Climatology
The main methods employed by climatologists are the analysis of observations and modelling of the physical processes that determine climate.
Arguably the most influential classic text concerning climate was On Airs, Water and Places[4] written by Hippocrates about 400 BCE.
[4] Chinese scientist Shen Kuo (1031–1095) inferred that climates naturally shifted over an enormous span of time, after observing petrified bamboos found underground near Yanzhou (modern Yan'an, Shaanxi province), a dry-climate area unsuitable at that time for the growth of bamboo.
[4] Early climate researchers include Edmund Halley, who published a map of the trade winds in 1686 after a voyage to the southern hemisphere.
This descriptive climatology was mainly an applied science, giving farmers and other interested people statistics about what the normal weather was and how great chances were of extreme events.
[11] Paleoclimatology is the attempt to reconstruct and understand past climates by examining records such as ice cores and tree rings (dendroclimatology).
Historical climatology is the study of climate as related to human history and is thus concerned mainly with the last few thousand years.
[10] The study of contemporary climates incorporates meteorological data accumulated over many years, such as records of rainfall, temperature and atmospheric composition.
Knowledge of the atmosphere and its dynamics is also embodied in models, either statistical or mathematical, which help by integrating different observations and testing how well they match.
These equations are coupled and nonlinear, so that approximate solutions are obtained by using numerical methods to create global climate models.
[15] Climate models use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice.
Examples are ICON [16] or mechanistically downscaled data such as CHELSA (Climatologies at high resolution for the Earth's land surface areas).
Oceans act as a moderating factor, so that land close to it has typically less difference of temperature between winter and summer than areas further from it.
[21] The atmosphere interacts with other parts of the climate system, with winds generating ocean currents that transport heat around the globe.
By their very nature, indices are simple, and combine many details into a generalized, overall description of the atmosphere or ocean which can be used to characterize the factors which effect the global climate system.
El Niño–Southern Oscillation (ENSO) is a coupled ocean-atmosphere phenomenon in the Pacific Ocean responsible for much of the global variability of temperature,[22] and has a cycle between two and seven years.
The layer of atmosphere above, the stratosphere is also capable of creating its own variability, most importantly the Madden–Julian oscillation (MJO), which has a cycle of approximately 30 to 60 days.
Modern climate change is caused largely by the human emissions of greenhouse gas from the burning of fossil fuel which increases global mean surface temperatures.
Warmer temperatures are causing further changes of the climate system, such as the widespread melt of glaciers, sea level rise and shifts of flora and fauna.
