Last reviewed 27 March 2020

The UK Government has announced a target of net zero for UK greenhouse gas emissions by 2050. John Barwise defines the key environmental terms and explains the mechanisms by which we could achieve this ambitious target.

Global warming changes the climate in unpredictable and often catastrophic ways. The process of change is happening so quickly these days that natural processes that sustain life on Earth are unable to adapt quick enough. The 1.5°C threshold set by the Intergovernmental Panel on Climate Change (IPCC) gives people and ecosystems more time to adjust to a rapidly changing environment.

This feature article explains the basics of global warming and the mechanisms in place to monitor, measure and mange greenhouse gas emissions to achieve net zero by 2050.

Global warming — the basics

Greenhouse gases: these naturally occurring gases such as water vapour, carbon dioxide and methane, sustain life on Earth by allowing the sun’s rays to pass through the atmosphere and warm the earth but preventing some of the warmth from escaping back into space.

Greenhouse gas (GHG) emission refers to the total mass of a particular GHG release to the atmosphere over a specified period of time.

Greenhouse effect: the rapid increase of carbon dioxide and other greenhouse gas emissions from human activity trap more of the heat from the sun, just like the heat trapped in a greenhouse hence the term.

Kyoto Protocol: an international treaty that commits countries to reduce the onset of global warming by reducing GHG concentrations in the atmosphere to “a level that would prevent dangerous anthropogenic interference with the climate system”.

Global warming potential (GWP) allows comparisons of the global warming impacts of different GHGs up to a specific time period, relative to an equivalent unit of carbon dioxide over the same period of time (the Kyoto Protocol adopted a 100-year time period). The larger the GWP, the more that particular gas warms the Earth compared to carbon dioxide over that time period.

The GWP of GHGs closely associated to human activities are as follows.

  • Carbon dioxide (CO2) — CO2 was chosen by the IPCC as the reference greenhouse gas and therefore has a GWP of 1. Globally, we emit CO2 to the atmosphere in enormous quantities mainly through burning fossil fuels for energy and transport. Most CO2 remains in the atmosphere for hundreds of years or is sequestered by vegetation and oceans. Other GHGs are recorded as CO2 equivalent (CO2e).

  • Methane (CH4) — methane is about 100 times more potent than CO2 but only lasts about 10–12 years in the atmosphere.  When averaged over a 20-year period, methane’s “greenhouse gas equivalency” is about 72 times that of CO2. On a timescale of 100 years, GWP equivalency drops to just 25 times that of CO2. Human sources of methane include fossil fuels (especially gas), livestock farming, landfills and waste, biomass burning and biofuels. A particular concern is the melting of permafrost in the Arctic and elsewhere caused by global warming, which has the potential to add significantly to global emissions.

  • Nitrous Oxide (N2O) — is the third most important GHG for the enhanced greenhouse effect after CO2 and CH4, and has a GWP value 265 times that of CO2 over a 100-year timescale. Atmospheric concentrations of nitrous oxide have increased by 16% since the industrial revolution. Around one third of the emissions are estimated to be due to human actions including from agriculture, fossil fuels and biomass and industrial processes. Nitrous oxide is emitted in smaller amounts than CO2 and methane.

  • Fluorinated Gases (F-gases) — chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) have high-GWP because they trap substantially more heat than CO2 for a given amount of mass. CFCs, used mainly for refrigeration, damaged the Earth’s protective ozone layer and were banned in 1987. Applications for other F-gases include refrigeration, air conditioning, foam blowing agents used in insulation, aerosols, fire protection and solvents. HFCs, which make up about 90% of F-gases, are widely used for foam insulation in buildings, as well as in refrigerators and freezers.

According to national statistics, CO2 is the most dominant greenhouse gas from the Kyoto “basket” of GHGs, accounting for 81% of total UK GHG emissions in 2018.

Carbon emissions reporting

It is a legal requirement for all quoted companies in the UK to report their annual GHG emissions. Streamlined Energy and Carbon Reporting (SECR), which replaces the carbon reduction commitment (CRC) is a UK Government requirement for mandatory annual reporting and disclosure of energy and carbon information within company accounts. 

Other reporting criteria may also include the Energy Saving Opportunity Scheme (ESOS), Climate Change Agreements (CCA) Scheme, and the EU Emissions Trading Scheme (ETS).

