Climate Change Past Present Future
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  • Chapman, D., & Davis, M. (2010). Climate change: past, present, and future. EOS, Transactions, American Physical Union, 91(37), 325–332. Synopsis: Temperature records from a wide variety of geographically diverse proxies show a consistent picture of our warming world. Slide set produced by LuAnn Dahlman NOAA climate office.
  • Since tree growth is influenced by climatic conditions, patterns in tree-ring widths, density, etc, reflect variations in climate.� In temperate regions where there is a distinct growing season, trees generally produce one ring a year, and thus record the climatic conditions of each year.�Trees can grow to be hundreds to thousands of years old and can contain annually-resolved records of climate for centuries to millennia. A cross section of a young conifer Photo Credits: NOAA Paleoclimatology Program Source: http://www.ncdc.noaa.gov/paleo/slides/slideset/index18.htm Corals build their hard skeletons from calcium carbonate, a mineral extracted from sea water. The carbonate contains isotopes of oxygen, as well as trace metals, that can be used to determine the temperature of the water in which the coral grew. These temperature recordings can then be used to reconstruct climate when the coral lived. Two sections of a coral core from the Galapagos. The cores are x-rayed so scientists can see the growth bands . Next, segments are marked for sampling: black lines represent annual bands, blue and red lines subdivide the year into quarters. The core is then cut along the lines and the individual segments analyzed in a laboratory . Photo Credits: Rob Dunbar Dept. of Geology and Geophysics, Rice University Source: http://www.ncdc.noaa.gov/paleo/slides/slideset/index13.htm Located high in mountains and the polar ice caps, ice accumulates from snowfall over many millenia. Scientists drill through the deep ice to collect ice cores that contain dust, air bubbles, or isotopes of oxygen, that can be used to interpret the past climate of that area. A section of an ice core taken on the Clark Glacier in the McMurdo Dry Valleys. A 160-meter core was extracted to study the climate in the area over the past 2,000 years. Credit : Emily Stone, Source: http://photolibrary.usap.gov/portscripts/portweb.dll?query&field1=filename&op1=matches&value=corecloseup.jpg&catalog=antarctica&template=usapgovmidthumbs All flowering plants produce pollen grains. Their distinctive shapes can be used to identify the type of plant from which they came. Pollen grains are well preserved in the sediment layers of ponds, lakes or the ocean. An analysis pollen grains in each layer tell us what kinds of plants were growing at the time the sediment was deposited.� Inferences can then be made about the climate based on the types of plants found in each layer. Morphological features of pollen spores from the Florida Everglades (USGS) http://sofia.usgs.gov/publications/papers/pollen_atlas/plate21-23.html
  • Since tree growth is influenced by climatic conditions, patterns in tree-ring widths, density, etc, reflect variations in climate.� In temperate regions where there is a distinct growing season, trees generally produce one ring a year, and thus record the climatic conditions of each year.�Trees can grow to be hundreds to thousands of years old and can contain annually-resolved records of climate for centuries to millennia. A cross section of a young conifer Photo Credits: NOAA Paleoclimatology Program Source: http://www.ncdc.noaa.gov/paleo/slides/slideset/index18.htm Corals build their hard skeletons from calcium carbonate, a mineral extracted from sea water. The carbonate contains isotopes of oxygen, as well as trace metals, that can be used to determine the temperature of the water in which the coral grew. These temperature recordings can then be used to reconstruct climate when the coral lived. Two sections of a coral core from the Galapagos. The cores are x-rayed so scientists can see the growth bands . Next, segments are marked for sampling: black lines represent annual bands, blue and red lines subdivide the year into quarters. The core is then cut along the lines and the individual segments analyzed in a laboratory . Photo Credits: Rob Dunbar Dept. of Geology and Geophysics, Rice University Source: http://www.ncdc.noaa.gov/paleo/slides/slideset/index13.htm Located high in mountains and the polar ice caps, ice accumulates from snowfall over many millenia. Scientists drill through the deep ice to collect ice cores that contain dust, air bubbles, or isotopes of oxygen, that can be used to interpret the past climate of that area. A section of an ice core taken on the Clark Glacier in the McMurdo Dry Valleys. A 160-meter core was extracted to study the climate in the area over the past 2,000 years. Credit : Emily Stone, Source: http://photolibrary.usap.gov/portscripts/portweb.dll?query&field1=filename&op1=matches&value=corecloseup.jpg&catalog=antarctica&template=usapgovmidthumbs All flowering plants produce pollen grains. Their distinctive shapes can be used to identify the type of plant from which they came. Pollen grains are well preserved in the sediment layers of ponds, lakes or the ocean. An analysis pollen grains in each layer tell us what kinds of plants were growing at the time the sediment was deposited.� Inferences can then be made about the climate based on the types of plants found in each layer. Morphological features of pollen spores from the Florida Everglades (USGS) http://sofia.usgs.gov/publications/papers/pollen_atlas/plate21-23.html
