The Intergovernmental Panel on Climate Change (IPCC) claim of human-caused global warming (AGW) is built on the assumption that an increase in atmospheric CO2 causes an increase in global temperature. The IPCC claim is what science calls a theory, a hypothesis, or in simple English, a speculation. Every theory is based on a set of assumptions. The standard scientific method is to challenge the theory by trying to disprove it. Karl Popper wrote about this approach in a 1963 article, Science as Falsification. Douglas Yates said,