Query: But that conclusion holds true only if there are no other sources of c12 increases which are not human caused.

Relevant passages:
Reason <=SEP=> Reason is the capacity for consciously making sense of things , applying logic , establishing and verifying facts , and changing or justifying practices , institutions , and beliefs based on new or existing information . It is closely associated with such characteristically human activities as philosophy , science , language , mathematics , and art and is normally considered to be a definitive characteristic of human nature .  Reason , or an aspect of it , is sometimes referred to as rationality .   Reasoning is associated with thinking , cognition , and intellect . Reasoning may be subdivided into forms of logical reasoning ( forms associated with the strict sense ) : deductive reasoning , inductive reasoning , abductive reasoning ; and other modes of reasoning considered more informal , such as intuitive reasoning and verbal reasoning . Along these lines , a distinction is often drawn between discursive reason , reason proper , and intuitive reason , in which the reasoning process -- however valid -- tends toward the personal and the opaque . Although in many social and political settings logical and intuitive modes of reason may clash , in other contexts intuition and formal reason are seen as complementary , rather than adversarial as , for example , in mathematics , where intuition is often a necessary building block in the creative process of achieving the hardest form of reason , a formal proof .   Reason , like habit or intuition , is one of the ways by which thinking comes from one idea to a related idea . For example , it is the means by which rational beings understand themselves to think about cause and effect , truth and falsehood , and what is good or bad . It is also closely identified with the ability to self-consciously change beliefs , attitudes , traditions , and institutions , and therefore with the capacity for freedom and self-determination .   In contrast to reason as an abstract noun , a reason is a consideration which explains or justifies some event , phenomenon , or behavior . The field of logic studies ways in which human beings reason formally through argument .   Psychologists and cognitive scientists have attempted to study and explain how people reason , e.g. which cognitive and neural processes are engaged , and how cultural factors affect the inferences that people draw . The field of automated reasoning studies how reasoning may or may not be modeled computationally . Animal psychology considers the question of whether animals other than humans can reason .

Scientific consensus on climate change <=SEP=> There is currently a strong scientific consensus that the Earth is warming and that this warming is mainly caused by human activities. This consensus is supported by various studies of scientists' opinions and by position statements of scientific organizations, many of which explicitly agree with the Intergovernmental Panel on Climate Change (IPCC) synthesis reports.  Nearly all actively publishing climate scientists (97–98%) support the consensus on anthropogenic climate change, and the remaining 2% of contrarian studies either cannot be replicated or contain errors.