Estimates of consumption-based greenhouse gas (GHG) emissions require greater scrutiny to reduce uncertainty about the data, the Committee on Climate Change (CCC) said.
The CCC assessed how GHG emissions are quantified and the implications for setting carbon budgets and measuring progress against climate change targets. Although its report concludes that the methodology used by the government for measuring the UK’s GHGs is rigorous, it points out that estimates of emissions generated in the production of imported goods are only experimental.
The estimates are based on complex data and methodologies in measuring it differ, which leads to a large uncertainty, the report warns.
Estimates are dependent on modelling the entire global economy, but there are no agreed international standards of data collection, according to the report. In addition, there are often gaps in data, which are not always available for the same time periods or updated regularly.
Consumption-based GHG statistics are used to assess whether measures to reduce UK territorial emissions do not lead to an increase in global emissions. The figures are also used to develop climate policy, and measure carbon-intensive supply chains and trade flows.
However, the CCC notes that, although different methodologies and datasets are used to measure consumption-based emissions, most estimates show a consistent trend. A range of recent studies have estimated the UK’s carbon footprint in 2010 as being in the range 722 to 915 MtCO2e.
Most show that estimates between 1990 and 2007 increased before falling after the financial crisis. They are currently at approximately the same level as in the mid-1990s.
In general, the methodology for measuring GHGs in the UK is robust, the CCC said, but estimates in some sectors were less certain than others.
Sectors with complex biological processes or diffuse sources such as waste, agriculture and land use, land use change and forestry (LULUCF) have higher levels of uncertainty than the energy use sectors, such as power and transport.
There is a high degree of uncertainty around estimates of emissions from agriculture, predominantly because accurately measuring nitrogen dioxide emissions from agricultural soils and methane emissions from enteric fermentation is difficult, the CCC found.
Last week, consultants at WSP|Parsons Brinckerhoff questioned the way carbon emissions from buildings and businesses were measured. Current methodology does not take account of when electricity is used, leading to misleading data, they said.
