Will there be forestry offsets toward ‘carbon neutrality’ for Irish agriculture?

Carbon neutrality has come to the forefront of climate mitigation policy in Ireland, particularly following the Paris Agreement's reference that states:

Carbon neutrality then is the idea of balancing sources and sinks, somehow neutralising the nett global warming effect of ongoing gross greenhouse gas emissions (including methane and nitrous oxide from agricultural sources) by achieving negative emissions, meaning verified carbon dioxide (CO₂) removals from the atmosphere into carbon sinks that can store additional carbon (in forestry or soils) or captured carbon dioxide for a very long time.

The IE-NETs project is assessing the potential of technologically challenging ways of achieving negative emissions in Ireland, such as Bioenergy with Carbon Capture and Storage (BECCS), but also less technological methods such as greatly enhancing traditional land use practices such as forestry and farmland management to store more carbon absorbed from the atmosphere through plant photosynthesis.  Land use carbon sources and removals are already counted, or at least accounted, in climate policy. Such carbon removals can potentially earn carbon credits to set against ongoing gross emissions of greenhouse gases from human activities. Later in this project we’ll be analysing the mitigation potential of forestry and short-rotation grasses and coppiced wood, so this post is an exploratory look at the topic and inviting input from other researchers.

Based on the recently released National Mitigation Plan, Irish government policy targeting 2030 and 2050 is currently set on ring-fencing forestry carbon dioxide removals as carbon credits to partially offset agriculture’s sectoral emissions through “an approach to carbon neutrality in the agriculture and land-use sector, including forestry, which does not compromise capacity for sustainable food production” (p.186-187). An interesting statement, but what does it mean?  How much of an "approach" is actually possible.

Here we explore some weighty questions that arise for Ireland’s agriculture and land-use climate mitigation plan: What amount of gross greenhouse gas (GHG) emissions is the agricultural sector likely to generate annually up to 2050? And, what amount of forestry carbon removals might be available as offsets against those gross emissions? In a future post we’ll look at how scientifically justified such so-called ‘offsets’ of carbon dioxide removals to forestry might be in balancing gross emissions of mostly non-CO₂ from Irish agriculture or CO₂ from fossil fuel burning. For now though we’ll look at the amount of carbon that could be stored, particularly in Irish forestry, up to 2050.

Usefully, Ireland’s agricultural research agency Teagasc has already carried out a substantial report, Carbon-Neutrality as a horizon point for Irish Agriculture (2013), describing five alternative scenarios for these goals (spoiler: the “horizon point” looks to be unachievable, given projected, continued high emissions). Figure 3.2, shown below, indicates that future agricultural GHG emissions could rise steadily from about 18.5 MtCO2eq/yr in 2010 to a higher level of about 22 MtCO2eq/yr from 2030 to 2050 (“MtCO2eq” means millions of tonnes of CO₂ equivalent, here using a metric called the 100 year Global Warming Potential, GWP100, to equate the climate impact of methane and nitrous oxide from agriculture with tonnes of CO₂).

In Section 3.2 the report then discusses offsetting gross emissions from agricultural production (especially from beef and dairy) through the accounting of negative emissions achieved through carbon sequestration in land use carbon sinks in soils and forestry. Grassland soils and forestry are expected to act as carbon sinks whereas peatlands and wetlands are sources of gross emissions. Even without counting peat extraction – for electricity, horticulture and home heating – peatland emissions are roughly estimated in the report as 2.2 MtCO2eq/yr (quoting the EPA as the source for this figure).

[It's worth noting here that, confusingly, the term ‘carbon sequestration’ is often used in policy documents to mean either the annual flow rate of CO₂ into a sink, or the stock of carbon in a sink, or both. Typically the term is being used to describe annual flow rate. Scientifically though, it is the total stock amount of reliably stored carbon that represents the long-term carbon sequestration relevant to climate change mitigation.]

Using soil carbon modelling results, the Teagasc report estimates that grassland sequestration rates between 2030 and 2050 could be 6.5 to 6.8 MtCO2eq/yr. However, soil carbon values are subject to very large uncertainties due to high variability in grassland productivity from year to year due to weather factors and (not mentioned in the report) there are saturation limits to soil carbon uptake. Recent research also suggests that rising atmospheric CO₂ (due to human-caused emissions) appears to result in greater nett leakage from soils to the atmosphere rather than increasing soil carbon. Moreover, with time, soil carbon can easily be lost if management to sequester carbon is not maintained. As Teagasc’s report notes, p. 37, ”there are concerns as to the permanence of these sinks under future climate change”.

