Climate tipping points: implications of paleo-climate records

Important lessons regarding current and future climate change trends can be derived from the paleo-climate record. Particularly from abrupt events such as the Oldest dryas (~16 kyr), Older dryas (~14 kyr), Younger dryas (12.9–11.7 kyr) and the ~8.2 kyr Laurentian ice melt event all of which occurred over time-scales of a few decades to a few years. IPCC model projections to 2100 and 2300 are examined, taking account of penetration of air masses through the weakened jet stream boundary and amplifying feedbacks from land, ocean and melting ice sheets. The linear temperature progressions presented in these projections have been questioned by Hansen et al. (2016) who suggest that high rates of Greenland and West Antarctic mass loss may drive significant transient cooling events (stadials). Already a slowdown in the Atlantic mid-Ocean overturning circulation (AMOC) and exceptional growth of a cold water region south and east of Greenland are observed. Hansen et al.’s projections suggest several decades-long stadial cooling of - ~3oC, which would markedly affect temperatures in Europe and North America. While cooling would temporarily reduce ocean temperatures in sub-polar regions and possibly beyond, warming would continue in tropical and continental regions, leading to large temperature gradients, storminess and an increase in extreme weather events.