The Greenhouse Gas Protocol, provides global standardised frameworks to measure and manage GHG emissions from private and public sector operations, value chains and mitigation actions.

  • Scope 1: direct emissions from owned or controlled sources. For example, onsite electricity generation, heating, cooling, business vehicles, fugitive emissions (eg refrigerants), agricultural emissions.

  • Scope 2: indirect emissions from the generation of purchased energy. Example include purchased electricity, heat and steam, etc.

  • Scope 3: also as known as value chain emissions, covers all other indirect emissions that occur in an organisation’s supply chain. These include purchased goods and services, employee commuting, business travel, upstream emissions from fuel extraction, waste and water.

The aim of all the various carbon and GHG reporting initiatives is to encourage organisations to implement energy efficiency measures as a way of reducing emissions, with the added benefit of cutting business costs and improving productivity.

Carbon footprinting

A carbon footprint is defined as the total GHG emissions caused by an individual, organisation, nation or a product, usually expressed as tonnes of carbon dioxide equivalent (CO2e) emitted every year, where CO2e is calculated as the mass of a given GHG multiplied by its GWP.  

Carbon footprints are measured by undertaking a lifecycle assessment (LCA) to determine the total GHG emissions associated with a particular individual, product or activity etc. The complex interactions between contributing processes in a lifecycle, including natural processes, means the total footprint of a particular product or activity cannot be calculated accurately. But it does provide a “best estimate” snapshot of the GHG emissions at a point in time, based on available data.

For businesses, calculating the carbon footprint of industry, product, or service is a complex task. Useful guides include the following.

  • ISO 14040:2006 Environment Management. Life Cycle Assessment defines LCA as the compilation and evaluation of the inputs, outputs and the potential environmental impacts of a product system. 

  • ISO 14067:2018 Carbon Footprint of Products specifies principles, requirements and guidelines for determining the carbon footprint of products, based on the method of LCA specified in ISO 14040.

  • PAS 2050 allows internal assessment of the existing lifecycle GHG emissions of goods and services.

A carbon footprint of a business is basically the sum of all GHG emissions (CO2e) associated with all processes, products, services and other activities across the supply chain and within a given timeframe (usually a year).

The UK's carbon footprint is an estimate of the UK’s GHG emissions and based on the consumption of all goods and services by households within the UK. They include estimates of emissions associated with each stage of the supply chain for those goods and services, regardless of whether or not their production process occurs within the UK. The footprint includes emissions associated with what the UK imports but excludes emissions associated with UK exports.

Carbon budgets

Carbon budgets restrict the amount of greenhouse gas the UK can legally emit in a five-year period. These are set in five-yearly carbon budgets from 2008 to 2050. Under the Climate Change Act, the Government can “borrow” or “bank” amounts from one budgetary period to another, which allows the Government to increase the budget by borrowing up to 1% from the succeeding period, if targets are not met. Conversely, if it has a surplus in a budgetary period, it can carry all or some of it forward to the next period.

The UK is on-course to comply with targets for the third carbon budget period (2018 to 2022), but on currently trajectories is likely to miss its targets for the fourth and fifth Carbon Budgets, without further action. The budgets were set originally with the aim of cutting GHG emissions by 80% by 2050. The revised commitment to net zero by 2050 will make the task much harder.

Net zero

In Europe, Denmark and Norway have enshrined net zero by 2050 in law, while Sweden's climate legislation commits the country to meeting the target by 2045. The European Commission has also proposed draft climate legislation that would commit all EU Member States to net zero carbon emissions by 2050, with further proposals to cut emissions by around 50% by 2030.

Achieving net zero is achievable but requires action across all sectors of the economy to reduce GHG emissions close to zero, particularly in transport, industry, power and land use. The remaining emissions will need to be compensated by expanding carbon sinks such as forest growth and other land-based sequestration schemes as well as carbon capture and storage.

Technologies exist that can reduce emissions close to zero across most sectors. Renewables and nuclear power used to generate electricity and heat can reduce demand for gas and other fossil fuels. Similarly, electricity and hydrogen technology can radically reform the transport sector — legislation to phase out of petrol and diesel vehicles will speed up this process. The rapid expansion of energy storage technology will play a vital role in shifting from fossil fuels to renewables.

