...but rather going by real climate science and not the hijacked agenda the alarmists turned the name into.
This could be a form of the No True Scotsman fallacy in the no REAL science would suggest that climate change was a problem, so the overwhelming majority of climate scientists are just the alarmists.
Problem is that the alarmists tend to ignore that in favor of the 'omg it is getting warmer' panic mode while completely ignoring that we are on a natural upswing from the last glaciating period.
This is just the person showing their ignorance in not understanding that the the natural upswing is separate from the man-made effects that are the problem.
Of course one of the agencies supposedly responsible for tracking such changes has been caught and called out on data whitewashing... manipulating data to make previous decades seem cooler while more recent to seem hotter.
Anecdotal. If this is true (I would ask for references), it is one example of literally hundreds of global climate agencies that all have released statements about the consensus. This would be like an atheist using Peter Popoff as evidence that Jesus didn't perform miracles.
You asked the best way to respond, and I really don't have an answer when it comes to people who deny overwhelming scientific consensus whether it be climate change, GMO safety, the age of the universe, evolution, and even the shape of the earth. I think the best we can ask is on what basis do they reject the overwhelming consensus and why they think they are more qualified to know the science they the 89-100%* of scientists that devote their lives to studying and researching some aspect of the field.
* This is the range of consensus on the area mentioned.