  • Since tree growth is influenced by climatic conditions, patterns in tree-ring widths, density, etc, reflect variations in climate.� In temperate regions where there is a distinct growing season, trees generally produce one ring a year, and thus record the climatic conditions of each year.�Trees can grow to be hundreds to thousands of years old and can contain annually-resolved records of climate for centuries to millennia. A cross section of a young conifer Photo Credits: NOAA Paleoclimatology Program Source: http://www.ncdc.noaa.gov/paleo/slides/slideset/index18.htm Corals build their hard skeletons from calcium carbonate, a mineral extracted from sea water. The carbonate contains isotopes of oxygen, as well as trace metals, that can be used to determine the temperature of the water in which the coral grew. These temperature recordings can then be used to reconstruct climate when the coral lived. Two sections of a coral core from the Galapagos. The cores are x-rayed so scientists can see the growth bands . Next, segments are marked for sampling: black lines represent annual bands, blue and red lines subdivide the year into quarters. The core is then cut along the lines and the individual segments analyzed in a laboratory . Photo Credits: Rob Dunbar Dept. of Geology and Geophysics, Rice University Source: http://www.ncdc.noaa.gov/paleo/slides/slideset/index13.htm Located high in mountains and the polar ice caps, ice accumulates from snowfall over many millenia. Scientists drill through the deep ice to collect ice cores that contain dust, air bubbles, or isotopes of oxygen, that can be used to interpret the past climate of that area. A section of an ice core taken on the Clark Glacier in the McMurdo Dry Valleys. A 160-meter core was extracted to study the climate in the area over the past 2,000 years. Credit : Emily Stone, Source: http://photolibrary.usap.gov/portscripts/portweb.dll?query&field1=filename&op1=matches&value=corecloseup.jpg&catalog=antarctica&template=usapgovmidthumbs All flowering plants produce pollen grains. Their distinctive shapes can be used to identify the type of plant from which they came. Pollen grains are well preserved in the sediment layers of ponds, lakes or the ocean. An analysis pollen grains in each layer tell us what kinds of plants were growing at the time the sediment was deposited.� Inferences can then be made about the climate based on the types of plants found in each layer. Morphological features of pollen spores from the Florida Everglades (USGS) http://sofia.usgs.gov/publications/papers/pollen_atlas/plate21-23.html
  • Since tree growth is influenced by climatic conditions, patterns in tree-ring widths, density, etc, reflect variations in climate.� In temperate regions where there is a distinct growing season, trees generally produce one ring a year, and thus record the climatic conditions of each year.�Trees can grow to be hundreds to thousands of years old and can contain annually-resolved records of climate for centuries to millennia. A cross section of a young conifer Photo Credits: NOAA Paleoclimatology Program Source: http://www.ncdc.noaa.gov/paleo/slides/slideset/index18.htm Corals build their hard skeletons from calcium carbonate, a mineral extracted from sea water. The carbonate contains isotopes of oxygen, as well as trace metals, that can be used to determine the temperature of the water in which the coral grew. These temperature recordings can then be used to reconstruct climate when the coral lived. Two sections of a coral core from the Galapagos. The cores are x-rayed so scientists can see the growth bands. Next, segments are marked for sampling: black lines represent annual bands, blue and red lines subdivide the year into quarters. The core is then cut along the lines and the individual segments analyzed in a laboratory . Photo Credits: Rob Dunbar Dept. of Geology and Geophysics, Rice University Source: http://www.ncdc.noaa.gov/paleo/slides/slideset/index13.htm Located high in mountains and the polar ice caps, ice accumulates from snowfall over many millenia. Scientists drill through the deep ice to collect ice cores that contain dust, air bubbles, or isotopes of oxygen, that can be used to interpret the past climate of that area. A section of an ice core taken on the Clark Glacier in the McMurdo Dry Valleys. A 160-meter core was extracted to study the climate in the area over the past 2,000 years. Credit : Emily Stone, Source: http://photolibrary.usap.gov/portscripts/portweb.dll?query&field1=filename&op1=matches&value=corecloseup.jpg&catalog=antarctica&template=usapgovmidthumbs All flowering plants produce pollen grains. Their distinctive shapes can be used to identify the type of plant from which they came. Pollen grains are well preserved in the sediment layers of ponds, lakes or the ocean. An analysis pollen grains in each layer tell us what kinds of plants were growing at the time the sediment was deposited.� Inferences can then be made about the climate based on the types of plants found in each layer. Morphological features of pollen spores from the Florida Everglades (USGS) http://sofia.usgs.gov/publications/papers/pollen_atlas/plate21-23.html
  • Image source http://www.ncdc.noaa.gov/paleo/pubs/oerlemans2005/glacierbay-lg.jpg
  • http://www.ncdc.noaa.gov/paleo/borehole/index.html
  • From 1850 through the present, systematic measurements of temperature can be compiled to estimate annual values for average global temperature. In Slideshow mode, click the name of any dataset to jump to a slide of information and the citation for that reference.
