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External forcings include natural phenomena such as volcanic eruptions and variations in the sun's output.
Radiative forcing is a measure of how various factors alter the energy balance of the Earth's atmosphere. Between the start of the Industrial Revolution inand the yearthe increase in the atmospheric concentration of carbon dioxide chemical formula: CO2 led to a positive radiative forcing, averaged over the Earth's surface areaof about 1.
The climate system will vary in response to changes in forcings. This internal variability is a result of complex interactions between components of the climate system, such as the coupling between the atmosphere and ocean see also the later section on Internal climate variability and global warming.
Human factors include the emissions of heat-trapping "greenhouse" gases and particulates as well as clearing of forests and other land-use changes. Attribution requires demonstrating that a signal is: Key attributions Greenhouse gases Carbon dioxide is the primary greenhouse gas that is contributing to recent climate change.
The Kyoto Protocol lists these together with hydrofluorocarbon HFCsperfluorocarbons PFCsand sulfur hexafluoride SF6 which are entirely artificial gases, as contributors to radiative forcing.
The chart at right attributes anthropogenic greenhouse gas emissions to eight Changes in land use pattern economic sectors, of which the largest contributors are power stations many of which burn coal or other fossil fuelsindustrial processes, transportation fuels generally fossil fuelsand agricultural by-products mainly methane from enteric fermentation and nitrous oxide from fertilizer use.
However, on a global scale, the concentration of water vapor is controlled by temperature, which influences overall rates of evaporation and precipitation. Between andabout two-thirds of anthropogenic CO2 emissions were produced from burning fossil fuels, and about one-third of emissions from changes in land use,  primarily deforestation.
A second reason that climate change has been attributed to land use is that the terrestrial albedo is often altered by use, which leads to radiative forcing.
This effect is more significant locally than globally. Aerosols produced are primarily black carbon.
Over the past years human activities have released increasing quantities of greenhouse gases into the atmosphere. This has led to increases in mean global temperature, or global warming. Other human effects are relevant—for example, sulphate aerosols are believed to have a cooling effect.
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.
The phrase "balance of evidence" suggested the English common-law standard of proof required in civil as opposed to criminal courts: In 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".
Evidence of the effect of external influences, both anthropogenic and natural, on the climate system has continued to accumulate since the TAR. The warming occurred in both the ocean and the atmosphere and took place at a time when natural external forcing factors would likely have produced cooling.
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.
This conclusion rests on multiple lines of evidence. Like the warming "signal" that has gradually emerged from the "noise" of natural climate variability, the scientific evidence for a human influence on global climate has accumulated over the past several decades, from many hundreds of studies.
No single study is a " smoking gun. The second line of evidence is from indirect estimates of climate changes over the last 1, to 2, years.
These records are obtained from living things and their remains like tree rings and corals and from physical quantities like the ratio between lighter and heavier isotopes of oxygen in ice coreswhich change in measurable ways as climate changes.
The lesson from these data is that global surface temperatures over the last several decades are clearly unusual, in that they were higher than at any time during at least the past years.
For the Northern Hemispherethe recent temperature rise is clearly unusual in at least the last 1, years see graph opposite. For example, when climate models are run with historical increases in greenhouse gases, they show gradual warming of the Earth and ocean surface, increases in ocean heat content and the temperature of the lower atmosphere, a rise in global sea level, retreat of sea ice and snow cover, cooling of the stratospherean increase in the amount of atmospheric water vapor, and changes in large-scale precipitation and pressure patterns.population change on land sue patterns while chapter five presents the root causes of land use change.
The change is presented as a culmination of the land tenure problem. global terrestrial land surface and has degraded about 60% of the ecosystems services in the past 50 years alone.
Land use and land cover (LUCC) change has been the most visible indicator of the human footprint and the most important driver of loss of biodiversity and other forms of land degradation.
Land use change • I = PAT relationship that considers environmental impact (I) to be a function of population (P), affluence (A), and technology (T) (Commoner ). patterns and processes of land use and land management change, and their root causes. Historical patterns of land use change were examined in six sites in three countries, Kenya, Tanzania and.
A variance is a deviation from the set of rules a municipality applies to land use and land development, typically a zoning ordinance, building code or municipal benjaminpohle.com manner in which variances are employed can differ greatly depending on the municipality.A variance may also be known as a standards variance, referring to the development standards .
pattern changes from the one seen in richer countries. The land use pattern in poorer countries is not that simple: · the closest ring to the CBD isn't a zone of old industry and cheap housing.