Critically assess why it is difficult to accurately forecast the amount of anthropogenic climate change we can expect to see by 2050

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In this essay the author will assess the difficulties with forecasting the amount of anthropogenic climate change we can expect to see by 2050. The author will use quotes, definitions and examples where appropriate.

Over the past 100 years, the world has seen an increase in global average temperatures. Since 1860, the global average temperature has increased by ‘0.6 degrees Celsius with a ninety-five percent confidence’. (Houghton, J, 2004:56) This increase is believed to be cause of the greenhouse effect, which “…refers to the reduction in outgoing infrared radiation to space due to the presence of the atmosphere.” (Harvey, L, 2000:95) This greenhouse effect is induced by natural and anthropogenic sources. The greenhouse effect is partly attributed to the emissions of ‘greenhouse gases’, such as water vapour, carbon dioxide, methane, ozone and nitrous oxide. (The Royal Society, 2002) The gases form a blanket over the earth which traps the sun’s radiation resulting in conditions similar to a greenhouse, see Figure A.

Figure A The ‘Greenhouse Effect’

                                        (Houghton, J, 2004:18)

Anthropogenic Carbon Dioxide (CO2) is a gas that is believed to be of main concern, as it is a prominent contributor to an ‘Enhanced’ Greenhouse effect. Since the industrial revolution, CO2 levels have increased by 30 percent, from 280 parts per million per volume in the 1700 (Houghton, J, 2004) to 377.38 ppmv in 2004 (Keeling, C and Whorf, T, 2005) accounting for 55% of total anthropogenic emissions. (Andrews, J et. Al, 1996:181) According to Manahan,

“Carbon Dioxide is increasing by about 1ppm per year.”

        (Manahan, 1991:341)

Methane (CH4), a component of natural gas has seen increases from 0.7 parts per billion during the pre-industrial period to 1.7 parts per billion (Manahan, 1991:341). Highlighting that; “Methane is going up at a rate of almost 0.02 ppm/year” (Manahan, S, 1991:341) accounting for 15% of total anthropogenic emissions. (Andrews, J et. Al, 1996:181) This is a small but significant increase as ‘CH4 is 20-30 times more effective at trapping heat compared to CO2’. (Manahan, S, 1991:341) These increases, along with many other greenhouse gases are attributed to the burning of fossil fuels, such as coal, oil and gas, and deforestation, leading to an ‘Enhanced’ greenhouse effect. Deforestation not only causes a reduction in CO2 absorption, but some deforestation requires the burning of trees for clearing which further increases the level of atmospheric CO2.

The greenhouse gases induce positive radiative forcing which leads to the potential effect of creating global climate change. Climate change is defined

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“A change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods.”

                                                                (UNFCCC, 2006)

This results in global sea-level rise through the melting of ice caps and glaciers and seawater expansion. According the IPCC, sea levels have risen by 1 to 2 millimetres per annum during the 20th century. Furthermore positive radiative forcing has attributed to global surface temperature increases (Watson, R et. Al, 2001). The effects cause extreme weather events to occur, for instance flooding, ...

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