Pathways toward Climate-Neutral Red Meat Production †

: Ruminant livestock industries can support the climate stabilization ambitions of the Paris Agreement through interventions that reduce GHG emissions (predominantly biogenic methane) and sequester carbon in landscapes. This study explored pathways for the Australian red meat industry (grazing, feedlot finishing, and domestic processing) to become climate neutral, whereby the radiative forcing (RF) footprint is plateaued and there is no additional forcing contribution. Emissions timeseries (CO 2 , N 2 O, CH 4 ) were compiled for 1990 to 2020 and projected to 2030 under a business-as-usual scenario (including an 18% increase in sheep and 13% increase in beef cattle) and with a range of production system and vegetation management interventions. The RF footprint peaked in 2018 at 7.13 mW/m 2 and decreased to 7.07 mW/m 2 in 2020. With the future expansion of the herd/flock and under business-as-usual conditions, the RF footprint is projected to increase by 2.8% by 2030. However, with a combination of interventions, production has the potential to increase with a decreasing RF footprint, a condition that can be described as climate neutral. The Australian red meat industry has made an historical contribution to global RF increase. However, with ongoing RF management, it is possible to increase food production within climate-neutral limits.


Introduction
The primary consensus for action to combat global climate change is the Paris Agreement [1], where Article 2 describes the ambitious goal of limiting global mean temperature rise to 1.5 • C above pre-industrial levels (well below 2 • C) to significantly reduce risks and impacts.With respect to this goal, the Intergovernmental Panel on Climate Change (IPCC) states that "Stabilizing the climate will require strong, rapid, and sustained reductions in greenhouse gas emissions, and reaching net zero CO 2 emissions" [2].This requirement to achieve net zero CO 2 emissions stems from the long-term impacts of these emissions, potentially lasting millennia [3,4].The IPCC also states that "Limiting other greenhouse gases and air pollutants, especially methane, could have benefits both for health and the climate" [2].By comparison, methane emissions have a relatively short atmospheric lifetime, in the order of 12 years [5], meaning that, in the case of biogenic methane, a steady emissions profile over time can be consistent with climate stabilization [6].
The differences between greenhouse gases, in terms of atmospheric lifetime and strength of greenhouse effect, complicate the development of multi-gas climate action strategies.Equivalence between different types of GHG emissions can be established using climate metrics (such as the 100-year global warming potential; GWP100), with results typically reported as CO 2 -equivalent emissions.However, it is well known that there is no absolute equivalence in climate impact [7][8][9].Each climate metric uses a different basis for comparison, for example, by estimating the relative impact at a certain future point in time, or over a chosen interval in time.Critically, depending on the climate metric chosen, the relative importance of different GHGs varies.The issue for ruminant livestock industries is that while there are substantial opportunities for CO 2 sequestration in landscapes [10,11], GHG emissions are substantially non-CO 2 .As such, there has been much recent interest in GHG assessment methods and metrics that can be used to inform climate action consistent with the Paris Agreement's climate stabilization goal [12].
For ruminant livestock industries, two main alternatives to the traditional 100-year global warming potential have emerged in recent years: the GWP* climate metric [13][14][15][16][17][18][19] and the radiative forcing (RF) footprint [20][21][22].The GWP* climate metric is similar in many ways to GWP100 except that pulses of long-lived emissions are evaluated alongside permanent rates of change of short-lived GHG emissions, such as methane.Through this approach, GWP* results are more easily interpreted in relation to future warming than when pulses of short-and long-lived GHG emissions are combined [23,24].The other approach, the RF footprint, is based on the same IPCC-derived equations as GWP100.However, the RF footprint reports present radiative forcing from current year emissions together with the radiative forcing from historical emissions remaining in the atmosphere.As such, it presents what might be described as a radiative forcing balance sheet, providing greater transparency regarding climate impacts over time.Climate neutral (in contrast to the terms carbon neutral and GHG neutral; [25]) is a term that has been applied when a system makes no net contribution to additional temperature increase or no net contribution to increase in radiative forcing [12,21,26].This study explores pathways for the Australian red meat industry to reach climate neutrality using the RF footprint approach.Insofar as it is known, this is the first study of this kind using this novel approach.

