Understanding Climate-1

What is climate?

On the simplest level, the weather is what is happening in the atmosphere at any given time. The climate, in a narrow sense, can be considered as the “average weather”, or in a more scientifically accurate way, it can be defined as “the statistical description in terms of the mean and variability of relevant quantities over a period of time”.

In a broader sense, climate is the status of the climate system which comprises the atmosphere, the hydrosphere, the cryosphere, the surface lithosphere and the biosphere. These elements all determine the state and dynamics of the Earth’s climate.

The atmosphere is the envelope of gas surrounding the Earth. The hydrosphere is the part of the climate system containing liquid water at the Earth’s surface and underground (e.g. oceans, rivers, lakes…). The cryosphere contains water in its frozen state (e.g. glaciers, snow, ice…). The surface lithosphere is the upper layer of solid Earth on land and oceans supporting volcanic activity which influence climate. The biosphere contains all living organisms and ecosystems over the land and in the oceans.

Climate Classification

Peel, M. C. and Finlayson, B. L. and McMahon, T. A. (2007)

People classify the climate in many different ways depending on who needs the information, how much they know about the climate system and what information they need to know. Most atlases have maps of temperature and precipitation around the world, and some contain maps of atmospheric pressure, prevailing winds, oceans currents and the amount of sea ice throughout the year. Many countries have more detailed classifications for various reasons. For example, the average dates of the first and last killing frost (a frost strong enough to kill plants and crops) are of value to farmers and growers, as is the average length of the frost-free growing season. In colder places, the number of days below freezing affects building design. “Degree-days” is a term often used by experts working on the energy consumption of buildings. Degree-days measure how many days in a given time period (often a month) were below or above a certain reference value (such as 18°C – 22°C). This indicates how many days that month the building needed either heating or cooling to be comfortable. It provides an indication of the energy needed for heating, air conditioning and refrigeration in homes and offices.

The most often used classification scheme is that of Vladimir Köppen, first presented in the early 1900’s and revised frequently since. The system, shown in the map above, is based on the idea that native plants and vegetation are the best indication of climate and so climate zone boundaries have been defined using the distribution of five different types of vegetation: tropical rain forest; hot desert flora; temperate deciduous forests; boreal forest and tundra.

Tropical rain forests are dense forests of trees containing other plants and animal species in regions of heavy, year round, rainfall in the tropics (e.g. the Amazon, Congo…) and the mid-latitudes (e.g. Eastern Australia, Florida, south Japan…).

Hot desert floras are plants mainly composed of ground-hugging shrubs and short woody trees found in tropical arid lands.

Temperate deciduous forests are plants mostly found in temperate climates. The dominant species are broad-leaved deciduous trees. Boreal forests or Taiga are found in the northern hemisphere over areas at the interface between temperate and polar climates. The dominant plant species are coniferous trees.

Tundra is characterized by tree growth hindered by low temperatures and a short growing season. The vegetation contains dwarf shrubs, sedges and grasses.

Other types of vegetation, such as bushlands or heathlands, are considered subdivisions of the main climactic types.