One of the more common arguments in support of a prominent role in carbon dioxide for shaping the global climate is that we can’t explain the 20th century warming without factoring it into the models. Of course, such an application of the exclusionary principle would rest upon several assumptions, namely that we understand enough about ALL the other factors that influence the climate to be able to fill in the blank that is CO2. So, do we know enough about the rest of the climate? The IPCC has the answer.
In this figure, the level of scientific understanding (LOSU) is shown for several key forcing factors. Notice that greenhouse gases are assigned a high level of uncertainty while solar irradiance and aerosols only have a low-level of certainty.
On one hand we are told that we understand the role of carbon dioxide well and the rest of the climate not so well, and on the other hand that we know enough about the rest of the climate to infer the role of CO2.