Context

Our recently published journal paper, McMullin et al. 2019, assesses Ireland’s maximum prudent ‘fair share’ of the Paris-aligned global carbon (CO2) budget, here termed our national CO2 quota, as c. 391 MtCO2, dating from 2015. This represents our estimate of an upper bound on the nett remaining “fair share” cumulative CO2 emissions available to Ireland, from the aggregate sector of fossil fuel energy and industrial processes (FFI) and land use (LU), from that time onward.  The paper compared this estimate with the likely cumulative emissions arising from both top-down policy goals and bottom-up projections based on actual policy measures. It found that, in all the considered policy scenarios, the quota would, in fact, already be exhausted by around 2024. Ireland would then start rapidly accumulating an implied “CO2 debt” — a “debt of (national) honour” or tacit commitment, imposed rather unilaterally on young citizens today, not only to achieve “nett zero” CO2 emissions to stabilize the debt (stop it growing larger), but to then quickly transition to sustained “nett negative” CO2 emissions over the following 2-3 decades, to “pay off” the debt and return to good faith alignment with achievement of the Paris agreement temperature goals.

However, that paper text was finalised shortly before the publication of a new “all of Government”, Irish Climate Action Plan 2019 (CAP-2019). In this blog post therefore, we attempt to assess whether this new plan gives a basis for substantially altering the (negative) policy assessments of the original paper. [Spoiler alert: the answer turns out to be "no"..]

Climate Action Plan 2019: What pathway of CO2 emissions reduction?

As we do not have a time machine to retrospectively start strong mitigation from 2015, and the measures in the new plan are unlikely to substantially change emissions for either 2019 or 2020, we will consider a set of pathways that all start by assuming that emissions for 2015 to 2020 are as recorded/projected in the most recent EPA projections (using the “with existing measures” data). 

Beyond 2020, the Climate Action Plan 2019 does not, in fact, clearly describe any target pathway either for national greenhouse gas emissions as a whole or for individual gases (such as CO2, the specific focus of the current discussion). This is a significant shortcoming in itself. Instead the plan equivocates between discussion of sectors defined nationally (such as an aggregate of “electricity generation, built environment and transport”) and sectors defined relative to EU policy measures (specifically demarcated between the EU Emissions Trading Scheme, ETS, and the non-ETS emissions). These different sectoral aggregates relate to each other in complex ways that are not explicitly decomposed in the plan, which makes interpretation difficult (and speculative!). Nonetheless, we will present a “best effort” attempt to arrive at a coherent definition of future CO2 emissions pathway(s) that are at least consistent with, if not explicitly mandated by, the plan.

The plan targets what it describes as a “2% per annum” reduction pathway specifically for the non-ETS emissions sector from 2021 to 2030, based on attainment of our agreed national level commitment to EU-wide emissions reduction under the Effort Sharing Regulation (ESR). It goes on to state that:

“... in the period between 2030 and 2050, a much steeper decline of 7% per annum will have to be achieved based on achieving a minimum 80% emissions reduction by 2050, relative to 1990.”  [p.27] 

Strictly, compounding year-on-year reductions at any fixed percentage rate would yield pathway segments that are mathematically exponential. However, mathematically linear pathways (characterised by reduction by a fixed absolute amount in each year, rather than by a compounding year-on-year percentage) are more typical in EU policies (such as the ESR) and for the presentation of indicative CO2 decarbonisation pathways by the Irish EPA, CCAC and SEAI. Further, the chart presented in the actual plan, illustrating the non-ETS emissions pathway to 2030 (p. 19), does in fact show a linear rather than exponential form. 

Accordingly, we will assume that the action plan is best interpreted as proposing to achieve emissions pathways (across sectors and gases?) that are, generally, piecewise linear from 2021-2030, and then again from 2031-2050, but potentially with different linear reduction rates in those two periods. Further, we will assume that, for 2021-2030. the rate (linear slope) will be fixed at c. 2% of the 2020 emissions rate. As already noted, this is stated explicitly in the plan for the non-ETS sector; and in the absence of more precise guidance, we will therefore extrapolate this to all national CO2 emissions (i.e., across both ETS and non-ETS). Beyond 2030, the reduction rate will be determined relative to a targeted point-in-time level in 2050. This later level is indicated to be (for the time being) an overall reduction of 80% relative to 1990 levels (at least for CO2, if not other gases) based on long term targets originally contained in the National Policy Position on Climate Action and Low Carbon Development of 2014. Those long term targets have expressly not been superseded in the new plan; though the plan does also commit (Action 1) that early consideration will be given to a “more ambitious” long term target of achieving “nett zero” emissions in 2050.

This yields an interpretation of the Climate Action Plan 2019 as envisaging (or committing to?) the following possible pathways for total future CO2 emissions in Ireland:

• From 2021-2030, a linear pathway characterised by successive annual reductions of 0.86 MtCO2 per year, each year, representing 2% of projected nett 2020 FFI+LU CO2 emissions, for an overall 20% reduction by 2030 relative to 2020.

• From 2031-2050 a divergence between two possible pathways, both again linear, and differing only in the “point-in-time” emissions level in 2050, being either:

• 80% reduction compared to 1990, implying annual reduction of 1.34 MtCO2 per year, each year, equivalent to 3.1% of the projected 2020 level; or

• nett zero in 2050, implying annual reduction of 1.72 MtCO2 per year, each year, equivalent to 4% of the projected 2020 level.

