurs in the atmosphere. As fossil fuels are burnt and their CO₂ is added to the atmosphere its d¹³C ratio reduces.

The reason that fossil fuel has a lower ratio of d¹³C is that photosynthesis and other organic activity favours the stable ¹²C isotope over the stable ¹³C isotope. Petroleum shows the ¹³C depletion to an even greater degree than its organic source matter, but in a ratio similar to that of the lipid fractions of those organisms.

Figure C – Atmospheric methane has also shown an increase but note that the rate of increase tapers off.

“Methane is one of the shortest-lived GHGs and makes up only 16% of annual global GHG emissions but is 23 times more effective at trapping heat than CO₂. According to the EPA, about 60% of the methane emitted to the atmosphere each year arises from human activities, such as drilling for and transporting natural gas and oil, maintaining landfills, mining coal, and farming.” Thacker. D [2]

“Between 1990 and 1997, U.S. methane emissions declined by about 1 million metric tons or 3.6 percent. The drop can be attributed to a 1.1 million metric ton decrease in emissions from coal mining and a 0.7 million metric ton decrease in emissions from landfills.37. The decline occurred despite increases in activity data for both the coal mining and waste management sectors.” [2]

Figure D – The CFC reduction coincides with implementation of the Montreal Protocol.

Note also the annual variations in gas concentration

References & Links

1. Holper. P "The Greenhouse Effect" Information sheet. (2002). CSIRO » [home page]
   » Available: http://www.cmar.csiro.au/e-print/open/holper_2001b.html [accessed 2007, April.29]
   
   
2. Thacker. P “Methane Reduction” Science News Environmental Science & Technology. ACS Publications » [home page]
   » Available: http://pubs.acs.org/subscribe/journals/esthag-w/2005/jun/science/pt_methane.html [accessed 2007, April.29]
   
   
3. “Reducing methane emissions” Report#:DOE/EIA-(99)]. EIA » [home page]
   » Available: http://www.eia.doe.gov/oiaf/1605/vr98rpt/front.html [accessed 2007, April.29]
   

» Back to top

Thermometric and proxy temperature measurements

In discussing global warming references are often made to proxy temperature measurements as distinct from the conventional everyday usage of thermometers or temperature sensors. Proxy measurements are indirect ways of assessing what historical temperature might have been. For example certain isotope ratios in ice cores are known to be related to temperature.

Thermometric
Direct temperature measurements using a thermometer calibrated against a set of temperature standards

eg:

- mercury thermometers or spectral analysis

Proxy temperature measurements
Indirect measurement inferred from a property more loosely related to temperature (the relationship may be less well understood or less reproducible and require more measurements and analysis before drawing a conclusion)

eg:

- tree ring widths
- sise of glaciers
- extent of sea ice
- isotopic measurements in ice cores

Photo by Mark Twickler NOAA [2]

References & Links

1. NOAA " Introduction to Paleoclimatology - Paleo Proxy Data" » [home page]
   » Available: http://www.ncdc.noaa.gov/paleo/primer_proxy.html [accessed 2007, May. 19]



2. Photo by Mark Twickler "Ice Core sample, GISP2 drill dome, Greenland" NOAA » [home page]
   » Available: http://www.ncdc.noaa.gov/paleo/icecore.html[accessed 2007, Feb. 24]

.

» Back to top

Ice Cores

Using ice cores to measure air temperature & CO₂ thousands of years ago. Jacka, C » [1]

Air Samples
“The snow near the surface of the ice sheet is like a sponge with channels of air between the snow grains. As snow accumulates on top, the underlying snow is compressed into ice and the air forms bubbles in the ice. These bubbles are samples of the atmosphere up to thousands of years ago.” » [1]

Temperature
“The ratio of oxygen isotopes, measured using a mass spectrometer on melted samples of the ice, gives an indication of the temperature” » [1]

Ice Core Dating
“By sampling at very fine intervals down the ice core, and provided that each annual layer of snow is thick enough, several samples from each year may be measured" » [1]

Additional Notes
The ratio of oxygen isotopes ¹⁸O to ¹⁶O in water from ice core samples can give a measure of climate temperatures, as water formed from ¹⁸O evaporates less readily than water formed from ¹⁶O and this difference in evaporation depends also on temperature. Similar evidence can be obtained from the measurement of oxygen isotopes in calcite from sediment cores in the ocean floor » [2]. Near the surface, i.e representing the last few hundred years, core material resolutions of one year can be obtained.The time resolution of deeper core samples becomes progressively harder to resolve.

