Present investigations of ocean-atmosphere interactions involve two concepts. The first is derived from experiments which suggest that regions in the ocean may significantly affect large-scale atmospheric processes over the continents, with a time-lag of 4-8 months. The second concept is a hypothesis that may help explain climate variability and large-scale weather anomalies. It assumes that water masses with abnormal temperatures may persist for long periods, are able to reach deep waters and migrate for long distances, and under certain conditions may reappear at the surface and induce large-scale anomalies of atmospheric circulation several months, or more probably, years later. These interactions of the ocean and the atmosphere determine the world's weather and are responsible for droughts, floods, storms, and other extreme weather conditions which take an annual toll in lives, crops, and property damage.
Much of these interactions begins in the Pacific Ocean, although they can affect climates as far away as North America and Africa. Among phenomena with significant influence on climate are those known as the El NiÃ±o/Southern Oscillation (ENSO). El NiÃ±o is the warming of South American coastal waters; Southern Oscillation is the movement of large areas of air pressure between the Pacific and Indian Oceans. These ocean-atmosphere events have occurred 9 times in the past 40 years. The climatic ripples of El NiÃ±o can spread around the world, as far as Europe. El NiÃ±o events can last for up to a year, destroying fisheries, causing floods and crop failures, and upsetting wildlife.
Climate can also be drastically changed by a big meteor strike, or by dust clouds from volcanoes. In 1816, a huge volcanic eruption at Tambora, Indonesia caused what was know as the "year without a summer". Dust thrown into the stratosphere reflected a high percentage of solar radiation back into space. In New England, USA it snowed in every month of the year, including July and August.