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Attribution of recent climate change

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	Topics Attribution of recent climate change Topic Home Attribution of recent climate change is the effort to scientifically ascertainScientific method Overview Scientific method is a body of techniques for investigating phenomena and acquiring new knowledge, as well as for correcting... mechanisms responsible for relatively recent changes observed in the EarthEarth Earth is the third planet in the solar system in terms of distance from the Sun, and the fifth largest.... 's climateClimate The climate is commonly considered to be the weather averaged over a long period of time, typically 30 years.... . The effort has focused on changes observed during the period of instrumental temperature recordInstrumental temperature record The instrumental temperature record shows the fluctuations of the temperature of the atmosphere and the oceans since the inv... , when records are most reliable; particularly on the last 50 years, when human activity has grown fastest and observations of the upper atmosphere have become available. The dominant mechanisms to which recent climate change has been attributed all result from human activity. They are: increasing atmosphericFacts About Atmosphere Atmosphere is the general name for a layer of gases that may surround a material body of sufficient mass.... concentrations of greenhouse gasGreenhouse gas Greenhouse gases are gaseous components of the atmosphere that contribute to the "greenhouse effect".... es global changes to land surface, such as deforestationDeforestation The conversion of forested areas to non-forest.... increasing atmospheric concentrations of aerosolAerosol Summary Aerosol, short for aerial solid, may refer to... s. Recent reports from the Intergovernmental Panel on Climate ChangeIntergovernmental Panel on Climate Change The Intergovernmental Panel on Climate Change was established in 1988 by two United Nations organizations, the World Meteor... (IPCC) report have concluded that: "Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenicAnthropogenic Anthropogenic effects or processes are those that are derived from human activities, as opposed to effects or processes that... greenhouse gasGreenhouse gas Greenhouse gases are gaseous components of the atmosphere that contribute to the "greenhouse effect".... concentrations." "From new estimates of the combined anthropogenic forcingRadiative forcing general concept, the term radiative forcing in climate science means any change in the radiation entering or leaving the cli... due to greenhouse gases, aerosolAerosol Aerosol, short for aerial solid, may refer to... s, and land surface changesLand use A land use is the activity land is used for.... , it is extremely likely that human activities have exerted a substantial net warming influence on climate since 1750." "It is virtually certain that anthropogenic aerosols produce a net negative radiative forcingRadiative forcing general concept, the term radiative forcing in climate science means any change in the radiation entering or leaving the cli... (cooling influence) with a greater magnitude in the Northern HemisphereNorthern Hemisphere Summary The Northern Hemisphere is the half of a planet's surface that is north of the equator .... than in the Southern HemisphereSouthern Hemisphere The Southern Hemisphere is the half of a planet's surface that is south of the equator.... . The panel, which represents consensusScientific opinion on climate change Statements by organizationsVarious prominent bodies have commented on global warming, most notably the Intergovernmental Panel on... in the scientific communityScientific community The scientific community consists of the total body of scientists, its relationships and interactions.... , defines "very likely," "extremely likely," and "virtually certain" as indicating probabilities greater than 90%, 95%, and 99%, respectively. Key attributions Greenhouse gases Scientific consensus has identified carbon dioxideCarbon dioxide Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms.... as the dominant greenhouse gasGreenhouse gas Greenhouse gases are gaseous components of the atmosphere that contribute to the "greenhouse effect".... forcing. (The dominant greenhouse gas overall is water vaporWater vapor Water vapor, also aqueous vapor, is the gas phase of water.... . Water vapor, however, has a very short atmospheric lifetime (about 10 days) and is very nearly in a dynamic equilibrium in the atmosphere, so it is not a forcingRadiative forcing general concept, the term radiative forcing in climate science means any change in the radiation entering or leaving the cli... gas in the context of global warming.) MethaneMethane The simplest hydrocarbon, methane, is