Your risk tolerance of 10 degrees is simply chosen to support an inaction agenda. 10 degrees is hell on earth. 6 degrees and human civilization likely cracks. 4 degrees is terrible. Even 2 degree warming is significant shifts in our biosphere.
As the World Bank has put it:
A world in which warming reaches 4°C above preindustrial levels (hereafter referred to as a 4°C world), would be one of unprecedented heat waves, severe drought, and major floods in many regions, with serious impacts on human systems, ecosystems, and associated services.
In fact, in a 4°C world climate change seems likely to become the dominant driver of ecosystem shifts, surpassing habitat destruction as the greatest threat to biodiversity. Recent research suggests that large-scale loss of biodiversity is likely to occur in a 4°C world, with climate change and high CO2 concentration driving a transition of the Earth´s ecosystems into a state unknown in human experience. Ecosystem damage would be expected to dramatically reduce the provision of ecosystem services on which society depends (for example, fisheries and protection of coastline—afforded by coral reefs and mangroves).
http://climatechange.worldbank.org/s...ry_English.pdf