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94-641: The Medieval Warm Period ( MWP ), also known as the Medieval Climate Optimum or the Medieval Climatic Anomaly , was a time of warm climate in the North Atlantic region that lasted from about 950 CE to about 1250 CE . Climate proxy records show peak warmth occurred at different times for different regions, which indicate that the MWP was not a globally uniform event. Some refer to
188-533: A La Niña -like configuration, but the data are insufficient to show how lake levels varied from year to year or what climatic conditions elsewhere in Australia were like. A 1979 study from the University of Waikato found, Temperatures derived from an O/O profile through a stalagmite found in a New Zealand cave ( 40°40′S 172°26′E / 40.67°S 172.43°E / -40.67; 172.43 ) suggested
282-484: A N(n,p) C reaction, direct uranium decay (though reported measured ratios of C/U in uranium-bearing ores would imply roughly 1 uranium atom for every two carbon atoms in order to cause the C/ C ratio, measured to be on the order of 10 ), or other unknown secondary sources of C production. The presence of C in the isotopic signature of a sample of carbonaceous material possibly indicates its contamination by biogenic sources or
376-559: A biome classification, as climate is a major influence on life in a region. One of the most used is the Köppen climate classification scheme first developed in 1899. There are several ways to classify climates into similar regimes. Originally, climes were defined in Ancient Greece to describe the weather depending upon a location's latitude. Modern climate classification methods can be broadly divided into genetic methods, which focus on
470-535: A high stand during the MWP. When human populations returned to the region, they encountered a land altered by climate change and had to reestablish ports. In the Iberian Central Range, there was elevated lake productivity and soil erosion, along with frequent intense runoff events. In Chesapeake Bay (now in Maryland and Virginia , United States ), researchers found large temperature excursions (changes from
564-510: A 30-year period. A 30-year period is used as it is long enough to filter out any interannual variation or anomalies such as El Niño–Southern Oscillation , but also short enough to be able to show longer climatic trends." The WMO originated from the International Meteorological Organization which set up a technical commission for climatology in 1929. At its 1934 Wiesbaden meeting, the technical commission designated
658-525: A direct comparison of carbon-14 levels in a sample, with tree ring or cave-deposit C levels of a known age, then gives the wood or animal sample age-since-formation. Radiocarbon is also used to detect disturbance in natural ecosystems; for example, in peatland landscapes, radiocarbon can indicate that carbon which was previously stored in organic soils is being released due to land clearance or climate change. Cosmogenic nuclides are also used as proxy data to characterize cosmic particle and solar activity of
752-419: A few global datasets exist. Global climate models can be dynamically or statistically downscaled to regional climate models to analyze impacts of climate change on a local scale. Examples are ICON or mechanistically downscaled data such as CHELSA (Climatologies at high resolution for the earth's land surface areas). The most talked-about applications of these models in recent years have been their use to infer
846-504: A gradual withdrawal, which was caused mainly by economic factors such as increased availability of farms in Scandinavian countries. Substantial glacial retreat in southern Europe was experienced during the MWP. While several smaller glaciers experienced complete deglaciation, larger glaciers in the region survived and now provide insight into the region's climate history. In addition to warming induced glacial melt, sedimentary records reveal
940-486: A location is affected by its latitude , longitude , terrain , altitude , land use and nearby water bodies and their currents. Climates can be classified according to the average and typical variables, most commonly temperature and precipitation . The most widely used classification scheme is the Köppen climate classification . The Thornthwaite system , in use since 1948, incorporates evapotranspiration along with temperature and precipitation information and
1034-523: A notably warm climate in many parts of the world, that lasted a few centuries around 1000–1200 CE , and was followed by a decline of temperature levels till between around 1500–1700 CE the coldest phase since the last ice age occurred. The era of warmer temperatures became known as the Medieval Warm Period and the subsequent cold period the Little Ice Age (LIA). However, the view that
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#17328518005361128-440: A nuclear reactor) are summarized in the table. Another source of carbon-14 is cluster decay branches from traces of naturally occurring isotopes of radium , though this decay mode has a branching ratio on the order of 10 relative to alpha decay , so radiogenic carbon-14 is extremely rare. The above-ground nuclear tests that occurred in several countries in 1955-1980 (see List of nuclear tests ) dramatically increased
