The Intergovernmental Panel on Climate Change has been warning about the implications of global warming since 1990. At the time, it predicted that business-as-usual emissions would result in a global mean temperature about 4 ° C above pre-industrial times by the end of the 21st century.
Weekly carbon dioxide concentrations in the atmosphere reached 410.8 parts per million in May 2017 at an observation station in Hawaii which is on course with the worst case IPCC 2014 scenario with a 4.3°C rise above pre-industrial times by the end of the century.
What’s especially scary is that large feedback loops will most certainly kick in at a 3°C rise including the release of massive amounts of carbon stored in the oceans. According to the authors, this risks pushing the temperature 7.8°C above pre-industrial times by 2100.
These are not tolerable degrees of climate change for our species, nor most others.