Production of greenhouse gas and global warming: the sectoral cumulative carbon emission budget view
Recently a new report on global warming has been published: how much do sectors like agriculture, construction and households have to increase the ‘Carbon-efficiency’ of their ‘production process’ to limit global warming to 2%? Oops – the report states (using a refined version of a methodology which has been pioneered by Ben and Jerry’s) freight transport has (as I understand it, the report is not explicit about this) increase its efficiency seven fold.
Some graphs and an excerpt.
Graph 1. Historical production of greenhouse gas, mind the increasing rate of increase.
Agriculture is a very, very important source of greenhouse gases. Eat less meat, drink less milk. Eat less ice cream. And we still have to build a few billion houses – while cement and steel are about the most CO2 intensive sectors there are… The report could have benefited from input output analysis, which enables a better coupling of CO2 production to different kinds of final demand. It is not too specific about how efficiency has to be increased. Interestingly, a whole score of NGO’s (WWF), companies (Coca Cola, Ford) and government organisations (UN) have been involved in writing the report.
Graph 2. Direct and indirect production of CO2 per sector (‘indirect’: when households use energy produced by a coal fired power plant).
Most recently, the concept of a cumulative carbon emission budget has entered the public domain. The principal driver of long-term warming is the total cumulative emission of CO2 over time.1 To limit warming caused by CO2 emissions to a given temperature target, cumulative CO2 emissions from all anthropogenic sources therefore need to be limited to a certain budget. Higher emissions in earlier decades simply imply lower emissions by the same amount later on (IPCC, 2014a). A global carbon budget is a practical and powerful concept that is easy to work with and communicate. In practice, even if in certain 2°C scenarios some sectors do not fully decarbonize, in the long term (beyond 2050), net zero emissions to the atmosphere must occur to avoid exceeding the budgeted CO2 amount that would lead to warming higher than 2°C. Limiting the global warming caused by anthropogenic CO2 emissions, with a probability of greater than 66 percent, to less than 2°C since pre-industrial levels will require cumulative CO2 emissions (the CO2 budget) to stay below 3,670 GtCO2 since the pre-industrial period. When taking non-CO2 gases into account, this remaining budget reduces to about 2,900 GtCO2 (IPCC, 2014a). Since 1,890 GtCO2 was emitted by 2011, the remaining CO2 budget from 2011 onward is 1,010 GtCO2 (IPCC, 2014a). This is the global budget at the core of the methodology. Over time the global budget will change: it will decrease as economic activity continues to emit CO2 into the atmosphere; new scientific evidence might lead to increases or decreases in emissions; or a new political and social consensus might arise to limit emissions. The authors acknowledge that regularly updating the global budget will be important for the robustness and integrity of the sector-based methodology as a tool to help companies setting emission reduction targets.