Climate proxies are devices that suggest the climate patterns of the past, even before those patterns were archived by humans.^[1] To produce the most precise results, systematic cross-verification between proxy indicators is necessary for accuracy in readings and record-keeping.^[2] The study of past climates is known as paleoclimatology.^[3] Examples of proxies include ice cores, tree rings, boreholes, corals, and lake and ocean sediments.

[edit] Ice Cores

[edit] Drilling

Ice Core sample taken from drill. Photo by Lonnie Thompson, Byrd Polar Research Center.

Ice cores are cylindrical samples from within ice sheets in the Greenland, Antarctic, and North American regions.^[4][5] First attempts of extraction occurred in 1956 as part of the International Geophysical Year. As original means of extraction, the U.S. Army’s Cold Regions Research and Engineering Laboratory used an 80-foot-long modified electrodrill in 1968 at Camp Century, Greenland, and Byrd Station, Antarctica. Their machinery could drill through 15-20 feet of ice in 40-50 minutes. From 1300 to 3000 feet in depth, core samples were 4 ¼ inches in diameter and 10 to 20 feet long. Deeper samples of 15 to 20 feet long were not uncommon. Every subsequent drilling team improves their method with each new effort.^[6]

[edit] Proxy

Presence of water molecule isotopic compositions of ¹⁶O and ¹⁸O in an ice core help determine past temperatures and snow accumulations.^[7] The heavier isotope (¹⁸O) condenses more readily as temperatures decrease and falls as precipitation, while the lighter isotope (¹⁶O) can fall in even colder conditions. The farther north an ¹⁸O isotope is discovered means a warming over time.^[8] Air bubbles in the ice conceal trapped gases, especially those of greenhouse gases, such as carbon dioxide and methane, and are also helpful in determining past climate changes.^[9]

From 1989-1992, the European Greenland Ice Core Drilling Project drilled in central Greenland at coordinates 72^o 35' N, 37^o 38' W. In their project, ice at a depth of 770 m were 3840 years old; 2521 m were 40,000 years old; and 3029 m at bedrock were 200,000 years old or more.^[10] However, ice cores can reveal the climate records for the past 650,000 years.^[11]

Location maps and a complete list of U.S. ice core drilling sites can be found on the website for the National Ice Core Laboratory: http://nicl.usgs.gov/coresite.htm^[12]

[edit] Tree Rings

Dendroclimatology is the science of determining past climates from trees (primarily properties of the annual tree rings). Tree rings are wider when conditions favor growth, narrower when times are difficult. Other properties of the annual rings, such as maximum latewood density (MXD) have been shown to be better proxies than simple ring width. Using tree rings, scientists have estimated many local climates for hundreds to thousands of years previous. By combining multiple tree-ring studies (sometimes with other climate proxy records), scientists have estimated past regional and global climates (see Temperature record of the past 1000 years).

Tree rings seen in a cross section of a trunk of a tree.

[edit] Boreholes

A borehole is a narrow shaft dug by a drilling rig or hand-operated rig for the extraction of resources, such as gases (i.e. natural gas) or water or other liquids (i.e. petroleum), for mineral exploration, or to give direction when installing underground facilities or piers. When a well screen and vertical casing are fit into a borehole to prevent collapsing, the hole is more commonly known as a well. Environmental consulting and engineering fields also use boreholes in their investigations and assessments, often to collect water or soil samples or rock cores.

The world’s deepest borehole is the Kola Superdeep Borehole on the Kola Peninsula in Scandinavian Russia. Its drilling lasted from 1970 to 1989 and reached a depth of 12,262 meters for geological studies.^[13]

More than 600 boreholes on all continents except Antarctica have been used as proxy for measuring temperature.^[14] The highest concentration of boreholes exist in North America and Europe. Their depths of drilling typically range from 200 to greater than 1,000 meters into the crust of the Earth.^[15] Boreholes can be used as proxies, because the cold and warm weather on the surface of the Earth send thermal waves into the underground of the planet, cooling or warming the subterranean rock. Paleoclimatologists lower thermometers into the holes to find the temperature, and then they subtract the effect of rising heat from inside the Earth. With this strategy, paleoclimatologists have compared their results to temperature records from weather stations and other proxies as early as 1860. All their borehole results have proven complementary to all such proxies. In response to this, Robert N. “Rob” Harris, an assistant professor of geophysics and geology at the University of Utah, claims, “We confirmed that ground and air temperatures do track each other."^[16] These confirmations have given paleoclimatologists the confidence that they can measure the temperature of 500 years ago. This is concluded by a depth scale of about 492 feet (150 meters) to measure the temperatures from 100 years ago and 1,640 feet (500 meters) to measure the temperatures from 1,000 years ago. ^[17]

