02. Temperature

Why do temperatures vary in different locations?

Ø Latitude – Temperature generally decreases with increasing latitude. Places in low latitudes such as Singapore which is located at 1.3° North have higher temperatures because they receive vertical sunrays and hence more concentrated insolation. Temperatures are higher as the vertical sunrays travel through shorter distance of the atmosphere and smaller amount of insolation is lost through reflection and scattering. Places of higher latitudes such as Alaska which is located at 54° North have lower temperatures because they receive slanted rays which are spread over a larger area.

Ø Altitude - The atmosphere is mainly heated by long wave radiation (heat energy) from the earth's surface (land or sea surfaces). Thus, the higher the altitude, the cooler the air temperature. With increasing altitude or elevation, air becomes less dense and contains less dust and water vapour. . Heat from the earth's surface thus escapes more rapidly, thereby lowering the air temperature. In general, air temperature decreases with increasing altitude at a rate of about 0.6°C to 0.65°C per 100 metres (or 6°C to 6.5°C per 1000 m) in a free atmosphere. Both Singapore and Quito located near the equator. However Quito is located at a higher altitude of 2850m above sea level and experience lower temperatures.

Ø Distance from the sea- Land heats up and cools faster than water or the sea.

Maritime effect - onshore winds blowing from the sea or ocean to coastal regions tend to lower summer temperatures and raise winter temperatures. Such moderating influence is called maritime influence and is confined to coastal areas. Thus, coastal regions have a cooler summer and a warmer /milder winter than inland regions. The annual range of temperature in coastal regions is therefore smaller than that in inland regions. This is particularly felt in temperate regions.

Continental effect - Inland regions situated at a great distance from the sea have hotter summers and colder winters than coastal regions. The annual range of temperature in inland regions is greater, and the climate is thus more extreme than that of coastal areas e.g. Anchorage, which is near to the coast and Fairbanks which is 110km inland, has a smaller temperature range of 20°C compared to Fairbanks 40°C.

Ø Cloud cover - Blanket effect of cloud produces small diurnal and annual ranges of temperature. Clouds reduce the amount of solar radiation that reaches the earth's surface and re-radiation that leaves the earth's surface. The dense cloud cover in equatorial / tropical regions reduces intense solar heating of the land in the daytime. At night thick clouds prevent rapid loss of long wave radiation (heat energy) from the earth's surface. . The result is that daytime temperatures in tropical equatorial regions do not rise too high (rarely exceeding 33°C) even though the angle of the mid-day sun is high. On the other hand, night temperatures in these regions do not fall too much. The diurnal range and annual range of temperature are therefore small. e.g. Singapore and other equatorial regions. Absence of cloud cover leads to great diurnal range of temperature. The cloud cover in deserts tends to allow maximum solar heating of the land in the daytime. Thus daytime temperatures rise high (often exceeding 38°C). At night there is little cloud cover in desert regions. There is rapid and maximum loss of heat energy by radiation from the heated land surface, and temperatures fall to 21°C or below 0°C. This produces a great diurnal temperature range in desert regions. e.g. Sahara Desert

Graphic mind map (sketch note) on factors affecting temperature at different places/locations