1222-480: A period of increased flooding, coinciding with the MWP, in eastern Europe that is attributed to enhanced precipitation from a positive phase NAO. Other impacts of climate change can be less apparent such as a changing landscape. Preceding the MWP, a coastal region in western Sardinia was abandoned by the Romans. The coastal area was able to substantially expand into the lagoon without the influence of human populations and
1316-567: A regional instead of global framing of climate variability in the preindustrial Common Era to aid in understanding. Lloyd D. Keigwin's 1996 study of radiocarbon -dated box core data from marine sediments in the Sargasso Sea found that its sea surface temperature was approximately 1 °C (1.8 °F) cooler approximately 400 years ago, during the LIA , and 1700 years ago, and was approximately 1 °C (1.8 °F) warmer 1000 years ago, during
1410-403: A slower rate to form CO 2 , radioactive carbon dioxide . The gas mixes rapidly and becomes evenly distributed throughout the atmosphere (the mixing timescale on the order of weeks). Carbon dioxide also dissolves in water and thus permeates the oceans , but at a slower rate. The atmospheric half-life for removal of CO 2 has been estimated at roughly 12 to 16 years in
1504-458: A stable oxygen (δ O) and carbon (δ C) isotope record at a decadal resolution from the Roman Warm Period to the MWP and the LIA . Patterson et al. conclude that the summer temperature stayed high but winter temperature decreased after the initial settlement of Iceland. The Mann et al. study found warmth exceeding 1961–1990 levels in southern Greenland and parts of North America during
1598-421: A time spanning from months to millions of years. Some of the meteorological variables that are commonly measured are temperature , humidity , atmospheric pressure , wind , and precipitation . In a broader sense, climate is the state of the components of the climate system , including the atmosphere , hydrosphere , cryosphere , lithosphere and biosphere and the interactions between them. The climate of
1692-633: A warm and humid MWP from 1,158 to 647 BP. Pollen from Madhya Pradesh dated to the MWP provides further direct evidence for increased monsoonal precipitation. Multi-proxy records from Pookode Lake in Kerala also reflect the warmth of the MWP. Sea surface temperatures in the Arabian Sea increased during the MWP, owing to a strong monsoon. During the MWP, the Arabian Sea exhibited heightened biological productivity. The Arabian Peninsula , already extremely arid in
1786-403: A wider sense is the state, including a statistical description, of the climate system." The World Meteorological Organization (WMO) describes " climate normals " as "reference points used by climatologists to compare current climatological trends to that of the past or what is considered typical. A climate normal is defined as the arithmetic average of a climate element (e.g. temperature) over
1880-649: Is cosmic ray action on nitrogen in the atmosphere, and it is therefore a cosmogenic nuclide . However, open-air nuclear testing between 1955 and 1980 contributed to this pool. The different isotopes of carbon do not differ appreciably in their chemical properties. This resemblance is used in chemical and biological research, in a technique called carbon labeling : carbon-14 atoms can be used to replace nonradioactive carbon, in order to trace chemical and biochemical reactions involving carbon atoms from any given organic compound. Carbon-14 undergoes beta decay : By emitting an electron and an electron antineutrino , one of
1974-484: Is 0.05 mm. Radiocarbon dating is a radiometric dating method that uses C to determine the age of carbonaceous materials up to about 60,000 years old. The technique was developed by Willard Libby and his colleagues in 1949 during his tenure as a professor at the University of Chicago . Libby estimated that the radioactivity of exchangeable C would be about 14 decays per minute (dpm) per gram of carbon, and this
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#17328518005362068-447: Is also generated inside nuclear fuels (some due to transmutation of oxygen in the uranium oxide , but most significantly from transmutation of nitrogen-14 impurities), and if the spent fuel is sent to nuclear reprocessing then the C is released, for example as CO 2 during PUREX . After production in the upper atmosphere, the carbon-14 reacts rapidly to form mostly (about 93%) CO ( carbon monoxide ), which subsequently oxidizes at
2162-549: Is as follows: "Climate in a narrow sense is usually defined as the "average weather", or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period ranging from months to thousands or millions of years. The classical period is 30 years, as defined by the World Meteorological Organization (WMO). These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in
2256-530: Is called the early Medieval Warm Period while MWP-II is called the conventional Medieval Warm Period. In 1965, Hubert Lamb , one of the first paleoclimatologists , published research based on data from botany , historical document research, and meteorology, combined with records indicating prevailing temperature and rainfall in England around 1200 CE and around 1600 CE . He proposed, evidence has been accumulating in many fields of investigation pointing to