Timeseries of GHG Emissions
Disaggregated timeseries of GHG emissions (CO 2 , N 2 O, and CH 4 ), covering cattle production (including feedlot finishing), sheep meat production, goat production, and domestic red meat processing, were compiled for the years 1990 to 2020.These data were primarily sourced from the Australian Greenhouse Emissions Information System [27] that contains the GHG emissions data used to support Australia's national reporting under the UNFCCC.Detailed descriptions of the methods used to compile the national inventory are available [28,29].These data covered emissions from enteric fermentation, manure management, agricultural soils, and liming and urea applications, along with land use and land use change.Other sources were used to determine emissions related to energy use on farms [30,31] and in feedlots [32].Emissions related to red meat processing were obtained from industry benchmarking studies [33].Concerning the national sheep flock, a protein mass allocation was used to partition emissions between wool and meat production [30].In Australia, only a very small proportion of the national flock are dairy sheep.Other details of the methodology, including the approach used to allocate emissions between cattle and sheep, are described in [34].These emission timeseries were subsequently extrapolated proportionally to 2030 using forecasts for livestock numbers and production supplied by the industry (Table 1).In summary, sheep and lamb numbers were forecast to increase almost 18% from 2020 to 2030.For beef cattle, the forecast increase was almost 13%.

Mitigation and Sequestration Interventions
In consultation with industry, a list of GHG mitigation and sequestration interventions was compiled (Table 2).These interventions are at various stages of technological development and adoption.Only interventions with a realistic potential for implementation prior to 2030 were considered, in line with the time horizon of the study.The interventions included feed additives, forage crops, breeding for lower enteric methane emissions, and improved herd/flock management.Vegetation management interventions were also considered, including trees on farms, soil carbon storage, and savannah burning management.For production system interventions, estimates of efficacy and adoption were obtained from recent reviews [35][36][37][38], with the aim of reflecting what might be reasonably possible in production environments as compared to controlled trial conditions.For example, in vitro studies simulating rumen digestion have demonstrated up to 99% reduction in methane formation by Asparagopsis macroalgae [39][40][41], and controlled feeding experiments have also shown very large reductions in some situations [42,43].However, this level of efficacy might not be achieved consistently over a range of production situations and a more conservative estimate of 49% was used for modelling [37].For vegetation management, the assumed adoption rates were based on published industry targets [44,45].An approximate S-shaped adoption curve was assumed.

Quantifying Radiative Forcing (RF) Footprints
The extrapolated timeseries of GHG emissions were modified according to the interventions described in Table 2. Scenarios were modelled for the business-as-usual baseline (without additional interventions), and for interventions applied individually and collectively.For each scenario, annual radiative forcing footprints were quantified, following [21,22] and using parameters and equations reported in the IPCC 5th Assessment Report [46].The results were reported in the units milli watts per square meter (mW/m 2 ) of radiative forcing using the reference year of 2005, coinciding with Australia's Nationally Determined Contribution under Article 4 of the Paris Agreement [47].For year t, the RF footprint was quantified by summing RF from current year emissions along with the RF from historical emissions remaining in year t, as described in Equation ( 1).The individual GHG emissions that were included were CO 2 , CH 4 , and N 2 O as these are the major climate forcing emissions associated with agriculture.Other GHGs and non-GHG climate forcing emissions were excluded due to insufficient timeseries data.RF t = RF associated with emissions in year t + RF associated with historical emissions remaining in year t (1)

Red Meat Industry RF Footprint
The profile of RF over time informs about the trajectory of RF and whether progress is being made to stabilize total cumulative RF, which is a requirement for climate stabilization, as expressed in the Paris Agreement.Considering the Australian red meat industry (beef cattle, sheep and lambs for meat, goats, and domestic processing), the RF footprint increased from 5.71 to 7.09 mW/m 2 over the decade 2005 to 2015, after which it plateaued, reaching a local maximum of 7.13 mW/m 2 in 2018 and decreasing to 7.07 mW/m 2 in 2020 (Figure 1A).
With future expansion of the herd and flock, the RF footprint is projected to increase marginally to 7.26 mW/m 2 in 2030 under a business-as-usual scenario (a 2.8% increase).In contrast, with the combination of interventions described in Table 2, the RF footprint remains relatively flat, but declines marginally to 6.81 mW/m 2 in 2030 (Figure 1B), a decrease of 3.6% from 2020.The reduction in RF footprint relative to the business-as-usual scenario was attributed partly to vegetation management (56.6%) and partly to production system innovations (43.4%) (Table 3).The most impactful production system innovation was improved herd management (culling of unproductive animals, supplementary feeding, improved grazing management, etc.) that contributed almost one quarter of the RF footprint reduction (Table 3).Some of the production system innovations made only a modest contribution to RF footprint reduction in the period to 2030.Considering the sheep meat sector of the Australian red meat industry (animals for mutton and lamb meat production), the RF footprint plateaued around 2008 when it

