Denialism in the context of "Historical revisionism"

Anti-scientific beliefs in a flat Earth are promoted by a number of organizations and individuals. The claims of modern flat Earth proponents are not based on scientific knowledge and are contrary to over two millennia of scientific consensus based on multiple confirming lines of evidence that Earth is roughly spherical. Flat Earth beliefs are classified by experts in philosophy and physics as a form of science denial.

Flat Earth groups of the modern era date from the middle of the 20th century; some adherents are serious and some are not. Those who are serious are often motivated by religion or conspiracy theories. Through the use of social media, flat Earth theories have been increasingly espoused and promoted by individuals unaffiliated with larger groups. Many believers make use of social media to spread their views.

Climate change denial (also global warming denial) is a form of science denial characterized by rejecting, refusing to acknowledge, disputing, or fighting the scientific consensus on climate change, which is based on extensive and diverse evidence. Those promoting denial commonly use rhetorical tactics to give the appearance of a scientific controversy where none exists. Climate change denial includes raising unreasonable doubts about the extent to which climate change is caused by humans, its effects on nature and human society, and understating the costs of climate change adaptation while overstating the costs of mitigating it. To a lesser extent, climate change denial can also be implicit when people accept the science but fail to reconcile it with their belief or action. Several studies have analyzed these positions as forms of denialism, pseudoscience, or propaganda.

Many issues that are settled in the scientific community, such as human responsibility for climate change, remain the subject of politically or economically motivated attempts to downplay, dismiss or deny them—an ideological phenomenon academics and scientists call climate change denial. Climate scientists, especially in the United States, have reported government and oil-industry pressure to censor or suppress their work and hide scientific data, with directives not to discuss the subject publicly. The fossil fuels lobby has been identified as overtly or covertly supporting efforts to undermine or discredit the scientific consensus on climate change.

Denial, in colloquial English usage, has at least three meanings:

• the assertion that any particular statement or allegation, whose truth is uncertain, is not true;
• the refusal of a request; and
• the assertion that a true statement is false.

In psychology, denialism is a person's choice to deny reality as a way to avoid a psychologically uncomfortable truth.