References & Links

1. Dr. T.H. Jacka, “Antarctic Ice Cores and Environmental Change” Glaciology Program, Antarctic CRC & Australian Antarctic Division » [home page]
   » Available: http://www.chem.hope.edu/~polik/warming/IceCore/IceCore2.html [accessed 2007, April. 29]
   
   
2. "Paleoclimatology: the Oxygen Balance" Earth Observatory. NASA » [home page]
   » Available: http://earthobservatory.nasa.gov/Study/Paleoclimatology_OxygenBalance/oxygen_balance.html [accessed 2007, April. 29]
   
   
3. Holli Riebeek “Paleoclimatology: The Ice Core Record” Earth Observatory. NASA » [home page]
   » Available: http://earthobservatory.nasa.gov/Study/Paleoclimatology_IceCores/ [accessed 2007, April. 29]
   
   
4. “Oldest Antarctic Ice Core Reveals Climate History” Science Daily » [home page]
   » Available: http://www.sciencedaily.com/releases/2004/06/040611080100.htm [accessed 2007, April.29]
   
   

» Back to top

Tree rings

This is an Xray of a small diameter core taken from a white spruce.
By taking a core one can study the weather record without killing the tree.
The thickness of the rings reflects both drought and temperature » [1]

» Read more here . . .

References & Links

1. J.Coggins; E.Sparrow “Tree Rings: A Study of Climate Change” NASA Athena Program » [home page]
   » Available: http://vathena.arc.nasa.gov/curric/land/global/treestel.html [accessed 2007, Feb. 24]
   
   
2. “NOAA's Paleoclimatology Tree Ring Data” » NOAA [home page]
   » Available: http://www.ncdc.noaa.gov/paleo/treering.html [accessed 2007, Feb. 24]

» Back to top

Some other climate proxies

Corals
Coral reefs can be thousands of years old and their chemical composition can report on: -temperature, precipitation, salinity, sea level, storms and freshwater runoff from nearby rivers.

Ocean sediments
The key reporter in ocean sediments are marine organism skeletons – the ratio of abundance of species that thrive in warm water vs cold water can indicate temperature. Chemical composition provides supporting information.

Boreholes
The temperature gradient down a bore hole can report on the regions temperature history for a few hundred years – the principle is analogous to what happens when a frozen steak is partly cooked. i.e it takes a while for heat changes to permeate the steak (or the ground).

References & Links

1. Dessler, A and Parson, E. "The Science & Politics Of Global Change" Cambridge University Press; 2006.
   


2. NOAA " Introduction to Paleoclimatology - Paleo Proxy Data" » [home page]
   » Available: http://www.ncdc.noaa.gov/paleo/primer_proxy.html [accessed 2007, May. 19]

» Back to top

Climate and Greenhouse Gas Variability

“In January 1998, the collaborative ice-drilling project between Russia, the United States, and France at the Russian Vostok station in East Antarctica yielded the deepest ice core ever recovered, reaching a depth of 3,623 m (Petit et al. 1997, 1999). Preliminary data indicate the Vostok ice-core record extends through four climate cycles, with ice slightly older than 400 kyr." Petit, J.R., et al » [1], NOAA » [2]

References are sometimes made to the relationship between CO₂ and temperature determined from "The Vostok Ice Core" record.
Care is needed in interpreting this relationship. [3] The graphs show a strong correlation between increases in CO₂ concentration and temperature rise. However, although CO₂ and methane can contribute to temperature increase it’s also been found that increases in temperature can help produce methane and CO₂ ! Consequently it’s hard to know from these graphs, which is cause and effect. Fischer; et al » [3]

It’s worth noting the relative speed with which temperature and CO₂ has risen in the last century but it may not be possible to see such fast fluctuating temperatures in records that are 100’s of thousands of years old. The data needs to be interpreted carefully.

