The Earth may be warming, but human activities are not responsible: Even if the Earth is warming, it is obviously part of the continuing recovery from the “little ice age,” the cool period from the fifteenth to eighteenth centuries.This argument tacitly assumes that the Earth’s climate system has a “normal” state that it pushes back to after unusually warm or cold periods, like a stretched spring returning to its normal length. While this might appear commonsensical, it has no foundation in either the record of how climate has varied or the fundamental physics of the atmosphere. The Earth’s climate has no “normal” state to which the climate seeks to return, so there is no reason to expect that an unusually cool period will be followed naturally by a return to warmer conditions.
Rather, when interpreting cause-and-effect in the temperature record, one has to consider the forcings. One can make a strong argument based on solar proxies (like sunspots) that the increasing temperature between the 17th century to about the middle of the 20th century was due to increasing solar forcing.
However, for the particularly rapid warming of the late 20th century, we have a good knowledge of the forcings of the climate. As I described here, we can eliminate solar variability as a primary driver. In fact, the only forcing that explains the warming is the increase in greenhouse gases.
In summary, there is no evidence that today’s particularly rapid warming is caused by the same thing as caused most of the warming over the last few centuries. By considering the forcings, we can conclude that most of the recent warming can be attrbituted to human activities. Thus, the argument that today's warming is simply a continuation of some natural trend is unsupported by any science.