This is why we do what we do!
So what would be safe? The answer is that “limiting the period and magnitude of temperature excursion above the Holocene range is crucial to avoid strong stimulation of slow feedbacks”.
In other words, aim to get temperatures back under the Holocene maximum of 0.5ºC, which implies a level of greenhouse gases below 320 parts per million (ppm) of atmospheric carbon dioxide (CO2), compared to the current level of 405 ppm.
Read the full article by David Spratt, published at Climate Code Red on 27/7/17, at http://www.climatecodered.org/2017/07/paris-15-2c-target-far-from-safe-say.html