User:Random account 47/Global climate change

The term global climate change is used to refer to a climate change of Earth. In the most general sense, it can means changes over any period of time and in all of the components of climate, including precipitation and clouds as well as temperature. Like regional climate change, global climate changes can be caused both by natural forces and by human activities.

Studying Global Climate
Much like meteorologists use weather models to predict weather,  climatologists use climate models to study and predict global climate, the Earth's statistical average weather.

One of the most important natural features of Earth's atmosphere they use in studying global climate and global climate changes is called the greenhouse effect. The greenhouse effect is the name given to the process which traps heat from the Sun and warms the planet. Some atmospheric gases, called greenhouse gases, prevent heat given off by the Earth after it has been warmed by the Sun to escape as it would if were there no greenhouse gases in our atmosphere. If there are more greenhouse gases in the air, the average temperature of Earth will increase. If there are less, it will decrease. See greenhouse effect for an in depth explanation about this scientific theory.

The study of global climate is relatively new, and not all scientists agree on the methods and tools used to study it. See climatology for more information about how climate is studied.

Global climate change factors
Global climate change factors, like regional climate change factors, are called climate forcings. There are many different ways that climate can be influenced, such as a change in the amount of heat from the sun, increased greenhouse gases from pollution or animals, plants absorbing more greenhouse gases, or dust and greenhouse gases from volcanic eruptions reflecting heat as well as contributing to a stronger greenhouse effect. Visit the climate forcings page to learn more about how climate is influenced.

Past Global Climate Changes
The study of past global climate is called Paleoclimatology. Earth normally goes through a periodic global climate change. Every 100,000 years the Earth's climate changes from what it is like now to an ice age. The last ice age ended 10,000 years ago and one theory to explain the periodic ice ages is orbital forcing (also known as the Milankovitch cycles). Paleoclimatologists and other scientists have also discovered evidence of apparently non-periodic past global climate changes. Here are some examples:

Snowball Earth
Snowball Earth, also alternately known as Varangian glaciation, is a hypothesis which proposes that in the ice age of the Precambrian, 4.5 billion years ago when multi-cellular life was just developing, much of the Earth's oceans were frozen over, with ice 1 km (0.6 miles) thick. Other similar "snowball Earth's" have been proposed for the ice age which occurred 2.3 billion years ago, during the first appearance of atmospheric oxygen.

Permian-Triassic extinction event
This was Earth's most severe and sudden extinction event and occurred approximately 252 million years ago. 90 percent of marine life and 70 percent of verterbrate species became extinct. There are theories which suggest a global climate change was part of the cause of this extinction event. Some of the climate forcings suggested are the release of methane, a greenhouse gas, from underwater ice crystals called clathrates. Another is markedly increased volcanic activity or even a combination of both.

Paleocene-Eocene Thermal Maximum
This was a great change in Earth's climate which occurred approximately 55 million years ago. The average temperature of the Earth rose almost 8 C in one thousand years, and due to this global warming the Earth's ocean and atmospheric circulation was severely upset. Like the Permian-Triassic extinction event, it also caused many creatures to die off. The release of methane from calthrates has been suggested for the cause of this global climate change.

Younger Dryas
Also referred to as "the Big Freeze," this short change, occurring approximately 12,000 years ago, was an abrupt climate change which scientists theorize was a result of a "shutdown" of the thermohaline conveyor, a type of ocean circulation which influences and regulates our climate. They believe the shutdown was caused by a sudden introduction of fresh water, likely from melting glaciers, into the normally salty ocean. Temperatures in Greenland were 15&deg;C lower than today's, and fossil evidence suggests the mean annual temperature dropped 5&deg;C in the United Kingdom.

Climate changes of 535-536
Reports of aberrant climate in the years 535 and 536, described as dark clouds with little sunlight, crop failures, and low temperatures, coincide with tree ring analyses in places as far apart as California and Finland. One hypothesis is that this change was caused by the eruption of the volcano Krakatoa.

Medieval warm period
This period of Earth's climate was characterized by high temperatures, with wine grapes growing up to 300 miles north of their current limits. It lasted about 400 years from the 10th to the 14th centuries. The reason for this particular global warming is not well known and, as with the Little Ice Age, some scientists believe the change may have only been regional.

Little Ice Age
The change to this global climate state, lasting through the 14th to 19th centuries is usually attributed to the reduction of solar activity or an increase in volcanoes. It is described as a modest global cooling of 1 C. However, some scientists argue that this change may have been regional rather than global.

Year Without a Summer
In 1816, dust from a volcanic eruption blocked sunlight over the northern hemipshere, reducing temperatures there significantly, with frost throughout the year killing crops and even snowstorms in the Canadian maritimes in June.

19th century to present global warming
The 19th century to present global warming page would be much like the current (Global warming) page.

Currently climatologists agree that the Earth is going through a global climate change, specifically, a global warming, and has been since the late 19th century. Most, but not all, of these scientists agree that the current global warming is being caused by an increase in greenhouse gases. Greenhouse gases created from pollution of fossil fuel combustion are what they believe is the main culprit.

Politics of Global Climate Change
The Kyoto Protocol proposes binding greenhouse gas limits for developed countries.