Could the climate sensitivity be less than 2°C? This YouTube video by Prof. Dessler laying out the case for a climate sensitivity of 2-4.5°C.
For the ambitious among you, you can download and run a full-blown research-grade climate model. Look here for more information. There are a lot of simple on-line climate models that you can play around with. Steve Easterbrook has compiled a very useful list of them on his blog.
Lacis, A. A. et al. The role of long-lived greenhouse gases as principal LW control knob that governs the global surface temperature for past and future climate change. Tellus B, [S.l.], v. 65, nov. 2013. This is a great article that lays out the physics of the greenhouse effect in great detail. Along the way, it explains: 1) why carbon dioxide is the "control knob" for the climate and 2) quantifies the contribution of each greenhouse agent to the total greenhouse effect. Water vapor is the most important (50%), followed by clouds (25%) and carbon dioxide (20%).
There is a lot of literature on estimating climate feedbacks in models and data. See, e.g., Dessler, A.E., Observations of climate feedbacks over 2000-2010 and comparisons to climate models, J. Climate, 26, 333-342, doi: 10.1175/JCLI-D-11-00640.1, 2013.
Some of the most scary climate scenarios involve carbon-cycle feedbacks; i.e., a warming climate melts permafrost, which releases methane or more carbon dioxide. Here is a review article in Nature, which concludes: "Here we find that current evidence suggests a gradual and prolonged release of greenhouse gas emissions in a warming climate" (doi:10.1038/nature14338). Here is another review of carbon cycle feedbacks.
For more about the climate effects of volcanic eruptions, read this great NYT article about the impacts of the enormous Tambora eruption in 2015.
On page 103, there is a reference to "Equation 6.4" in the second full paragraph. This should be equation 6.3.