Net zero: why is it necessary?
What's the logic behind a net zero emissions target, and who is moving to set one?
By Dr Simon Cran-McGreehin@SimonCMcG
A number of countries, including the UK, have made commitments to move to a net zero emissions economy. This is in response to climate science showing that in order to halt climate change, carbon emissions have to stop – reducing them is not sufficient. ‘Net zero’ means that any emissions are balanced by absorbing an equivalent amount from the atmosphere.
In order to meet the 1.5°C global warming target in the Paris Agreement, global carbon emissions should reach net zero around mid-century. For developed nations such as the UK, the date may need to be earlier. Many have already set such dates.
The science of ‘carbon budgets’
Climate science is clear that to a close approximation, the eventual extent of global warming is proportional to the total amount of carbon dioxide that human activities add to the atmosphere.
So, in order to stabilise climate change, CO2 emissions need to fall to zero. The longer it takes to do so, the more the climate will change. Emissions of other greenhouse gases also need to be constrained. In the Paris Agreement, governments agreed to keep global warming ‘well below’ 2 degrees Celsius, and to ‘make efforts’ to keep it below 1.5ºC. The Intergovernmental Panel on Climate Change (IPCC) released a report in October 2018 on the 1.5ºC target; it concluded that global emissions need to reach net zero around mid-century to give a reasonable chance of limiting warming to 1.5ºC.
Why ‘net zero’?
In many sectors of the economy, technologies exist that can bring emissions to zero. In electricity, it can be done using renewable and nuclear generation. A transport system that runs on electricity or hydrogen, well-insulated homes and industrial processes based on electricity rather than gas can all help to bring sectoral emissions to absolute zero.
However, in industries such as aviation the technological options are limited; in agriculture too, it is highly unlikely that emissions will be brought to zero. Therefore some emissions from these sectors will likely remain; and in order to offset these, an equivalent amount of CO2 will need to be taken out of the atmosphere – negative emissions. Thus the target becomes ‘net zero’ for the economy as a whole. The term ‘carbon neutrality’ is also used.
Sometimes a net zero target is expressed in terms of greenhouse gas emissions overall, sometimes of CO2 only. The UK Climate Change Act now expresses its net zero emissions target by 2050 in terms of greenhouse gases overall.
The only greenhouse gas that can easily be absorbed from the atmosphere is carbon dioxide. There are two basic approaches to extracting it: by stimulating nature to absorb more, and by building technology that does the job.
Plants absorb CO2 as they grow, through photosynthesis. Therefore, all other things being equal, having more plants growing, or having plants growing faster, will remove more from the atmosphere. Two of the easiest and most effective approaches for negative emissions, then, are afforestation – planting more forest – and reforestation – replacing forest that has been lost or thinned. Technical options include BioEnergy with Carbon Capture and Storage (BECCS) and Direct Air Capture (see our Negative Emissions briefing.)
Who is moving to net zero?
A number of countries have already set targets, or committed to do so, for reaching net zero emissions on timescales compatible with the Paris Agreement temperature goals. They include the UK, Germany, France, Spain, Norway, Denmark, Switzerland, Portugal, New Zealand, Chile, Costa Rica (2050), Sweden (2045), Iceland, Austria (2040) and Finland (2035). The tiny Himalayan Kingdom of Bhutan and the most forested country on earth, Suriname, are already carbon-negative – they absorb more CO2 than they emit.
In addition, the European Union recently agreed to enshrine its political commitment to be climate neutral by 2050 in its European Climate Law.
The principle that rich nations should lead on climate change is enshrined in the UN climate convention that dates back to 1992, and was reconfirmed in the Paris Agreement. Therefore, if the science says ‘global net zero by mid-century’, there is a strong moral case for developed countries adopting an earlier date.
So far, the UK, France, Sweden, Norway and Denmark have enshrined their net zero targets in national law. Other nations including Spain, Chile and Fiji are looking to do so.
In the UK
Immediately after the IPCC published its Special Report on 1.5°C in October 2018, the governments of the UK, Scotland and Wales asked their official advisers, the Committee on Climate Change (CCC), to provide advice on the UK and Devolved Administrations’ long-term targets for greenhouse gas emissions.
The CCC had previously indicated that the UK should be aiming for net zero emissions by 2045-2050 in order to be compatible with the 1.5ºC Paris Agreement goal.
The CCC delivered its advice in May 2019. Its recommendations were:
- For the UK, a new target: net-zero greenhouse gases by 2050 (up from the existing emissions reductions target of 80% from 1990 levels by 2050);
- For Scotland, a net-zero date of 2045, 'reflecting Scotland’s greater relative capacity to remove emissions than the UK as a whole';
- For Wales, a 95% reduction in greenhouse gases by 2050, reflecting it having 'less opportunity for CO2 storage and relatively high agricultural emissions that are hard to reduce'.
The governments of Wales and Scotland swiftly accepted the CCC's advice, and on 12 June 2019, the UK government laid a statutory instrument to amend the 80% target in the Climate Change Act 2008. Just two weeks later, the new net zero target (100% from 1990 levels by 2050) was formally signed into law.
Only a matter of days before France could complete the feat, the UK had pipped them to it and become the first G7 country to legislate for net zero greenhouse gas emissions by 2050.