Assess the impact of air emissions on global warming

How to work out the impact of air emissions on global warming if you're applying for a bespoke environmental permit.

You must read this guide if you’re applying for a bespoke environmental permit and your activity produces air emissions.

Read the risk assessment overview first. It explains the other steps you need to take in completing your risk assessment.

Work through the following steps to calculate your impact on global warming.

  1. Identify your greenhouse gas emissions.
  2. Work out the impact these emissions have on global warming.
  3. Work out the impact of your ‘process option’ on global warming.
  4. Add up the impacts from steps 2 and 3 for each of your current or proposed process options to give the total impact on global warming.

A process option is a production process you aim to follow (eg making iron in a blast furnace) and the method you take to prevent or minimise emissions from it.

Knowing the impact of emissions on global warming will help you:

  • choose a process option (if you can choose from more than one) that has the least impact on global warming
  • establish the best available techniques to control emissions

Risk assessment tool

You can use the risk assessment tool to help complete this part of your permit application. It can do the calculations in this guide for you.

Identify greenhouse gas emissions

Identify all greenhouse gases your site produces.

You must list each of your:

Direct emissions

Direct emissions are produced by the energy your activity uses from storing, handling and processing at your site. They include any heat or power you produce directly at your site.

Direct emissions aren’t limited only to energy use - they can arise from any manufacturing process in which a substance releases a greenhouse gas.

Indirect emissions

Indirect emissions are produced from the heat or power imported into your site (eg electricity you buy from a supplier).

Indirect emissions also include energy used away from your site by others (eg when your site’s waste is treated elsewhere).

Treat any direct or indirect carbon dioxide emissions that come from renewable energy sources (eg from waste or from ‘biomass’ - biodegraded waste) as having an impact of ‘0’ on global warming.

Calculate impact of emissions on global warming

  1. Do this calculation: annual tonnes produced of the released greenhouse gas, multiplied by the appropriate global warming potential factor. The result should be shown in annual tonnes produced.
  2. Repeat this calculation for all substances released.
  3. Add up the totals to get the total impact of your emissions for your site.

Greenhouse gases: impact of your emissions

Substance Global warming potential factor
Carbon dioxide 1
Carbon tetrachloride 1400
Chloroform 4
CFC-11 4000
CFC-12 85000
CFC-13 11700
CFC-113 5000
CFC-114 9300
CFC-115 9300
H-1301 5600
HCFFC-22 1700
HCFC-123 93
HCFC-124 480
HCFC-141b 630
HCFC-142b 2000
HCFC-225ca 170
HCFC-225cb 530
HFC-23 12000
HFC-32 550
HFC-41 97
HFC-43-10mee 1500
HFC-125 3400
HFC-134 1100
HFC-134a 1300
HFC-152a 120
HFC-143 330
HFC-143a 4300
HFC-227ea 3500
HFC-236fa 6300
HFC-245ca 640
Methane 21
Methylene chloride 9
Methyl chloroform 110
Nitrous oxide 310
Perfluorocyclobutane 10000
Perfluoroethane 11900
Perfluorohexane 9000
Perfluoromethane 5700
Perfluoropentane 8900
Sulphur hexafluoride 23900

Global warming impact of energy used by your process option

You must work out the impact on global warming from the energy used by your process option, or (if you can choose from more than one) each process option.

The risk assessment tool will do these calculations for you. If you’re not using the tool, you must complete the following steps.

Direct and indirect carbon dioxide emissions

For each type of energy (eg electricity) used in an option list separately in annual kg its:

  • direct carbon dioxide emissions
  • indirect carbon dioxide emissions

Calculate carbon dioxide emissions by multiplying the amount of energy you use in annual kg by the relevant multiplier (also known as ‘conversion factor’) for carbon dioxide.

Calculate annual tonnes of carbon dioxide produced

Different conversion factors apply depending on how you measure the energy you use (ie megawatt hours or gigajoules).

Fuel Conversion factor: tonnes per megawatt hour Conversion factor: tonnes per gigajoule
Electricity 0.166 0.0462
Coal 0.3 0.0832
Coke 0.43 0.1192
Gas oil 0.25 0.0693
Heavy fuel oil 0.26 0.0722
Petrol 0.24 0.0667
Liquid petroleum gas (LPG) 0.23 0.0638
Jet kerosene 0.24 0.0667
Ethane 0.2 0.0557
Naphtha 0.26 0.0722
Refinery gas 0.2 0.0191
Petroleum coke 0.34 0.0946
Natural gas 0.19 0.0528

Treat any heat and power from a direct or indirect renewable source as having ‘0’ carbon dioxide impact.

Energy efficiency conversion factor: indirect emissions

You must use 2 additional conversion factors if you use any of the following indirect energy sources.

Energy source Conversion factor 1 Conversion factor 2
Electricity from National Grid 2.4 0.166
Electricity from other suppliers Ask your supplier Ask your supplier

Where you’re told to ‘ask your supplier’, ask them for either:

  • the ‘delivered to primary conversion factor’, for conversion factor 1
  • the ‘primary carbon dioxide factor’ in tonnes per megawatt hour, for conversion factor 2

Energy efficiency conversion factor: direct emissions

You must use additional conversion factors if you use any of the following direct energy sources.

Energy source Conversion factor 1 Conversion factor 2
Coal 1 0.3
Coke 1 0.43
Gas oil 1 0.25
Heavy fuel oil 1 0.26
Petrol 1 0.24
Liquid petroleum gas (LPG) 1 0.23
Jet kerosene 1 0.24
Ethane 1 0.24
Naphtha 1 0.2
Refinery gas 1 0.2
Petroleum coke 1 0.34
Natural gas 1 0.19
Other sources 1 Ask your supplier for the primary carbon dioxide factor in tonnes per megawatt hour

Conversion factor: tonnes to kg

Because you must show the total carbon dioxide impact in annual kg produced, you need to use an additional conversion factor of 1000. (This is because other conversion factors in this guide have been calculated based on tonnes rather than kg.)

Calculate your total impact on global warming

Add up:

  • the impact of emissions on global warming
  • the impact each option has on global warming

The result is the the total impact (kg of carbon dioxide) on global warming produced from your site’s activities.

Rank global warming impact of different options

If there’s more than one process option you can use, you must include the impact for each option in your assessment.

Rank these options to show which has the least impact on global warming and which has the most.


  • 1: Option 2 - 2,821,750 annual kg of carbon dioxide
  • 2: Option 1 - 3,131,600 annual kg of carbon dioxide
  • 3: Option 3 - 3,539,600 annual kg of carbon dioxide

Check if you need to complete further risk assessments

Check if you need to complete more assessments as part of your permit application.

Submit the data you’ve calculated in this guide with your permit application.

Published 1 February 2016