Part V
Top left: Vapour trails from aeroplanes in the sky above the city of Bayreuth, Upper Franconia, Germany. The vapour trails impact the radiation budget of the Earth (“global dimming”) and atmospheric chemical processes. Bottom left: Agricultural uses in the American Midwest, an area that was originally an open oak woodland and grassland. Top right: Thunderstorms caused by convection from forest fires, which are used to clear land in Malaysia. Bottom right: Fish farms, used to rear crabs, on the north coast of Java, where originally mangrove swamps were growing; owing to the spread of diseases, only a small proportion of this area is still useable. (Photos: E.-D. Schulze)
The surface of the Earth has an area of about 510 million km2, of which about 361 million km2 are oceans, i.e. 71% of the Earth’s surface is covered by oceans. The continental area is about 149 million km2, but only about 134 million km2 (90% of continents) are ice-free. At present, virtually the entire ice-free surface of the Earth is used by humans for food and feed production, raw material extraction and processing, settlements, infrastructure or tourism. According to Running (2008), original vegetation has been entirely displaced by humans from about 50% of the Earth’s surface, and the other half is used for grazing, hunting, gathering and tourism. About 3.5% of the land area is under conservation. Globally, about 70% of freshwater withdrawal by humans is used for irrigation (WWAP 2014). In 2010, 3.5 million tonnes of waste were produced worldwide every day, which is estimated to increase to more than 6 million tonnes by 2025 (Hoornweg et al. 2013). Invading plants replaced 20% of original plants in ecosystems (up to 50% in some vegetation types), but this process appears to have been initiated by human activities (Pearce 2015). About 20% of the known bird species are extinct, and 60% of fish stocks are overused by humans for food or to provide fishmeal as feed for farmed fish (Naylor et al. 2000) or animal husbandry. This list could be easily continued and extended.
Plants and ecosystems play a key role in many aspects of global change. Plants are Earth’s primary producers, source of atmospheric oxygen, sink for atmospheric carbon dioxide and the basis for global food security. From an economic point of view, plants are an important resource for clothing (e.g. cotton, hemp, flax), medical drugs, furniture and timber. Plant biomass has also become an increasingly important alternative to fossil fuel and it is used as biofuel for the continuously growing energy requirements of modern societies. In addition, ecosystems provide many services that are important to humankind, for example, filtration and purification of air and water, storage of carbon dioxide, aesthetic services and tourism (Chap. 21: Global Biogeochemical Cycles).
The growing demands on Earth’s land surface for food and feed production, biodiversity conservation, protection of terrestrial carbon sinks and urbanisation conflict with each other and are even sometimes mutually exclusive. A sustainable use of Earth’s terrestrial ecosystems requires a deep understanding and ability to model (Chap. 22: Dynamic Global Vegetation Models) plant ecology at a global scale under changing environmental, socio-economic and political boundary conditions (Chap. 23: Global Change and Terrestrial Ecosystems).
References
Hoornweg D, Bhada-Tata P, Kennedy C (2013) Waste production must peak this century. Nature 502:615–617
Naylor RL, Goldburg RJ, Primavera JH, Kautsky N, Beveridge MCM, Clay J, Folke C, Lubchenko J, Mooney H, Troell M (2000) Effect of aquaculture on world fish supply. Nature 405:1017–1025
Pearce F (2015) The new wild: why invasive species will be Nature’s salvation. Beacon Press, Boston
Running SW (2008) Ecosystem disturbance, carbon, and climate. Science 321:652–657
WWAP (2014) The United Nations World Water Development Report 2014: Water and Energy. Paris, UNESCO