The definition of climate action has been vague until recently. Now though, the Paris Agreement, ratified by Ireland and the EU last year, together with ever-stronger climate science, are making the reality of the challenge much clearer. National and EU climate policy can now be updated to align actions with the science and equity research relating to the Paris temperature limits. Here we take a look at what that might mean with the help of a new article in the journal Science written by a team including some very well known climate scientists:

A roadmap for rapid decarbonization

By Johan Rockström, Owen Gaffney, Joeri Rogelj, Malte Meinshausen, Nebojsa Nakicenovic, Hans Joachim Schellnhuber

Science 24 Mar 2017 : 1269-1271  DOI: 10.1126/science.aah3443

The key Paris objectives are to limit global warming to "well below 2ºC" (while pursuing efforts toward 1.5ºC) "in accordance with best available science” and “on the basis of equity”. Knowing that CO2 emissions, in particular, must effectively be reduced to zero on a net basis to limit global warming, the world must aim “to reach global peaking of greenhouse gas emissions as soon as possible” and all nations – richer, developed nations first – are to "undertake rapid reductions" in emissions.

The question is, what does this mean practically? How fast do emissions need to fall to align Ireland’s and the EU’s climate action with the Paris goals? What management options are available? To what extent can continued fossil fuel and agriculture emissions be offset by methods that might take greenhouse gases like carbon dioxide back out of the atmosphere? What offsetting “negative emissions” methods, if practicable, might work best for the world in general, and here in Ireland, in particular? What are the risks involved if we design current climate action based on hypothesised future negative emissions technologies?

To assist with climate action policy decisions, these are questions that the EPA-funded research project, ie-nets, hopes to help answer.

In this new article, Rockström et al. define “a roadmap for rapid decarbonization” by spelling out what they describe as a "carbon law”, a pathway aiming to halve net global emissions in every decade.  The overarching aim of the roadmap is to stay within the ‘global carbon budget’, which is the maximum amount of total future carbon dioxide emissions possible to give a good chance of limiting climate change to well below 2ºC.  The authors say that this ‘carbon law’ guidance – cutting emissions by 50% every decade – can be applied as a climate action policy objective in all countries, most importantly in nations with high per capita emissions.

Take a look at the chart below to see the precipitous urgency of what such a path now requires. Getting high emissions down to a level where negative emissions can have some effect is clearly an important take-home message from this.  Rockström et al. do say that there is some leeway in their carbon budget to allow for more emissions if the negative emissions technologies prove unfeasible, but that still means that each nation's emissions need to decline as quickly as they outline to match action with Paris-level ambition.

This roadmap starkly demonstrates the extreme scale and speed of managed transformation now needed to slow and if possible stop future climate change – the task would have been a lot easier if we had started 10 or 20 years ago when global emissions were much lower and the remaining carbon budget was much larger. Fossil fuel and total energy use now needs to drop rapidly to give time to increase the amount of low-carbon energy production.

Intentional carbon dioxide removal from the atmosphere and at emission sources such as power stations and cement factories would be needed if any effective offsetting is to be possible. The carbon dioxide captured would need transporting by pipeline to a storage location and then permanently stored in deep geological storage– in the Irish case this might, for example, be in the exhausted Kinsale gas field. Afforestation also helps, though mainly by replacing past and ongoing deforestation.  

As the article makes very clear, it is early and deep actions across all sectors that makes the biggest difference between climate action success and failure. Even if they prove to be viable at scale, negative emissions technologies like bioenergy carbon capture and storage (BECCS) can only offset limited amounts of emissions. The 2ºC ‘carbon law’ roadmap would mean total emissions from fossil fuel use and land-use will need to continue to drop by about 50% in each decade, even if and when negative emissions begin to be available after 2030. Investing in research and development needs to happen now though if negative emissions are to be at all achievable toward decarbonisation aligned with Paris goals.

There is great danger, and large global costs of inaction, in not actually cutting total emissions enough (or at all) in the very short term. As shown in the chart below, if emissions continue at the current high level then the entire global carbon budget available, to give a 2 in 3 chance of remaining below the Paris 2ºC limit, will be exhausted within twenty years. By 2037 it would all be gone.  If humanity could collectively manage cutting emissions by about 5% per year, approximately halving total global emissions by 2030 and again by 2040, then this early action will effectively “save” carbon budget that could then be available to be managed for future use until up to 2100 or even beyond.

Below is an indicative chart of two possible emission pathways for Ireland with the same total future carbon budget. Saving carbon budget for later decades requires rapid, near-term, emission reductions across the whole economy.

The good news is that global CO2 emissions appear to have stopped increasing for the time being, having levelled out over the past three years. If governments around the world could act now to ensure that this levelling off is indeed the necessary peak in global emissions then we can now get a head start on the rapid decarbonisation path to halving current emissions by 2030.

As Rockström et al. say, this will require “Herculean efforts”.  Unlike some commentators, they make no pretence that the task of limiting emissions will be easy.  Instead, their article gives a strong sense of the Olympian scale of collective effort required over the next decades, especially by the highest emitters, to limit dangerous climate change. Above all, the climate scientists’ article makes very clear that the urgent need now is for strong, near-term action to cut emissions quickly, including reductions in consumption, while also investing in low-carbon energy and researching the longer term potential for negative emissions technologies.