The thing is the IPCC is kind of the authoritative body on global warming. Their synthesis reports are basically meta analysis for all climate change related sc

The thing is the IPCC is kind of the authoritative body on global warming. Their synthesis reports are basically meta analysis for all climate change related science. They produce these reports using a team of volunteer scientists working through a consensus based process. Which means everyone on the team has to agree to everything in the report. This process is inherently conservative. Language has constantly been tempered to avoid any fear of sounding alarmist or even slightly going out on a limb. So the latest science is pretty much always running out ahead of the IPCC showing it to be underestimating the impacts.