Paleoclimatology Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Paleoclimatology involves the reconstruction of past climates prior to the instrumental period. Paleoclimatology focuses on: (1) describing past climates, (2) understanding the natural and anthropogenic processes responsible for these patterns, and (3) using this knowledge of past climates and climate dynamics to identify and understand potential responses to climatic forcing. Detailed views of the modern climate can be obtained using available instrumental records and documentary or historical sources of information, but their short temporal resolution and/or sparse spatial coverage limits their ability to capture the variability that is inherent in the climate system. Paleoclimatology, therefore, extends instrumental and historical records further back in time, enabling the capture of a greater range of variability. This enhances not only our understanding of climate variability in terms of mean conditions, extremes, and states, but also improves insight into the dynamic forces controlling the operation of the climate system.

Examples of research areas that interest paleoclimatologists include: abrupt climate change, hydrological variability, land-cover change, sea-level rise, and modeling the potential response of the climate system to natural and anthropogenic forcing. Paleoclimate research methods involve the testing of specific hypotheses such as how to identify the forcing mechanism(s) or drivers responsible for specific climate events that occurred in the past (for example, the Dust Bowl, Little Ice Age, mid-Holocene aridity in central North America, and the Younger Dryas). One important field of paleoclimate research centers on identifying potential surprise behavior in the climate system, the mechanisms responsible for these nonlinear responses, and ultimately the impacts that may result.

Paleoclimatologists extract paleoclimatological data from a plethora of natural archives, or proxies, such as corals, ice cores, marine and lake sediment, tree rings, and spleothems. For example, ice cores recovered from alpine glaciers located in South America, Africa, and Central Asia and high latitude ice sheets located in Greenland and Antarctica have provided detailed records of atmospheric trace gas concentrations (CO2, CH4), temperature (O18,⸹D), storminess (dust), and volcanic eruptions (SOx ) extending back over hundreds of thousands of years. The European Project for Ice Coring in Antarctica (EPICA) recently completed an ice-drilling project at Dome C, Antarctica that provided a climate record spanning the last 740,000 years. The data from Dome C suggests that a tight coupling between trace greenhouse gases and Antarctic temperature variations has existed for the last four glacial cycles (420,000 years).

Paleoclimate research is increasingly utilizing global and regional climate models to generate simulations of past climates and evaluate the role feedbacks play in the different climate subsystems (atmosphere, ocean, land surface, sea ice, and land ice) at various spatial and temporal scales. A recently completed study, the Paleoclimate Modeling Intercomparison Project (PMIP), systematically assessed the ability of the current generation of general circulation models (GCMs) to simulate past climates that differed significantly from present climate conditions. The output from these models was directly compared to biophysical and geochemical proxy records to evaluate how well models can simulate past conditions. Studies such as PMIP demonstrate that the current generation of general circulation models (GCMs) can simulate known past climatic conditions and events with skill, strengthening their ability to predict future climate change.

With respect to temporal scales, the paleoclimate record reveals that earth’s climate varies on a number of different timescales: long-term (106 years), medium-term (104 -105 years) and short-term (101-102 years). Long-term changes are generally associated with changes in the distribution of landmasses on the earth’s surface, often referred to as continental drift, but more aptly described as plate tectonics. For example, the movement of landmasses from the equatorial region approximately 300 million years ago (Gondwana) to the poles facilitated the development of high latitude ice sheets and led to the last Great Ice Age. Changes in ocean circulation and orogenesis also operate on a similar timescale and impact climate globally. For example, the uplift of the Himalayan and Tibetan Plateau resulted in the development of the Asian monsoon, which affects global atmospheric circulation patterns.

Medium-term changes are associated with the periodic global expansion and contraction of glaciers during the last 2.8 million years (Pleistocene). The cyclical expansion and contraction of alpine glaciers and large continental ice sheets, with an overall periodicity of approximately 100,000 years, has been linked to astronomical forcing. The CLIMAP (Climate: Long-range Investigation, Mapping, and Prediction) Project and SPECMAP (Spectral Mapping Project) helped identify that variations in the earth’s orbital parameters (orbital eccentricity, precession of the equinoxes and obliquity) were responsible for the dramatic glacial-interglacial cycles evidenced globally in marine and ice core records. Short-term alterations in climate are associated with changes in the concentration of atmospheric trace-gases, such as CO2 and CH4, changes in solar output, and variations in volcanic and anthropogenic aerosol forcing. It appears that slight changes in solar output may explain much of the variability evidenced in the climate system during the past 1,000 years, but the rate and magnitude of warming experienced during the 20th century strongly suggests that this variation has been amplified by human activity.

With nine of the warmest years on record (global land temperatures) having occurred since 1995, global climate change has become part of the lexicon. Changes are occurring in many of the climate subsystems, and many of these changes can be attributed, in part, to anthropogenic forcing. From variations in storm frequency and intensity, to the future of coastal communities and settlements, to changes in local and regional ecosystems, paleoclimatic records provide context and evidence regarding the potentially deleterious effects of climate change.

Questions still remain, however, regarding the degree to which human activity can be implicated as a forcing factor responsible for the modification of the behavior of the climate system. The value of the paleoclimate record lies in its ability to provide a broader context, that is, sufficiently long records to circumscribe baseline conditions and facilitate separating human-induced climate change from natural cycles. It is only with this longer-term perspective that the full range of variability that exists within the climate system can be captured; this will improve the understanding of the dynamic forces controlling the operation of the climate system.

Bibliography:

Raymond Bradley, Paleoclimatology: Reconstructing Climates of the Quaternary (Harcourt Academic Press, 1999);
CLIMAP Project Members, “The Surface of the Ice-Age Earth,” Science (v.191, 1976);
EPICA Community Members, “Eight Glacial Cycles from an Antarctic Ice Core,” Nature (v.429, 2004);
John Imbrie et , “On the Structure and Origin of Major Glaciation Cycles: The 100,000 Year Cycle,” Paleoceanography (v.8, 1993);
E. Mann, R.S. Bradley, and M.K. Hughes, “Northern Hemisphere Temperatures during the Past Millennium: Inferences, Uncertainties, and Limitations,” Geophysical Research Letters (v.26, 1999);
Jonathan T. Overpeck, “Paleoclimatology and Climate System Dynamics: S. National Report to International Union of Geodesy and Geophysics 1991-1994,” Reviews of Geophysics (v.33/Supplement, 1995).