a gas with a chemical formula of CH4.... and nitrous oxideNitrous oxide Nitrous oxide, also known as dinitrogen oxide or dinitrogen monoxide, is a chemical compound with chemical formu... are also major forcing contributors to the greenhouse effectGreenhouse effect The greenhouse effect, first discovered by Joseph Fourier in 1824, and first investigated quantitatively by Svante Arrhenius... . The Kyoto ProtocolKyoto Protocol The Kyoto Protocol to the United Nations Framework Convention on Climate Change is an amendment to the international treaty ... lists these together with Hydrofluorocarbons (HFCs), Perfluorocarbons (PFCs), and Sulphur hexafluoride (SF6), which are entirely artificial (i.e. anthropogenic) gases which also contribute to radiative forcing in the atmosphere. The chart at right attributes anthropogenic greenhouse gas emissions to eight main economic sectors, of which the largest contributors are power stations (many of which burn coalCoal Coal is a fossil fuel extracted from the ground by underground mining or open-pit mining .... or other fossil fuelFacts About Fossil fuel Fossil fuels are hydrocarbons formed from the remains of dead plants and animals.... s), industrialIndustry An industry is generally any grouping of businesses that share a common method of generating profits, such as the "music ind... processes (among which cementCement In the most general sense of the word, cement is a binder, a substance which sets and hardens independently, and can bind ot... production is a dominant contributor), transportation fuelFuel Fuel is any material that is capable of releasing energy when its chemical or physical structure is changed or converted.... s (generally fossil fuelFossil fuel Fossil fuels are hydrocarbons formed from the remains of dead plants and animals.... s), and agriculturalAgriculture Farming redirects here. For Farming in computer games, see Farmer .... by-products (mainly methane from enteric fermentationEnteric fermentation Enteric fermentation is fermentation that takes place in the digestive systems of animals.... and nitrous oxide from fertilizerFertilizer Overview Fertilizers or fertilisers are compounds given to plants with the intention of promoting growth; they are usually app... use). Land use Climate change is attributed to land useLand use A land use is the activity land is used for.... for two main reasons. While 66% of anthropogenic CO₂Carbon dioxide Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms.... emissions over the last 250 years have resulted from burning fossil fuels, 33% have resulted from changes in land use, primarily deforestationDeforestation The conversion of forested areas to non-forest.... . Deforestation both reduces the amount of carbon dioxide absorbed by deforested regions and releases greenhouse gases directly, together with aerosols, through biomass burningSlash and burn Slash and burn is an agricultural procedure widely used in forested areas.... that frequently accompanies it. A second reason that climate change has been attributed to land use is that the terrestrial albedoAlbedo Albedo is a ratio of scattered to incident electromagnetic radiation power, most commonly light.... is often altered by use, which leads to radiative forcingRadiative forcing general concept, the term radiative forcing in climate science means any change in the radiation entering or leaving the cli... . This effect is more significant locally than globally. Livestock and land use Worldwide, livestock production occupies 70% of all land used for agriculture, or 30% of the ice-free land surface of the Earth. Scientists attribute more than 18% of anthropogenic greenhouse gas emissions to livestock and livestock-related activities such as deforestation and increasingly fuel-intensive farming practices. Specific attributions to the livestock sector include: 9% of global carbon dioxideCarbon dioxide Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms.... emissions 35-40% of global methaneMethane The simplest hydrocarbon, methane, is a gas with a chemical formula of CH4.... emissions (chiefly due to enteric fermentationEnteric fermentation Enteric fermentation is fermentation that takes place in the digestive systems of animals.... and manureManure Manure is organic matter used as fertilizer in agriculture.... ) 64% of global nitrous oxideNitrous oxide Nitrous oxide, also known as dinitrogen oxide or dinitrogen monoxide, is a chemical compound with chemical formu... emissions, chiefly as a result of fertilizerFertilizer Fertilizers or fertilisers are compounds given to plants with the intention of promoting growth; they are usually app... use. Attribution of 20th century climate change Over the past 150 years human activities have released increasing quantities of greenhouse gasGreenhouse gas Greenhouse gases are