(We note that the 2031-2050 annual reduction rate of “3.1% of the projected 2020 level”, cited here as based on achieving 80% reduction relative to 1990 by 2050, appears substantially less than the 7% cited in the Action Plan. This discrepancy precisely illustrates the difficulties that arise due to the mixture of different and potentially ambiguous approaches to sectoral divisions, time baselines, and percentage and absolute reductions that are used at different points in the plan text, lacking clear cross-referencing, decomposition, or transparent mapping to public datasets, calculations or audit trails.) 

In Figure 1 we compare these two CAP-2019 based pathways with a reference linear pathway that is constrained to just use up (without overshoot or entering CO2 debt) our estimated maximum prudent ‘fair share’ quota of c. 391 MtCO2 (dating from 2015). Based on the projected accumulated emissions to 2020, this quota-constrained reference pathway would require successive annual reductions of 6.0 MtCO2 per year (representing 14% of the projected 2020 emissions level), each year from 2021 until it reaches nett zero, which would occur by about 2028 (and maintaining net-zero emissions thereafter). 

Figure 1: Annual emission pathways.

In figure 2 we show the corresponding cumulative depletion of the fair share quota (starting at the assessed prudent value of 391 MtCO2 as of 2015, in all cases). By construction, the theoretical Paris-aligned, no-overshoot, linear pathway would exactly exhaust the quota (c. 2028) and does not enter carbon debt (as there are no further nett emissions). By contrast, the Climate Action Plan pathways both exhaust the entire quota as early as 2024 and subsequently overshoot into CO2 debt. The pathway to -80% by 2050 reaches a cumulative CO2 debt of 615 MtCO2 (that would still continue to deepen even thereafter); and the pathway to nett zero by 2050 levels out (but does not yet start reversing) CO2 debt at 535 MtCO2 at that year. 

It is notable that the supposedly very significant increase of ambition represented by “nett zero” annual emissions by 2050 actually makes only a modest difference (c. 13%) to the level of CO2 debt accumulated by that time (albeit, it would at least have stopped growing under the nett zero constraint). Thus, the critical criterion in evaluating the effectiveness of CO2 mitigation is not some nominal “point-in-time” (2050) emissions rate, but the pathway toward such a point. Even for exactly the same “point-in-time” target (the same overall reduction in annual emissions), early cuts are much more significant than later ones, simply due to their additional duration in time. Conversely, procrastination not only implies that the deeper, presumably more politically challenging, reductions are kicked down the road, but that they may then have to be achieved against a background of potentially much more severe climate impacts (nationally and globally).

Figure 2: Ireland’s 2015 remaining quota of 391 MtCO2 is depleted by the nett CO2 emissions in each year for each pathway. CO2 debt occurs if or when the remaining quota becomes negative, tacitly implying a commitment to subsequent nett negative emissions to “pay back” this debt.

For comparison, our journal paper assessed inter alia the evolution of cumulative CO2 emissions that would have arisen if an exponential (consciously front-loaded) pathway toward even the nominally “less ambitious” 80% reduction by 2050 target had been immediately initiated when that point-in-time objective was originally adopted in 2014. While that would have still resulted in significant carbon debt (relative to our assessed prudent quota), it would have reached a level of only about 350 MtCO2 by 2050, substantially (35-45%) less than either of the pathways now suggested by the new 2019 plan. Thus, rather than representing increased ambition, this plan appears rather to retrospectively endorse a de facto erosion of ambition that has occurred since the National Policy Position was formally adopted (where “ambition” is here measured by cumulative CO2, as properly reflects the underlying physical science).

Conclusion: delay continues to undermine CO2 mitigation effectiveness

We conclude that the publication of the Climate Action Plan 2019 does not materially alter the (critical) findings of our earlier paper. The mitigation trajectories implied by the plan, insofar as they can be inferred, still prima facie suggest a very early exhaustion of our assessed prudent ‘fair share’ (Paris-aligned) CO2 quota, with consequent emergence of CO2 debt and tacit commitment to future “debt repayment” in the form of achieving large scale nett removal of CO2 from atmosphere, sustained over an extended period of time, currently with very poorly quantified cost and significant risk of failure.

On the positive side, the action plan does propose very significant strengthening of Irish climate action governance in the immediate future, including the introduction of a system of binding five-yearly “emissions budgets”, extending at least 15 years into the future. This is a very positive commitment which does represent significant opportunity for a step change in mitigation urgency and effectiveness. However, to realise this opportunity, it is strongly recommended that the governance reforms should also explicitly incorporate some overall binding cumulative CO2 emissions limit (quota), adopted on a statutory basis. While this statutory quota might, of course, still differ from the specific value identified in the current research, it is essential that it be scientifically and ethically informed on a basis of prudence and global equity, and be accompanied by a transparent articulation of how it is claimed to align with the Paris Agreement goals. Further, to the extent that any proposed sequence of five-year budgets would subsequently imply overshoot of this statutory quota, there should be a governance requirement to explicitly recognise this anticipated emergence of CO2 debt, and for that to be coupled with immediate planning for how the extent and duration of such debt will be limited.