2350-462: Is discussed in terms of global warming , which results in redistributions of biota . For example, as climate scientist Lesley Ann Hughes has written: "a 3 °C [5 °F] change in mean annual temperature corresponds to a shift in isotherms of approximately 300–400 km [190–250 mi] in latitude (in the temperate zone) or 500 m [1,600 ft] in elevation. Therefore, species are expected to move upwards in elevation or towards
2444-907: Is evidence for an unusually high production rate in AD 774–775 , caused by an extreme solar energetic particle event, the strongest such event to have occurred within the last ten millennia. Another "extraordinarily large" C increase (2%) has been associated with a 5480 BC event, which is unlikely to be a solar energetic particle event. Carbon-14 may also be produced by lightning but in amounts negligible, globally, compared to cosmic ray production. Local effects of cloud-ground discharge through sample residues are unclear, but possibly significant. Carbon-14 can also be produced by other neutron reactions, including in particular C (n,γ) C and O (n,α) C with thermal neutrons , and N (n,d) C and O (n, He) C with fast neutrons . The most notable routes for C production by thermal neutron irradiation of targets (e.g., in
2538-406: Is in the oceans. The following inventory of carbon-14 has been given: Many human-made chemicals are derived from fossil fuels (such as petroleum or coal ) in which C is greatly depleted because the age of fossils far exceeds the half-life of C. The relative absence of CO 2 is therefore used to determine the relative contribution (or mixing ratio ) of fossil fuel oxidation to
2632-502: Is insufficient on its own to explain the MWP and that an external forcing had to be one of the causes. The MWP is generally thought to have occurred from about 950 CE to about 1250 CE , during the European Middle Ages . Some researchers divide the MWP into two phases: MWP-I, which began around 450 CE and ended around 900 CE , and MWP-II, which lasted from about 1000 CE to about 1300 CE ; MWP-I
2726-430: Is small compared to the doses from K (0.39 mSv/year) and radon (variable). C can be used as a radioactive tracer in medicine. In the initial variant of the urea breath test , a diagnostic test for Helicobacter pylori , urea labeled with about 37 kBq (1.0 μCi ) C is fed to a patient (i.e. 37,000 decays per second). In the event of a H. pylori infection, the bacterial urease enzyme breaks down
2820-518: Is still used as the activity of the modern radiocarbon standard . In 1960, Libby was awarded the Nobel Prize in chemistry for this work. One of the frequent uses of the technique is to date organic remains from archaeological sites. Plants fix atmospheric carbon during photosynthesis; so the level of C in plants and animals when they die, roughly equals the level of C in the atmosphere at that time. However, it thereafter decreases exponentially; so
2914-756: Is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues (1949) to date archaeological, geological and hydrogeological samples. Carbon-14 was discovered on February 27, 1940, by Martin Kamen and Sam Ruben at the University of California Radiation Laboratory in Berkeley, California . Its existence had been suggested by Franz Kurie in 1934. There are three naturally occurring isotopes of carbon on Earth: carbon-12 ( C), which makes up 99% of all carbon on Earth; carbon-13 ( C), which makes up 1%; and carbon-14 ( C), which occurs in trace amounts, making up about 1-1.5 atoms per 10 atoms of carbon in
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3008-436: Is the preferred method although more recently, accelerator mass spectrometry has become the method of choice; it counts all the carbon-14 atoms in the sample and not just the few that happen to decay during the measurements; it can therefore be used with much smaller samples (as small as individual plant seeds), and gives results much more quickly. The G-M counting efficiency is estimated to be 3%. The half-distance layer in water
3102-569: Is used in studying biological diversity and how climate change affects it. The major classifications in Thornthwaite's climate classification are microthermal, mesothermal, and megathermal. Finally, the Bergeron and Spatial Synoptic Classification systems focus on the origin of air masses that define the climate of a region. Paleoclimatology is the study of ancient climates. Paleoclimatologists seek to explain climate variations for all parts of
3196-406: Is what you expect, weather is what you get." Over historical time spans, there are a number of nearly constant variables that determine climate, including latitude , altitude, proportion of land to water, and proximity to oceans and mountains. All of these variables change only over periods of millions of years due to processes such as plate tectonics . Other climate determinants are more dynamic:
3290-491: The LIA . Peak temperatures did not rise as to the level of the late 20th century, which were unprecedented in the area during the study period of 1600 years. Ge et al. studied temperatures in China for the past 2000 years and found high uncertainty prior to the 16th century but good consistency over the last 500 years highlighted by the two cold periods, 1620s–1710s and 1800s–1860s, and the 20th-century warming. They also found that
