Climate-change denial could have disastrous consequences, if it delays global action to cut carbon emissions. Denialism is gaining popularity because people have difficulty differentiating deniers' twisted arguments from the legitimate concerns of genuine sceptics. We must stop deniers presenting themselves as the rightful regulators of scientific debate.

Denial of the science of climate change is eroding public understanding of the issue and seems to be undermining trust in scientists (see This loss of public confidence — after a cold winter in Europe and elsewhere, and the 'Climategate' e-mails controversy — was highlighted at February's meeting of the American Association for the Advancement of Science in San Diego, California (R. J. Cicerone Science 327, 624; 2010).

Denialism is motivated by conviction rather than evidence. It has been applied to a wide range of issues, including evolution and the link between HIV and AIDS. Deniers use strategies that invoke conspiracies, quote fake experts, denigrate genuine experts, deploy evidence selectively and create impossible expectations of what research can deliver. They rely on misrepresentation and flawed logic (P. Diethelm and M. McKee Eur. J. Public Health 19, 2–4; 2009).

By contrast, scepticism starts with an open mind, weighs evidence objectively and demands convincing evidence before accepting any claim. It contributes to the debate and forms the intellectual cornerstone of scientific enquiry.

The public should understand the difference between deniers and sceptics, so that their trust in scientists is not threatened at a time when humanity needs us most. We need to expose the spurious nature of denialist arguments and draw attention back to the primary evidence.

As scientists, we have a duty to communicate our research honestly and accessibly. We do not need to speak with one voice about climate change, but we should stand together to defend proper scientific debate.