Anthropogenic Activities Have Modified Weather and Climate

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change is the alteration of weather and climate attributes orvariables and it is a result of an interplay of factors Climate ranging from natural phenomenon to human factors [Zhakata and Makarau 1995] .Major components of the climate system include ,temperature , precipitation,humidity, pressure and others . According to Waugh [2000] climate refers to the longterm atmospheric behaviour while weather refers to the state of the atmosphere at a local level and on a short term scale. This paper will focus on the modification of weather and climate by human beings.Hunnington in Zhakata and Makarau [1995] asserts that the driving force for the climatic system is the net absorption of solar radiation by the earth, atmosphere and oceans. He further argues that any form of interference with the above system, whether intentionally or unintentionally will lead to weather and climate modification and the modification can either be positive or negative.

According to Tyson [1987] human activities have a significant effect on climate.Bearing this assertion in mind it will be noted that human beings will intentionally modify weather and climate for their benefit,usually in industry and agriculture. Mkandla [1996] argues that because of unreliable rainfall in most parts of Zimbabwe,the department of meteorological services carry out cloud seeding to enhance the chances to precipitation .This leads to climate change since precipitation is artificially induced,thus diverting fromthe idealized precipitation process.Mabuya and Gariwe [2011] observe that human beings are the principal culprits in the weather and climate modification. In Zimbabwe and other countries wherethere is winter cropping, crops need to be protected against frost. Commercial farmers in Zimbabwe, especially in wheat production use large electric heaters which are placed at the edges of the fields and then large fans are used to blow hot air into the field thus creating a micro climate which is warmer than the surrounding area. Wind breakers arealso used to protect crops against strong winds.Thisinfluences or affects both wind speed and direction from their natural state creating a modification in climate. Wind speed and direction are diverted from their natural state hence the creation of a micro climate.

According to Waugh [2000] the extensive changes in land use have a climatic effect both on a macro and micro dimension. He argues that,massive deforestation in the equatorial rainforest where thereis massive timber harvesting,tillage of grasslands in savannaregions and desertification in the Sahel region which is adirect result of poor land management systems like overstocking, increasing the albedo of the surface which eventually alters the earth’s radiation balance.In other words when the land remains bare it absorbs and retains a lot of heat during the day, At night, the rate of short wave radiation is very high creating an area of high pressure due to the falling of temperature. This scenario leads to the divergence or reversal of winds leading to low rainfall,this argument, to some extent explains long drought spells in the Sahel region.

According to Mkandla [1996] a change in land use from forest to the farm land is believed to increase carbon dioxide content in the atmosphere,since the process of carbon fixation which occurs during photosynthesis would have been disturbed. Therefore since vegetation,which utilizes carbon dioxide during photosynthesis would have been depleted,carbon dioxide starts to accumulate in the atmosphere. To some extent this explains the high temperatures experienced in most parts of Zimbabwean rural areas where there is alarming deforestation because of fire wood poaching. Briggs and Smithson assert that since the industrial revolution the amount of atmospheric carbon dioxide and other greenhouse gases like methane, nitrous, oxide and chlorofluorocarbons [CFCs]...
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