3384-484: The thermohaline circulation of the ocean leads to a 5 °C (9 °F) warming of the northern Atlantic Ocean compared to other ocean basins. Other ocean currents redistribute heat between land and water on a more regional scale. The density and type of vegetation coverage affects solar heat absorption, water retention, and rainfall on a regional level. Alterations in the quantity of atmospheric greenhouse gases (particularly carbon dioxide and methane ) determines
3478-491: The Arctic region and oceans. Climate variability is the term to describe variations in the mean state and other characteristics of climate (such as chances or possibility of extreme weather , etc.) "on all spatial and temporal scales beyond that of individual weather events." Some of the variability does not appear to be caused systematically and occurs at random times. Such variability is called random variability or noise . On
3572-504: The EASM and ENSO are responsible for increased precipitation in the region during the MWP. However, other sites in southern China show aridification and not humidification during the MWP, showing that the MWP's influence was highly spatially heterogeneous. Modelling evidence suggests that EASM strength during the MWP was low in early summer but very high during late summer. In far eastern Russia , continental regions experienced severe floods during
3666-456: The EU's Copernicus Climate Change Service, average global air temperature has passed 1.5C of warming the period from February 2023 to January 2024. Climate models use quantitative methods to simulate the interactions and transfer of radiative energy between the atmosphere , oceans , land surface and ice through a series of physics equations. They are used for a variety of purposes, from the study of
3760-572: The Earth as a single point and average outgoing energy. This can be expanded vertically (as in radiative-convective models), or horizontally. Finally, more complex (coupled) atmosphere–ocean– sea ice global climate models discretise and solve the full equations for mass and energy transfer and radiant exchange. Radiocarbon Carbon-14 , C-14 , C or radiocarbon , is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons . Its presence in organic matter
3854-554: The Earth during any given geologic period, beginning with the time of the Earth's formation. Since very few direct observations of climate were available before the 19th century, paleoclimates are inferred from proxy variables . They include non-biotic evidence—such as sediments found in lake beds and ice cores —and biotic evidence—such as tree rings and coral. Climate models are mathematical models of past, present, and future climates. Climate change may occur over long and short timescales due to various factors. Recent warming
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3948-685: The MWP and three cool phases, two of which could be related to the LIA . Other research in northeastern Japan showed that there was one warm and humid interval, from 750 to 1200, and two cold and dry intervals, from 1 to 750 and from 1200 to now. The Indian Summer Monsoon (ISM) was also enhanced during the MWP with a temperature driven change to the Atlantic Multi-decadal Oscillation (AMO), bringing more precipitation to India . Vegetation records in Lahaul in Himachal Pradesh confirm
4042-502: The MWP as the Medieval Climatic Anomaly to emphasize that climatic effects other than temperature were also important. The MWP was followed by a regionally cooler period in the North Atlantic and elsewhere, which is sometimes called the Little Ice Age (LIA). Possible causes of the MWP include increased solar activity, decreased volcanic activity, and changes in ocean circulation. Modelling evidence has shown that natural variability
4136-587: The MWP display a strong correlation with the North Atlantic Oscillation (NAO). The Norse colonization of the Americas has been associated with warmer periods. The common theory is that Norsemen took advantage of ice-free seas to colonize areas in Greenland and other outlying lands of the far north. However, a study from Columbia University suggests that Greenland was not colonized in warmer weather, but
4230-602: The MWP in the Southern Ocean lagged the MWP's onset in the North Atlantic by approximately 150 years. A sediment core from the eastern Bransfield Basin, in the Antarctic Peninsula , preserves climatic events from both the LIA and the MWP. The authors noted, "The late Holocene records clearly identify Neoglacial events of the LIA and Medieval Warm Period (MWP)." Some Antarctic regions were atypically cold, but others were atypically warm between 1000 and 1200. Corals in
4324-509: The MWP than during the LIA and 0.65 °C (1.2 °F) warmer than the decades before the study. The MWP has been noted in Chile in a 1500-year lake bed sediment core, as well as in the Eastern Cordillera of Ecuador . A reconstruction, based on ice cores, found that the MWP could be distinguished in tropical South America from about 1050 to 1300 and was followed in the 15th century by
4418-615: The MWP to LIA , was found for northeast and central-east China but not for northwest China and the Tibetan Plateau . During the MWP, the East Asian Summer Monsoon (EASM) was the strongest it has been in the past millennium and was highly sensitive to the El Niño Southern Oscillation (ENSO). The Mu Us Desert witness increased moisture in the MWP. Peat cores from peatland in southeast China suggest changes in
