Which five factors determine climate change?

Climate change and climate protection
Which factors determine the climate of our earth?

DKK The climate is created by a system of various coupled influencing variables and comprises different sub-systems that are dynamically linked to one another. The dynamics of the climate system and the resulting statistics of the climate are shaped by the widely differing time scales of the individual components.
Fig. 1
The climate system, consisting of the atmosphere, land surfaces, snow and ice, oceans and other water bodies and living organisms, is complex and interactive. The atmospheric part of the climate system characterizes the climate most clearly; Climate is often defined as "average weather". The climate is usually described as the mean value with its fluctuations in temperature, precipitation and wind during a certain period of time, ranging from months to millions of years (the classic period is 30 years). The climate system changes over time under the influence of its own internal dynamics and due to changes in external factors that influence the climate (so-called "forcings"). External drives are, for example, natural phenomena such as volcanic eruptions or fluctuations in solar radiation, as well as changes in the atmospheric composition caused by humans. The sun supplies the climate system with energy. The earth's radiation balance can be changed by three factors:
1. through changes in the amount of incoming radiation - for example through changes in the sun itself or through changes in the earth's orbit;
2. by changing the proportion of solar radiation reflected from the earth (called "albedo"; e.g. by changing the cloud cover, the atmospheric particles or the vegetation)
3. by changing the long-wave heat radiation of the earth (e.g. by changing greenhouse gas concentrations).
The climate reacts to such changes with a variety of feedback mechanisms, both directly and indirectly. The amount of energy that reaches the upper limit of the atmosphere every second on an area of ​​one square meter facing the sun during the day is 1370 watts. This value is called the solar constant. Averaged over the entire earth, this results in an average value of 342 watts per square meter (see Figure 2). About 30% of the incoming solar radiation is reflected back into space by the atmosphere (107 watts / m²). About 2/3 of this reflection is mainly determined by clouds and small particles known as aerosols in the atmosphere (77 watts / m²). The remaining third is mainly reflected by light earth surfaces - such as snow, ice and deserts - (30 watts / m²). The strongest change in the reflection caused by atmospheric aerosols occurs when large volcanic eruptions hurl gases and aerosols up into the stratosphere. Rain typically washes aerosols from the atmosphere within a week or two. However, during a massive volcanic eruption, the material released into the atmosphere is thrown well above the cloud line, which means that these aerosols typically affect the climate for about a year or two before they are carried out of the atmosphere through the troposphere and precipitation. Larger volcanic eruptions can therefore cause a drop in global surface temperature of around half a degree Celsius, which can last for months or even years. Some man-made aerosols also reflect sunlight to a significant extent.
Fig 2
Approximately 240 W / m2 is not reflected and is therefore absorbed by the atmosphere and the earth's surface. In order to balance the incoming energy, the earth in turn has to radiate the same energy back into space. The earth does this by emitting long-wave radiation. Everything on earth continuously emits long-wave radiation. This is e.g. the heat energy that you feel in a fire. The warmer an object, the more infrared radiation it emits. To emit 240 W / m², a surface would have to have a temperature of around –19 ° C. This is much colder than the actual conditions on the earth's surface (the global average temperature of the surface is around 14 ° C). Instead, the associated –19 ° C is found at an altitude of approx. 5 km above the surface.
Fig 3
The reason the earth's surface is so warm is the presence of greenhouse gases, which partially hold back the long-wave radiation coming from the surface. This reflection is known as the natural greenhouse effect. The most important greenhouse gases are water vapor and carbon dioxide. The two most common constituents of the atmosphere - nitrogen and oxygen - have no such effect. Clouds can also act like greenhouse gases. On the other hand, they also reflect solar radiation back into space before it reaches the earth's surface. This effect has a cooling effect and thus counteracts the greenhouse effect. Clouds tend to have a cooling effect on the climate (although the warming effect can be felt locally: cloudy nights tend to stay warmer than clear nights because the clouds reflect long-wave energy back to the earth's surface). Human activities intensify the greenhouse effect by releasing greenhouse gases. The amount of carbon dioxide in the atmosphere, for example, has increased by around 35% since the beginning of industrialization. This increase is attributable to human activities such as fossil fuel burning and cutting down forests. As a result, mankind has drastically changed the chemical composition of the atmosphere - with considerable effects on the climate. The spherical shape of the earth and the inclination of the earth's axis have a great influence on the radiation intensity. At higher latitudes, a certain amount of radiation is distributed over a larger area than at lower latitudes. This energy is transported from the equator to higher latitudes via atmospheric and oceanic currents as well as storm systems. Energy is also needed to evaporate water from the sea or land surface. This energy, also known as latent heat, is released when water vapor condenses in clouds (see illustration). The atmospheric circulation is mainly driven by the release of this latent heat. The atmospheric circulation in turn drives the ocean circulation to a large extent, through wind influences on the water surface, through changes in the ocean surface temperature and through changes in the salinity caused by precipitation and evaporation. Due to the Earth's rotation, atmospheric circulation patterns tend to be east-west rather than north-south. Embedded in the westerly winds of the middle latitudes, there are large-scale weather systems that transport the heat to the poles. These weather systems are the well-known migratory low and high pressure systems and the associated cold and warm fronts. Due to temperature differences between the land surface and the ocean, obstacles such as mountain ranges and ice sheets, the atmospheric waves that comprise large parts of the Earth's circulatory system are often geographically anchored, although the amplitude of the wave can change over time. Because of the large-scale wave patterns, a particularly cold winter over North America can be combined with a particularly warm winter elsewhere in the hemisphere. Changes in various components of the climate system, such as B. Ice sheet sizes, type and distribution of vegetation, temperature of the atmosphere or the ocean influence the large-scale circulation properties of the atmosphere and the oceans. There are many feedback mechanisms in the climate system that can either reinforce (“positive feedback”) or reduce (“negative feedback”) a change in radiative forcing. For example, rising greenhouse gas concentrations cause the earth's climate to warm and snow and ice can begin to melt. The resulting darker land and water surfaces absorb a larger part of the incident solar energy and thus increase the warming, which in turn causes a larger melt, etc., whereby a self-reinforcing cycle is set in motion. This mechanism, known as the “ice albedo effect,” amplifies the initial warming caused by the rise in greenhouse gases. Scientists go to great lengths to determine, understand and precisely quantify feedback mechanisms in order to capture the complexity of our earth's climate system.
Fig 4
Source (unless otherwise indicated): IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 96-97, FAQ 1.1.

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