Effects of CO2 on climate change Current studies indicate that radiative forcing by greenhouse gases is the primary cause of global warming. Greenhouse gases are also important in understanding Earth’s climate history. According to these studies, the greenhouse effect, which is the warming produced as greenhouse gases trap heat, plays a key role in regulating Earth’s temperature.
Over the last 600 million years, carbon dioxide concentrations have varied from perhaps 5000 ppm to less than 200 ppm, due primarily to the effect of geological processes and biological innovations. Royer et al. have used the CO2-climate correlation to derive a value for the climate sensitivity. There are several examples of rapid changes in the concentrations of greenhouse gases in the Earth’s atmosphere that do appear to correlate to strong warming, including the Paleocene–Eocene thermal maximum, the Permian–Triassic extinction event, and the end of the Varangian snowball earth event.
During the modern era, the naturally rising carbon dioxide levels are implicated as the primary cause of global warming since 1950. According to the Intergovernmental Panel on Climate Change (IPCC), 2007, the atmospheric concentration of CO2 in 2005 was 379 ppm³ compared to the pre-industrial levels of 280 ppm³. Thermodynamics and Le Chatelier’s principle explain the characteristics of the dynamic equilibrium of a gas in solution such as the vast amount of CO2 held in solution in the world’s oceans moving into and returning from the atmosphere. These principles can be observed as bubbles which rise in a pot of water heated on a stove; gases dissolved in liquids are released under certain circumstances.
Variations in solar activity during the last several centuries based on observations of sunspots and beryllium isotopes.
The sun is the ultimate source of essentially all heat in the climate system. Energy is also provided by the gravitational pull of the Moon (manifested as tidal power), in addition to geothermal energy provided by the hot inner core of the Earth. The energy output of the sun, which is converted to heat at the Earth’s surface, is an integral part of shaping the Earth’s climate. On the longest time scales, the sun itself is getting brighter with higher energy output; as it continues its main sequence, this slow change or evolution affects the Earth’s atmosphere. It is thought that, early in Earth’s history, the sun was too cold to support liquid water at the Earth’s surface, leading to what is known as the Faint young sun paradox.
On more modern time scales, there are also a variety of forms of solar variation, including the 11-year solar cycle and longer-term modulations. However, the 11-year sunspot cycle does not manifest itself clearly in the climatological data. Solar intensity variations are considered to have been influential in triggering the Little Ice Age, and for some of the warming observed from 1900 to 1950. The cyclical nature of the sun’s energy output is not yet fully understood; it differs from the very slow change that is happening within the sun as it ages and evolves.