gaseous components of the atmosphere that contribute to the "greenhouse effect".... es into the atmosphereEarth's atmosphere Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity.... . This has led to increases in mean global temperature, or global warmingGlobal warming Global warming is the observed increase in the average temperature of the Earth's atmosphere and oceans in recent decades.... . Other human effects are relevant—for example, sulphate aerosolParticulate Particulates, alternatively referred to as particulate matter, aerosols or fine particles, are tiny particles of... s are believed to lead to cooling—and natural factors also contribute. According to the historical temperature record of the last century, the Earth's near-surface air temperature has risen around 0.74 ±Plus-minus sign The plus-minus sign is a mathematical symbol commonly used to indicate the precision of an approximation, or as a convenient... 0.18 °CelsiusCelsius The Celsius scale is a temperature scale named after the Swedish astronomer Anders Celsius , who first proposed a similar sy... (1.3 ± 0.32 °FahrenheitFahrenheit Overview Fahrenheit is a temperature scale named after the German physicist Gabriel Fahrenheit , who proposed it in 1724.... ). A historically important question in climate change research has regarded the relative importance of human activity and non-anthropogenicAnthropogenic Anthropogenic effects or processes are those that are derived from human activities, as opposed to effects or processes that... causes during the period of instrumental recordInstrumental temperature record The instrumental temperature record shows the fluctuations of the temperature of the atmosphere and the oceans since the inv... . In the 1995 Second Assessment Report (SAR), the IPCCIntergovernmental Panel on Climate Change Overview The Intergovernmental Panel on Climate Change was established in 1988 by two United Nations organizations, the World Meteor... made the widely-quoted statement that "The balance of evidence suggests a discernible human influence on global climate". The phrase "balance of evidence" suggested the (English) common-law standard of proof required in civil as opposed to criminal courts: not as high as "beyond reasonable doubt". In 2001 the Third Assessment Report (TAR) refined this, saying "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities". The 2007 fourth assessment report (WG1 AR4) strengthened this finding: "Anthropogenic warming of the climate system is widespread and can be detected in temperature observations taken at the surface, in the free atmosphere and in the oceans. Evidence of the effect of external influences, both anthropogenic and natural, on the climate system has continued to accumulate since the TAR." Over the past five decades there has been a global warming of approximately 0.65 °C (1.17 °F) at the Earth's surface (see historical temperature record). Among the possible factors that could produce changes in global mean temperature are internal variability of the climate system, external forcing, an increase in concentration of greenhouse gases, or any combination of these. Current studies indicate that the increase in greenhouse gases, most notably CO₂, is mostly responsible for the observed warming. Evidence for this conclusion includes: Estimates of internal variability from climate models, and reconstructions of past temperatures, indicate that the warming is unlikely to be entirely natural. Climate models forced by natural factors and increased greenhouse gases and aerosols reproduce the observed global temperature changes; those forced by natural factors alone do not. "Fingerprint" methods indicate that the pattern of change is closer to that expected from greenhouse gas-forced change than from natural change. The plateau in warming from the 1940s to 1960s can be attributed largely to sulphate aerosol cooling. In 2001, the U.S. National Academy of SciencesUnited States National Academy of Sciences The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the... released a report supporting the IPCC’s conclusions regarding the causes of recent climate change. It stated, "Greenhouse gases are accumulating in Earth’s atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise. Temperatures are, in fact, rising. The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes are also a reflection of natural variability." Detection vs. attribution Detection and attribution of climate signals, as well as its common-sense meaning, has a more precise definition within the climate change literature, as expressed by the IPCC. Detection of a signal requires demonstrating that an observed change is statistically significantly different from that which can be explained by natural internal variability. Attribution requires demonstrating that a signal is: unlikely to