Emissions reduction: Scrutinize CO2 removal methods

The viability and environmental risks of removing carbon dioxide from the air must be assessed if we are to achieve the Paris goals, writes Phil Williamson.

In Paris last December, the 196 parties to the United Nations Framework Convention on Climate Change (UNFCCC) agreed to balance the human-driven greenhouse-gas budget some time between 2050 and 2100. This commitment is intended to limit the increase in global average temperature above pre-industrial levels to “well below 2 °C” — and preferably to 1.5 °C.

A balanced greenhouse-gas budget either requires that industry and agriculture produce zero emissions or necessitates the active removal of greenhouse gases from the atmosphere (in addition to deep and rapid emissions cuts). In most modelled scenarios that limit warming to 2 °C, several gigatonnes of carbon dioxide have to be extracted and safely stored each year. For more ambitious targets, tens of gigatonnes per year must be removed.

Many CO2-removal techniques have been proposed. Whether any of them could work at the scale needed to deliver the goal of the Paris agreement depends on three things: feasibility, cost and acceptability. A crucial component of all of these approaches is the non-climatic impacts that large-scale CO2-removal could have on ecosystems and biodiversity.

Until now, the UNFCCC's scientific advisory body, the Intergovernmental Panel on Climate Change (IPCC), has paid relatively little attention to such impacts. It has fallen to other groups to review insights and gaps in our understanding of the influence of CO2-removal techniques on ecology to  make broad assessments of climate-engineering schemes; and to carry out comparative modelling studies7.

It is time for the IPCC, governments and other research-funding agencies to invest in new, internationally coordinated studies to investigate the viability and relative safety of large-scale CO2removal.

Read the comment published in Nature