Climate
[5] Finally, the Bergeron and Spatial Synoptic Classification systems focus on the origin of air masses that define the climate of a region.
For example, as climate scientist Lesley Ann Hughes has written: "a 3 °C [5 °F] change in mean annual temperature corresponds to a shift in isotherms of approximately 300–400 km [190–250 mi] in latitude (in the temperate zone) or 500 m [1,600 ft] in elevation.
"[11]The World Meteorological Organization (WMO) describes "climate normals" as "reference points used by climatologists to compare current climatological trends to that of the past or what is considered typical.
A 30-year period is used as it is long enough to filter out any interannual variation or anomalies such as El Niño–Southern Oscillation, but also short enough to be able to show longer climatic trends.
At its 1934 Wiesbaden meeting, the technical commission designated the thirty-year period from 1901 to 1930 as the reference time frame for climatological standard normals.
"[16] Over historical time spans, there are a number of nearly constant variables that determine climate, including latitude, altitude, proportion of land to water, and proximity to oceans and mountains.
The density and type of vegetation coverage affects solar heat absorption,[18] water retention, and rainfall on a regional level.
Examples of genetic classification include methods based on the relative frequency of different air mass types or locations within synoptic weather disturbances.
It uses evidence with different time scales (from decades to millennia) from ice sheets, tree rings, sediments, pollen, coral, and rocks to determine the past state of the climate.
[24] Details of the modern climate record are known through the taking of measurements from such weather instruments as thermometers, barometers, and anemometers during the past few centuries.
[26] Since the 1960s, the launch of satellites allow records to be gathered on a global scale, including areas with little to no human presence, such as the Arctic region and oceans.
In some cases, current, historical and paleoclimatological natural oscillations may be masked by significant volcanic eruptions, impact events, irregularities in climate proxy data, positive feedback processes or anthropogenic emissions of substances such as greenhouse gases.
These changes can be caused by processes internal to the Earth, external forces (e.g. variations in sunlight intensity) or human activities, as found recently.
The accumulation of snow and ice during a glacial period increases the surface albedo, reflecting more of the Sun's energy into space and maintaining a lower atmospheric temperature.
Suggested causes of ice age periods include the positions of the continents, variations in the Earth's orbit, changes in the solar output, and volcanism.
[40] According to the EU's Copernicus Climate Change Service, average global air temperature has passed 1.5C of warming the period from February 2023 to January 2024.
[41] Climate models use quantitative methods to simulate the interactions and transfer of radiative energy between the atmosphere,[42] oceans, land surface and ice through a series of physics equations.
Examples are ICON[43] or mechanistically downscaled data such as CHELSA (Climatologies at high resolution for the earth's land surface areas).
Finally, more complex (coupled) atmosphere–ocean–sea ice global climate models discretise and solve the full equations for mass and energy transfer and radiant exchange.
