Global warming is mostly anthropogenic

Alleged coolingMy opponent claims that the atmosphere cooled between 2001 and 2008. However, this does not imply that global warming has stopped. Even in a period of long-term warming, surface temperatures can show short-term cooling trends. For example, there have been 54 cooling periods lasting 9 years in the HadCRU dataset (1). Many of these cooling periods have occurred in the context of long-term warming. As Dr. Liebmann concluded, the recent cooling trend between 2001 and 2008 was “neither statistically significant nor unusual in the context of trend variability in the historical record” (2). Therefore, the alleged cooling was probably due to natural variability, including a strong La Nina which occurred in 2008. During La Nina, heat is transferred from the atmosphere into the ocean. Meanwhile, the opposite occurs during El Nino. These natural weather phenomena, which have occurred for thousands of years, can change annual temperatures by as much as .2ºC. Over short time periods, atmospheric temperature trends closely reflect the behavior of these events. However, over time, the cooling caused by La Nina events balances the warming induced by El Nino events. Thus, these natural variations have practically no influence on atmospheric temperatures over long time scales. According to the World Meteorological Organization, data must be averaged over 30 years to eliminate nearly all year-to-year temperature variations (3). Trends over time scales significantly shorter than 30 years clearly have little meaning. They’re highly uncertain and can't be used to accurately predict long-term trends. This undoubtedly applies to the cooling between 2001 and 2008. In essence, we cannot tell if global warming is continuing simply by looking at short-term atmospheric trends.Nevertheless, it’s still possible to determine if global warming has continued in the past decade. We can do so by examining the heat content of the entire climate system, including the oceans, land, atmosphere, and ice. The planet’s total heat content is not influenced by natural variations like El Nino and La Nina. These oscillations simply redistribute heat throughout the climate system; they cannot create or destroy heat.Researchers have found that the climate system as a whole has continued to accumulate heat since 2000 (4-5). This proves that global warming is continuing, regardless of the short-term atmospheric cooling trend. Climate Model ValidationMy opponent claims that climate models are inaccurate, citing two blog articles. I will begin by examining the second article, his reference number 7 in round 3. This article purports to demonstrate that the cooling trend between 2001 and 2008 is inconsistent with model projections. However, this article compares temperature data to the IPCC’s projection of 0.2 degrees of warming per decade. That projection was based on several model runs averaged over many different initial conditions to eliminate natural variability. However, as I demonstrated above, the temperature record contains large amounts of natural variability on time scales less than a couple decades. Clearly, the IPCC’s projection of the long-term global warming signal is not directly comparable to 8 years of temperature data. Instead, we should compare the temperature data to short-term model projections which include natural variability. When we do so, we realize that model projections are indeed consistent with observations. As NASA scientist Gavin Schmidt noted, “Claims that a negative observed trend over the last 8 years would be inconsistent with the models cannot be supported” (6). I will now examine my opponent’s other article which supposedly demonstrates that climate model projections are inconsistent with observational data. This article compares temperature data to model projections from 1990. However, these projections were based on an emissions scenario which assumed that methane concentrations would increase linearly from 1990 to 2030 (7). In actuality, the growth of methane concentrations slowed greatly in the first decade of the twenty-first century (8). Thus, it’s highly unlikely that the projections from 1990 would ever match the observational data. Notably, this does not mean that climate models are inherently inaccurate. Emissions scenarios are not developed by models themselves, but rather by scientists and other experts. Creating highly accurate scenarios is extremely difficult, as no one can foresee what actions will be taken to mitigate global warming. My analysisMy opponent had three main objections to my analysis which demonstrated that CO2 could account for more than 75% of the observed global warming since 1870. First, as my opponent stated, “Her analysis is wrong...Lindzen gave the figure for CO2 warming assuming all other things equal. That means that the result would occur if there is nothing that either amplifies or diminishes the effect of CO2. Therefore, Pro would have to at minimum prove that there were no positive or negative feedback mechanisms.”This claim doesn’t make much sense. I did indeed account for the feedback processes, and Lindzen’s value was never even used in my calculation. As I explained clearly, I was attempting to determine the transient climate sensitivity parameter which would be necessary to produce .6º of warming. By definition, this parameter is a measure of how greatly the climate system amplifies any radiative forcing (9). My calculations showed that transient climate sensitivity would have to be greater than .375ºC/W/m2 in order for the resolution to be valid. This is a positive value, meaning that the feedback processes must, as a whole, amplify CO2 induced warming. I then compared this calculated climate sensitivity parameter to several climate model simulations. As it turned out, the models all simulated parameters larger than .375, indicating that there are indeed very strong positive feedbacks. My opponent has also suggested that global warming should be measured from 1978. Although warming can be measured from this year, it doesn't necessarily have to be. It makes sense to measure global warming from the industrial revolution, when we started emitting carbon dioxide in significant quantities.Nevertheless, I have conducted a similar analysis measuring global warming from 1980. I have also used observationally based estimates of the climate sensitivity parameter, as an alternative to climate model predictions.Constraints on past warming attributable to CO2The Earth has warmed about .5ºC since 1980. To determine how much warming is anthropogenic, we first need to estimate CO2’s radiative forcing relative to that year. As I’ve mentioned previously, we can use the following formula to do so.∆F = 5.35 ln(C/Co)C is the current concentration of atmospheric CO2, which is approximately equal to 390 ppm. Co is the concentration of CO2 in 1980, which equals about 345 ppm. Thus, carbon dioxide’s radiative forcing is .66 W/m2. Meanwhile, recent independent observations indicate that the Earth’s transient climate sensitivity parameter is .67ºC/W/m2, at absolute lowest (10). We can now determine the minimum amount of global warming that CO2 is responsible for by multiplying .66 by .67. This gives us a value of .44ºC. Therefore, at least 88% of the .5º observed temperature rise since 1980 is anthropogenic. Clearly, the resolution is valid.ConsensusMy opponent claims that, "The Climategate scandal revealed that CO2 crisis advocates put top priority on preventing skeptics from being published." However, this is not the case. The Independent Climate Change Email Review investigated the CRU scientists' actions relating to peer review. The investigation concluded that the CRU's actions were normal and didn't threaten the integrity of peer review (11).Concluding RemarksI urge everyone to vote pro! I've provided several research articles to support my claims, but my opponent has not provided a single one.I'll post my references in the comments section.