New England and Europe experienced snowfalls and frosts throughout the summer of 1816. Britannica botanist Melissa Petruzzello explores what keeps the world green… or not. First, the shape of Earth’s orbit around the Sun, varies from nearly circular to elliptical (eccentric), with periodicities of 100,000 and 413,000 years. Over the last 50 years, human activities – particularly the burning of fossil fuels – have released sufficient quantities of carbon dioxide and other greenhouse gases to trap additional heat in the lower atmosphere and affect the global climate. Credit: NASA/JPL-Caltech. Climate is influenced by a multitude of factors that operate at timescales ranging from hours to hundreds of millions of years. This becomes obvious when scientists probe beyond changes in the average temperature of the planet and look more closely at geographical and temporal patterns of climate change. Croll’s controversial idea was taken up by Serbian mathematician and astronomer Milutin Milankovitch in the early 20th century. Variations in carbon dioxide release by volcanoes and ocean rifts over millions of years can alter the chemistry of the atmosphere. The carbon cycle causes an exchange of CO2 between the biosphere and the oceans on the one hand and the atmosphere on the other. A full understanding of the Earth system requires knowledge of how the system and its components have changed through time. Carbon dioxide, methane, and water vapour are the most important greenhouse gases, and they have a profound effect on the energy budget of the Earth system despite making up only a fraction of all atmospheric gases. While we have experienced environmental challenges, 50 years of progress has shown us what we can do when we pull together. Climate change, periodic modification of Earth’s climate brought about as a result of changes in the atmosphere as well as interactions between the atmosphere and various other geologic, chemical, biological, and geographic factors within the Earth system. 2. A recent example is the 1991 eruption in the Philippines of Mount Pinatubo, which had measurable influences on atmospheric circulation and heat budgets. For example, the chemical weathering of the rising Tibetan Plateau may have played an important role in depleting the atmosphere of carbon dioxide during a global cooling period in the late Cenozoic Era. The luminosity, or brightness, of the Sun has been increasing steadily since its formation. Extreme weather events can compound many of these health threats. In the last 130 years, the world has warmed by approximately 0.85oC. Greenhouse gases are gas molecules that have the property of absorbing infrared radiation (net heat energy) emitted from Earth’s surface and reradiating it back to Earth’s surface, thus contributing to the phenomenon known as the greenhouse effect. Vegetation also influences greenhouse gas concentrations; living plants constitute an important sink for atmospheric carbon dioxide, whereas they act as sources of carbon dioxide when they are burned by wildfires or undergo decomposition. The feedbacks involve different components that operate at different rates and timescales. At the same time, the transfer of water molecules from soil to the atmosphere is mediated by vegetation, both directly (from transpiration through plant stomata) and indirectly (from shading and temperature influences on direct evaporation from soil). Weathering rates are related to the mass, elevation, and exposure of bedrock. The pursuit of this understanding has led to development of Earth system history, an interdisciplinary science that includes not only the contributions of Earth system scientists but also paleontologists (who study the life of past geologic periods), paleoclimatologists (who study past climates), paleoecologists (who study past environments and ecosystems), paleoceanographers (who study the history of the oceans), and other scientists concerned with Earth history. Nevertheless, a full appreciation of the nature and magnitude of climatic change did not come about until the late 18th and early 19th centuries, a time when the widespread recognition of the deep antiquity of Earth occurred. Climate data from volcanic events indicate that just one large eruption is enough to cause global cooling of around 0.3°C and between 1 and 2 years. Vegetation also influences greenhouse gas concentrations; living plants constitute an important sink for atmospheric carbon dioxide, whereas they act as sources of carbon dioxide when they are burned by wildfires or undergo decomposition. Climate is often defined loosely as the average weather at a particular place, incorporating such features as temperature, precipitation, humidity, and windiness. There are also natural factors that force the climate to change, known as 'forcings'. Earth system science is composed of a wide range of disciplines, including climatology (the study of the atmosphere), geology (the study of Earth’s surface and underground processes), ecology (the study of how Earth’s organisms relate to one another and their environment), oceanography (the study of Earth’s oceans), glaciology (the study of Earth’s ice masses), and even the social sciences (the study of human behaviour in its social and cultural aspects). These and other feedbacks among the various components of the Earth system are critical for both understanding past climate changes and predicting future ones. The concentration of CO2 in the atmosphere is subject to variation even without human intervention. The leading cause of climate change is human activity and the release of greenhouse gases. For instance, climate influences the distribution of vegetation on Earth’s surface (e.g., deserts exist in arid regions, forests in humid regions), but vegetation in turn influences climate by reflecting radiant energy back into the atmosphere, transferring water (and latent heat) from soil to the atmosphere, and influencing the horizontal movement of air across the land surface. Biblical scripture and other early documents refer to droughts, floods, periods of severe cold, and other climatic events. The atmosphere is a dynamic fluid that is continually in motion. Many of the causes of climate change are external to the Earth system. Carbon dioxide is emitted from volcanoes and vents in rift zones and subduction zones. London: The Royal Society Science Policy Centre, 2010. Studies of Earth system history also specify the full array of states the system has experienced in the past and those the system is capable of experiencing in the future. Variations in the rate of spreading in rift zones and the degree of volcanic activity near plate margins have influenced atmospheric carbon dioxide concentrations throughout Earth’s history. Milankovitch proposed that the mechanism that brought about periods of glaciation was driven by cyclic changes in eccentricity as well as two other orbital parameters: precession (a change in the directional focus of Earth’s axis of rotation) and axial tilt (a change in the inclination of Earth’s axis with respect to the plane of its orbit around the Sun). 1. However, these phrases are not exact synonyms. At geologic timescales, however, release of this greenhouse gas can have important effects. For a detailed description of the development of Earth’s atmosphere, see the article atmosphere, evolution of. All these factors change through time. Perhaps the most intensively discussed and researched topic in climate variability is the role of interactions and feedbacks among the various components of the Earth system. Wherever possible, paleoclimatologists try to use multiple lines of evidence to cross-check their conclusions. Paleoclimatologists study these natural archives by collecting cores, or cylindrical samples, of sediments from lakes, bogs, and oceans; by studying surface features and geological strata; by examining tree ring patterns from cores or sections of living and dead trees; by drilling into marine corals and cave stalagmites; by drilling into the ice sheets of Antarctica and Greenland and the high-elevation glaciers of the Plateau of Tibet, the Andes, and other montane regions; and by a wide variety of other means. Individual volcanic eruptions can release large quantities of sulfur dioxide and other aerosols into the stratosphere, reducing atmospheric transparency and thus the amount of solar radiation reaching Earth’s surface and troposphere. Climate change: A Summary of the Science. Climate is influenced by a multitude of factors that operate at timescales ranging from hours to hundreds of millions of years. 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