Climate System

As a dynamic interplay of interdependent geospheres, energy sources and both long- and short-term cycles of change throughout earth’s history, the climate system is in constant flux.

The Earth´s climate is governed through complex interactions among the atmosphere (air), hydrosphere (water), lithosphere (earth), biosphere (living organisms) and cryosphere (ice). The atmosphere, primarily composed of nitrogen, oxygen and argon, serves as the medium of the climate. Over time, variations in the composition of atmospheric elements, particularly the concentration of greenhouse gases like carbon dioxide, methane, and nitrous oxide, affect the heat content of the atmosphere and, consequently, the climate.

The hydrosphere includes all of Earth´s water bodies, such as oceans, lakes, rivers, groundwater and water vapour, which can store substantial amounts of thermal energy. This stored heat is distributed globally by atmospheric and oceanic circulation systems, thus regulating the climate. The portion of the hydrosphere comprising solid water forms, such as sea ice, shelf ice, snow, glaciers, ice sheets, and permafrost, is known as the cryosphere. Snow- and ice-covered surfaces reflect solar radiation, exerting a cooling effect, while their insulating properties prevent the loss of ground and ocean heat to the atmosphere.

The lithosphere, the Earth´s solid outer shell, including the Earth´s surface, also plays a significant role by influencing the climate through varied topographies and soil types. Long-term geological processes, such as plate tectonics, mountain formation, weathering and volcanism, as well as their interactions with the atmosphere, are also crucial in this context.

The distribution and lifestyles of humans, plants and animals belong to the biosphere and affect the climate, such as by the binding of carbon dioxide through photosynthesis and its conversion into biomass. All these geospheres influence each other, forming an interconnected system that constitutes the climate system. Changes within the system are often triggered by external factors, but within the interconnected climate system, they are not implemented evenly or immediately and feedback mechanisms can either stabilize or destabilize the system.

Since the formation of our planet 4.6 billion years ago, the sun has been the main energy source for our climate system. Over this time, about a third of the sun´s hydrogen has been converted into helium, leading to a slow expansion of the sun and a gradual increase in its luminosity. The incoming shortwave solar radiation reaching Earth is unaffected by the greenhouse gases in the atmosphere. However, the longwave heat radiation from Earth back into space is partially absorbed by these gases, creating an average surface temperature of 15 °C. Without this natural greenhouse effect, the temperature would be –18 °C, making life on Earth impossible.

The climate system is also influenced by cyclical changes in Earth´s orbit around the sun. These include:

• Axial tilt variation between 22° and 24.5°: This 41,000-year cycle affects seasonal differences in day length.
• Variations of Earth´s orbit around the sun between an elliptical and circular shape: This 100,000- and 400,000-year cycle results in seasons of varying climatic intensity.
• Precession of Earth´s axis and orbital ellipse: In a 23,000-year cycle, Earth´s distance from the sun changes seasonally. Currently, winter in the Northern Hemisphere is closer to the sun than the Northern Hemisphere´s summer, which is influencing the climate.

All naturally occurring greenhouse gases, such as water vapour, carbon dioxide, nitrous oxide, ozone, and methane, are now also influenced by human activities. Chlorofluorocarbons (CFCs), which are entirely human-made, not only harm the ozone layer in the stratosphere but also act as potent greenhouse gases. The ways human activities contribute to greenhouse gas emissions differ depending on the specific gas.

In addition to human-generated greenhouse gases, the continuous introduction of aerosols from anthropogenic sources, particularly during the rapid economic development in the second half of the 20^th century, significantly influenced the climate with their cooling effect. However, the rise in aerosol emissions also had serious health and environmental consequences. Since around 1980, efforts to reduce air pollution, along with the decline of heavy industry in Eastern Europe, led to a trend reversal, improving the health of people and forests in Europe but reducing an anthropogenic climate driver that had previously masked the warming effect of greenhouse gases from 1950 to 1980.

Climate is statistically derived from long-term weather data. To record parameters such as temperature, precipitation, wind and solar radiation, GeoSphere Austria has maintained a comprehensive national network of measurement stations since 1851. As instrumental measurements are only available for the past 150–200 years, GeoSphere Austria uses geomorphological, biological, and geochemical methods to reconstruct the climate over longer periods. These include studying land deformations caused by glaciers, fossil pollen, snails, molluscs and the chemical composition of clay minerals, sediments, and microfossils. These analyses provide insights into climate and environmental conditions over the past 500 million years.

The extensive database of direct and indirect climate indicators allows for reconstructing the climate history and its influencing factors, forming the basis for understanding current and anticipated future climates and their local impacts on Austria and the Alpine region.

The verified measurement data are used in scientific research and to provide climatological products and services. These serve as information and planning foundations on climate issues for federal ministries and states, municipalities, companies, private individuals and the media.