  • All proxy records are smoothed to reflect variation on the scale of decades or longer. In Slideshow mode, click the name of any dataset to jump to a slide of information and the citation for that reference.
  • All proxy records are smoothed to reflect variation on the scale of decades or longer. In Slideshow mode, click the name of any dataset to jump to a slide of information and the citation for that reference.
  • All proxy records are smoothed to reflect variation on the scale of decades or longer. In Slideshow mode, click the name of any dataset to jump to a slide of information and the citation for that reference.
  • All proxy records are smoothed to reflect variation on the scale of decades or longer. Note how all the proxy records show generally the same trends. In Slideshow mode, click the name of any dataset to jump to a slide of information and the citation for that reference.
  • In Slideshow mode, click the name of any dataset to jump to a slide of information and the citation for that reference.
  • In Slideshow mode, click the name of any dataset to jump to a slide of information and the citation for that reference.
  • In Slideshow mode, click the name of any dataset to jump to a slide of information and the citation for that reference. Temperatures have increased 1.1˚ C since 1700.
  • In Slideshow mode, click the name of any dataset to jump to a slide of information and the citation for that reference. What does the future look like? The C3 scenario is based on holding carbon emissions at our present level.
  • In Slideshow mode, click the name of any dataset to jump to a slide of information and the citation for that reference.
  • In Slideshow mode, click the name of any dataset to jump to a slide of information and the citation for that reference.
  • In Slideshow mode, click the name of any dataset to jump to a slide of information and the citation for that reference.

Climate Change Past Present Future Climate Change Past Present Future Presentation Transcript

  • Climate Change:Present, Past, and Future Based on an article and graphics by David S. Chapman and Michael G. Davis, Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah featuring datasets considered by the Intergovernmental Panel on Climate Change and the National Research Council Slide set produced by LuAnn Dahlman NOAA climate office
  • IntroductionThis presentation shows scientific estimates of globalaverage temperature from 1000 to 2100. Eachdataset, calculated from instrumental records, proxyrecords, or projections, has been published in peer-reviewed literature.Additional information explaining how thosetemperatures were derived is on the slides thatfollow the graphs of the datasets. Full citations foreach dataset are included on the explanation slides.Notes about each slide are available in thedownloadable PowerPoint, in Normal view.
  • Paleoclimatology: The study of past climate, from timesprior to instrumental weather measurements.Proxy Data – Information from natural recorders ofclimate variability.Widely used proxy climate data include: •Corals •Tree Rings •Ice Core records •Fossilized Tree Pollen •Boreholes •Glacier Lengths
  • Paleoclimatology - The study of past climate, from times prior to instrumental weather measurements. CoralsCorals build their hardskeletons from calciumcarbonate, a mineral extractedfrom sea water. The carbonatecontains isotopes of oxygen,as well as trace metals, thatcan be used to determine thetemperature of the water inwhich the coral grew. Thesetemperature recordings canthen be used to reconstructclimate when the coral lived.Shown above are two sections of a coral core from the Galapagos. The coresare x-rayed so scientists can see the growth bands. Next, segments are markedfor sampling: black lines represent annual bands, blue and red lines subdividethe year into quarters. The core is then cut along the lines and the individualsegments analyzed in a laboratory .