References & Links

1. Petit, J.R., J. Jouzel, D. Raynaud, N.I. Barkov, J.-M. Barnola, I. Basile, M. Benders, J. Chappellaz, M. Davis, G. Delayque, M. Delmotte, V.M. Kotlyakov, M. Legrand, V.Y. Lipenkov, C. Lorius, L. Pépin, C. Ritz, E. Saltzman, and M. Stievenard. 1999. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature 399: 429-436.
   
   
2. “Vostok Ice Core” NOAA Satellite & Information Service. » [home page]
   » Available: http://www.ncdc.noaa.gov/paleo/icecore/antarctica/vostok/vostok.html [accessed 2007, Feb. 26]
   
   
3. Hubertus Fischer, Martin Wahlen, Jesse Smith, Derek Mastroianni, Bruce Deck » [home page]
   “Ice Core Records of Atmospheric CO₂ Around the Last Three Glacial Terminations” Science Vol. 283. no. 5408, (March 1999)
   » Available: http://www.sciencemag.org/cgi/content/abstract/283/5408/1712 [accessed 2007, April 5]

» Back to top

The Historical Temperature and Carbon Dioxide Records

The temperature and CO₂ records of the last thousand years show similar trends and the sharp increase of the last twenty or thirty years is of particular interest. The data is summarised and critiqued in the references below.

“There is solid evidence for global warming in the 20th century. In addition to the global-average surface warming of 0.6^oC, the lower atmosphere and upper ocean have warmed, snow and ice cover have declined, global-average sea-level has risen 10 to 20 cm, high temperatures have increased, and frost seasons have become shorter (IPCC, 2001). Is the warming of the 20th century unusual or just part of natural variability? Temperatures during the past 1,000 years can provide a measure of natural climate variability. While thermometer records are widely available for the last 140 years, earlier temperature records must be reconstructed from proxy data (tree-rings, sediments, ice cores and corals). Most proxy data are limited to the northern hemisphere.” Australian Greenhouse Office » [1]

Sometimes it is suggested that the rapid rise in temperature of the last 50 years is a recovery from the little ice age which spanned the 13th to 17th centuries. Another argument is that this century's temperature increase is similar to the temperature peak that occurred in 1000 AD. Arguments against this are that the little ice age may have been local to Europe and that over the last 100 years the magnitude of temperature rise and the speed with which it has occurred are too great for it to be comparable with the long term climate record or atmospheric science. (see also next section). Additionally there are now a large number of climate models that cannot reproduce the rise in temperature in the 20th century without taking account of the increase in anthropogenic greenhouse gas. This evidence has been extensively reviewed by the IPCC over the last decade and it is generally accepted in the scientific community that anthropogenic CO₂ is the more credible explanation for global warming. Australian Greenhouse Office » [1], Dessler, A and Parson, E. » [2]

CO₂ and the 1999 IPCC Temperature Reconstruction for the Last Thousand Years [3]

(Note for an updated temperature record see [4] or the next section)

References & Links

1. “How unusual is the late 20th century warming. Australian Greenhouse Office”
   » Available: http://www.greenhouse.gov.au/science/hottopics/pubs/topic3.pdf [accessed 2007, Feb. 24]



2. Dessler, A and Parson, E. "The Science & Politics Of Global Change" Cambridge University Press; 2006.



3. “IPCC 3 rd Assessment Report: “Climate Change 2001: The Scientific Basis ” Appendix I: Glossary
   » Available: http://www.grida.no/climate/ipcc_tar/wg1/518.htm [accessed 2007, Feb. 24]



4. IPCC WG1 AR4 Final Report "The Physical Science Basis - Technical Summary" (February, 2007) » (home page)
   » Available: http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_TS.pdf accessed [2007, May.17]

