Correct Answer :   long-term damage done by a tonne of CO2, emissions in a given year.

Note : Scientists expect climate change to have increasingly negative consequences for society, from rising sea levels to more frequent heatwaves. There is broad agreement that initial, modest benefits – for instance, increased yields for some crops in some regions – will be outweighed by costs as temperatures rise. One way to get a handle on this question is through the Social Cost of Carbon (SCC), which tries to add up all the quantifiable costs and benefits of emitting one additional tonne of CO2, in monetary terms. This value can then be used to weigh the benefits of reduced warming against the costs of cutting emissions.