Now published as: Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous
Atmos. Chem. Phys., 16, 3761-3812, 2016
Leading Climate Scientists: ‘We Have A Global Emergency,’ Must Slash CO2 ASAP
In looking over the published version, I noticed the use of an older climate model that reduces computational loads by using a simplified method of calculating CH4/CO2 equivalents.
In the atmosphere, CH4 is 84 times more powerful as a greenhouse gas on a current basis, but CH4 oxidizes to CO2 with a CH4 half-life of ~12 years. Thus, over a 100 year period, CH4 is only 25 times as powerful a greenhouse gas as CO2. The model simply converts all the CH4 into the 100 year CO2 equivalent by multiplying by a factor of 25.
Looking at atmospheric monitoring data last for 25 years, I note that the concentration of CH4 increases, rather than declining as the model assumes. Calculating annual forcing using the monitoring data, results in forcing ranging from 3 w/m^2 to 3.6 w/m^2. Using the 100-year modeled conversion factor gives forcing of 1.8 w/m^2 to 2.5 w/m^2 over the period 1990 - 2015. Note the annual data number is 44% higher.
Looking at Fig. S16, it seems that the model takes until ~2060 to arrive at forcing of 3.6 w/m^2. Thus, I expect to see weather in the next 30 years, that Hansen et al. does not model as occurring for another 50 years.
Temperature rise of 2C is likely to arrive much sooner than any of the standard climate models project, and coming faster as a result of more intense forcing will produce more intense temperature gradients, which will drive more intense storms than Hansen et al offer.
Greenhouse gas driven climate change is different from climate change driven by orbital mechanics (e.g., past ice ages and past interglacial periods). In greenhouse gas driven climate change, the lower atmosphere gets warmer while the upper atmosphere gets colder. Thus, in greenhouse gas driven climate change, there is always a nearby source of very cold air to drive very intense, cold storms.
Wicked storms are coming, and we will need better knitting to stay warm.