Removing Atmospheric Carbon Dioxide Using Large Land Or Ocean Areas Will Change Earth Albedo And Force Climate

When large surface areas of the Earth are altered, radiative forcing due to changes in surface reflectance can drive climate change. Yet to achieve the necessary scale to remove the substantial amounts of carbon dioxide from the atmosphere relevant for ameliorating climate change, enhanced rock weathering (ERW) will need to be applied to very large land areas. Likewise, marine carbon dioxide removal (mCDR) must alter a large fraction of the ocean surface waters to have a significant impact upon climate. We show that surface albedo modification (SAM) associated with ERW or mCDR can easily overwhelm the radiative forcing from the decrease of atmospheric CO2 over years or even decades. A change in albedo as small as parts per thousand has a radiative impact comparable to the removal of 10 tons of carbon per hectare. SAM via ERW can be either cooling or warming. We identify some of the many questions raised by radiative forcing due to these forms of CDR.