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

TL;DR

Large-scale land or ocean carbon dioxide removal methods significantly alter Earth's surface reflectance, potentially overshadowing the climate effects of CO2 reduction and causing unintended warming or cooling.

Contribution

This paper demonstrates that surface albedo modifications from large-scale CDR methods can dominate radiative forcing, highlighting previously underappreciated climate impacts.

Findings

Albedo changes of parts per thousand can match the radiative impact of removing 10 tons of CO2 per hectare.

SAM from ERW can cause both cooling and warming effects.

Large surface area modifications can overshadow the climate benefits of CO2 removal.

Abstract

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.