Currently, the phenomenon of so-called ”climate change” is not fully understood, but there are several hypotheses that may attempt to explain them.
Astronomical causes
(The variations of parameters and those of the temperature, https://commons.wikimedia.org/wiki/File:Milankovitch_Variations.png)
This theory proposed by Milutin Milanković between 1911 and 1941, confirmed by the study of oxygen-18, and broadly endorsed by the scientific community, explains the glacial/interglacial climate cycles by variations of eccentricity, obliquity and precession of Earth . According to this theory, without anthropogenic forcing the planet would enter a new cooling era, or entering an exceptionally long and stable interglacial phase (still 50 thousand years).
Another theory, compatible with the other, is that of solar cycles, developed by the German Heinrich Schwabe in 1840, then by the American George Hale in 1906. She explains the low climatological changes that take place every 11 years, cycle corresponding to that of sunspots which have a periodicity of 11 years; when the number of sunspots is important, the Sun emits more energy (Earth thus receives more) and therefore a change in temperature takes place. This radiation influences in a complex way the cloud (see physical principle of the cloud chamber) and therefore both the planetary albedo and the greenhouse effect due to clouds and water vapor. These spots are cooler (4500 K) than the surface of the sun (approximately 5800 K), but they correspond to an increase in the X-rays which can increase 1.000 times for 1% in the visible light in the periods of intense activity. The little ice age observed between 1645 and 1715 is an illustration of the theory of the influence of temperature variations due to the sunspot cycle. An unusually low number of sunspots were observed there.
Interstellar dust clouds
This theory is the most controversial. For some scientists, when the solar system passes through an interstellar cloud of dust, some of the light energy is absorbed; this affects the amount of heat that reaches Earth and thus on climate.
Movement of continents to the poles
To understand the influence of the movements of continents, we must first know that ocean currents have a major influence on climate change, the continents have actually no direct influence on the climate but allow, by moving, the formation or stopping of ocean currents.
The example of the Antarctic before the breakup of the Gondwana super-continent, the Antarctic climate was hot and humid; from Australia, Africa and South America have migrated to north, the various straits were opened and a circular ocean current (called Circumpolar Current) began. In some time, the climate changed to meet current one with a huge ice cap that fell into place on the Antarctic continent, despite its aridity (the driest area in the world), but all the snow accumulates floor, because at -45 °C average, the sublimation pressure is negligible; Ablation is due to the wind and calving glaciers on coasts. On the other hand, the ocean “treadmill” rotates approximately 2.000 years. If the thermohaline circulation were to be interrupted, the climate would be significantly disrupted.
The two computer models of climates (US and European) give fairly similar results but are largely dependent on human factors.
Volcanic crises
(Eruption of Mount Pinatubo in 1991)
The gaseous emissions from volcanoes have two opposite effects: aerosols (SO2 and dust) obscure the atmosphere, increasing rainfall and cool climate; in a second time, the large amounts of emitted greenhouse gases cause a greenhouse effect. The greenhouse effect has the consequence, as the climate in a greenhouse, to amplify the temperature differences: if there is the sun, the heat is retained and reflected, if there is no sun, heat enters harder and therefore it is colder. The majority of species extinctions of the past seems to be due to a sudden climate change.
The fall of the Chicxulub meteorite is often cited as the underlying cause of the collapse of biodiversity in the late Jurassic, but it seems (Courtillot 2004) that volcanic eruptions (induced or independent of meteoritic impact) that have left traps (in the Deccan, India) have the most gigantic drastically disrupted the climate for hundreds of years at a rate exceeding the rate of possible evolutionary adaptations of species. In particular, the crisis of the Siberian traps is associated with the slaughter of the Permian. Significant and measurable disruptions following the eruption of Pinatubo (1991) and from 1783 to 1784, that of Lakagígar (Icelandic eruption cloud which left a mark in European mortality records (Courtillot, 2005)). In 1815, the eruption of Tambora also had global climate consequences, with strong disturbances in 1816.
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