4512-710: The MWP was a global event was challenged by other researchers. The IPCC First Assessment Report of 1990 discussed the: Medieval Warm Period around 1000 CE (which may not have been global) and the Little Ice Age which ended only in the middle to late nineteenth century. It stated that temperatures in the: late tenth to early thirteenth centuries (about 950–1250 CE ) appear to have been exceptionally warm in western Europe, Iceland and Greenland. The IPCC Third Assessment Report from 2001 summarized newer research: evidence does not support globally synchronous periods of anomalous cold or warmth over this time frame, and
4606-470: The MWP while nearby islands experienced less precipitation leading to a decrease in peatland. Pollen data from this region indicates an expansion of warm climate vegetation with an increasing number of broadleaf and decreasing number of coniferous forests. Adhikari and Kumon (2001), investigating sediments in Lake Nakatsuna , in central Japan , found a warm period from 900 to 1200 that corresponded to
4700-541: The MWP, which the study defines as from 950 to 1250, with warmth in some regions exceeding temperatures of the 1990–2010 period. Much of the Northern Hemisphere showed a significant cooling during the LIA , which the study defines as from 1400 to 1700, but Labrador and isolated parts of the United States appeared to be approximately as warm as during the 1961–1990 period. Greenlandic winter oxygen isotope data from
4794-669: The MWP. Using sediment samples from Puerto Rico , the Gulf Coast , and the Atlantic Coast from Florida to New England , Mann et al. found consistent evidence of a peak in North Atlantic tropical cyclone activity during the MWP, which was followed by a subsequent lull in activity. Iceland was first settled between about 865 and 930, during a time believed to be warm enough for sailing and farming. By retrieval and isotope analysis of marine cores and from examination of mollusc growth patterns from Iceland , Patterson et al. reconstructed
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#17328518005364888-550: The Medieval Warm Period to have occurred between [... about 1050–1400 CE ] and to have been 0.75 °C [1.4 °F] warmer than the Current Warm Period. More evidence in New Zealand is from an 1100-year tree-ring record. Climate Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over
4982-545: The North Atlantic have been noticed. The nature and extent of the MWP has been marked by long-standing controversy over whether it was a global or regional event. In 2019, by using an extended proxy data set, the Pages-2k consortium confirmed that the Medieval Climate Anomaly was not a globally synchronous event. The warmest 51-year period within the MWP did not occur at the same time in different regions. They argue for
5076-441: The Northern Hemisphere. The transfer between the ocean shallow layer and the large reservoir of bicarbonates in the ocean depths occurs at a limited rate. In 2009 the activity of C was 238 Bq per kg carbon of fresh terrestrial biomatter, close to the values before atmospheric nuclear testing (226 Bq/kg C; 1950). The inventory of carbon-14 in Earth's biosphere is about 300 megacuries (11 E Bq ), of which most
5170-581: The Western United States. Aridity was more prevalent in the southeastern United States during the MWP than the following LIA, but only slightly; this difference may be statistically insignificant. Droughts in the MWP may have impacted Native American settlements also in the Eastern United States , such as at Cahokia . Review of more recent archaeological research shows that as the search for signs of unusual cultural changes has broadened, some of
5264-630: The above-ground nuclear tests of the 1950s and 1960s. Though the extra C generated by those nuclear tests has not disappeared from the atmosphere, oceans and biosphere, it is diluted due to the Suess effect . Carbon-14 is produced in coolant at boiling water reactors (BWRs) and pressurized water reactors (PWRs). It is typically released into the air in the form of carbon dioxide at BWRs, and methane at PWRs. Best practice for nuclear power plant operator management of carbon-14 includes releasing it at night, when plants are not photosynthesizing . Carbon-14
5358-579: The amount of C in tooth enamel , or the carbon-14 concentration in the lens of the eye. In 2019, Scientific American reported that carbon-14 from nuclear testing has been found in animals from one of the most inaccessible regions on Earth, the Mariana Trench in the Pacific Ocean. The concentration of C in atmospheric CO 2 , reported as the C/ C ratio with respect to a standard, has (since about 2022) declined to levels similar to those prior to
5452-425: The amount of C in the atmosphere and subsequently the biosphere; after the tests ended, the atmospheric concentration of the isotope began to decrease, as radioactive CO 2 was fixed into plant and animal tissue, and dissolved in the oceans. One side-effect of the change in atmospheric C is that this has enabled some options (e.g. bomb-pulse dating ) for determining the birth year of an individual, in particular,
5546-462: The amount of solar energy retained by the planet, leading to global warming or global cooling . The variables which determine climate are numerous and the interactions complex, but there is general agreement that the broad outlines are understood, at least insofar as the determinants of historical climate change are concerned. Climate classifications are systems that categorize the world's climates. A climate classification may correlate closely with
