http://www.nature.com/nature/journal/v529/n7585/full/529162a.html http://www.nature.com/nature/journal/v529/n7585/full/nature16494.html
"The past rapid growth of Northern Hemisphere continental ice sheets, which terminated warm and stable climate periods, is generally attributed to reduced summer insolation in boreal latitudes. Yet such summer insolation is near to its minimum at present, and there are no signs of a new ice age. This challenges our understanding of the mechanisms driving glacial cycles and our ability to predict the next glacial inception. Here we propose a critical functional relationship between boreal summer insolation and global carbon dioxide (CO2) concentration, which explains the beginning of the past eight glacial cycles and might anticipate future periods of glacial inception. Using an ensemble of simulations generated by an Earth system model of intermediate complexity constrained by palaeoclimatic data, we suggest that glacial inception was narrowly missed before the beginning of the Industrial Revolution. The missed inception can be accounted for by the combined effect of relatively high late-Holocene CO2 concentrations and the low orbital eccentricity of the Earth. Additionally, our analysis suggests that even in the absence of human perturbations no substantial build-up of ice sheets would occur within the next several thousand years and that the current interglacial would probably last for another 50,000 years. However, moderate anthropogenic cumulative CO2 emissions of 1,000 to 1,500 gigatonnes of carbon will postpone the next glacial inception by at least 100,000 years. Our simulations demonstrate that under natural conditions alone the Earth system would be expected to remain in the present delicately balanced interglacial climate state, steering clear of both large-scale glaciation of the Northern Hemisphere and its complete deglaciation, for an unusually long time." GR- While it is one thing to warm and acidify the planet, it takes some serious juju to override the orbital control of glacial-interglacial cycles. While we can debate whether this is a good or bad thing and unintentional, is there now any doubt about the ability for humans to affect the climate and chemistry of the entire planet for many millennia? Given that we are capable of these amazing powers, it would seem a small step to figure out how to do this in a way that is in the best interest of Earth's inhabitants. As to where to start, the prologue by Michael Crucifix provides a clue:"Such long-term consequences [of our CO2 emissions] may seem surprising, given that the emissions will occur over a few centuries at most and that anthropogenic CO2 will eventually be absorbed by the oceans. But for this absorption to occur, carbonate minerals in the ocean will need to be dissolved, to counteract the increase in ocean acidity that occurs when CO2 is absorbed, and which limits the amount of CO2 that can be dissolved. This takes time. In fact, the mean half-life of CO2 in the atmosphere is of the order of 35,000 years6. Consequently, anthropogenic CO2 will still be in the atmosphere in 50,000 years' time, and even 100,000 years, which is enough to prevent any glaciation." GR - So, in addition to figuring out how to reduce emissions, might focussing on how to hasten mineral weathering and thus reducing the half life of CO2 in the atmosphere be a more obvious starting point, than say asking land biology to (unnaturally) do the heavy lifting as advocated by IPCC et al? Shall we try to enhance existing, proven, global scale CO2 capture and sequestration, or try to convert biology from a major carbon and nutrient recycler to to a major carbon and nutrient storer? Or worse, shall we place all of our money on a completely artificial, costly and risky system that bears no resemblance to proven, global scale processes (CCS)? I'd say its time for a rational discussion about the pathways facing us and where to focus our efforts and treasure, assuming we decide that warming, acidification and lack of glacials isn't a good thing. Greg https://www.researchgate.net/profile/Greg_Rau -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout.
