The Earth's ecosystem is a complex of both biotic, or living, elements such as plants, animals and bacteria, and abiotic, or nonliving, factors such as weather, cloud cover and landscape features like lakes and mountains. These abiotic elements are subject to change from a variety of forces, such as earthquakes, wind erosion and volcanic eruptions. Volcanic activity affects global abiotic factors such as temperature and the composition of the atmosphere, with consequences for the Earth's ecosystem as a whole.
Large volcanic eruptions produce huge quantities of ash and gases. These ash clouds dim the sun, decreasing the amount of sunlight which reaches the Earth. Gases such as sulfur dioxide, hydrogen chloride and hydrogen fluoride fill the lower atmosphere, combining with water to form aerosols that absorb sunlight and scatter it back into space. Historically, the years after large volcanic eruptions have seen cooler weather, such as 1816's "Year Without a Summer" after the eruption of Mount Tambora in 1815.
Because eruptions produce enormous amounts of gases and particles, these events send volcanic particles into the upper reaches of the atmosphere where they remain trapped, resulting in brilliant sunsets. Atmospheric haze contributes to warming of the Earth and health hazards for vulnerable people, as the ash and gas clouds from these eruptions circle the globe several times following an event.
Among the gases produced during an eruption is carbon dioxide, which contributes significantly to global warming through the greenhouse effect. In the greenhouse effect, these gases absorb the planet's thermal radiation and re-radiate it back to the surface, increasing temperatures. Although many substances, a number of which are human-produced, contribute to the greenhouse effect, volcanic activity remains a significant source of these climate-affecting gases, which may linger indefinitely in the atmosphere.