You apparently don't, because there are countless scientists who deliver alternatives, so we don't have to strip ourself from enjoying life in every possible way.
Though if I had to guess, it's going to be stuff like "build a shit ton of nuclear power plants, use e fuels for cars, use green hydrogen, develop fusion power, and generally do all the things that allow us to believe that we have to change absolutely nothing in our lives."
If you read into his other posts he is saying her approach of blocking people from living their lives is ineffective. It is like protesting something by blocking off a highway people need to use to make a living.
At this point who notices protests? They are so commonplace unless tens of thousands of people are involved. I agree that this will catch the public eye and may motivate people to side with her, but it could have the opposite effect as well. People rely on fossil fuels to get through their day (e.g. commuting, heating their homes, electric generation even). Making it more expensive may frustrate people who are more concerned about making ends meet than the climate.
It sucks, but there are limits to how practical it is to disrupt a crucial resource.
these countless scientists (accounting for less than 2% of the scientific community), are they in the room with us right now?
Also Greta doesn't control literally anyone, doesn't require unwavering devotion and most importantly it is not a spiritual belief that human-made climate change is a thing. In fact it's a well established fact by now.
Because 1 moron screaming that the sky is green does not make the sky green just because he's "providing an alternative" to what the other 99 people are saying after looking up at the sky and seeing it is blue. Scientists are also not telling people to repent, they're telling people there needs to be a system change and they're also telling politicians that they need to enact policies to contrast climate change, and the same is what activists ask for. You'd know if you spent some time looking at what they say rather than what the media says about them.
You know who actually is both telling people to repent for their own emissions and also spreading misinformation about climate change and financing those "alternative science"? Oil companies. I wonder why.