  • Paleoclimatology - The study of past climate, fromtimes prior to instrumental weather measurements. Tree RingsSince tree growth is influenced byclimatic conditions, patterns in tree-ring widths, density, etc, reflectvariations in climate. In temperateregions where there is a distinctgrowing season, trees generallyproduce one ring a year, and thusrecord the climatic conditions of eachyear. Trees can grow to be hundredsto thousands of years old and cancontain annually-resolved records ofclimate for centuries to millennia.Shown at right is a cross section of ayoung conifer
  • Paleoclimatology - The study of past climate, from times prior to instrumental weather measurements.Ice CoresLocated high in mountains andthe polar ice caps, iceaccumulates from snowfallcompressed over manythousands of years.Scientists drill through the deepice to collect ice cores thatcontain dust, air bubbles, orisotopes of oxygen, that can beused to interpret the pastclimate of that area. Shown above is a section of an ice core taken on the Clark Glacier in the McMurdo Dry Valleys. A 160-meter core was extracted to study the climate in the area over the past 2,000 years.
  • Paleoclimatology - The study of past climate, from times prior to instrumental weather measurements.Fossilized PollenAll flowering plants produce pollengrains. Their distinctive shapes can beused to identify the type of plant fromwhich they came. Pollen grains arewell preserved in the sediment layersof ponds, lakes or the ocean. Ananalysis pollen grains in each layer tellus what kinds of plants were growingat the time the sediment wasdeposited. Inferences can then bemade about the climate based on thetypes of plants found in each layer.The image right, shows features ofpollen spores from the FloridaEverglades (USGS)
  • Paleoclimatology - The study of past climate, from timesprior to instrumental weather measurements.Glacier LengthsA study of glacier lengthover time indicates thechange in temperature.Scientists have recordedthe activity of 169 glaciersfrom around the world. Aglacier that is becominglonger is growing due toaccumulation of snow. Aglacier that is receding isloosing mass. Most glaciersworld wide are showingsimilar loss of mass. The image, above, is an aerial view of glaciers.
  • Paleoclimatology - The study of past climate, from timesprior to instrumental weather measurements.Borehole dataBorehole data are direct measurements oftemperature from boreholes drilled into theEarth crust. Departures from the expectedincrease in temperature with depth (thegeothermal gradient) can be interpreted interms of changes in temperature at thesurface in the past. These changes intemperature have slowly diffused downward,warming or cooling layers meters below thesurface. The image to the right is a borehole drill.
  • From 1850 through thepresent, systematicinstrumental measurements oftemperature can be compiledto estimate annual values foraverage global temperature. This record is shown in black,below.
  • All proxy records, shown bythe green line, are smoothedto reflect variation on thescale of decades or longer.Note the similarities of theproxy and instrumentalrecords from the year 1800to present.
  • Additional sets of proxyrecords, drawn in the nextfew slides, show similarpatterns.
  • Additional sets of proxyrecords, show a similarpatterns.
  • This linerepresents thechange intemperature of1.1 ˚C sincethe 1700s.
  • The next few slides show projections of future temperature based on the IPCCscenarios: C3, B1, A1B, A2. Each scenario is slightly different, and less optimistic. In the C3 storyline, CO2 concentrations are held at the same level as they were in 2000. The projection indicates that the world will continue to warm through 2100 due to the lengthy response time of the climate system. B1 population peaks at about 8.7 billion at mid-century, then declines to around 7 billion at the end of the century. In this scenario, countries come together to use both technology and general environmental controls to decrease emissions, leading to a temperature increase of less than 2°C above the year 2000 level. The A1B story line has population peak around 8.7 billion at midcentury, then decrease toward 7 billion at the end of the century. This scenario entertains efficient technologies with a balance between fossil fuel and non– fossil fuel energy sources. Global temperature increase in scenario A1B is ~2.5°C. In scenario A2, population increases at current growth rates to 15 billion in 2100, accompanied by a heterogeneous economic theme of self- reliance and preservation of local identities. Global temperature increase with scenario A2 approaches 4°C by 2100.
  • Note: The next few slides provide more information and credits for thedatasets presented in this PowerPoint. They are optional information.
