An Assessment of The Extent of Human Impact on Climate Change The fact that earth’s atmosphere has heated up over the last hundred years is a fact widely accepted within the scientific community. The last hundred years has seen huge swaths of the Great Barrier Reef turn white, entire glaciers disappear, and ocean level rise that has consumed crucial farmland, threatening the economic stability of entire countries. Additionally, NASA has reported that 16 out of the 17 hottest years on record have occurred within the past 20 years (NASA). This evidence has compelled most scientists to shift the argument from whether or not global warming is occurring to why it is occurring. The impact of natural cycles and fluctuations on climate change should not be ignored, but greenhouse gas emissions and deforestation caused by recent industrial development have certainly upset our atmosphere and our planet. While there is significant evidence of natural contributions to climate change phenomena, research indicates that human activity is by far the largest contributor. The Earth’s atmosphere contains many gases, some of which are called trace gases. These trace gases are the ones of which absorb heat. The ability of the greenhouse gases to trap the heat is influenced by many characteristics of the gas. Greenhouse gases can come in many different forms, including carbon dioxide, methane, nitrous oxide, and fluorinated gases. There are many sources of these gases that can be found in the atmosphere. The radiation that is emitted from the sun is absorbed by the gas, which gets trapped near the Earth’s surface in the atmosphere. Some of the energy is emitted back from the Earth’s surface in the form of infrared rays. The longer wavelengths that are going away from the earth are absorbed by the greenhouse gases. They are then emitted in all directions to warm the earth. Greenhouse gases are very important for the earth as well, but too much can be harmful. Without these greenhouse gases, the radiation would bounce back in the atmosphere and leave Earth. Greenhouse gases prevent the radiation from leaving the surface of the Earth. If the concentration of greenhouse gases was to stay constant over the course of a few hundred years, the average temperature of the Earth would rise 4-6 degrees Fahrenheit while sea level could rise 1-3 feet (Davis, Caldeira, & Matthews, 2010).Burning fossil fuels is not only unsustainable but also harmful to the environment. Fossil fuels originate as carbon life forms. After these die, they are buried in the ground and the pressure added to the carbon turns it into usable forms of energy, such as coal and oils. Fossil fuels are used to do many things. Humans burn fossil fuel at power plants to produce energy, which is then used in cars and other machinery. As the fossil fuels are burned, the reaction releases carbon dioxide (see Equation A1). Oil production rates are incredibly high, about 3900 million tons of oil per year. Not far behind are coal and natural gas at about 3700 million tons per year (Hook & Tang, 2013). The speed at which humans are consuming fossil fuels exceeds the speed at which they can be produced by natural processes. Due to the fact that there is a finite amount of carbon on Earth, it is constantly undergoing phase changes. As these fossil fuels are burned it continually adds to the production of carbon dioxide. Carbon dioxide is a form of a greenhouse gas. In a current report from BP, “Emissions of CO2 from energy consumption increased by only 0.1% in 2016. During 2014-16, average emissions growth has been the lowest over any three-year period since 1981-83,” (BP, 2017). Even though the rate is .1%, BP said this has been the lowest rate since 1981-83. Nowhere do they say that the amount has gone down. EPA estimates apportion the production of atmospheric carbon dioxide from various sources as follows: 35% from energy generation, 32% from transportation, 15% from industrial sources, 10% from residential sources, and the remaining 7% from natural processes (EPA, 2017). As shown in Figure B3, carbon dioxide produced by fossil fuel combustion accounts for 56.6% of all greenhouse gases in the atmosphere (IPCC, 2007). Among the most significant human contributions to global warming is deforestation. The definition of deforestation varies widely, but in its broadest terms, it can be defined as the loss of tree cover. Deforestation contributes to global warming in two major ways. The first of these is releasing carbon into the atmosphere. One way this occurs is through the release of soil carbon. Over time, carbon from dead vegetation can build up in the soil underneath tree cover and after deforestation, the soil becomes exposed to sunlight. Upon becoming exposed to sunlight, the rise in temperature within the soil causes an increase in the rate of soil carbon oxidation. This increase in oxidation leads to an increase of carbon dioxide release to the atmosphere. Although soil carbon release is debated, there are studies that show it indeed releases carbon into the air (Cerri et al.,1991). Human-induced disturbances to the soil such as logging operations also cause a large increase in soil carbon release. Removal of forests releases more carbon than natural biodegradation because human removal is accompanied by activities such as logging and farming that churn the soil and increase carbon release rates. The second way that deforestation releases carbon into the atmosphere is through lumber utilization. The rate of this carbon emission heavily depends on how the lumber is utilized. The carbon within lumber used in buildings can remain trapped for a hundred years, while lumber used in paper typically remains trapped for less than a year (Skog & Nicholson, 2000). In both examples, the carbon eventually finds its way to the atmosphere since matter cannot be created nor destroyed. The third most crucial way deforestation releases carbon into the atmosphere is through forest fires. Forest fires can be natural or anthropogenic and in both cases, large amounts of carbon dioxide are emitted into the atmosphere in a short amount of time. Anthropogenic fires tend to transfer more carbon dioxide into the atmosphere than naturally-occurring ones (Krawchuk et al., 2009). This is in part because human created fires are often deliberately intended to clear land for agricultural purposes, which require large swaths of land. Additionally, human-induced fires often occur in areas where natural fires are extremely rare, such as tropical forests in South America. Ecosystems where forest fires are rare are less likely to