[edit] Corals

Ocean coral skeletal rings, or bands, also share paleoclimatological information, similarly to tree rings. In 2002, a report was published on the findings of Drs. Lisa Greer and Peter Swart, associates of University of Miami at the time, in regard to stable oxygen isotopes in the calcium carbonate of coral. Cooler temperatures tend to cause coral to use more heavier isotopes in its structure, while warmer temperatures result in more normal oxygen isotopes being built into the coral structure. Denser water salinity also tends to contain the heavier isotope. Greer’s coral sample from the Atlantic Ocean was taken in 1994 and dated back to 1935. Greer recalls her conclusions, “When we look at the averaged annual data from 1935 to about 1994, we see it has the shape of a sine wave. It is periodic and has a significant pattern of oxygen isotope composition that has a peak at about every twelve to fifteen years.” Surface water temperatures have coincided by also peaking every twelve and a half years. However, since recording this temperature has only been practiced for the last fifty years, correlation between recorded water temperature and coral structure can only be drawn so far back.^[18]

[edit] Lake and Ocean Sediments

Similar to their study on other proxies, paleoclimatologists examine oxygen isotopes in the contents of ocean sediments. Likewise, they measure the layers of varve (deposited fine and coarse silt or clay)^[19] laminating lake sediments. Lake varves are primarily influenced by:

• Summer temperature, which shows the energy available to melt seasonal snow and ice
• Winter snowfall, which determines the level of disturbance to sediments when melting occurs
• Rainfall^[20]

[edit] Global Warming

Some paleoclimatologists also claim to find evidence of global warming with their results from climate proxies, while other critics argue that the warming represents a return to natural conditions after a cooling period in the 1800s. Since the beginning of the Industrial Revolution in the late 18th century, the temperature of the Earth in the Northern Hemisphere has increased about two degrees Fahrenheit (1.1 degrees Celsius). In particular to boreholes, there have been very few measurements from sites in the Southern Hemisphere, but measurements from these locations still correspond with the warming marked by the measurements from the Northern Hemisphere. ^[21]

[edit] Water isotopes and temperature reconstruction

Ocean water is mostly , with small amounts of HD¹⁶O and . In Vienna Standard Mean Ocean Water (VSMOW) the ratio of D to H is and O-18 to O-16 is . Fractionation occurs during changes between condensed and vapour phases: the vapour pressure of heavier isotopes is lower, so vapour contains relatively more of the lighter isotopes and when the vapour condenses the precipitation preferentially contains heavier isotopes. The difference from VSMOW is expressed as δ¹⁸O = 1000‰ ; and a similar formula for δD. δ values for precipitation are always negative. The major influence on δ is the difference between ocean temperatures where the moisture evaporated and the place where the final precipitation occurred; since ocean temperatures are relatively stable the δ value mostly reflects the temperature where precipitation occurs. Taking into account that the precipitation forms above the inversion layer, we are left with a linear relation:

δ ¹⁸O = aT + b

which is empirically calibrated from measurements of temperature and δ as a = 0.67 ‰/^oC for Greenland and 0.76 ‰/^oC for East Antarctica. The calibration was initially done on the basis of spatial variations in temperature and it was assumed that this corresponded to temporal variations (Jouzel and Merlivat, 1984). More recently, borehole thermometry has shown that for glacial-interglacial variations, a = 0.33 ‰/^oC (Cuffey et al., 1995), implying that glacial-interglacial temperature changes were twice as large as previously believed.