  • Instrumental RecordSurface temperatures for Earth are most reliably known for the period 1850 to present.This is the time for which there has been reasonable global coverage of stationsmeasuring temperature in a systematic manner. The records show that since 1850,global average temperature increased by about 0.8°C, with much of the warmingoccurring since 1975.----------------------------------------------------------------------------------------------------------------------Philip Brohan and colleagues at universities in the United Kingdom published this recordof global average temperatures (called HadCRUT3). The data set was based on aprevious global temperature data set called HadCRUT which was derived frominstrumental records. The old temperature record was modified to reflect improvementsin estimating sea surface temperature and land data. The study also included acomprehensive set of uncertainty estimates for the data, including estimates ofmeasurement and sampling error, temperature bias effects, and the effect of limitedobservational coverage on large-scale averages.Brohan, P., J. J. Kennedy, I. Harris, S. F. B. Tett, and P. D. Jones (2006), Uncertaintyestimates in regional and global observed temperature changes: A new data set from1850, J. Geophys. Res., 111, D12106, doi:10.1029/2005JD006548.
  • Proxy RecordsTemperatures can be deduced from natural records such as Tree rings Sediments in the ocean or lakes Corals Subsurface rock, soil, or ice temperatures Layers of ice In Slide Show mode, click any item above for further information----------------------------------------------------------------------------------------------------------The Esper et. al. record was extracted from tree-ring chronologies from 14 sitesin the Northern Hemisphere. At the time of publication, Jan Esper and and FritzSchweingruberwere affiliated with the Swiss Federal Research Institute inSwitzerland. Edward Cook was affiliated with Lamont-Doherty EarthObservatory at Columbia University, New York, in the United States.Esper, J., E. R. Cook, and F. H. Schweingruber (2002), Low-Frequency Signals inLong Tree-Ring Chronologies for Reconstructing Past Temperature VariabilityScience 22 March 2002: Vol. 295 no. 5563 pp. 2250-2253 DOI:10.1126/science.1066208
  • Proxy RecordsTemperatures can be deduced from natural records such as Tree rings Sediments in the ocean or lakes Corals Subsurface rock, soil, or ice temperatures Layers of ice In Slide Show mode, click any item above for further information----------------------------------------------------------------------------------------------------------The Mann and Jones record of past temperatures is based on ice boreholes, icecores, sediment records, and tree-ring chronologies. At the time of publication,Michael E. Mann was affiliated with the Department of Environmental Sciencesat the University of Virginia in Charlottesville, Virginia in the USA. Philip D.Jones is affiliated with the Climatic Research Unit at University of East Anglia inNorwich, in the United Kingdom.Mann, M. E., and P. D. Jones (2003), Global Surface Temperatures over thePast Two Millennia Geophysical Research Letters Vol. 30, No. 15, 1820, August2003 doi: 10.1029/2003GL017814
  • Proxy RecordsTemperatures can be deduced from natural records such as Tree rings Sediments in the ocean or lakes Corals Subsurface rock, soil, or ice temperatures Layers of ice In Slide Show mode, click any item above for further information----------------------------------------------------------------------------------------------------------Anders Moberg and colleagues from Sweden and Russia published atemperature record deduced from tree rings and lake and ocean sediments.Moberg, A., D. M. Sonechkin, K. Holmgren, N. M. Datsenko, and W. Karlén(2005), Highly variable Northern Hemisphere temperatures reconstructedfrom low- and high-resolution proxy data Nature, Vol. 433, No. 7026, pp. 613 -617, 10 February 2005.
  • Proxy RecordsTemperatures can be deduced from natural records such as Tree rings Sediments in the ocean or lakes Corals Subsurface rock, soil, or ice temperatures Layers of ice In Slide Show mode, click any item above for further information----------------------------------------------------------------------------------------------------------Gabriele Hegerl, along with two of her Duke University colleagues and a collaborator inthe United Kingdom developed their temperature reconstruction as follows: “We uselarge-ensemble energy balance modeling and simulate the temperature response topast solar, volcanic and greenhouse gas forcing to determine which climate sensitivitiesyield simulations that are in agreement with proxy reconstructions. After accounting forthe uncertainty in reconstructions and estimates of past external forcing, we find anindependent estimate of climate sensitivity that is very similar to those frominstrumental data.”Hegerl, G. C., T. J. Crowley, W. T. Hyde, and D. J. Frame (2006), Climate sensitivityconstrained by temperature reconstructions over the past seven centuries. Nature440, 1029-1032 (20 April 2006) | doi:10.1038/nature04679
  • Glacier LengthsHistorical paintings, photographs, and other documents enable researchers toestimate the change in glacier mass balance over time and deducecorresponding temperatures. Additionally, dating of plant materials that werecovered by glaciers and recently exposed provide information about the timingof changes in glacier lengths.----------------------------------------------------------------------------------------------------------J. Oerlemans of the Institute for Marine and Atmospheric Research at UtrechtUniversity in the Netherlands constructed a temperature history for differentparts of the world from 169 glacier length records. Using a first-order theory ofglacier dynamics, he related changes in glacier length to changes intemperature. The derived temperature histories are fully independent of proxyand instrumental data used in earlier reconstructions.Oerlemans, J. (2005) Extracting a Climate Signal from 169 Glacier RecordsScience Vol. 308, No. 5722, pp. 675-677, 29 April 2005.
