Abby L. Harvey
GHG Monitor
11/7/2014
The use of fossil fuels without carbon capture and storage technologies must be phased out by 2100, according to the Intergovernmental Panel on Climate Change Synthesis Report released early this week. The report looks at various scenarios or “representative concentration pathways (RCPs)” ranging from a high greenhouse gas scenario (RCP8.5), to a stringent mitigation scenario (RCP2.6). The results of these scenarios would result in global temperature rise between two degrees for the stringent scenario and more the four degrees for the baseline scenarios. To stay on the two degree pathway, action much be taken now and efforts must continue to grow into the future “Substantial cuts in greenhouse gas emissions over the next few decades can substantially reduce risks of climate change by limiting warming in the second half of the 21st century and beyond,” the report says. “Global mean surface warming is largely determined by cumulative emissions, which are, in turn, linked to emissions over different timescales. Limiting risks across reasons for concern would imply a limit for cumulative emissions of CO2. Such a limit would require that global net emissions of CO2 eventually decrease to zero.”
To reach that goal of zero carbon emissions, the report says, the use of low- and no-carbon energy technologies must be increased significantly. "The share of low-carbon electricity supply (comprising renewable energy (RE), nuclear and CCS, including BECCS) increases from the current share of approximately 30 [percent] to more than 80 [percent] by 2050 and 90 [percent] by 2100, and fossil fuel power generation without CCS is phased out almost entirely by 2100," the report says.
Because of CO2’s long life in the atmosphere, the effects of the damage that has already been done will be felt well into the future, even if mitigation actions begin now. “Warming will continue beyond 2100 under all RCP scenarios except RCP2.6. Surface temperatures will remain approximately constant at elevated levels for many centuries after a complete cessation of net anthropogenic CO2 emissions,” the report says “A large fraction of anthropogenic climate change resulting from CO2 emissions is irreversible on a multi-century to millennial time scale, except in the case of a large net removal of CO2 from the atmosphere over a sustained period.”
If progress to combat climate change stalls where it is now however, the situation will become very dire rather quickly the report warns. “Without additional mitigation efforts beyond those in place today, and even with adaptation, warming by the end of the 21st century will lead to high to very high risk of severe, widespread and irreversible impacts, globally. Estimates of warming in 2100 without additional climate mitigation efforts are from 3.7 °C to 4.8 °C compared with pre-industrial levels,” the report says. “The risks associated with temperatures at or above 4°C include severe and widespread impacts on unique and threatened systems, substantial species extinction, large risks to global and regional food security, consequential constraints on common human activities, increased likelihood of triggering tipping points (critical thresholds), and limited potential for adaptation in some cases.”
Potential Need for Carbon Dioxide Removal Technology
As current CO2 concentrations continue to build up, the need for mature carbon dioxide removal processes becomes more urgent, especially in cases where there is an overshoot of the target parts per million goal, the report indicates. This is somewhat worrisome as advancement in carbon removal processes has been slow. “Depending on the level of overshoot, overshoot scenarios typically rely on the availability and widespread deployment of bioenergy with carbon dioxide capture and storage (BECCS) and afforestation in the second half of the century. The availability and scale of these and other Carbon Dioxide Removal (CDR) technologies and methods are uncertain, and CDR technologies and methods are, to varying degrees, associated with challenges and risks,” the report says, also noting that “CDR is also prevalent in many scenarios without overshoot to compensate for residual emissions from sectors where mitigation is more expensive.”
The longer mitigation is put off, according to the report, the stronger reliance will be on these as yet unproven technologies. “Scenarios that are likely to maintain warming at below 2 C are characterized by a 40 [percent] to 70 [percent] reduction in GHG emissions by 2050, relative to 2010 levels, and emissions level near zero or below in 2100. Scenarios with higher emissions in 2050 are characterized by a greater reliance on Carbon Dioxide Removal (CDR) technologies beyond mid-century, and vice versa,” the report says. “Scenarios that are likely to maintain warming at below 2°C include more rapid improvements in energy efficiency and a tripling to nearly a quadrupling of the share of zero- and low-carbon energy supply from renewable energy, nuclear energy and fossil energy with carbon dioxide capture and storage (CCS), or bioenergy with CCS (BECCS) by the year 2050.”
