The climate of the Earth is affected by a number of factors that are called climate “forcings”. This is because they force the overall climate system to change. These forces are typically divided into two categories: positive and negative forcings. Certain factors that influence the total positive or negative forcing of the earth system include, surface reflectivity (albedo), greenhouse gases, and atmospheric aerosols (volcanic sulfates, industrial output). Positive forcings contribute to the increase in the earth’s temperature, and negative forcings contribute to the decrease in the earth’s temperature. The figure below shows the main climate forcings that lead to the warming and cooling of the overall temperature of the earth.
Figure 11: Radiative Forcing for Greenhouse Gases and Other Climate Forcing Agents
The albedo of the earth refers to the reflective power of a surface. An example shows that the fresh snow has a reflective surface of 40-80%. However when the snow melts it exposes more of the ocean, forest, and crops, which have only a 5-15% reflective surface seen below in the graph. This results in the more of the sun’s rays being absorbed by earth’s surface and less rays being reflected back into the atmosphere. This repetitive cycle increases the overall temperature causing more and more snow to melt.
Figure 12: Percentage of diffusely reflected sun light in relations to various surface conditions
Deforestation is often thought about when discussing the issue of global warming and the alarming use of fossil fuels. To answer this question we must look at the global carbon cycle as a whole and the reduction of biomass. Biomass takes carbon out of the atmosphere while it is living, however once it is burned or dies it releases massive amounts of CO2 back into the atmosphere. It is estimated that 12 million hectares of forests are cleared annually. As seen from the graph below, it is estimated that about 8 billions tons of CO2 comes from deforestation which is about 20% of all carbon emissions. The world’s rainforest is a living ecosystem that is needed to absorb CO2 from the atmosphere. The rainforest will store the carbon but with the ever-increasing demand for land, the carbon sink is getting released early and often into the atmosphere causing the overall CO2 emissions to dramatically increase. Deforestation isn’t the main source of CO2 emissions but it is a vital issue that needs to be monitored in the fight against global warming.
Figure 13: Annual emissions and absorptions from land-use change activities, global estimates
References:
http://www.realclimate.org/index.php/archives/2007/02/aerosols-the-last-frontier/
http://climatelab.org/Forests
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