Forestry is subject to scientifically and politically contested carbon accounting rules, again resulting in significant uncertainties in estimating sequestration rates and forest carbon stock change over time. Nonetheless, using modelling based on continuing replanting of managed forestland and continued afforestation (additional forest) a rate of about 8,000 hectares per year, the Teagasc report gives the following chart for projected nett GHG emissions (gross emissions less gross removals) from forest land. Note in the chart that the carbon dioxide removals are the negative values.

As this chart shows, current fairly high sequestration rates in growing forest decline after 2020 with the national forest stock then maturing on average, reflecting a past decline in afforestation rates, taking in less CO₂ as it grows more slowly. The projections appear to indicate that mature forest will be harvested shortly after 2030 and replanted, but as shown CO₂ removals are reduced to near zero on average from 2035 to 2050.

Depending on accounting, and on future forest management and afforestation, this looks concerning because it seems possible that the forestry offsets available for agriculture will be very low or even non-existent after 2035.  Overall, counting soils and forestry, Teagasc estimate a total offsetting potential of -5.5 MtCO2eq/yr in 2050 (-0.8 forestry, -6.8 soils, +2.2 wetlands) but as noted there are big uncertainties making these removal estimates unreliable. In terms of climate risk assessment, more uncertainty adds to cost and adds to the pressure to act sooner – even before, and while trying to resolve uncertainty.

A similar projection and interpretation, showing alternative afforestation rates is shown below, redrawn (to match the Teagasc figure’s presentation) from Figure 5.3 in RDS/IIEA (2016), again apparently showing a significant forest harvest and consequent loss of annual sequestration flow around 2035, levelling off until after 2050. Looking at the Figure below, from 2017 (the first year of the NMP) onwards to 2050, at the projected NMP afforestation rate of 8,000 hectares per year average carbon removal rate by forests might be of the order of -4 MtCO2eq/yr, adding up to about 132 MtCO2eq removed in total from 2017 to 2050.

So 4 MtCO2eq/yr in CO₂ removals due to forestry falls very far short of offsetting the 22 MtCO2eq/yr gross emissions from agriculture. This estimate is in line with the expectation of offsetting only about a fifth of the sector’s emissions as stated in the National Mitigation Plan:

the forest sector, through afforestation and the use of forest-based biomass (FBB) and wood products, offers considerable scope for climate change mitigation, equivalent to 20-22% of agricultural emissions on an annual basis.  National Mitigation Plan p. 125

However, you may have spotted a mystery in this carbon accounting story. What happens to the carbon in the large area of trees that appear to get felled after 2030?  Some but not all of it may well go into wood products that have some sequestration value, but, concerningly, the Teagasc report says:                 

Fuelwood use is assumed to increase in the projected harvest from 7% of total roundwood production in 2011, to 21% by 2030 and a constant rate of 21 % to 2050. This is consistent with bioenergy targets and timber demand projections. Teagasc p. 39

If an increased proportion of the harvested carbon is simply going to end up being burned and adding to CO₂ in the atmosphere then that loss will need to be looked at carefully. Furthermore, the UK Department of Energy and Climate Change biomass carbon calculator shows that using roundwood for bioenergy can be worse than burning coal in emissions per unit energy produced, when assessed on a full lifecycle basis for timescales relevant to pathways aligned with the Paris Agreement. Very strong, well monitored and carefully enforced sustainability criteria are therefore needed to ensure that waste wood and not roundwood is used for bioenergy. However, financially, increased demand for waste potentially increases the economic value of harvesting forest relative to leaving it uncut as sequestered carbon, possibly creating incentives opposed to climate change mitigation.

A further serious question for climate mitigation and carbon neutrality in agriculture and land use is whether the net carbon stock in Irish forests will be increasing to 2050, enabling mitigation, or whether there is a danger that the planned harvesting, possibly boosted by bioenergy demand, could actually decrease carbon stocks, thereby reducing the carbon sequestration value of standing forest. The chart below, giving a look at Ireland’s forestry history since 1925 and projections to 2035 for annual hectares of afforestation and clearfell gives a few (inconclusive) clues.

