Carbon Dioxide Emission Management in Power Generation. Prof. Lars O. Nord

Table 1.1 Global warming potential (GWP) – relative to CO₂ – as well as atmospheric concentration and lifetime of selected greenhouse gases.

      Source: Data are based on CDIAC (2010).

For a much longer time frame, data from the Vostok ice core provide an insight into the variations in CO₂ levels for the past four glacial–interglacial cycles. In January 1998, the collaborative ice-drilling project between Russia, the United States, and France at the Russian Vostok station in East Antarctica yielded the deepest ice core ever recovered, reaching a depth of 3623 m (Petit et al. 1999). Data from this project are displayed in Figure 1.1. One conclusion from the authors was that present-day atmospheric burdens of CO₂ seem to have been unprecedented during the past 420 000 years. Note that the mean resolution for the CO₂ measurements was about 1500 years.

1.3 Natural Accumulations and Emissions of CO₂

There are many examples of natural emissions of CO₂ to the atmosphere. Forest fires and grass fires are natural phenomena, which release large amounts of CO₂ to the atmosphere. On the other hand, after such fires, new trees and grass will grow and eventually bind more or less the same amount of CO₂ as was released. One can say that as long as the total amount of biomass on a global basis is constant over a longer period of time, the combustion, decay, and growth of biomass is balanced with respect to CO₂. In this respect, the use of biomass for energy purposes can be regarded as CO₂ neutral. Consequently, if the amount of biomass is increasing through an expansion of the area covered by forests, this contributes to reducing the amount of CO₂ in the atmosphere. In reality, there is a significant ongoing reduction in biomass globally by man-made forest fires and wood cutting, which contributes to about 20% of the annual increase in greenhouse gas emissions.