Key Points

Climate is classified using three broad approaches. These are empirical (based on observed data like temperature), genetic (based on causes), and applied (for a specific purpose).

The most widely used system is V. Koeppen's empirical classification. It connects climate with vegetation distribution using mean annual and monthly temperature and precipitation data.

Koeppen identified five major climatic groups using capital letters. A, C, D, and E represent humid climates, while B represents dry climates.

Group A climates are defined by an average temperature of 18 C or higher in the coldest month. Sub-types include Af (Tropical wet), Am (Tropical monsoon), and Aw (Tropical wet and dry).

In Group B climates, potential evaporation is greater than precipitation. They are subdivided into Steppe or semi-arid (BS) and Desert (BW).

These mid-latitude climates have a coldest month average temperature higher than minus 3 C but below 18 C. They generally have warm summers and mild winters.

Found in large continental areas in the Northern Hemisphere, Group D climates have a coldest month average temperature of minus 3 C or below.

Group E climates exist poleward of 70 degrees latitude and have an average temperature below 10 C for all months. They include Tundra (ET) and Ice Cap (EF) climates.

Small letters indicate precipitation patterns: f for no dry season, m for monsoon, w for winter dry, and s for summer dry. Small letters a, b, c, d refer to temperature severity.

Geological records, tree rings, and historical accounts show that climate change is a natural and continuous process. Earth has witnessed many alterations between glacial and inter-glacial periods.

The 1990s was the warmest decade of the 20th century. The year 1998 is considered the warmest year of the millennium.

Causes are grouped into astronomical (sunspots, Milankovitch cycles) and terrestrial (volcanism). The most important human-induced cause is the increasing concentration of greenhouse gases.

The greenhouse effect is the process where certain gases in the atmosphere trap long-wave radiation from the Earth's surface, causing the atmosphere to warm.

The main greenhouse gases are Carbon Dioxide (CO2), Chlorofluorocarbons (CFCs), Methane (CH4), Nitrous Oxide (N2O), and Ozone (O3). CO2 is the most abundant.

Proclaimed in 1997, the Kyoto Protocol is an international agreement that binds industrialized nations to reduce their emissions of greenhouse gases.

Global warming can lead to rising sea levels from melting glaciers and thermal expansion of seawater. This threatens to inundate large coastal areas and islands.