be due entirely to internal variability; consistent with the estimated responses to the given combination of anthropogenic and natural forcing not consistent with alternative, physically plausible explanations of recent climate change that exclude important elements of the given combination of forcings. Detection does not imply attribution, and is easier than attribution. Unequivocal attribution would require controlled experiments with multiple copies of the climate system, which is not possible. Attribution, as described above, can therefore only be done within some margin of error. For example, the IPCC's Fourth Assessment ReportIPCC Fourth Assessment Report The Fourth Assessment Report of the IPCC is the next in line of a series of authoritative reports on climate change by the I... says "it is extremely likely that human activities have exerted a substantial net warming influence on climate since 1750," where "extremely likely" indicates a probability greater than 95%. Following the publication of the Third Assessment Report (TAR) in 2001, "detection and attribution" of climate change has remained an active area of research. Some important results include: A review of detection and attribution studies by the International Ad HocAd hoc *Ad hoc* is a Latin phrase which means "for this [purpose]." It generally signifies a solution that has been tailored to a... Detection and Attribution Group found that "natural drivers such as solar variability and volcanic activity are at most partially responsible for the large-scale temperature changes observed over the past century, and that a large fraction of the warming over the last 50 yr can be attributed to greenhouse gas increases. Thus, the recent research supports and strengthens the IPCC Third Assessment Report conclusion that 'most of the global warming over the past 50 years is likely due to the increase in greenhouse gases.'" Multiple independent reconstructions of the temperature record of the past 1000 yearsTemperature record of the past 1000 years The temperature record of the past 1000 years describes the reconstruction of temperature for the last 1000 years on the Nor... confirm that the late 20th century is probably the warmest period in that time Two papers in Science in August 2005 resolve the problem, evident at the time of the TAR, of troposphericFacts About Troposphere The Troposphere is the lowermost portion of Earth's atmosphere.... temperature trends. The UAH version of the record contained errors, and there is evidence of spurious cooling trends in the radiosonde record, particularly in the tropics. See satellite temperature measurementsSatellite temperature measurements Satellites have been sensing the temperature of the troposphere since 1979; the usable balloon record begins in 1958.... for details; and the 2006 US CCSP report. Barnett and colleagues say that the observed warming of the oceans "cannot be explained by natural internal climate variability or solar and volcanic forcing, but is well simulated by two anthropogenicAnthropogenic Anthropogenic effects or processes are those that are derived from human activities, as opposed to effects or processes that... ally forced climate models," concluding that "it is of human origin, a conclusion robust to observational sampling and model differences" Bratcher and Giese observed conditions that "could be an indication of a climate regime shift to pre-1976 conditions." Bratcher and Giese conclude: "The results presented here do not preclude the possibility that anthropogenic sources of greenhouse gases have contributed to global warming. However the results do indicate that the human forced portion of global warming may be less than previously described." Findings that complicate attribution to CO₂ Warming sometimes leads CO₂ increases Factors other than increased CO₂ concentrations can initiate warming or cooling episodes (see e.g., orbital forcingOrbital forcing Orbital forcing, or Milankovitch theory, describes the effect on climate of slow changes in the tilt of the Earth's ax... ). The ice core record shows that on some occasions temperature starts rising hundreds of years before CO₂ increases. Such results confirm that the relationship between CO₂ and climate can go in both directions: changes in CO₂ concentrations affect climate, while changes in climate can affect CO₂ concentrations. One proposed mechanism for this effect is increased release of sequestered CO₂ from oceans as circulation patterns shift, perhaps abruptly, in response to climate change. A more speculative and polemical inference sometimes drawn is that the causal relationship between temperature rises and global CO₂ concentrations is only one-way, so that historical increases in CO₂ have been nothing more than the product of independently rising temperatures. However, a strictly "one-way" view of the relationship between CO₂ and temperature contradicts basic results in physics, specifically the fact that the absorption and emission of infrared radiation by CO₂ increases as its atmospheric concentration increases. First principles as well as empirical observation suggest that positive feedbacks from CO₂ concentrations amplify warming initially caused by other factors: Close analysis of the relationship between the two curves [i.e., temperature and CO₂] shows that, within the uncertainties of matching their timescales, the temperature led by a few centuries. This is expected, since it was changes in the Earth’s orbital parameters (including the shape of its orbit around the Sun, and the tilt of Earth’s axis) that caused the small initial temperature rise. This then raised atmospheric CO2 levels, in part by outgassing from the oceans, causing the temperature to rise further. By amplifying each other’s response, this “positive feedback” can turn a small initial perturbation into a large climate change. There is therefore no surprise that the temperature and CO2 rose in parallel, with the temperature initially in advance. In the current case, the situation is different, because human actions are raising the CO2 level, and we are starting to observe the temperature response. Present CO₂ levels greatly exceed the range found in the ice core data. Isotopic analysis of atmospheric CO₂ confirms that fossil fuel burning is the source of most of the CO₂ increase, unlike during prior interglacial periods. As noted above, models that include increased CO₂ levels when simulating recent climate match the observed data far better than those that do not. Warming on other planets? Over the last two decades proxy evidence of local or planetary warming has been observed on MarsMars Mars is the fourth planet from the Sun in our solar system and is named after Mars, the Roman god of war.... , PlutoFacts About Pluto Pluto is the second-largest known dwarf planet in the solar system.... , JupiterJupiter Jupiter is the fifth planet from the Sun and the largest within the solar system.... , and NeptuneNeptune Neptune is the eighth and outermost planet in our solar system.... 's largest moon TritonTriton (moon) Triton , or Neptune I, is the planet Neptune's largest moon.... . It has sometimes been asserted in the popular press that this points to a solar explanation for the recent warming on Earth. Physicist Khabibullo AbdusamatovKhabibullo Abdusamatov Khabibullo Ismailovich Abdusamatov is the supervisor of the project of the Russian section of the International Space Stat... claims that solar variationSolar variation Solar variations are fluctuations in the amount of energy emitted by the Sun.... has caused global warming on Earth, and that the coincident warmings "can only be a straightline consequence of the effect of the one same factor: a long-time change in solar irradiance." This view is not accepted by other scientists. Planetary physicist Colin Wilson responded, "His views are completely at odds with the mainstream scientific opinion," and climate scientist Amato Evan stated, "the idea just isn't supported by the theory or by the observations." Charles Long of Pacific Northwest National LaboratoryPacific Northwest National Laboratory The Pacific Northwest National Laboratory is one of nine United States Department of Energy multiprogram national laboratori... , who studies radiative transfer, says "That's nuts...It doesn't make physical sense that that's the case." Jay PasachoffFacts About Jay Pasachoff Jay Myron Pasachoff is an American astronomer.... , an astronomy professor at Williams CollegeWilliams College Williams College is a private, coeducational, highly selective liberal arts college located in Williamstown, Massachusetts.... , said that Pluto's global warming was "likely not connected with that of the Earth. The major way they could be connected is if the warming was caused by a large increase in sunlight. But the solar constant—the amount of sunlight received each second—is carefully monitored by spacecraft, and we know the Sun's output is much too steady to be changing the temperature of Pluto." Instead, scientific opinion is that these changes are caused by other factors, such as orbital irregularities or (in the case of Mars) changes in albedoAlbedo Overview Albedo is a ratio of scattered to incident electromagnetic radiation power, most commonly light.... as a result of dust storms. See also Aviation and climate changeAviation and climate change Overview Aviation contributes to global warming in a number of ways, the most significant of which is the combustion of kerosene in flight.... External links - Blog on current climate change issues by active climatologists "The Climate of Man", The New Yorker (2005): , , by Shaviv by Mike Lockwood and Claus Frohlich