Absolute Emissions versus Avoided Emissions

Absolute Emissions versus Avoided Emissions

In the context of GHG Emissions and limiting anthopogenic factors of Climate Change the distinction between Absolute Emissions and Avoided Emissions highlights the nature of this sustainability constraint: namely the existence of a Carbon Budget that requires limiting the total cumulative emissions of CO2.

The context of the carbon budget constraint is the natural wikipedia:Carbon cycle. The global carbon cycle connects major reservoirs of carbon by pathways of exchange:

• The atmosphere
• The terrestrial biosphere
• The ocean, including dissolved inorganic carbon and living and non-living marine biota
• The sediments, including fossil fuels, freshwater systems, and non-living organic material.
• The Earth's interior (mantle and crust).

These carbon stores interact through biological and geological processes. The influence of enhanced atmospheric emissions produced by human activity overlays on these pre-existing processes. Since the pre-industrial period to 2011, approximately 1890 Gigatonnes of CO2 (GtCO2) have already been emitted globally, and 2050 GtCO2 up to 2015. Scientific estimations of the remaining global emissions budgets differ due to varied methodological approaches, and considerations of thresholds. Estimated amounts are linked with some probability to specific target scenarios (eg wikipedia:Special Report on Global Warming of 1.5 °C).

When considering a GHG Project one may consider either its incremental effect on GHG Emissions (versus the best estimate Baseline Emissions) or absolute emissions. The later is more directly comparable to the total carbon budget.