The projected clearfell rate seem to match the likely afforestation rate. Mature forest, resulting from the 1985 to 2000 afforestation, will be progressively harvested after 2030, as indicated in the emissions/removals charts above, removing carbon from the forest stock that will then only be slowly compensated in atmospheric removals through replanting and further afforestation.

So, given Irish forest management projections, there may be two potential problems.  First, to avoid carbon stock decreases, the harvest rate may well need to drop quickly after 2020 to reflect the past fall-off in afforestation around the year 2000. Second, there should be a concern that the nett remaining carbon stock in Irish forests could actually go down even in the short term with such high clearfell rates. This would be a big problem because the mitigation value of forest carbon is primarily in its actual level of stored carbon, not in the sequestration flow rates (see Mackey et al, 2013).

Another danger inherent in these projections is that Ireland might potentially be accused, as New Zealand has been, of creative emissions accounting towards its climate targets, for example by accumulating offsetting credits for annual sequestration up to 2030 but only in anticipation of emitting this carbon due to harvesting the trees shortly after the EU 2030 period expires.

The potential for problems in emission accounting is further exacerbated by the EU’s scientifically incorrect policy assumption that bioenergy can be accounted as carbon neutral even though the extraction emissions from land use (such as clearfelling) are not limited by EU targets, while sequestration removals are uncertain, particularly in soils. So far it does not appear that these concerns will be substantively addressed in the upcoming EU Emissions Sharing Regulation (ESR) for the 2021 to 2030 targets.

The high uncertainty in carbon sequestration flows to and from soils and forestry appear to fall very far short of reliably enabling carbon neutrality in Ireland’s agriculture and land use sector. This means that any policy reliant on sequestration would require significant funding to ensure site specific monitoring and verification of land use stocks and flows, adding to mitigation costs in the sector. Subject to further research, including by IE-NETS, it seems possible that carbon stocks in Irish forest could even reduce if increased bioenergy demand leads to unsustainable harvesting. This outcome would not only reduce the mitigation value of Irish forestry it would add to sectoral emissions.  Committing to increasing carbon sequestration in Ireland's forestry will careful management and monitoring of forest growth and, likely, enforced limits to future timber harvesting.

Given that the NMP only claims forestry will fill only about 20-22% of the necessary "gap" to neutrality and soils perhaps a highly questionable 30%, the claim of any "approach" to achieving carbon neutrality for Irish agriculture by 2050, under current projections of cattle numbers, seems to be lacking substance in reality. Even if the potential sequestration was to be achieved and even if the offsetting makes scientific sense then it is still likely to fall very far short of enabling carbon neutrality in the sector. This is why the Teagasc report gives a “Pathway E” that is described as being “based on a societal acceptance that food production is associated with GHG emissions”, which opens a very different (political) line of argument subject to other scientific objections, including the different amounts of GHGs relating to different methods of food production.  Given the projections of sources and sinks for the sector, if achieving carbon neutrality is not possible then actually stating it as policy – as though it is achievable – is remarkable.

Unfortunately, given the urgency required to align mitigation action with the climate stabilisation targets in the Paris Agreement, there is now little time to delay action by waiting for research into optimal emission pathways, even though the ongoing research is critical to providing information to support better decision-making. Instead, climate reality may mean cutting emissions first and looking for offsets later. In the near term, leaving forest trees standing, and growing more of them, as carbon stores may be preferable to releasing the carbon for bioenergy (unless the CO₂ can be immediately captured and safely stored, via so-called carbon capture and sequestration technology, CCS). To increase understanding of these issues, our IE-NETs research is looking at Ireland’s land carbon storage and bioenergy potential within possible national decarbonisation pathways aligned with meeting the Paris Agreement.

In a future blogpost we will come back to the question of whether the idea of offsetting land use sequestration against continued fossil fuel and/or agricultural emissions is scientifically justified. Hopefully though, this post has given some sense of the limits to forestry carbon sequestration and the improbability of achieving carbon neutrality in the agriculture and land use sector through carbon sequestration in forestry and soils.