Define climate denier, please
I can actually answer both:
A climate alarmist is someone who agrees with the hypothesis that the planet is on the verge of a catastrophic climate change, generally assumed to be related to an increase in the average global temperature which is generally linked to human industrial activity, most notably the type of activity which involves the combustion of fossil carbon sources. This person will see the hypothetical climate catastrophe as the most important issue facing mankind and generally is willing to take drastic steps to limit its impact.
A climate denier is someone who does not agree with the hypothesis of an upcoming climate catastrophe. This does not imply the climate denier claims there is no such thing as climate change nor that human activity can and does influence climate, just that this person does not believe in an upcoming catastrophic climate upheaval.
The fact that these two terms are bandied around so easily shows how infected and polarised this issue has become. This is unfortunate as there are good arguments on both sides of the divide. The 'alarmists' generally want to get rid of fossil fuel dependencies which I consider to be a good idea, just not for the reasons they state and not with the urgency they crave. Fossil fuels are large sources of pollution (which is mostly but not entirely unrelated to the climate discussion), they are the root cause of many international conflicts. The 'deniers' generally want to keep a balance between the environmental and economical impact of reneging on or using fossil carbon sources which I tend to agree with even though I do not subscribe to the school of 'eternally growing economies'. Many on the 'denier' side are willing to increase the use of nuclear energy while many on the 'alarmist' side are averse to this option even though it offers many benefits in their goal of reducing carbon emissions. This is most likely related to the fact that the people who are on the 'alarmist' side of the divide generally identify with environmental causes which have (often successfully) fought investments in nuclear energy.
This is why it would be beneficial for all involved to open a true discussion on this subject, without throwing epithets at any and all who do not agree to the fully to a stated position.