I cannot let pass Colin Alexander’s assertion that the hypothesis of human-induced climate change may not be correct as we don’t know what caused warm periods in Roman and medieval times (Oxford Today, Trinity Term, Letters, p. 8). This assertion is wrong in logic as well as in science.
In logic, we may not know what ‘A’ was that previously caused ‘B’, but that does not imply that we cannot know that ‘C’ causes ‘B’ today. This is a logical fallacy known as a non sequitur.
This is one of 176 myths perpetrated by those who deny that climate change is happening and largely man-made according to skepticalscience.com. The link between man-made emissions and recent global warming is based on basic principles of Physics discovered in the 19th century and uncontroversial until the implications started to be realized.