the key thing to know first is that for the last 10,000 years on earth, the climate has been relatively stable, unusually stable, and by stable i mean temperature has varied, it's gone up and down, but it's stayed on a fairly narrow band of about plus or minus 1 degree celsius, and all of advanced human civilisation has taken place during these 10,000 years, the development of agriculture, the written word, the wheel, the iphone, everything we know, everything we have built, we have done in this period of relative climate stability.