In buildings, retrofit measures to improve insulation will drastically reduce heating demand, while ground and air-sourced heat pumps and other technologies can also replace gas heating systems. Industrial processes powered by clean electricity rather than gas and coal will similarly reduce GHG emissions.

Beyond carbon cutting to carbon neutral

To achieve net zero targets, the UK’s total GHG emissions must be matched by the removal of the same amount of emissions from the environment. The measures outlined above will go a long way to reduce emissions but will not achieve net zero targets. Additional measures for the removal of GHGs, such as carbon sequestration and off-setting, will be needed.

Aviation, for example, relies heavily on fossil fuels and technology alternatives are limited, although changes are happening. Boeing has managed to significantly reduce emissions on their Airbuses and other new planes by using lighter materials and more efficient engines.

The UK aviation industry has pledged to cut its net carbon emissions to zero by 2050 despite a 70% growth in passenger numbers to 2050. The Sustainable Aviation coalition has produced a “decarbonisation road map” outlining how aviation can cut its carbon footprint including sourcing sustainable aviation fuel, such as oil from nicotine-free tobacco and developing hybrid and fully electric aircraft. But more significantly the industry intends to cut more than a third of its emissions through global market-based carbon investment in carbon removal solutions saving 25.8 Mt CO2.

Similarly, UK agriculture currently creates around 10% of the UK’s GHG emissions. Initiatives are under way to achieve net zero emissions by 2040 by changing the types of commodities the sector produces and reducing carbon intensive products such as livestock, as well as boosting productivity by eliminating waste and capturing methane from manure for heating. Another element of the plan is to sequester carbon from the atmosphere by planting more woods and hedges to soak up CO2 and introducing ways to increase the carbon content of the soil.

Carbon capture and storage (CCS)

CCS is the process of capturing waste CO2 and storing it. Natural sequestration through reforestation does this, but more applications are needed to deal with industrial emissions, such as those from cement works, iron and steel production and other high CO2 emitting industries.

Carbon dioxide can be captured directly from the air or from an industrial source using a variety of technologies. Recent studies suggest applying CCS to a conventional power plant could reduce CO2 emissions by approximately 80–90% compared to a plant without CCS. Storing CO2 in deep geological formations is considered the most practical way to sequester emissions.

In his first budget, Chancellor Rishi Sunak announced a cash injection in the form of a new CCS Infrastructure Fund of £800 million to help establish two UK sites to store “millions of tonnes of carbon dioxide” that would otherwise be released into the atmosphere. In a separate project, a trial of bioenergy with CCS to remove a small amount of CO2 while producing energy at the same time.

Carbon negativity

The concept of negative carbon emissions goes beyond carbon neutral by aiming to remove more CO2 than a particular activity or process generates in the first place. It means neutralising the emissions associated with a particular entity or activity and then taking additional steps to remove additional CO2 from the atmosphere.

This is entirely feasible. Once a business has calculated its total emissions and carbon footprint, and taken measures to bring total emissions to zero, it can take additional steps to ensure the removal of additional CO2 from the atmosphere.

Examples might include sequestering more carbon by planting more trees or supporting moorland restoration. Other options might include purchasing carbon offsets from a third party which support the reduction of CO2 elsewhere. Offsetting schemes are used by companies and individuals to invest in various environmental projects around the world as a way of compensating for their own footprints. Projects vary from large hydro schemes, forestry and methane capture, to smaller community cooking stove schemes etc.

This is a popular option for airline companies and highly polluting industries. Although many argue that offsetting is often used as the cheaper, rather than choosing the most effective option for reducing carbon footprints. Verification of global offsetting schemes has also been the subject of much debate in recent years, with accusations that many schemes do not fulfil the reduction of GHGs they claim.

And finally…

The UK’s commitment to a target of net zero for UK GHG emissions by 2050 is ambitious but achievable. All the mechanisms for monitoring and measuring progress are in place, along with existing and emerging technologies to make it happen, both in the UK and elsewhere.

The crucial international climate change talks to be held in Glasgow in November (although this is no longer certain), may well prove to be the turning point for a truly global effort by world leaders to slow global warming and prevent the devastating impacts of climate change on society and the world economy.