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Global change in broad sense refers to planetary-scale changes in the Earth system. It is most commonly used to encompass the variety of changes connected to the rapid increase in human activities which started around mid-20th century, i.e., the Great Acceleration. While the concept stems from research on the climate change, it is used to adopt a more holistic view of the observed changes. Global change refers to the changes of the Earth system, treated in its entirety with interacting physicochemical and biological components as well as the impact human societies have on the components and vice versa. Therefore, the changes are studied through means of Earth system science. (Full article...)

Effects of climate change are well documented and growing for Earth's natural environment and human societies. Changes to the climate system include an overall warming trend, changes to precipitation patterns, and more extreme weather. As the climate changes it impacts the natural environment with effects such as more intense forest fires, thawing permafrost, and desertification. These changes impact ecosystems and societies, and can become irreversible once tipping points are crossed. Climate activists are engaged in a range of activities around the world that seek to ameloriate these issues or prevent them from happening.


The effects of climate change vary in timing and location. Up until now the Arctic has warmed faster than most other regions due to climate change feedbacks. Surface air temperatures over land have also increased at about twice the rate they do over the ocean, causing intense heat waves. These temperatures would stabilize if greenhouse gas emissions were brought under control. Ice sheets and oceans absorb the vast majority of excess heat in the atmosphere, delaying effects there but causing them to accelerate and then continue after surface temperatures stabilize. Sea level rise is a particular long term concern as a result. The effects of ocean warming also include marine heatwaves, ocean stratification, deoxygenation, and changes to ocean currents. The ocean is also acidifying as it absorbs carbon dioxide from the atmosphere. (Full article...)

Circumnavigation is the complete navigation around an entire island, continent, or astronomical body (e.g. a planet or moon). This article focuses on the circumnavigation of Earth.

The first circumnavigation of the Earth was the Magellan Expedition, which sailed from Sanlucar de Barrameda, Spain in 1519 and returned in 1522, after crossing the Atlantic, Pacific, and Indian oceans. Since the rise of commercial aviation in the late 20th century, circumnavigating Earth is straightforward, usually taking days instead of years. Today, the challenge of circumnavigating Earth has shifted towards human and technological endurance, speed, and less conventional methods. (Full article...)

The temperature record of the last 2,000 years is reconstructed using data from climate proxy records in conjunction with the modern instrumental temperature record which only covers the last 170 years at a global scale. Large-scale reconstructions covering part or all of the 1st millennium and 2nd millennium have shown that recent temperatures are exceptional: the Intergovernmental Panel on Climate Change Fourth Assessment Report of 2007 concluded that "Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1,300 years." The curve shown in graphs of these reconstructions is widely known as the hockey stick graph because of the sharp increase in temperatures during the last century. this broad pattern was supported by more than two dozen reconstructions, using various statistical methods and combinations of proxy records, with variations in how flat the pre-20th-century "shaft" appears. Sparseness of proxy records results in considerable uncertainty for earlier periods.

Individual proxy records, such as tree ring widths and densities used in dendroclimatology, are calibrated against the instrumental record for the period of overlap. Networks of such records are used to reconstruct past temperatures for regions: tree ring proxies have been used to reconstruct Northern Hemisphere extratropical temperatures (within the tropics trees do not form rings) but are confined to land areas and are scarce in the Southern Hemisphere which is largely ocean. Wider coverage is provided by multiproxy reconstructions, incorporating proxies such as lake sediments, ice cores and corals which are found in different regions, and using statistical methods to relate these sparser proxies to the greater numbers of tree ring records. The "Composite Plus Scaling" (CPS) method is widely used for large-scale multiproxy reconstructions of hemispheric or global average temperatures; this is complemented by Climate Field Reconstruction (CFR) methods which show how climate patterns have developed over large spatial areas, making the reconstruction useful for investigating natural variability and long-term oscillations as well as for comparisons with patterns produced by climate models. (Full article...)

The Space Age is a period encompassing the activities related to the space race, space exploration, space technology, and the cultural developments influenced by these events, beginning with the launch of Sputnik 1 on October 4, 1957, and continuing to the present.

This period is characterized by changes in emphasis on particular areas of space exploration and applications. Initially, the United States and the Soviet Union invested unprecedented amounts of resources in breaking records and being first to meet milestones in crewed and uncrewed exploration. The United States established the National Aeronautics and Space Administration (NASA) and the USSR established the Kosmicheskaya programma SSSR to meet these goals. This period of competition gave way to cooperation between those nations and emphasis on scientific research and commercial applications of space-based technology. (Full article...)

The Arab world (Arabic: اَلْعَالَمُ الْعَرَبِيُّ al-ʿālam al-ʿarabī), formally the Arab homeland (اَلْوَطَنُ الْعَرَبِيُّ al-waṭan al-ʿarabī), also known as the Arab nation (اَلْأُمَّةُ الْعَرَبِيَّةُ al-ummah al-ʿarabiyyah), the Arabsphere, or the Arab states, comprises a large group of countries, mainly located in Western Asia and Northern Africa. While the majority of people in the Arab world are ethnically Arab, there are also significant populations of other ethnic groups such as Berbers, Kurds, Somalis and Nubians, among other groups. Arabic is used as the lingua franca throughout the Arab world.

The Arab world is at its minimum defined as the 19 states where Arabs form at least a plurality of the population. At its maximum it consists of the 22 members of the Arab League, an international organization, which on top of the 19 plurality Arab states also includes the Comoros, Djibouti and Somalia. The region stretches from the Atlantic Ocean in the west to the Arabian Sea in the east, and from the Mediterranean Sea in the north to the Indian Ocean in the southeast. The eastern part of the Arab world is known as the Mashriq, and the western part as the Maghreb. (Full article...)

A world war is an international conflict that involves most or all of the world's major powers. Conventionally, the term is reserved for two major international conflicts that occurred during the first half of the 20th century, World War I (1914–1918) and World War II (1939–1945), although some historians have also characterised other global conflicts as world wars, such as the Nine Years' War, the War of the Spanish Succession, the Seven Years' War, the French Revolutionary and Napoleonic Wars, the Cold War, and the War on Terror. (Full article...)