» Back to top

Uncertainties & The Hockey Stick Graph

Introduction

The Hockey Stick graph compared global thermometric temperatures in the late 20th century with proxy data for the last 1000 years. Mann published the work in 1999 and it was used in the 2001 IPCC report. The graph has been debated and reviewed for some years. The debate concerns the validity of using bristle pine cones for proxy data, methods of calculation, whether the records are a global representation of temperature and whether they correspond with a "Medieval Warming Period" and the subsequent "Little Ice Age". The US National Research Council's Board on Atmospheric Sciences and Climate were given the specific charter to look at this data and have reviewed temperature records spanning the last 2000 years. They published the results of their review in 2006 » [1]. In brief their summary suggests that: -

• a "Medieval Warm Period" and a subsequent "Little Ice Age" were consistent with a range of different proxy measurements
• the geographical extent and magnitude of the "Medieval Warm Period" and "Little Ice Age" are uncertain
• the temperature reconstructions are increasingly uncertain with the age of the record, particularly prior to AD 900
• they confirm the global warming of about 0.6 degrees C observed during the 20th century and that this is likely to have been warmer than any period in the last four centuries. They warn about the difficulty of comparing present day temperatures with those from reconstructions from proxy data prior to 1600.

The latest temperature reconstructions produced by the IPCC are given below from their February 2007 release of the Working Group I Report "The Physical Science Basis" » [2]. It also shows the distribution of measurements from which the reconstructions were made.

References & Links

1. Executive Summary (2006) "Surface Temperature Reconstructions for the Last 2,000 Years"
   National Research Council - Board on Atmospheric Sciences and Climate Division on Earth and Life Studies,
   » Available: http://books.nap.edu/execsumm_pdf/11676.pdf accessed [2007, May.17]



2. IPCC WG1 AR4 Final Report "The Physical Science Basis - Technical Summary" (February, 2007) » (home page)
   » Available: http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_TS.pdf accessed [2007, May.17]



3. Kerr R, "Millennium's Hottest Decade Retains Its Title, for Now" Science 11 February 2005: Vol. 307. no. 5711, pp. 828 - 829



4. Michael Le Page "Climate change: A guide for the perplexed" NewScientist.com news service
   » Available: http://environment.newscientist.com/channel/earth/dn11462 accessed [2007, May.17]

» Back to top

The surface & troposphere temperature records

For several years there was concern about discrepancies between earth surface and satellite temperature measurements NOAA NCDC » [3]. These have now been resolved. The graph below shows the original data and the text and references describe where the error occurred.

Atmospheric temperature can be determined using microwave sounding units (MSU) that measure the microwave radiation from oxygen. A source of concern for many years was the discrepancy between MSU assessments of the lower troposphere temperature and thermometric measurements made at the earth ’s surface. Satellite measurements initially indicated very little change in the lower troposhere temperature despite the increases being measured at the earth's surface. In 2005 Mears and Wentz determined that a diurnal correction was needed on the "Satellite-Derived Lower Tropospheric Temperature". When corrected, tropospheric measurements were found to be consistent with those at the earth's surface » [1]. In 2006 the US Climate Change Science Program reviewed the data, confrmed the nature of the discrepancies and determined that the reconciled data was in agreement with the earth surface measurements. Mears CA and Wentz FJ » [1]; US Climate Change Science Program » [2]

“Given the range of model results and the overlap between them and the available observations, there is no conflict between observed changes and the results from climate models.”US Climate Change Science Program » [2]

Surface Satellite Temperature Discrepancy Data NOAA NCDC » [3]

References & Links

1. Mears CA and Wentz FJ “The Effect of Diurnal Correction on Satellite-Derived Lower Tropospheric Temperature” Science 2 September 2005: Vol. 309. no. 5740, pp. 1548 - 1551 DOI: 10.1126/science.1114772. Science » [home page]
   » Available: http://www.sciencemag.org/cgi/content/short/309/5740/1548 [accessed 2007, Feb. 24]
   
