Introduction
It is extremely evident that since humans have existed, they have had a significant impact on the earth. Humans have contributed to the trends of Carbon Dioxide (CO2) and other greenhouse gases in the early Holocene from anthropogenic activities such as agriculture, deforestation, seasonal biomass burning and producing waste (Ruddiman et al., 2008). However, it is debateable that natural influences, such as warming temperatures from the earth’s precession cycle and natural sinks and uptakes, may also have been a contributor to high rates of greenhouse gases in the early Holocene (Broecker, 2006; Wei et al., 2015). This essay will be addressing both the anthropogenic and natural influences on trends of greenhouse gases in the earth’s atmosphere during particular periods of time. These periods of time include the early Holocene, the industrial era and our current time period.
Early Holocene Greenhouse Gas Trend
During the early Holocene, there was a dramatic rise in greenhouse gas emissions. Ruddiman (2003) suggests that major human influences to global climate and the environment began thousands of years before the industrial revolution, with domestication of livestock and crops, which over thousands of years has led to a global spread of agriculture. The dramatic rise in greenhouse gases during the early Holocene is evident during the Bronze Age (~4500 years ago), which followed a substantial methane decrease approximately 5000 years ago (fig. 1.) (Ruddiman et al., 2008).
A claim by Ruddiman (2003) suggests that these greenhouse gas emissions were primarily anthropogenic in origin, rather than natural, and proposes an anthropogenic 40ppm CO2 rise had prevented another ice age (Broecker, 2006). This early theory has been widely debated and tested with other theories, for example comparing the ocean’s present dissolved inorganic carbon inventory with that of which it would have been roughly 8000 years ago. This shows that according to Ruddiman’s early theory, the amount of CO2 in the ocean would have surpassed that which is in the atmosphere by a factor of five (Broecker, 2006). However, Ruddiman’s early theory was later supported by Ruddiman (2013) which discusses the historical and archaeological data regarding earth’s condition approximately 7000 years ago. This data showed that the first humans in all regions used a greater amount of land per capita per person, especially due to agricultural activities, which may have resulted in an increase in CO2 into the atmosphere (Kaplan, 2010).
In China approximately 5000 to 1000 years ago, rice irrigation was estimated to have caused an atmospheric methane (CH4) increase of ~70ppb, which is a large portion of the 100ppb increase drawn from ice core measurements (fig. 2) (Ruddiman, 2013). This shows that as irrigation increases, so does CH4 in the earth’s atmosphere, and supports Ruddiman’s (2003) early theory that the increase of CO2 emissions was primarily human induced.
It is also important to recognise that the earth’s orbit during the Holocene is somewhat lesser than those of the previous three interglacials (fig. 3), which could possibly explain a natural rise in CO2 during the early Holocene (Broecker, 2006).
The Industrial Era
It is debated that the most significant effects on the earth’s atmosphere occurred during the industrial era (1850) (Steffen et al., 2007). This is due to the fact that humans have had a severe impact on the environment, due to mostly the anthropogenic influences rather than natural influences. These anthropogenic influences include the use of mechanised agriculture, mechanised earth-moving, the use of industrial fertilisers, construction of industrial power plants, the use of fossil fuels and many other influences which are major factors that have contributed to the increase of greenhouse gases in the atmosphere (Ruddiman, 2013). The industrial revolution was also followed by animal extinctions, land clearance, forest cuttings, habitat transformations, soil erosion and rice irrigation (Ruddiman et al., 2015).
There was such a great amount of impact on the earth’s environment during the industrial era that is has been argued the industrial revolution should be classified as the beginning of the Anthropocene (Ruddiman, 2013).This is evident when viewing figure 4, which displays an obvious increase of CO2 and CH4 by 1850, which is linked to land changes due to a rapid increase in population and burning fossil fuels (Ruddiman, 2013).
There are two differing views on historical land-use. These are the industrial view, which estimates that the industrial era was the period when the majority of deforestation occurred, and the early anthropogenic view suggests that approximately three quarters of total forest clearance occurred prior to the industrial era (figure 5). Ruddiman (2013) suggests that due to the evidence of early anthropogenic influences on the emission of greenhouse gases in the earth’s atmosphere, and early land-cover change, it is more likely that the early anthropogenic view is accurate and that large amounts of deforestation begun thousands of years before the industrial era (1850). This is supported by the extensive forest clearing which took place to make way for agriculture, for example rice irrigation in china, beginning approximately 5000 years ago (Ruddiman et al., 2008).
Relating to the early anthropogenic view, Ruddiman (2013) suggests that the early Holocene trend is most likely anthropogenic rather than natural due to evidence from previous interglacials. The past three interglacial trends had an early rise in CO2 and CH4 followed by an average continual decline, however, the CO2 and CH4 trend during the current interglacial has been steadily increasing. This suggests human induced influences have had an effect on the amount of greenhouse gases in the earth atmosphere (Ruddiman, 2013).
Most Recent Trends in Greenhouse Gases
There is no denying that the increase in earth’s population and the development of new technologies has caused a continual increase in greenhouse gases since the industrial era. It is important to note that developed countries have contributed to 51.9% of greenhouse gases between the years of 1850 and 2010, respectively (Wei et al., 2015). The greenhouse gases which are remaining in the earth’s atmosphere are related to the issue of global warming temperatures. However, anthropogenic influences are not the only cause of greenhouse concentrations, natural sinks and uptakes also contribute to the atmospheric composition and global rising temperature (Wei et al., 2015).
Developing countries have been found to have a consistently higher emission level of CH4 than that of developed countries between the years of 1890 to 2005. This may be due to the great reduce in CH4 emissions from developed countries and the increase in CH4 from developing countries, regarding the use of energy, industry and agriculture (Wei et al., 2015). According to Wei et al., (2015) 53% of Arctic sea-ice extent decrease is caused by developing countries. However, this decline may be affected by the natural inconsistency of large-scale atmospheric circulation.
It is evident that during the past 50 years, humans have irrefutably changed the world’s ecosystems more expeditiously and extensively than in any other period of human history (Steffen et al., 2007). Many more species are becoming extinct and multiple atmospheric greenhouse gas concentrations are causing the earth to rapidly become warmer. This is evident in the increasing momentum of industrialisation and huge increase in human population (fig. 6).
Conclusion
It is evident that there were both anthropogenic and natural influences that effected the eras between the early Holocene and the current period. It is argued that a portion of the rise in greenhouse gases is caused by natural influences such as the earth’s precession cycle, natural sinks and uptakes, and atmospheric circulation. However, there is an enormous amount of evidence which supports the fact that the trends in the periods from the early Holocene to the current time are mostly caused by anthropogenic influences. This is clear from large amounts of early agriculture and deforestation, the beginning of the industrial era which trends show was a major event causing greenhouse gases to rapidly increase, and now the current rise in population and industrialisation of the present times causing a continual upward trend of greenhouse gases in earth’s atmosphere, resulting in warming of the earth.
References
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