  • Borehole TemperaturesSubsurface temperatures measured in boreholes register not only the steadystate heat flowing out from Earth’s interior, but also changes in past surfacetemperature. Heat of the Earth’s atmosphere diffuses into the Earth’s crustsuch that progressively deeper regions of the subsurface hold signatures for thetemperatures of progressively older times. More information on boreholes >----------------------------------------------------------------------------------------------------------Shaopeng Huang and a colleague at the University of Michigan, working with acollaborator from Canada used present-day temperatures in 616 boreholesfrom all continents except Antarctica to reconstruct century-long trends intemperatures over the past 500 years at global, hemispheric and continentalscales.Huang, S.. Pollack, H.N. & Shen, P.-Y. Temperature trends over the past fivecenturies reconstructed from borehole temperatures. Nature 403, 756-758(17 February 2000) | doi:10.1038/35001556
  • Borehole + Surface Air TemperaturesSubsurface temperatures measured in boreholes register not only the steadystate heat flowing out from Earth’s interior, but also changes in past surfacetemperature. Heat of the Earth’s atmosphere diffuses into the Earth’s crustsuch that progressively deeper regions of the subsurface hold signatures for thetemperatures of progressively older times.----------------------------------------------------------------------------------------------------------Robert N. Harris and David S. Chapman, working at the University of Utah in theUnited States developed a temperature reconstruction using a hybrid approachthat utilized both borehole and surface air temperature information. Theirmethod yielded a baseline temperature prior to the instrumental recordsuggesting warming of about 1.1°C since ~1750.Harris, R. N., and D. S. Chapman (2001), Mid-latitude (30°–60° N) climaticwarming inferred by combining borehole temperatures with surface airtemperatures, Geophys. Res. Lett., 28(5), 747–750,doi:10.1029/2000GL012348.
  • Future Climate Projections: Intergovernmental Panel on Climate Change(IPCC)For its Fourth Assessment Report released in 2007, the IPCC considered severalpossible futures based on factors including population growth, economicdevelopment, and technological change. Each scenario was linked to estimatesof how the concentration of greenhouse gases in the atmosphere wouldchange over time. Twenty-three different climate models used the scenarios asinput to make projections of global average temperature through the year2100. Solid lines represent the average projection; shaded areas show therange of results.----------------------------------------------------------------------------------------------------------In the C3 storyline, CO2 concentrations are held at the same level as they werein 2000. The projection indicates that the world will continue to warm through2100 due to the lengthy response time of the climate system.Intergovernmental Panel on Climate Change (IPCC) (2007), Climate Change2007: The Physical Science Basis—Contribution of Working Group I to theFourth Assessment Report of the Intergovernmental Panel on Climate Change,edited by S. Solomon et al., 996 pp., Cambridge Univ. Press, New York.
  • Future Climate Projections: Intergovernmental Panel on Climate Change(IPCC)For its Fourth Assessment Report released in 2007, the IPCC considered severalpossible futures based on factors including population growth, economicdevelopment, and technological change. Each scenario was linked to estimatesof how the concentration of greenhouse gases in the atmosphere wouldchange over time. Twenty-three different climate models used the scenarios asinput to make projections of global average temperature through the year2100. Solid lines represent the average projection; shaded areas show therange of results.----------------------------------------------------------------------------------------------------------B1 population peaks at about 8.7 billion at mid-century, then declines toaround 7 billion at the end of the century. In this scenario, countries cometogether touse both technology and general environmental controls to decreaseemissions, leading to a temperature increase of less than 2°C above the year2000 level.Intergovernmental Panel on Climate Change (IPCC) (2007), Climate Change2007: The Physical Science Basis—Contribution of Working Group I to the
  • Future Climate Projections: Intergovernmental Panel on Climate Change(IPCC)For its Fourth Assessment Report released in 2007, the IPCC considered severalpossible futures based on factors including population growth, economicdevelopment, and technological change. Each scenario was linked to estimatesof how the concentration of greenhouse gases in the atmosphere wouldchange over time. Twenty-three different climate models used the scenarios asinput to make projections of global average temperature through the year2100. Solid lines represent the average projection; shaded areas show therange of results.----------------------------------------------------------------------------------------------------------The A1B story line has population peak around 8.7 billion at midcentury, thendecrease toward 7 billion at the end of the century. This scenario entertainsefficient technologies with a balance between fossil fuel and non– fossil fuelenergy sources. Global temperature increase in scenario A1B is ~2.5°C.Intergovernmental Panel on Climate Change (IPCC) (2007), Climate Change2007: The Physical Science Basis—Contribution of Working Group I to theFourth Assessment Report of the Intergovernmental Panel on Climate Change,edited by S. Solomon et al., 996 pp., Cambridge Univ. Press, New York.
