Grave to Irreversible

I went to a lecture recently on sustainable issues. In relation to climate change, it seems scientists have a chart which goes from grave, very grave, runaway to irreversible ... and their current assessment of our situation sits between very grave and runaway. If we don't take urgent action now, it will be in the irreversible category by 2050.  The forecast being that without strong steps being taken within 20 years, the climate will be 4-5 degrees hotter by the end of the century.  Pretty serious situation, especially when so many governments are what he referred to as sustainable illiterates! It's a strange thing .. and I've felt it myself at times, that one can hear the facts ...yet they don't really register in real terms of evoking a response.  Why is that ? Are we just so flooded with information and imagery .. often horrendous things like violence and famine...that we've developed this ability to shut off from the impact of the truth staring us in the face?