An examination of some feedback mechanisms in the carbon dioxide climate problem

Abstract

A radiative convective equilibrium model has been used both alone and in conjunction with a mixed-layer oceanic model to explore the consequences of some possible secondary climatic responses resulting from a precursor CO2-induced warming. Calculations were performed for both standard (300 p.p.m.) and doubled CO2 amounts. This permitted several feedback mechanisms to be examined and quantified. For example, a 10% increase in existing low cloud amount (0.302 to 0.332) was found to completely compensate for the surface and tropospheric warming caused by doubling the CO2 amount. A similar compensation was obtained by increasing low cloud albedo from 0.69 to 0.74. A combination of these two perturbations required such small individual increases that it raised the question whether general circulation models with self-predicting cloud properties would be able to attain sufficient accuracy to realistically evaluate such subtleties in an assessment of the CO2 climate problem. An interesting aspect of the temperature compensation associated with the cloud amount and albedo increases was that this compensation did not extend to the stratosphere, which experienced a general cooling. The potential climatic consequences of this cooling are discussed. The impact of surface wind changes over the ocean attributable to a CO2 warming was also considered and shown to affect both the sea surface temperature and mixed-layer depth noticeably. A number of potential feedback mechanisms associated with such wind changes were identified, and served to stress the need to take more recognition of the ocean’s role in assessing the CO2 problem. The possibility of an increase in the number of hurricanes and other severe tropical storms resulting from a general warming of the low latitude oceans from a CO2 increase was noted.