Abrupt climate change is a form of climate change which occurs on a radically accelerated scale, with changes occurring within the span of several decades rather than over the course of centuries. It is characterized by a rate of change which exceeds the time scale of the external influences pushing the climate change, often caused by a cascading effect which causes the climate to change rapidly. It can also have a tremendous impact on the environment and living organisms, because it happens too rapidly to accommodate adaptation.
In the late 20th century, climate change became a major topic in the news, as researchers and advocacy organizations began to explore the influence of human activities on the climate, and to explore the extent of human-mediated climate change. Debate continues over how much influence human activity had on the observed climate changes which started to occur around the 1800s. Researchers were concerned with identifying the human influence to determine whether or not humans could step in to reverse climate change.
However, climate change has been a part of the planet's history since it was formed. The Earth has historically experienced a broad array of climates, and climate patterns are highly cyclical in nature. Abrupt climate change occurs at a rate far more rapid than the rate of the human-influenced climate change observed in the 20th century, and there are several historical examples of abrupt climate change including the Permian-Triassic Extinction Event and the Younger Dryas Event.
In abrupt climate change, temperatures can skew within a few decades, causing a radical shift in the environment. Both warming and cooling can occur during abrupt climate change, along with changes in rainfall level and other weather events. The rapid changes proceed so quickly that it is not possible to adapt to the changed climate, and for highly specialized organisms which have evolved in a very specific environment, abrupt climate change can trigger extinction or a radical reduction in numbers.
Global warming is certainly one form of climate change, and most researchers agree than humans have definitely contributed to global warming. The radical rise in carbon dioxide levels around the world which occurred during the 19th and 20th centuries has been clearly documented and compared to historic levels with the use of ice cores and other samples which can be used to identify particulate matters and dissolved gases in the atmosphere at various points in history. Although researchers do not think that humans can trigger abrupt climate change, some agree that humans could take steps to reduce the severity of such change, or to prevent it altogether by eliminating triggering events which develop in response to human pressures on the climate. For example, humans cannot directly interfere with the great ocean conveyor belt which plays a critical role in the Earth's climate, but global warming caused by human activities which elevate carbon dioxide levels could result in the release of large amounts of freshwater into the ocean, which would disrupt the conveyor belt and cause abrupt climate change.