  • Future Climate Projections: Intergovernmental Panel on Climate Change(IPCC)For its Fourth Assessment Report released in 2007, the IPCC considered severalpossible futures based on factors including population growth, economicdevelopment, and technological change. Each scenario was linked to estimatesof how the concentration of greenhouse gases in the atmosphere wouldchange over time. Twenty-three different climate models used the scenarios asinput to make projections of global average temperature through the year2100. Solid lines represent the average projection; shaded areas show therange of results.----------------------------------------------------------------------------------------------------------In scenario A2, population increases at current growth rates to 15 billion in2100, accompanied by a heterogeneous economic theme of self- reliance andpreservation of local identities. Global temperature increase with scenario A2approaches 4°C by 2100.Intergovernmental Panel on Climate Change (IPCC) (2007), Climate Change2007: The Physical Science Basis—Contribution of Working Group I to theFourth Assessment Report of the Intergovernmental Panel on Climate Change,edited by S. Solomon et al., 996 pp., Cambridge Univ. Press, New York.
  • Tree Rings (Text from http://www.nap.edu/catalog/11676.html)Tree ring formation is influenced by climatic conditions, especially in areas near the edgeof the geographic distribution of tree species. At high latitudes and/or at high elevations,tree ring growth is related to temperature, and thus trees from these sites arecommonly used as a basis for surface temperature reconstructions. Cores extractedfrom the trees provide annually resolved time series of tree ring width and of woodproperties, such as density and chemical composition, within each ring. In some cases,records from living trees can be matched with records from dead wood to create asingle, continuous chronology extending back several thousand years.Tree ring records offer a number of advantages for climate reconstruction, includingwide geographic availability, annual to seasonal resolution, ease of replication, andinternally consistent dating. Like other proxies, tree rings are influenced by biologicaland environmental factors other than climate. Site selection and quality controlprocedures have been developed to account for these confounding factors. In theapplication of these procedures, emphasis is placed on replication of records both withina site and among sites and on numerical calibration against instrumental data.----------------------------------------------------------------------------------------------------------Surface Temperature Reconstructions for the Last 2,000 Years (2006) Committee onSurface Temperature Reconstructions for the Last 2,000 Years, National ResearchCouncil. ISBN: 0-309-66144-7, 160 pages http://www.nap.edu/catalog/11676.html
  • Corals (Text from http://www.nap.edu/catalog/11676.html)The annual bands in coral skeletons provide information about environmentalconditions at the time that each band was formed. This information is mostlyderived from changes in the chemical and isotopic composition of the coral,which reflects the temperature and isotopic composition of the water in whichit formed. Since corals live mostly in tropical and subtropical waters, theyprovide a useful complement to records derived from tree rings. Coral skeletonchemistry is influenced by several variables, and thus care must be taken whenselecting coral samples and when deriving climate records from them. Thus far,most of the climate reconstructions based on corals have been regional in scaleand limited to the last few hundred years, but there is now work towardestablishing longer records by sampling fossil corals.----------------------------------------------------------------------------------------------------------Surface Temperature Reconstructions for the Last 2,000 Years (2006)Committee on Surface Temperature Reconstructions for the Last 2,000 Years,National Research Council. ISBN: 0-309-66144-7, 160 pageshttp://www.nap.edu/catalog/11676.html
  • Ice Cores (Text from http://www.nap.edu/catalog/11676.html)Oxygen isotopes measured in ice cores extracted from glaciers and ice caps can be usedto infer the temperature at the time when the snow was originally deposited. For themost recent 2,000 years, the age of the ice can in most places be determined bycounting annual layers. The isotopic composition of the ice in each layer reflects boththe temperature in the region where the water molecules originally evaporated farupwind of the glacier and the temperature of the clouds in which the water vapormolecules condensed to form snowflakes. The long-term fluctuations in temperaturereconstructions derived from ice cores can be cross-checked against the verticaltemperature profiles in the holes out of which they were drilled (see below). Ice-isotope-based reconstructions are available only in areas that are covered with ice that persistson the landscape (e.g., Greenland, Antarctica, and some ice fields atop mountains inAfrica, the Andes, and the Himalayas). The interpretation of oxygen isotopemeasurements in tropical ice cores is more complicated than for polar regions because itdepends not only on temperature but also on precipitation in the adjacent lowlands.----------------------------------------------------------------------------------------------------------Surface Temperature Reconstructions for the Last 2,000 Years (2006) Committee onSurface Temperature Reconstructions for the Last 2,000 Years, National ResearchCouncil. ISBN: 0-309-66144-7, 160 pages http://www.nap.edu/catalog/11676.html