5640-422: The atmosphere. C and C are both stable; C is unstable, with half-life 5700 ± 30 years. Carbon-14 has a specific activity of 62.4 mCi/mmol (2.31 GBq/mmol), or 164.9 GBq/g. Carbon-14 decays into nitrogen-14 ( N ) through beta decay . A gram of carbon containing 1 atom of carbon-14 per 10 atoms, emits ~0.2 beta (β) particles per second. The primary natural source of carbon-14 on Earth
5734-426: The causes of climate, and empiric methods, which focus on the effects of climate. Examples of genetic classification include methods based on the relative frequency of different air mass types or locations within synoptic weather disturbances. Examples of empiric classifications include climate zones defined by plant hardiness , evapotranspiration, or more generally the Köppen climate classification which
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#17328518005365828-409: The climate became colder and stormier around 1250, their diet steadily shifted towards ocean sources. By around 1300, seal hunting provided over three quarters of their food. By 1350, there was reduced demand for their exports, and trade with Europe fell away. The last document from the settlements dates from 1412, and over the following decades, the remaining Europeans left in what seems to have been
5922-411: The consequences of increasing greenhouse gases in the atmosphere, primarily carbon dioxide (see greenhouse gas ). These models predict an upward trend in the global mean surface temperature , with the most rapid increase in temperature being projected for the higher latitudes of the Northern Hemisphere. Models can range from relatively simple to quite complex. Simple radiant heat transfer models treat
6016-543: The context of environmental policy , the term "climate change" often refers only to changes in modern climate, including the rise in average surface temperature known as global warming . In some cases, the term is also used with a presumption of human causation, as in the United Nations Framework Convention on Climate Change (UNFCCC). The UNFCCC uses "climate variability" for non-human caused variations. Earth has undergone periodic climate shifts in
6110-406: The conventional terms of 'Little Ice Age' and 'Medieval Warm Period' are chiefly documented in describing northern hemisphere trends in hemispheric or global mean temperature changes in past centuries. Global temperature records taken from ice cores, tree rings , and lake deposits have shown that the Earth may have been slightly cooler globally (by 0.03 °C or 0.1 °F) than in the early and
6204-421: The date of death or fixation can be estimated. The initial C level for the calculation can either be estimated, or else directly compared with known year-by-year data from tree-ring data ( dendrochronology ) up to 10,000 years ago (using overlapping data from live and dead trees in a given area), or else from cave deposits ( speleothems ), back to about 45,000 years before present. A calculation or (more accurately)
6298-536: The decay of radioactive material in surrounding geologic strata. In connection with building the Borexino solar neutrino observatory, petroleum feedstock (for synthesizing the primary scintillant) was obtained with low C content. In the Borexino Counting Test Facility, a C/ C ratio of 1.94×10 was determined; probable reactions responsible for varied levels of C in different petroleum reservoirs , and
6392-674: The distant past. Carbon-14 is produced in the upper troposphere and the stratosphere by thermal neutrons absorbed by nitrogen atoms. When cosmic rays enter the atmosphere, they undergo various transformations, including the production of neutrons . The resulting neutrons (n) participate in the following n-p reaction (p is proton ): The highest rate of carbon-14 production takes place at altitudes of 9 to 15 kilometres (30,000 to 49,000 ft) and at high geomagnetic latitudes . The rate of C production can be modeled, yielding values of 16,400 or 18,800 atoms of C per second per square meter of Earth's surface, which agrees with
6486-583: The dynamics of the weather and climate system to projections of future climate. All climate models balance, or very nearly balance, incoming energy as short wave (including visible) electromagnetic radiation to the Earth with outgoing energy as long wave (infrared) electromagnetic radiation from the Earth. Any imbalance results in a change in the average temperature of the Earth. Climate models are available on different resolutions ranging from >100 km to 1 km. High resolutions in global climate models require significant computational resources, and so only
6580-418: The early patterns (such as violence and health problems) have been found to be more complicated and regionally varied than had been previously thought. Other patterns, such as settlement disruption, deterioration of long-distance trade, and population movements, have been further corroborated. The climate in equatorial eastern Africa has alternated between being drier than today and relatively wet. The climate
6674-557: The global carbon budget that can be used to backtrack, but attempts to measure the production time directly in situ were not very successful. Production rates vary because of changes to the cosmic ray flux caused by the heliospheric modulation (solar wind and solar magnetic field), and, of great significance, due to variations in the Earth's magnetic field . Changes in the carbon cycle however can make such effects difficult to isolate and quantify. Occasional spikes may occur; for example, there