regenerate and recover from them. After so many years of growing without any fire, a human-induced fire can completely devastate entire sections of a rainforest. When rain forests are wiped out, they do not completely regenerate and instead end up as brush fields with less vegetation (Krawchuk et al., 2009). In sharp contrast, natural fires are part of the natural carbon cycle, with carbon emissions balanced by regrowth over the long run. This natural carbon cycle leads to the second crucial way deforestation impacts global warming, photosynthesis. When considering the impact on photosynthesis, is helpful to use a mass balance, as shown in Equation A2. Photosynthesis is a process whereby plants take in carbon dioxide and emit oxygen. Therefore, this process represents the “SINKS” term in the balance of carbon dioxide in the atmosphere. Deforestation reduces the capacity of earth’s plants to carry out photosynthesis since forests represent a large share of the earth’s vegetation, causing the “SINKS” term to decrease. While the “SINKS” term decreases, human activities such logging, farming, and the combustion of fossil fuels all cause the “SOURCES” term to increase. In a sustainable, or “steady-state,” system, the “ACCUMULATION” term equals zero. Most scientists agree that the Earth’s atmosphere existed in a steady state before the Industrial Revolution (Bonan, 2008). However, the increase in “SOURCES” and decrease in “SINKS” throws the system out of equilibrium, resulting in a buildup of carbon dioxide in the atmosphere. A crucial point to note is that the effect of deforestation on carbon dioxide in the atmosphere is twofold. Not only are there less forests to absorb carbon dioxide, but those very same forests that are supposed to be absorbing are instead being converted into carbon dioxide. Considering the evidence supporting anthropogenic causes of climate change, it is important to evaluate natural factors and their impact by comparison. An ideal scientific approach includes a variable to be measured and a constant to be controlled, but in our ever-changing universe it is difficult to account for and normalize every simultaneous event that may contribute to global warming trends. While there are certainly some natural causes of climate change, many people are prone to give more weight to these natural causes than present scientific study supports. Here we will address a couple of naturally-occurring events that have caused uncertainty as to the degree to which humans can be held responsible for climate change.Volcanic eruptions produce large amounts of sulfur dioxide (SO2), which condenses to form clouds of aerosol particles. Aerosols produced by specific volcanic events have been known to remain in the atmosphere for five or more years (Allen, 1996). The impact of these aerosols on the chemical composition of our atmosphere is so significant that some may be led to think that human impact is negligible in comparison. Adding to the counterargument is the fact that small-scale warming effects due to these aerosols have also been observed in some select areas, including Fukuoka, Japan after the 1979 eruption of Sierra Negra in Mexico (Fujiwara, Shibata, & Hirono, 1982). However, ironically enough, the scientific community has concluded that volcanic aerosols generally have a cooling effect on the Earth’s surface as particles reflect incoming sunlight back into the stratosphere (Swingedouw et al, 2017). For example, studies have estimated that the eruption of Mt. Pinatubo in 1991 reduced the mean global temperature by 0.5 K when measured 18 months after the event (Soden et al, 2002). This cooling trend has been observed after most major volcanic events, as shown in Figure B4, and indicates an overarching cooling pattern even if warming can be observed in select areas.NASA defines irradiance as “…the amount of light energy from one thing hitting a square meter of another each second” (Zell, 2008). In the context of climate change, we are concerned with solar irradiance as it impacts earth. Solar irradiance varies due to the 11-year sun cycle and due to sunspots, which indicate unevenness in the sun’s surface temperature. Researchers believe that the sun has been more active in the last 60 to 70 years than it was in the preceding millennium, with activity including the formation of high-energy isotopes and sunspots (Mishchenko et al., 2007). This variation in the intensity of the light energy that Earth receives from the sun has been a legitimate cause of uncertainty in climate change data because it is difficult to distinguish between anthropogenic warming and warming due to solar irradiance. While uncertainty does exist, research does not support that the impact of solar irradiance is anywhere near equal to that of human activity. As indicated in Figure B5, the IPCC estimates the radiative forcing of global warming caused by total solar irradiance amounts to only about 8% as much as human activity, even during the past few decades of high solar activity (IPCC, 2007). More conservative climate modeling has suggested that total solar irradiance may account for 10-30% of global warming from 1980-2002 (Scafetta & West, 2005), but even these numbers indicate that a huge majority of observed warming trends have been caused by human activity. At present, scientists have no reason to expect that solar irradiance, even if it were to be accurately quantified, could upset the conclusion that human contributions to climate change far outweigh natural ones. After evaluating research conducted on both natural and anthropogenic causes of global climate change, it is apparent that climate change can be attributed to human activity to a much greater extent than to natural causes. While human have certainly made great technological and societal advancements over the past 100 years, these advancements have come at a cost to the environment and Earth as a whole. Humans have pumped billions of gallons of fossil fuels from the ground and then burned the fuel, releasing harmful greenhouse gases. Humans have also cut down entire forests to gain access to the resources that are in and under them. While natural factors have been known to impact the earth’s surface temperatures, these impacts have either been misunderstood, as in the case of volcanic aerosols, or overestimated, as in the case of total solar irradiance. It was not until recent years that humans were completely able to the understand the harm that has been done to the Earth. By understanding these causes, humans can change current habits and work to reverse the damage that has already been done.