  • Marine and Lake Sediments (Text from http://www.nap.edu/catalog/11676.html)Cores taken from the sediments at the bottoms of lakes and ocean regions can be analyzed toprovide evidence of past climatic change. Sediment cores can be analyzed to determine thetemperature of the water from which the various constituents of the sediment were deposited. Thisinformation, in turn, can be related to the local surface temperature. Records relevant totemperature include oxygen isotopes, the ratio of magnesium to calcium, and the relativeabundance of different microfossil types with known temperature preferences (such as insects) orwith a strong temperature correlation (e.g., diatoms and some other algae). Changes in theproperties of sediments are also of interest. For example, during cold epochs icebergs streamingsouthward over the North Atlantic carried sand and gravel and deposited it in sediments at thelatitudes where they melted; the properties of this material are indicative of the generally colderconditions in the region where the icebergs originated. Ocean and lake sediments typicallyaccumulate slowly, and the layering within them tends to be smoothed out by bottom-dwellingorganisms. Hence it is only in regions where sedimentation rates are extraordinarily high (e.g., theBermuda Rise, the northwest coast of Africa) or in a few oxygen-deprived areas (e.g., the SantaBarbara Basin, the Cariaco Basin off Venezuela, or in deep crater lakes) that sediments can be datedaccurately enough to provide information on climate changes during the last 2,000 years. Moreslowly accumulating sediments from ocean basins throughout the world are one of our mainsources of information on climate variations on timescales of millennia and longer.----------------------------------------------------------------------------------------------------------Surface Temperature Reconstructions for the Last 2,000 Years (2006) Committee on SurfaceTemperature Reconstructions for the Last 2,000 Years, National Research Council. ISBN: 0-309-66144-7, 160 pages http://www.nap.edu/catalog/11676.html
  • Boreholes (Text from http://www.nap.edu/catalog/11676.html)Past surface temperatures can be estimated by measuring the vertical temperature profile downboreholes drilled into rock, frozen soils, and ice. Temperature variations at the Earth’s surfacediffuse downward with time by the same process that causes the handle of a metal spoon to warmup when it is immersed in a cup of hot tea. The governing equation for this process can be used toconvert the vertical profile of temperature in a borehole into a record of surface temperatureversus time. Features in the vertical temperature profile are smoothed out as they propagatedownward, resulting in a loss of information. Hence, large-scale surface temperaturereconstructions based on borehole measurements typically extend back only over a few centuries,with coarse time resolution. Hundreds of holes have been drilled to depths of several hundredmeters below the surface at sites throughout the Northern Hemisphere and at a smaller number ofsites in the Southern Hemisphere. Many of these “boreholes of opportunity” were drilled for otherreasons such as mineral exploration. Specialists acknowledge several different types of errors inborehole-based temperature reconstructions, such as an imperfect match between groundtemperature and near-surface air temperature, but available evidence indicates that these errorsdo not significantly influence reconstructions for large regions using many boreholes. Boreholesdrilled through glacial ice to extract ice cores are free from many of these problems and can beanalyzed jointly with the oxygen isotope record from the corresponding core, yielding a muchlonger and more accurate temperature reconstruction than is possible with boreholes drilledthrough rock or permafrost. However, ice-based boreholes are available only in areas with a thickcover of ice.------------------------------------------------------------------------------------------------------------------------------------Surface Temperature Reconstructions for the Last 2,000 Years (2006) Committee on SurfaceTemperature Reconstructions for the Last 2,000 Years, National Research Council. ISBN: 0-309-66144-7, 160 pages http://www.nap.edu/catalog/11676.html