Weather Climate and Climate Change

Weather describes the short-term (i. e., hourly and daily) state of the atmosphere. It is not the same as climate, which is the long-term average weather of a region including typical weather patterns, the frequency and intensity of storms, cold spells, and heat waves. However, climate change refers to changes in long-term trends in the average climate, such as changes in average temperatures. In Intergovernmental Panel on Climate Change (IPCC) terms, climate change refers to any change in climate over time, whether due to natural variability or as a result of human activity. Climate variability refers to changes in patterns, such as precipitation patterns, in the weather and climate. Finally, the greenhouse effect (global warming) is a progressive and gradual rise of the earth's average surface temperature thought to be caused in part by increased concentrations of CFCs in the atmosphere.

In the past, there have been claims that all weather and climate changes are caused by variations in the solar irradiance, countered at other times by the assertion that these variations are irrelevant as far as the lower atmosphere is concerned (Trenberth et al., 2007). The existence of the atmosphere gives rise to many atmospheric and meteorological events. Greenhouse gases are relatively transparent to visible light and relatively opaque to infrared radiation. They let sunlight enter the atmosphere and, at the same time, keep radiated heat from escaping into space. Among the major greenhouse gases are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which contribute to global warming (climate change) effects in the atmosphere. Atmospheric composition has changed significantly since pre-industrial times and the CO2 concentration has risen from 280 parts per million (ppm) to around 370 ppm today, which corresponds to about a 0.4% increase per year. On the other hand, CH4 concentration was about 700 parts per billion (ppb) but has reached 1700 ppb today, and N2O has increased from 270 ppb to over 310 ppb. Halocarbon does not exist naturally in the atmosphere, but since the 1950s it has accumulated in appreciable amounts causing noticeable greenhouse effects. These concentration increases in the atmosphere since the 1800s are due almost entirely to human activities.

The amount of the solar radiation incident on the earth is partially reflected again into the earth's atmosphere and then onward into the space. The reflected amount is referred to as the planetary albedo, which is the ratio of the reflected (scattered) solar radiation to the incident solar radiation, measured above the atmosphere. The amount of solar radiation absorbed by the atmospheric system plays the dominant role in the generation of meteorological events within the lower atmosphere (troposphere) and for the assessment of these events the accurate determination of planetary albedo is very important. The absorbed solar energy has maximum values of 300 W/m2 in low latitudes. On the basis of different studies, today the average global albedo is at about 30% with maximum change of satellite measurement at ±2%, which is due to both seasonal and inter-annual time scales. Furthermore, the maximum (minimum) values appear in January (July). The annual variations are as a result of different cloud and surface distributions in the two hemispheres. For instance, comparatively more extensive snow surfaces are present in the northern European and Asian land masses in addition to a more dynamic seasonal cycle of clouds in these areas than the southern polar region. Topography is the expression of the earth's surface appearance, height, and surface features. It plays an effective role both in the generation of meteorological events and solar radiation distribution. Although the surface albedo is different than the planetary albedo, it makes an important contribution to the planetary albedo. The cloud distribution is the major dominant influence on the earth surface incident solar energy. Since the albedo is a dominant factor in different meteorological and atmospheric events, its influence on the availability of solar radiation has an unquestionable significance. The calculation of solar energy potential at a location is directly related to albedo-affected events and the characteristics of surface features become important (Chap. 3). In general, the albedo and hence the solar radiation energy potential at any location is dependent on the following topographical and morphological points:

1. The type of surface

2. The solar elevation and the geometry of the surface (horizontal or slope) relative to the sun

3. The spectral distribution of the solar radiation and the spectral reflection

Table 2.1 indicates different surface albedo values with the least value being for a calm sea surface at 2%, and the maximum for a fresh snow surface reaching up to 80%. In general, forests and wet surfaces have low values and snow-covered

Table 2.1 Albedo values


Albedo (%)

New snow

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