El albedo Albedo is the ratio of reflected to incident energy in the wavelength of visible light, which causes planets to shine. Since planets have no energy of their own, they reflect some of the light they receive from the Sun. Albedo is not a constant value and varies according to several factors, primarily the inclination of the incident irradiation and nature of the reflecting surface. In simple terms, the ability of a surface to reflect is directly related to its color: a light body reflects more light than a dark body. This property has important implications in climatology and in the study of climate changes over time.
For example, the albedo of snow-covered ground is considerably greater than that of a meadow. Snow has an average albedo of 0,7, while the albedo of a green forest is only 0,2. This means that 70% of the solar energy incident on snow is reflected back into space, while only 20% is reflected in the case of forests. On a global level, mean albedo of the Earth is approximately 0,3, which indicates that around 30% of the solar energy that enters the atmosphere is returned to space in the form of direct radiation. This percentage is essential to understanding the energy balance from the earth.
The albedo of the continents is approximately 34%, while that of the oceans reaches a 26%, and that of the medium and low altitude clouds is located between the 50% and the 70%These variations in albedo are fundamental to the energy balance of the Earth and, therefore, for the regulation of its climate. Albedo not only defines how light is reflected, but also has a significant impact on global temperature and climate.
In terms of energy balance, on a planetary scale, the balance is established as equal to zero; however, in different regions of the Earth's surface, this balance is far from constant. There are areas that receive more energy than they emit, while others emit more than they receive. Generally, energy balances tend to be in excess in regions located between the parallels 35º and 40º. At these latitudes, energy inputs and outputs are equal, and beyond these parallels, the balance becomes deficient. This phenomenon is related to the climate change global.
Variations in the amount of energy received and emitted are crucial, as they directly influence the heating o cooling of the air, and are determining factors in the distribution of different climates and in atmospheric circulation. Understanding albedo and the Earth's energy balance is essential to analyzing how these elements interact and affect the global climate.
El global radiation balance refers to the difference between solar energy reaching the atmosphere and the energy lost to space. Under steady-state conditions, energy losses equal energy inputs. However, locally, it is observed that at high latitudes, radiated energy tends to be greater than received energy, and vice versa at lower latitudes. This imbalance is compensated by heat transport mechanisms, including atmospheric circulation (winds) and the ocean circulation in the context of global warming.
The Earth, at the upper limit of its atmosphere, receives a relatively constant amount of solar radiation, estimated at 2 calories/cm² per minute, known as the solar constantThis amount of energy is essential for maintaining our planet's temperature. The radiation leaving the Earth is divided into different categories:
- Shortwave radiation: This form of radiation corresponds to the energy reflected by the Earth's surface, which includes oceans, soil, clouds, and particles in the atmosphere. The albedo represents about 30% of total radiation, although this value may vary with time and atmospheric conditions.
- Longwave radiation: This type of radiation refers to the thermal energy emitted by the Earth, primarily in the form of infrared radiation. The atmosphere retains some of this radiation, contributing to the greenhouse effect and affecting global temperatures.
The law of Stefan-Boltzmann states that the amount of energy radiated by a blackbody, as the Earth is assumed to be in this context, is related to the fourth power of its temperature in Kelvin. When we assess the Earth's energy balance, it is important to consider how the absorbed energy equals the energy radiated back into space. If the Earth receives more energy than it emits, its temperature will increase, while if it emits more than it receives, its temperature will decrease. This is vital to understanding how humans have altered the energy balance.
The atmosphere plays a crucial role in this energy balance, since the greenhouse gases, such as carbon dioxide and methane, trap some of the emitted infrared radiation, which further warms the planet. This phenomenon is essential to understanding the climate change and how human activity has altered this natural balance, a topic that has been discussed in depth in several studies.
El radiative forcing It refers to the change in the Earth's energy balance due to external factors. It is measured in watts per square meter (W/m²) and can be positive (causing warming) or negative (causing cooling). Factors that can influence radiative forcing include:
- Greenhouse gas concentrations: The increase in gases such as CO₂, CH₄ and N₂O traps heat in the atmosphere, which increases positive radiative forcing.
- Aerosol sprays: Depending on their composition, aerosols can have positive or negative radiative forcing. For example, sulfate aerosols tend to reflect solar radiation back into space, while soot can warm the atmosphere.
- Changes in land use: Activities such as deforestation alter the albedo of the Earth's surface, which in turn impacts radiative forcing. Reducing forest areas generally increases albedo and, therefore, could slow warming.
- Solar variations: Changes in solar activity also affect radiative forcing, although these effects are generally minor compared to the impacts of greenhouse gas concentrations in the context of the global warming.
El radiative forcing It is a central concept in climatology, as it allows us to quantify the impact of different factors on the Earth's energy balance. According to the report of the IPCC, anthropogenic radiative forcing in 2011, compared to 1750, was 2,29 W/m², indicating a faster increase since 1970 due to elevated greenhouse gas concentrations. This is crucial for understanding the evolution of .
This forcing is essential for modeling climate change and predicting how variations in the energy balance may affect global temperatures in the future. Current climate models consider radiative forcing as one of the main variables to consider in understanding and mitigating the impact of climate change.
You should check the value of the extraterrestrial solar radiation. Isc = 1367 W / m ^ 2