what is the palaeclimate record
what are the characteristics of vostok ice core period
El hombre lleva mas de 150 años registrando la temperatura de la tierra, mediante estas recopilaciones de la temperatura se han modelado estudios del comportamiento de este durante la historia de la tierra. esto se hace usando el oxigeno y otros factores como referencia según la cantidad de tiempo.
The temperature record shows fluctuations of the temperature of the atmosphere and the oceans through various time span.
What is Pleistocene glaciation?
The instrumental record of the Earth\'s temperature based on direct measurements (using thermometers), and extends back only 150 years or so. Temperatures further back in time are reconstructed from a variety of proxy data. These include historical documents, together with natural archives of climate-sensitive phenomena, such as the growth or retreat of glaciers, tree rings, corals, sediments and ice cores.
In general, the proxy data record becomes more sparse and more imprecise the further back in time we go. Nevertheless, it has proved possible to produce a reasonably reliable reconstruction of how global temperature has varied throughout most of the Earth\'s history. This is known as the palaeoclimate record (from the Greek palaios for ‘ancient’).
Dendroclimatology depends on the fact that trees in many parts of the world experience an annual growth cycle. Each year\'s growth (the thickness and/or density of a ring) depends on the local temperature and moisture conditions, creating a unique record that can then be matched with overlapping records from other trees to produce longer time series.
Annual records typically go back 500 to 700 years. In a few cases, the preservation of fossil trees has allowed continuous records from 11,000 years ago to the present to be constructed.
In a similar way, cyclical responses lead to annual banding in corals, which can provide information about sea-surface temperatures, sea level and other ocean conditions - typically back to some 400 years ago.
Layered sediments on lake and ocean floors are another rich source. The types of pollen trapped in lake sediments reveal shifting patterns of vegetation, and thus indirect information about temperature and moisture conditions. Records can go back some 100,000 years.
In marine sediments, analysis of microfossils can provide data on seawater temperature and salinity (salt content), atmospheric CO2 and ocean circulation. Less common deposits of coarse debris can point to the break up of ice sheets and the release of detritus from melting icebergs. Marine sediments provide information from time periods ranging from 20,000 years to 180 million years ago.
Long ice cores drilled out of the Greenland and Antarctic ice sheets yield a wealth of information. For example, past temperatures can be determined by oxygen isotope analysis . 99% of the oxygen on Earth is the isotope 16O; most of the rest is isotope 18O. Because water molecules containing the different isotopes (i.e. H2 16O and H2 18O) have slightly different physical properties, it turns out that the 18O/16O ratio in ice locked up on land is affected by the ambient temperature at the time when the ice formed.
Thus, fluctuations in the oxygen isotope ratio in an ice core provide a proxy for temperature changes back through time.. The cores also include atmospheric fallout such as wind-blown dust, volcanic ash, pollen, etc. - along with trapped air bubbles.
Drilled in Antarctica, the Vostok ice core provides a temperature record that goes back several hundreds of thousands of years. Beyond about 10,000 years ago, it tells a story of an unstable climate oscillating between short warm interglacial periods and longer cold glacial periods about every 100,000 years - with global temperatures varying by as much as 5 to 8 °C - interspersed by many more short-term fluctuations.
By contrast, global temperatures over the last 10,000 years or so seem to have been much less variable, fluctuating by little more than one or two degrees. In short, the interglacial period in which we live, known as the Holocene, appears (on available evidence) to have provided the longest period of relatively stable global climate for at least 400,000 years. It is almost certainly no coincidence that this is also when many human societies developed agriculture and when the beginnings of modern civilisations occurred.
Nous enverrons les instructions pour reinitialiser votre mot de passe à votre adresse e-mail associée. Veuillez marquer votre adresse e-mail actuelle.