Science has long had a formal method for deciding whether evidence is any good - called the Peer Review Process. Scientists make their work public and invite anyone to check their findings. The details of scientific studies are published in journals where the work is first closely checked by reviewers who are expert scientists in the same area. Readers are invited to repeat the experiments to see if they come up with similar results. Only if others are able to repeat the work and get the same results is the work seen as maybe having some value. This public process of checking results keeps the standard of evidence very high.

The evidence for climate change has been found all over the world by thousands of scientists, who are almost all coming to the same conclusions

A tiny minority of people claim that the science of climate change is wrong and that if any change is happening, it is not the result of human activity. Most are not scientists and even fewer are qualified in climate science. Importantly, most do not publish their opinions in scientific journals, where their ideas can be checked by others through the peer review process. Instead many "climate sceptics" promote their ideas through television and newspapers, where the only checking done is by journalists. 

Journalists are usually not scientists

Journalists are not climate science experts either and are often unable to properly check ideas presented to them as "science". Most journalists have little or no training in science and few know whether the person they are talking to genuinely understands the subject. Rather, journalists are trained to look for two sides to every story. So even if 99% of expert scientists say that climate change is happening, many journalists will give equal attention to the 1% of non-expert, non-scientist sceptics who claim that it is not happening. 

As a result, this tiny handful of climate sceptics get a lot of attention and publicity, even though the vast majority of professional climate scientists disagree with them.