Climate variability and change: Difference between revisions

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The term climate change is used to refer to changes in the Earth's climate. Generally, this is taken to mean changes in the temperature, though 'climate' encompasses many other variables (precipitation, clouds, etc). 'Climate change' includes natural and anthropogenic forcing; 'global warming' is usually used to mean changes with predominantly anthropogenic forcing.

For information on climate change over various periods, and the data sources available, see historical temperature record

Climate change factors

Climate changes occur due to internal and external, natural and anthropogenic factors. Internal factors are factors associated with the complexity of the climate systems which are chaotic non-linear dynamic systems. External factors can be natural factors (such as increased solar radiation) and anthropogenic factors (due to human actions).

Natural Factors

The main natural external factor is the variability in the amount, and geographic and temporal distribution of, solar radiation that reaches Earth. The solar radiation can change on short (yearly to century) timescales because of solar cycles and on century to millenial timescales because of cyclic changes in Earth's orbit. On much longer (hundreds of millions of years) timescales, the Sun is getting hotter.

It is clear that natural external factors have caused significant climate changes in the past, and it is probable that internal factors have too.

The Medieval Warm Period was caused by internal factors and natural external factors only. The subsequent Little Ice Age is usually attributed to the reduction of solar activity. Some scientists have claimed that the observed warming since 1860 is a natural climate recovery from the Little Ice Age. (Source: The Skeptical Environmentalist)

Human Factors

Anthropogenic factors are acts by humans (Homo sapiens) that change the environment and influence the climate.

The main anthropogenic factors are the emission of greenhouse gases which are thought to contribute to the greenhouse effect, the depletion of stratospheric ozone, changes in land use and the emission of aerosols such as sulphates. (Source: IPCC)

Large amounts of anthropogenic greenhouse gases have been emitted to the atmosphere since the beginning of the industrial revolution. Since 1750, the carbon dioxide concentration has increased by 31%, methane has increased 151%, nitrous oxide has increased 17% and tropospheric ozone has increased 36%. (Source: IPCC)

The majority of the anthropogenic carbon dioxide is produced by the combustion of fossil fuels. Methane is mainly produced by cattle and by emissions of landfills. It is thought that the reduction in tropical forested area has also played a role, as old forests store large amounts of carbon. However, growing forests in North America and Russia contribute to absorbing carbon dioxide (they act as CO₂ sinks), and since 1990, the amount of carbon absorbed may be larger than the amount released by deforestation (source???).

Not all the CO₂ emitted to the atmosphere accumulates there; half of it is absorbed by oceans and forests.

Evaluation of the relative importance of various factors

The relative importance of each of the proposed causes can only be established through the quantification of the factors involved. Internal and external factors can be quantified by the analysis of climate simulations based on the best climate models.

The influence of external factors can be compared using the concept of radiative forcing. A positive radiative forcing warms the planet, and negative radiative forcing cools the planet. Anthropogenic emissions of greenhouse gases, stratospheric ozone depletion, and solar radiation have positive radiative forcing, whereas aerosols and land use changes have negative radiative forcing. (Source: IPCC)

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-The term '''climate change''' is sometimes used to refer to all forms of climatic inconsistency, but because the [[Earth]]'s [[climate]] is never static, the term is more properly used to imply a significant change from one climatic condition to another. In some cases, 'climate change' has been used synonymously with the term, '[[global warming]]'; scientists however, tend to use the term in the wider sense to also include natural changes in climate.
+The term '''climate change''' is used to refer to changes in the [[Earth]]'s [[climate]]. Generally, this is taken to mean changes in the temperature, though 'climate' encompasses many other variables (precipitation, clouds, etc). 'Climate change' includes natural and anthropogenic forcing; '[[global warming]]' is usually used to mean changes with predominantly anthropogenic forcing.
+For information on climate change over various periods, and the data sources
-The invention of measures of heat and of atmospheric moisture, pressure, and precipitation, is extremely recent. Hence, ancient physicists have left us no thermometric or barometric records, no tables of the fall, evaporation, and flow of waters, and even no accurate maps of coast lines and the course of rivers. Their notices of these phenomena are almost wholly confined to excessive and exceptional instances of high or of low temperatures, extraordinary falls of rain and snow, and unusual floods or droughts. Our knowledge of the meteorological condition of the earth, at any period more than three centuries before our own time, is derived from these imperfect details, from the vague statements of ancient historians and geographers in regard to the volume of rivers and the relative extent of forest and cultivated land, from the indications furnished by the history of the agriculture and rural economy of past generations, and from other almost purely casual sources of information.
+available, see [[historical temperature record]]
 == Climate change factors ==
-Climate changes occur due to internal and external factors.
+Climate changes occur due to internal and external, natural and anthropogenic factors.
 Internal factors are factors associated with the complexity of the climate systems which are chaotic non-linear [[dynamic system]]s.
 External factors can be natural factors (such as increased [[solar radiation]]) and anthropogenic factors (due to human actions).
@@ Line 11: / Line 12: @@
 === Natural Factors ===
-The main natural external factor is the variability in the amount of solar radiation that reaches Earth.
+The main natural external factor is the variability in the amount, and geographic and temporal distribution of, solar radiation that reaches Earth.
-The solar radiation can change because of [[solar cycle]]s, because of cyclic changes in Earth's orbit, and because the [[Sun]] is getting hotter.
+The solar radiation can change on short (yearly to century) timescales because of [[solar cycle]]s and on century to millenial timescales because of cyclic changes in Earth's orbit. On much longer (hundreds of millions of years) timescales, the [[Sun]] is getting hotter.
-Scientists agree that internal factors and natural external factors can cause significant climate changes.
+It is clear that natural external factors have caused significant climate changes in the past, and it is probable that internal factors have too.
-The [[Medieval Warm Period]] mentioned above had a magnitude similar to the warming in the 20th century, and it is agreed that these changes were caused by internal factors and natural external factors only.
+The [[Medieval Warm Period]] was caused by internal factors and natural external factors only.
 The subsequent [[Little Ice Age]] is usually attributed to the reduction of solar activity.
 Some scientists have claimed that the observed warming since
@@ Line 36: / Line 37: @@
 Methane is mainly produced by cattle and by emissions of landfills.
 It is thought that the reduction in tropical forested area has also played a role, as old forests store large amounts of [[carbon]].
-However, growing [[forest]]s in [[North America]] and [[Russia]] contribute to absorbing [[carbon dioxide]] (they act as [[CO2 sink|CO<sub>2</sub> sinks]]), and since 1990, the amount of carbon absorbed is larger than the amount released by [[deforestation]].
+However, growing [[forest]]s in [[North America]] and [[Russia]] contribute to absorbing [[carbon dioxide]] (they act as [[CO2 sink|CO<sub>2</sub> sinks]]), and since 1990, the amount of carbon absorbed may be larger than the amount released by [[deforestation]] (source???).
 Not all the CO<sub>2</sub> emitted to the atmosphere accumulates there; half of it is absorbed by [[ocean]]s and forests.
-The real importance of each of the proposed causes can only be established through the exact quantification of every factor involved.
+=== Evaluation of the relative importance of various factors ===
+The relative importance of each of the proposed causes can only be established through the quantification of the factors involved.
 Internal and external factors can be quantified by the analysis of climate simulations based on the best [[climate model]]s.
@@ Line 48: / Line 52: @@
 (Source: IPCC)
-See also: [[Climate model]]
+See also: [[Climate model]]; [[global warming]]