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According to this report from The Times,

Greenhouse gas emissions fell in every sector — including transport, industry and energy — in 2018, but emissions from homes went up 4 per cent, government data shows.

Is it true that emissions from homes went up by 4%? And if so, how did they measure this?

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tl;dr: There was a 4% increase in CO2 emissions from the residential sector due to demand for natural gas for heating. When adjusted for temperature, there was a decrease of around 1.5%


Residential emissions

The UK's open government data website provides annual data on greenhouse gas emissions by sector. In February 2020, the latest statistical data was released. Here's the chart for residential emissions:

Greenhouse gas emissions from the residential sector, UK 1990-2018 (MtCO2e)

From the executive summary of the 2018 report (pdf):

There was an increase of 3.8% (2.5 MtCO2e) in residential sector emissions, driven by an increase in the use of natural gas for heating due to colder weather in the first half of 2018.

There are a few more details given on page 19:

Temperature was the main driver of the 4% increase in residential emissions between 2017 and 2018. The average temperature across the year was on average the same in 2018 as in 2017, but 2018 had a particularly cold February and March, with average temperatures over 3 degrees Celsius lower than in 2017 in both months, increasing the use of natural gas for heating.

Temperature adjustment

The provisional statistics for 2018, released in March 2019, include a temperature adjustment. From page 10 of the report (pdf):

Between 2017 and 2018: There was a 2.8 per cent (1.8 Mt) increase in residential emissions. [...] [This increase] can largely be explained by colder weather in Q1 2018 than the previous year. On a temperature adjusted basis between 2017 and 2018: There was a 1.5 per cent (1.1 Mt) decrease in residential emissions.

The final data includes emissions in addition to those from heating, so while the final total is higher, it seems reasonable to assume that the temperature adjustment would be roughly the same (since most emissions due to uses other than heating wouldn't be included).

The temperature adjustment is made by comparing the demand for heat in a given year to the average . Details of the methodology used to make this adjustment are in the methodology summary (pdf) on page 6-7:

  • A simple linear regression is established between the quarterly emissions for a given sector/fuel type and the quarterly average heating degree days, from 2002 to the latest year for which a final GHG emissions estimates are available. [...]
  • CO2 emissions are adjusted for each sector and fuel by using the gradient from the regression model as an estimate of the additional emissions per additional heating degree day. For a given quarter we look at the number of heating degree days by which it deviated from what the typical amount of heating required at that time of the year (as given by the long-term average for the period 1981-2010).
  • Multiplying this deviation by our estimate of the additional emissions per additional heating degree day for the given sector/fuel type gives the estimated temperature effect on CO2 emissions. This temperature effect is then removed to give the temperature adjusted emissions for that quarter.

How are emissions measured?

All emissions are reported on a "by source" basis, following IPCC conventions on reporting GHG emissions. Table 13 (MS Excel or ODS) provides details of where the data comes from:

Sectoral details, methodologies and data sources

The data on residential use of natural gas (the major contributor to residential emissions) is provided to the government annually by the gas network operators.

Data on emissions of specific gases, by sector and end-use, can be accessed at the National Atmospheric Emissions Inventory's UK emissions data selector.

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