6768-421: The global temperature and produce an interglacial period. Suggested causes of ice age periods include the positions of the continents , variations in the Earth's orbit, changes in the solar output, and volcanism. However, these naturally caused changes in climate occur on a much slower time scale than the present rate of change which is caused by the emission of greenhouse gases by human activities. According to
6862-578: The lower C levels in methane, have been discussed by Bonvicini et al. Since many sources of human food are ultimately derived from terrestrial plants, the relative concentration of C in human bodies is nearly identical to the relative concentration in the atmosphere. The rates of disintegration of potassium-40 ( K) and C in the normal adult body are comparable (a few thousand decays per second). The beta decays from external (environmental) radiocarbon contribute about 0.01 mSv /year (1 mrem/year) to each person's dose of ionizing radiation . This
6956-458: The maximum distance traveled is estimated to be 22 cm in air and 0.27 mm in body tissue. The fraction of the radiation transmitted through the dead skin layer is estimated to be 0.11. Small amounts of carbon-14 are not easily detected by typical Geiger–Müller (G-M) detectors ; it is estimated that G-M detectors will not normally detect contamination of less than about 100,000 decays per minute (0.05 μCi). Liquid scintillation counting
7050-653: The mean temperature of that time) during the MWP (about 950–1250) and the Little Ice Age (about 1400–1700, with cold periods persisting into the early 20th century), which are possibly related to changes in the strength of North Atlantic thermohaline circulation . Sediments in Piermont Marsh of the lower Hudson Valley show a dry MWP from 800 to 1300. In the Hammock River marsh in Connecticut , salt marshes extended 15 kilometres (9.3 mi) farther westward than they do in
7144-539: The mid-20th century. Palaeoclimatologists developing region-specific climate reconstructions of past centuries conventionally label their coldest interval as "LIA" and their warmest interval as the "MWP". Others follow the convention, and when a significant climate event is found in the "LIA" or "MWP" timeframes, they associate their events to the period. Some "MWP" events are thus wet events or cold events, rather than strictly warm events, particularly in central Antarctica , where climate patterns that are opposite to those of
7238-456: The modern time scale, their observation frequency, their known error, their immediate environment, and their exposure have changed over the years, which must be considered when studying the climate of centuries past. Long-term modern climate records skew towards population centres and affluent countries. Since the 1960s, the launch of satellites allow records to be gathered on a global scale, including areas with little to no human presence, such as
7332-404: The most common atmospheric variables (air temperature, pressure, precipitation and wind), other variables such as humidity, visibility, cloud amount, solar radiation, soil temperature, pan evaporation rate, days with thunder and days with hail are also collected to measure change in climate conditions. The difference between climate and weather is usefully summarized by the popular phrase "Climate
7426-425: The neutrons in carbon-14 decays to a proton and the carbon-14 ( half-life of 5700 ± 30 years ) decays into the stable (non-radioactive) isotope nitrogen-14 . As usual with beta decay, almost all the decay energy is carried away by the beta particle and the neutrino. The emitted beta particles have a maximum energy of about 156 keV, while their weighted mean energy is 49 keV. These are relatively low energies;
7520-705: The other hand, periodic variability occurs relatively regularly and in distinct modes of variability or climate patterns. There are close correlations between Earth's climate oscillations and astronomical factors ( barycenter changes, solar variation , cosmic ray flux, cloud albedo feedback , Milankovic cycles ), and modes of heat distribution between the ocean-atmosphere climate system. In some cases, current, historical and paleoclimatological natural oscillations may be masked by significant volcanic eruptions , impact events , irregularities in climate proxy data, positive feedback processes or anthropogenic emissions of substances such as greenhouse gases . Over
7614-402: The past state of the climate. It demonstrates periods of stability and periods of change and can indicate whether changes follow patterns such as regular cycles. Details of the modern climate record are known through the taking of measurements from such weather instruments as thermometers , barometers , and anemometers during the past few centuries. The instruments used to study weather over
7708-462: The past, including four major ice ages . These consist of glacial periods where conditions are colder than normal, separated by interglacial periods. The accumulation of snow and ice during a glacial period increases the surface albedo , reflecting more of the Sun's energy into space and maintaining a lower atmospheric temperature. Increases in greenhouse gases , such as by volcanic activity , can increase
