As are human CO2 & SO2 estimates. Simple truth is, we have gone through many many changes in our atmosphere, and we will continue to do so. I am without doubt an advocate for change on our behalf. But to blame ourselves is foolhardy to the maximum. BBC just said that the northern Ice limit is the lowest since record. Records started 200 years ago. Yet we know that the north passage was open some 1500 years ago. What caused that? CO2 levels are known to have been toxic to humans during the Jurassic period. What caused that. I live near a mountain, it has sea bed fossils, excluding uplift - which we know the amount - was still several hundred feet higher that we are now. How high was the water level then?