When should we change our behavior before its too late?

The answer to this question is simple: NOW

Currently we still face consequences of unrelenting business as usual (see World Scientists’ Warning of a Climate Emergency 2021 - academic.oup.com, 28th July 2021)

As per https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions there are several possible scenarios:

ourworldindata.org | Future emission scenarios

1.5°C emissions pathways:

1.5°C emissions pathways

The sooner we make it to change course, the better!

 

A short search yielded these (among lots of others):

https://www.scientists4future.org/stellungnahme/fakten/ (Report is: here; 2019)

Temperatures | Climate Action Tracker (actual 2100 warming projections)

ourworld.unu.edu - Climate Change  (some articles about the climate change topics)

https://www.iflscience.com/environment/global-temperatures-are-on-track-to-rise-4-degrees-celsius-by-2084/ (May 24, 2018)

www.ipcc.ch - Long-term Climate Change:Projections, Commitmentsand Irreversibility (2013)

Please start to research on your own...