Da dire anche a proposito di modelli e incertezze che di recente è riapparsa al questione dei tempi di capacità di riassorbimento da parte della terra e degli oceani in particolare della Co2 e dei gas serra in genere emessi dalle attività umane..
Negli ultimi rapporti IPCC si parlava di tempi stimabili in alcune centinaia di anni. Studi recenti invece hanno indicato tempi molto più lunghi necessari al sistema per ritornare a una condizione simile a quella iniziale.
La questione non è secondaria in quanto, qualora venissero confermati questi ultimi studi, il tentativo di porre rimedio al GW attraverso la riduzione delle emissioni potrebbe risultare marginale.



Riporto un passo di uno di questi studi: (testo completo su Carbon is forever : article : Nature Reports Climate Change)


Unlike other human-generated greenhouse gases, CO2 gets taken up by a variety of different processes, some fast and some slow. This is what makes it so hard to pin a single number, or even a range, on CO2's lifetime. The majority of the CO2 we emit will be soaked up by the ocean over a few hundred years, first being absorbed into the surface waters, and eventually into deeper waters, according to a long-term climate model run by Archer. Though the ocean is vast, the surface waters can absorb only so much CO2, and currents have to bring up fresh water from the deep before the ocean can swallow more. Then, on a much longer timescale of several thousand years, most of the remaining CO2 gets taken up as the gas dissolves into the ocean and reacts with chalk in ocean sediments. But this process would never soak up enough CO2 to return atmospheric levels to what they were before industrialization, shows oceanographer Toby Tyrrell of the UK's National Oceanography Centre, Southampton, in a recent paper.
Finally, the slowest process of all is rock weathering, during which atmospheric CO2 reacts with water to form a weak acid that dissolves rocks. It's thought that this creates minerals such as magnesium carbonate that lock away the greenhouse gas. But according to simulations by Archer and others, it would take hundreds of thousands of years for these processes to bring CO2 levels back to pre-industrial values.




Figure 1: Long lifetime.

Several long-term climate models, though their details differ, all agree that anthropogenic CO2 takes an enormously long time to dissipate. If all recoverable fossil fuels were burnt up using today's technologies, after 1,000 years the air would still hold around a third to a half of the CO2 emissions. "For practical purposes, 500 to 1000 years is 'forever,'" as Hansen and colleagues put it. In this time, civilizations can rise and fall, and the Greenland and West Antarctic ice sheets could melt substantially, raising sea levels enough to transform the face of the planet.