Impact of future Greenland deglaciation on global weathering fluxes and atmospheric CO2

About 1.76×10^6 km2 of Greenland are currently covered by ice. It is expected that this large ice mass will melt away over the next 3000 years if anthropogenic CO2 emissions continue to rise (Alley et al., 2006). As a result, the bedrock currently covered by ice will lie free and become subject to chemical weathering. The resulting weathering fluxes will contribute to increase both the consumption rate of atmospheric CO2 and the production rate of riverine bicarbonate.
Increasing these two fluxes will tend to decrease the atmospheric CO2 partial pressure, as a result of the modified ocean-atmosphere carbon cycle. Chemical weathering may thus possibly act as a negative feedback in the Greenhouse World. Other changes (e.g., vegetation cover and additional climate change) concomitant with the melting of the Greenland ice-sheet may either amplify or dampen, if not reverse the weathering effect.
Here we use the intermediate complexity Earth System model CLIMBER-2 to quantify and analyse the weathering
flux changes that result from the projected melting of the Greenland ice sheet and the implications for atmospheric CO2.
The biogeochemical module of CLIMBER-2 has been extended to account for the consumption of atmospheric CO2
and the production of riverine bicarbonate by continental weathering processes, as a function of geographically
distributed runoff (interactively provided by the CLIMBER-2 climate module) and lithology (derived from Amiotte Suchet et al., 2003). We find that the increased weathering processes alone would lead to a sustained 0.2 ppm/kyr decrease in atmospheric pCO2. The climate change resulting from the deglaciation of Greenland reduces the magnitude of this trend to 0.1 ppm/kyr. Only in the case where the effect of freshly comminuted bedrock is taken into account (Clark et al., 2006) does the weathering feedback help to reduce atmospheric
pCO2 by about 10 ppm in 5000 years.

Alley R.B. et al. (2005) Science 310, 456–460.
Amiotte Suchet P. et al. (2003) Global Biogeochemical Cycles 17, 1139, doi:10.1029/2002GB001891.
Clark P.U. et al. (2006) Quaternary Science Reviews 25, 3150–3184.