[edit] See also

• Paleothermometer
• Ice core
• Dendrochronology

[edit] Notes

1. ^ “Climate Proxy.”
2. ^ “Climate Change 2001: 2.3.2.1 Palaeoclimate proxy indicators."
3. ^ Bruckner, Monica. “Paleoclimatology: How Can We Infer Past Climates?”
4. ^ Strom, Robert. Hot House. p. 255
5. ^ “Core Location Maps.”
6. ^ Vardiman, Larry, Ph.D. Ice Cores and the Age of the Earth. p. 9-13
7. ^ Strom, Robert. Hot House. p. 255
8. ^ “Paleoclimatology: the Oxygen Balance.”
9. ^ Strom, Robert. Hot House. p. 255
10. ^ “The GRIP Coring Effort.”
11. ^ Strom, Robert. Hot House. p. 255
12. ^ “Core Location Maps.”
13. ^ “Objectives - Kola Superdeep Borehole (KSDB) - IGCP 408: ‘Rocks and Minerals at Great Depths and on the Surface.’”
14. ^ Huang, Shaopeng, et al. “Temperature trends over the past five centuries reconstructed from borehole temperatures.”
15. ^ Environmental News Network staff. “Borehole temperatures confirm global warming.”
16. ^ “Borehole Temperatures Confirm Global Warming Pattern.”
17. ^ Environmental News Network staff. “Borehole temperatures confirm global warming.”
18. ^ “Coral Layers Good Proxy for Atlantic Climate Cycles.”
19. ^ "Varve."
20. ^ “Climate Change 2001: 2.3.2.1 Palaeoclimate proxy indicators"
21. ^ “Borehole Temperatures Confirm Global Warming Pattern.”

[edit] References

• “Borehole Temperatures Confirm Global Warming Pattern.” UniSci. 27 Feb. 2001. 7 Oct. 2009. [1]
• Bruckner, Monica. “Paleoclimatology: How Can We Infer Past Climates?” Microbial Life. 29 Sept. 2008. 23 Nov. 2009. [2]
• "Climate Change 2001: 2.3.2.1 Palaeoclimate proxy indicators." IPCC. 2003. Sept. 23, 2009. [3]
• "Climate Proxy." RealClimate. 28 Nov. 2004. 17 Sept. 2009. [4]
• “Coral Layers Good Proxy for Atlantic Climate Cycles.” Earth Observatory. Webmaster: Paul Przyborski. 7 Dec. 2002. 2 Nov. 2009. [5]
• “Core Location Maps.” National Ice Core Laboratory. 9 Apr. 2009. 23 Nov. 2009. [6]
• "Dendrochronology." Merriam-Webster Online Dictionary. Merriam-Webster Online. 2009. 2 Oct. 2009. [7]
• Environmental News Network staff. “Borehole temperatures confirm global warming.” CNN.com. 17 Feb. 2000. 7 Oct. 2009. [8]
• “The GRIP Coring Effort.” NCDC. 26 Sept. 2009. [9]
• "Growth ring." Encyclopædia Britannica. Encyclopædia Britannica Online. 2009. 23 Oct. 2009. [10]
• Huang, Shaopeng, et al. “Temperature trends over the past five centuries reconstructed from borehole temperatures.” Nature. 2009. 6 Oct. 2009. [11]
• “Objectives - Kola Superdeep Borehole (KSDB) - IGCP 408: ‘Rocks and Minerals at Great Depths and on the Surface.’” International Continental Scientific Drilling Program. 18 July 2006. 6 Oct. 2009. [12]
• “Paleoclimatology: the Oxygen Balance.” Earth Observatory. Webmaster: Paul Przyborski. 24 Nov. 2009. 24 Nov. 2009. [13]
• Schweingruber, Fritz Hans. Tree Rings: Basics and Application of Dendrochronology. Dordrecht: 1988. 2, 47-8, 54, 256-7.
• Strom, Robert. Hot House. New York: Praxis, 2007. 255.
• Vardiman, Larry, Ph.D. Ice Cores and the Age of the Earth. El Cajon: ICR, 1996. 9-13.
• "Varve." Merriam-Webster Online Dictionary. Merriam-Webster Online. 2009. 2 Nov. 2009. [14]
• Wolff, E. W. (2000) History of the atmosphere from ice cores; ERCA vol 4 pp 147-177