Unpacking the DECC inventory… Part 1: non-CO2 greenhouse gases

My previous post on the Carbon Plan 2011 led me to look at the UK greenhouse gas inventory on the website of the Department of Energy and Climate Change (DECC). These statistics allow us to assess progress towards the targets set by the Climate Change Act 2008, and were the basis of the numbers reported in the Carbon Plan 2011.  I was interested to see how greenhouse gas (GHG) emissions from the various sectors of the economy have changed since 1990.

This post is definitely for people who like to look at graphs! It is entirely descriptive, to give the overall picture of how UK GHG emissions have changed since 1990.

[Update: Feb 2013 In early 2013, DECC’s website moved to http://www.gov.uk, and many of the links in this post now don’t work. Some of the documents are now here:
https://www.gov.uk/government/publications/final-uk-emissions-estimates]

From the data tables from 2010 (excel – backup link here) I chose 1990 and 2009 as the start and end dates for calculating percentage changes, as these were the dates used in the Carbon Plan 2011. Over this time, annual greenhouse gas emissions fell 26 per cent (a reduction of 200 MtCO2e). This reduction can be broken down among the various greenhouse gases as follows, each reported as MtCO2e, that is, converted to ‘CO2-equivalents’.

Over half of the 200 MtCO2e fall was due to a 113 Mt reduction in annual carbon dioxide emissions. 28 % was due to methane (55 MtCO2e) and 16 % to nitrous oxide (33 MtCO2e). Fluorinated gases were about the same in 2009 as they had been in 1990.

This graph shows the UK’s greenhouse emissions since 1990, and the percentage change in each of the gases. [Update, 5 Dec 2012: For all of the graphs in this post, the data are plotted from 1990 to 2010 (all available years) but the percentage changes from 1990 to 2009 are shown in the legend. This is for comparison with the Carbon Plan 2011 which quotes emissions data from 1990 to 2009.]

These emissions are also reported by economic sector.  The following plot of GHG emissions by end user shows that the main sectors are business, transport and residential, which together make up 70 to 80 per cent of the total emissions. Falls in emissions from these three sectors made up just under half of the total emissions reductions since 1990 (business contributed 35 % of the overall fall, transport 0 %, and residential 13%). The remainder of the reductions came from other sectors such as industrial process and waste management.

Consider for now only the non-CO2 greenhouse gases – methane, nitrous oxide (N2O), and fluorinated gases (F-gases). Emissions of these gases  have fallen 49 per cent (in CO2 equivalents) since 1990:

For each gas in turn, I have plotted the emissions from each of the main sectors that produce that gas. All gases are shown in ‘CO2 equivalents’. To calculate these for methane and N2O, I have used DECC’s estimates of their ‘Global Warming Potential’ factors given in table 10 of the inventory.

First, methane.  Half of the fall in methane emissions was due to improvements in waste management (landfill). (We should note that all waste management emissions are modelled rather than measured according to table 13 in the inventory.) Most of the remainder of the reductions can be traced back to fixing leaks in the gas supply, and changing how methane emissions from coal mines are handled (according to the DECC inventory user guide (pdf) on this page).

Second, nitrous oxide (N2O). Most of the fall in nitrous oxide was due to reductions in Industrial Process emissions (which I discussed in my previous post).

Third, fluorinated gases (F-gases). These are a relatively small component of overall emissions and were about the same in 2009 as they had been in 1990. However, individual components of these emissions changed a lot. The almost complete disappearance of these gases from ‘industrial process’ (see my previous post) has been offset by a huge increase in ‘residential’ and ‘business’ emissions, giving a very small net increase since 1990. The increases are almost all attributed to ‘refrigeration and air conditioning’ in the business sector and ‘aerosols and metered dose inhalers’ in the residential sector.

So, to summarise, 44 % of the fall in annual UK greenhouse gas emissions since 1990 has been due to decreased emissions of methane, nitrous oxide and fluorinated gases. We should note that large uncertainties are associated with these figures due to (i) the estimates of relative global warming potential of the various gases, (ii) uncertainties in determining historical emissions of the gases, and (iii) the models used to estimate some of these emissions e.g. methane from landfill sites. DECC does not hide these uncertainties (see e.g. tables 10 and 11 in the inventory), but they are not emphasised in the headline figures announced in documents such as the Carbon Plan.

This post is now long enough. I plan to discuss CO2 emissions in part 2.

Update, 5 Dec 2012: These figures are based on Tables 3, 5, 6 and 7 of the DECC spreadsheet, and not on the totals in Table 1, which are slightly different to the other tables, for reasons I have yet to fathom. Thanks to an email correspondent for pointing out this discrepancy.

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2 thoughts on “Unpacking the DECC inventory… Part 1: non-CO2 greenhouse gases

  1. Pingback: Unpacking the DECC Inventory… Part 2: Carbon Dioxide | My Garden Pond

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