7802-508: The poles in latitude in response to shifting climate zones." Climate (from Ancient Greek κλίμα 'inclination') is commonly defined as the weather averaged over a long period. The standard averaging period is 30 years, but other periods may be used depending on the purpose. Climate also includes statistics other than the average, such as the magnitudes of day-to-day or year-to-year variations. The Intergovernmental Panel on Climate Change (IPCC) 2001 glossary definition
7896-450: The present day, was even drier during the MWP. Prolonged drought was a mainstay of the Arabian climate until around 660 BP, when this hyperarid interval was terminated. There is an extreme scarcity of data from Australia for both the MWP and the LIA . However, evidence from wave-built shingle terraces for a permanently-full Lake Eyre during the 9th and the 10th centuries is consistent with
7990-609: The present due to higher sea levels. Prolonged droughts affected many parts of what is now the Western United States , especially eastern California and the west of Great Basin . Alaska experienced three intervals of comparable warmth: 1–300, 850–1200, and since 1800. Knowledge of the MWP in North America has been useful in dating occupancy periods of certain Native American habitation sites, especially in arid parts of
8084-486: The thirty-year period from 1901 to 1930 as the reference time frame for climatological standard normals. In 1982, the WMO agreed to update climate normals, and these were subsequently completed on the basis of climate data from 1 January 1961 to 31 December 1990. The 1961–1990 climate normals serve as the baseline reference period. The next set of climate normals to be published by WMO is from 1991 to 2010. Aside from collecting from
8178-458: The total carbon dioxide in a given region of Earth's atmosphere . Dating a specific sample of fossilized carbonaceous material is more complicated. Such deposits often contain trace amounts of C. These amounts can vary significantly between samples, ranging up to 1% of the ratio found in living organisms (an apparent age of about 40,000 years). This may indicate contamination by small amounts of bacteria, underground sources of radiation causing
8272-528: The tropical Pacific Ocean suggest that relatively cool and dry conditions may have persisted early in the millennium, which is consistent with a La Niña -like configuration of the El Niño-Southern Oscillation patterns. In 2013, a study from three US universities was published in Science magazine and showed that the water temperature in the Pacific Ocean was 0.9 °C (1.6 °F) warmer during
8366-428: The variability or average state of the atmosphere over time scales ranging from decades to millions of years. These changes can be caused by processes internal to the Earth , external forces (e.g. variations in sunlight intensity) or human activities, as found recently. Scientists have identified Earth's Energy Imbalance (EEI) to be a fundamental metric of the status of global change. In recent usage, especially in
8460-536: The warming effect in fact lasted for only very briefly. Around 1000 CE the climate was sufficiently warm for the Vikings to journey to Newfoundland and to establish a short-lived outpost there. Around 985, Vikings founded the Eastern and Western Settlements , both near the southern tip of Greenland. In the colony's early stages, they kept cattle, sheep, and goats, with around a quarter of their diet from seafood. After
8554-462: The warming from the 10th to the 14th centuries in some regions might be comparable in magnitude to the warming of the last few decades of the 20th century, which was unprecedented within the past 500 years. Generally, a warming period was identified in China, coinciding with the MWP, using multi-proxy data for temperature. However, the warming was inconsistent across China. Significant temperature change, from
8648-448: The years, the definitions of climate variability and the related term climate change have shifted. While the term climate change now implies change that is both long-term and of human causation, in the 1960s the word climate change was used for what we now describe as climate variability, that is, climatic inconsistencies and anomalies. Climate change is the variation in global or regional climates over time. It reflects changes in
8742-456: Was drier during the MWP (1000–1270). Off the coast of Africa, Isotopic analysis of bones from the Canary Islands' inhabitants during the MWP to LIA transition reveal the region experienced a 5 °C (9.0 °F) decrease in air temperature. Over this period, the diet of inhabitants did not appreciably change, which suggests they were remarkably resilient to climate change . The onset of
8836-533: Was originally designed to identify the climates associated with certain biomes . A common shortcoming of these classification schemes is that they produce distinct boundaries between the zones they define, rather than the gradual transition of climate properties more common in nature. Paleoclimatology is the study of past climate over a great period of the Earth 's history. It uses evidence with different time scales (from decades to millennia) from ice sheets, tree rings, sediments, pollen, coral, and rocks to determine
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