Info

Volcanic Activity 1600 1700

m i i i i i i i i i i i I i l" i i i ' i i i i r i i 11 i i i i i i i | i i l 1300 1400 1500 1600 1700

Year AD

1800 1900 2000

m i i i i i i i i i i i I i l" i i i ' i i i i r i i 11 i i i i i i i | i i l 1300 1400 1500 1600 1700

Year AD

1800 1900 2000

Figure 2.11 Record of volcanic eruptions in the GISP 2 ice core and calibrated visible optical depth for ad 1300 to 2000, together with the names of major volcanic eruptions. Note that the record reflects eruptions in the northern hemisphere and equatorial region only; optical depth estimates depend on the latitude and the technique used for calibration.

Source: Updated after Zielinski et al. (1995), Journal of Geophysical Research 100 (D), courtesy of the American Geophysical Union, pp. 20, 950, Fig. 6.

centration derived from volcanic dust is extremely irregular (see Figure 2.11), but individual volcanic emissions are rapidly diffused geographically. As shown in Figure 2.12, a strong westerly wind circulation carried the El Chichón dust cloud at an average velocity of

20 m s-1 so that it encircled the globe in less than three weeks. The spread of the Krakatoa dust in 1883 was more rapid and extensive due to the greater amount of fine dust that was blasted into the stratosphere. In June 1991, the eruption of Mount Pinatubo in the

Philippines injected twenty megatons of SO2 into the stratosphere. However, only about twelve eruptions have produced measurable dust veils in the past 120 years. They occurred mainly between 1883 and 1912, and 1982 and 1992. In contrast, the contribution of man-made particles (particularly sulphates and soil) has been progressively increasing, and now accounts for about 30 per cent of the total.

The overall effect of aerosols on the lower atmosphere is uncertain; urban pollutants generally warm the atmosphere through absorption and reduce solar radiation reaching the surface (see Chapter 3C). Aerosols may lower the planetary albedo above a high-albedo desert or snow surface but increase it over an ocean surface. Thus the global role of tropospheric aerosols is difficult to evaluate, although many authorities now consider it to be one of cooling. Volcanic eruptions, which inject dust and sulphur dioxide high into the stratosphere, are known to cause a small deficit in surface heating with a global effect of -0.1° to -0.2°C, but the effect is short-lived, lasting only a year or so after the event (see Box 13.3). In addition, unless the eruption is in low latitudes, the dust and sulphate aerosols remain in one hemisphere and do not cross the equator.

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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