   
2. "Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences" Synthesis and Assessment Product 1.1 April 2006 U.S. Climate Change Science Program » [home page]
   » Available: http://www.climatescience.gov/Library/sap/sap1-1/third-draft/default.htm [accessed 2007, Feb. 24]
   
   
3. “NOAA Temperature Trends: Annual temperature anomalies” Climate of 2003 Annual Review, NOAA NCDC » [home page]
   » Available: http://www.ncdc.noaa.gov/oa/climate/research/2003/ann/global.html [accessed 2007, Feb. 24]

» Back to top

The glacier record

The melting of glaciers is frequently cited as an indication of climate change. This is just one of very many similar paired records of glaciers held in databases around the world.

Muir Glacier August 13, 1941 William O. Field	Muir Glacier August 31, 2004 Bruce F. Molnia (USGS).

“Between 1941 and 2004 the glacier retreated more than twelve kilometers (seven miles) and thinned by more than 800 meters (875 yards). Ocean water has filled the valley, replacing the ice of Muir Glacier; the end of the glacier has retreated out of the field of view. The glacier’s absence reveals scars where glacier ice once scraped high up against the hillside. In 2004, trees and shrubs grow thickly in the foreground, where in 1941 there was only bare rock. This is just one of a series of paired glacier records.”

How to use the data base

The data base referenced below assumes detailed knowledge of US glaciers. If you are new to this area the easiest way to access it is:

• click on "Search Database"
• click in the "State/Province" search parameter box
• click "Submit"
• you will be given a drop down list to select from

References & Links

1.  NSIDC/WDC for Glaciology, Boulder, compiler. 2002, updated 2006. Online glacier photograph database. Boulder, Colorado USA: National Snow and Ice Data Center/World Data Center for Glaciology. Digital media.
   National Snow and Ice Data Center/World Data Center for Glaciology » [home page]
   » Available: http://nsidc.org/data/g00472.html [accessed 2007, Feb. 24]

» Back to top

Tundra to Wetlands

Tundra are those regions of frozen soil between the treeline and the icecap of the Arctic. Recently ther have been reports of tundra melting. As these regions melt they may release large volumes of carbon dioxide and methane, adding to a greenhouse effect. This effect is exacerbated as snow and ice tend to reflect radiation whereas lakes, soil and vegetation are darker and absorb it.

“Perennial or year-round sea ice in the North Polar region has decreased 3% per decade, and the area of the Greenland ice sheet surface that melts during summer has increased dramatically. The extent of tundra, which until recently covered about 24% of land in the Northern Hemisphere, has also declined steeply--15% since the 1970s. As permafrost melts, some of the grayish mosses that typically blanket the tundra are replaced by greener and darker shrubs and trees” Hileman B, Overland E » [1]

“Shown below are two photographs from the same location in Alaska, showing Permafrost degradation on the Tanana Flats in the transition from tundra to wetlands over the last twenty years” Jorgensen MT » [2]; NOAA NDC » [3]

Tundra

Wetlands

References & Links

1. James E Overland (NOAA) quoted in "Climate” Bette Hileman, C&EN Washington » [home]
   » Available: http://pubs.acs.org/cen/coverstory/8150/8150climatechange.html [accessed 2007, April. 09]
   
   
2. Jorgenson MT, Racine CH, Walters JC, Osterkamp TE (2001) Permafrost degradation and ecological changes associated with a warming climate in central Alaska. Climatic Change 48: 551- 579
   
   
3. “Permafrost degradation on the Tanana Flats” NOAA » [home]
   » Available: http://www.arctic.noaa.gov/detect/land-tundra.shtml [accessed 2007, Feb. 24]
   
   
4. "Permafrost Degradation in Central Alaska" CO₂ Science, Center for the Study of Carbon Dioxide and Global Change » [home]
   » Available: http://www.co2science.org/scripts/CO2ScienceB2C/articles/V4/N17/C2.jsp

» Back to top

» Index

» Next page