Mankind Is the Main Cause of Global Warming

I agree with the alternate definition he provided. Looking back to the definition I cited in round 1, I defined global warming as ". .. the average temperature of Earth's atmosphere and oceans since the late 19th century, and its projected continuation. " This means that any arguments regarding natural factors' effects on the climate before the late 19th century and long term climate projection of there being another ice age are irrelevant. I'm not contending that natural factors have no effect on the climate, or even that they are not usually the only cause of climate change. All I'm arguing is that the global warming since the late 19th century has been driven mostly by anthropogenic forcings. [1]Since my opponent provided no other arguments, all I will do in this round is show how comparing natural factors and anthropogenic factors shows that humans are the main cause of global warming. The most important of the natural climate forcings is the sun. It is the source of the Earth's energy. This energy comes from the radiation emitted as a result of fusion reactions at the core of the sun. This radiation is known as the Total Solar Irradiance (TSI). Any change in the TSI causes energy imbalances on the Earth. This energy imbalance can be calculated using the formula below: Delta means change, so Delta(F) means the change in energy (i. e. energy imbalance) and Delta(TSI) means the change in solar irradiance. The 0.7 factor comes from the fact that the Earth reflects about 30% of the solar radiation it receives, and the 1/4 factor comes from spherical geometry. Changes in temperature are proportional to the energy imbalance. This can be expressed in the formula below: Lambda is the constant of proportionality, representing the climate sensitivity (discussed in my first argument) in this case. The only thing that's left is to actually determine the values. First, the change in TSI (in this case, between 1900 and 1950). "Although Wang, Lean, and Sheeley's reconstructionputs the change in TSIsince 1900 at about 0.5 W-m-2, previous studies have shown a larger change, so we'll estimate the change in TSI at 0.5 to 2 W-m-2. " This corresponds to an energy imbalance of around 0.1-0.35 W-m-2. Next, the lambda factor. I explained in the last article that the statistically most probable value for the climate sensitivity was around 3 degrees C. But, there was a lot of variation. "Studies have given a possible range of values of 2 to 4.5°C warming for a doubling of CO2, which corresponds to a range of 0.54 to 1.2°C/(W-m-2) for λ. " This gives range of values from 0.05 to 0.4 degrees C, with a most probable value of 0.15 degrees C (corresponding to the statistically most likely climate sensitivity). In other words, solar activity from 1900 to 1950 raised the temperature of the Earth 0.15 degrees C. [2]Looking at the effect of CO2 emissions over that same period, humans increased the concentration of CO2 in the atmosphere by about 20 parts per million, giving a range of values of 0.14-0.32 degrees C for the effect of that emission on the climate, with the most probable being 0.22 degrees C. [2]This corresponds to CO2 amounting for 60% of the warming from 1900-1950. After that, it gets higher. CO2 emissions rise exponentally, and changes in the TSI start getting less positive, and eventually become negative after 1975. "Therefore, the solar forcing combined with theanthropogenicCO2forcing and other minor forcings (such as decreased volcanic activity) can account for the 0.4°C warming in the early 20th century, with the solar forcing accounting for about 40% of the total warming. Over the past century, this increase inTSIis responsible for about 15-20% of global warming. But sinceTSIhasn't increased in at least the past 32 years (and more like 60 years, based onreconstructions), the Sun is not directly responsible for the warming over that period. " Solar activity cannot account for the warming after 1975, and even before that was a smaller factor than CO2. [2]This can be shown in the image below: [3]CO2 correlates with CO2 more than solar activity, especially after 1975. There are other natural forcings, ozone concentrations and volcanic activity being the other major ones. The ozone layer of the atmosphere blocks the sun's UV radiation from reaching the Earth. Lowering levels of ozone may cause warming then by allowing more solar radiation to reach the Earth. However, while ozone levels were decreasing before 1995, they are now increasing (regardless, the declining ozone levels were also caused by humans). And the volcanic activity forcing has actually had a cooling effect on the climate. "Foster and Rahmstorf (2011) used a multiple linear regression approach to filter out the effects of volcanic andsolar activity, and the El NiñoSouthern Oscillation(ENSO). They found that volcanic activity, as measured by aerosol optical thickness data (AOD) has only caused between 0.02 and 0.04°C per decade warming from 1979 through 2010 (Table 1, Figure 2), or about 0.06 to 0.12°C warming of the surface and lowertroposphere, repsectively, since 1979 (out of approximately 0.5°C observed surface warming). "[4]In total, all the forcings, both natural and anthropogenic, can be shown below: [3]Greenhouse gases are far more important than solar activity (note that sulfate levels mostly correlate with volcanic activity). ConclusionI don't have anything more to say, since this is all my opponent talks about. Anthropogenic forcings were more important for global warming than natural forcings. Sources[1]: . http://en.wikipedia.org...[2]: . https://www.skepticalscience.com...[3]: . http://solar-center.stanford.edu...[4]: . https://www.skepticalscience.com...