Climate Stabilization at 2oC and “Net Zero” Emissions

Abstract:

The goal to stabilize global average surface temperature at 2^oC above pre-industrial level has been extensively discussed in climate negotiations. A number of recent publications state that achieving this goal will require net anthropogenic carbon emissions (which may include a carbon sink by carbon capture and sequestration and reforestation) to be reduced to zero between years 2050 and 2100. In this study we explore possible emission scenarios under which surface warming will not exceed 2^oC, by means of emission driven climate simulations with an Earth System Model of intermediate complexity linked to an Economic Projection and Policy Analysis Model. We carried out a number of simulations from 1861 to 2500 for different values of parameters defining the strength of the climate system response to radiative forcing and the strength of the carbon cycle and under different anthropogenic emission scenarios.

Results of our simulations suggest that anthropogenic emissions do not have to be zero by 2050 or 2100 because of carbon sinks in oceans and terrestrial ecosystems. Anthropogenic CO₂ emissions falling from today’s 36 GtCO₂/year to 11-25 GtCO₂/year by 2050 and then to 4.5-12 GtCO₂/year by 2100 is consistent with a 2°C target for the range of climate sensitivity similar to the IPCC likely range.

Long-term changes in the surface temperature depend on the emissions profiles after 2100. For post-2100 carbon emissions decreasing at a rate of about 0.2% per year, natural ecosystems will be able to absorb enough carbon, that together with decreases in emissions of other GHGs, can prevent surface temperature from rising.

Technology mixes and costs to achieve the 2°C target are highly dependent on the assumptions about the future costs of low-carbon and zero-carbon technologies. In all scenarios, the energy system required substantial transformations in a relatively short time. Under current assumptions about the cost trajectories for the needed technologies, the 2°C stabilization would incur a reduction in global consumption of goods and services (relative to no climate policy) of 5-10% in 2050 and 15-22% in 2100.