Sheep Meat Sector RF Footprint
Considering the sheep meat sector of the Australian red meat industry (animals for mutton and lamb meat production), the RF footprint plateaued around 2008 when it reached 1.11 mW/m 2 (Figure 2A).By 2020, the RF footprint had declined marginally to 1.07 mW/m 2 .However, with a projected increase in the size of the flock of almost 18% over the next decade (Table 1), the RF footprint is projected to increase marginally by around 1.3% to 1.09 mW/m 2 under a business-as-usual scenario (Figure 2A).In contrast, with the combination of interventions described in Table 2, the RF footprint remains relatively flat (Figure 2B), but with an additional decline to 1.02 mW/m 2 in 2030, a decrease of 5.3% compared to 2020.The reduction in RF footprint relative to the business-as-usual scenario was attributed mainly to carbon sequestration in trees planted on farms (>70%) (Table 4).Production system innovations contributed the balance, with improved flock management (culling of unproductive animals, supplementary feeding, improved grazing management, etc.) being the most important.
Methane 2024, 3, FOR PEER REVIEW 7 attributed mainly to carbon sequestration in trees planted on farms (> 70%) (Table 4).Production system innovations contributed the balance, with improved flock management (culling of unproductive animals, supplementary feeding, improved grazing management, etc.) being the most important.

Beef Cattle Sector RF Footprint
Considering the beef cattle sector of the Australian red meat industry (including feedlot finishing), the RF footprint increased from 4.65 to 5.93 mW/m 2 over the decade 2005 to 2015, after which it plateaued, reaching a local maximum of 5.99 mW/m 2 in 2018 and decreasing back to 5.94 mW/m 2 in 2020 (Figure 3A).With future expansion of the herd, the forecast is expected to be of the order of around 13% over the next decade (Table 1), and the RF footprint is projected to marginally increase by around 2.9% to 6.11 mW/m 2 under a business-as-usual scenario (Figure 3A).In contrast, with the combination of interventions in Table 2, the RF footprint remains relatively flat, but declines marginally to 5.73 mW/m 2 in 2030 (Figure 3B), a decrease of 3.5% from 2020.Compared to the businessas-usual scenario, the intervention that made the largest single contribution to reducing the RF footprint was improved herd management (Table 5).Carbon sequestration in trees on farm made the next largest contribution, followed by savannah burning management, underscoring the importance of vegetation management in radiative forcing management.
Methane 2024, 3, FOR PEER REVIEW trees on farm made the next largest contribution, followed by savannah burning m ment, underscoring the importance of vegetation management in radiative forcing agement.

Discussion
The purpose of this study was to explore the pathways for the Australian red meat industry to reach climate neutrality.Here, climate neutrality was assessed using the RF footprint approach and is considered to have been achieved when the footprint has plateaued and there is no additional contribution to radiative forcing, which is a requirement for climate stabilization [12].This approach differs from carbon neutrality, which, according to the IPCC, is a condition that only applies to a balancing of anthropogenic CO 2 emissions and removals [25].Considering the substantial non-CO 2 emissions associated with the red meat industry, such an approach is deemed too limited in scope.The approach to climate neutrality taken in this study also differs from greenhouse gas neutrality, which, according to the IPCC, is a condition that relates to a balancing of metric-weighted anthropogenic emissions and removals [25].The difficulty with this approach is the requirement for a climate metric that establishes equivalence between different GHGs.As discussed in the Introduction, there is no absolute equivalence in climate impact that can be established between different GHGs, and the equivalency factors vary between different climate metrics.Though the GWP100 climate metric is often used by convention, there is no scientific basis to justify its use in preference to another climate metric, and there are implied value judgements [46].Furthermore, when organisations commit to GHG neutrality using the GWP100 climate metric, it is not apparent what the impact on future radiative forcing and warming will be as this will depend on the specific basket of GHG emissions involved [48][49][50].As such, it can be difficult to reconcile metric-weighted GHG emission reports and commitments with the climate stabilization goal of the Paris Agreement, especially where there are substantial short-lived emissions, as in the case of ruminant livestock industries.
As for the Australian red meat industry, it was found that climate neutrality occurred in 2019 when the industry's RF footprint decreased by 0.02 mW/m 2 in that year (Figure 1A).Climate neutrality was sustained again in 2020 when the industry's RF footprint decreased by a further in 0.04 mW/m 2 .With the production of sheep and lambs for meat, climate neutrality was achieved in 2010 and has been more or less maintained since then (Figure 2A).With the beef cattle sector, climate neutrality was achieved in 2019 and sustained in 2020 (Figure 3A).A key finding from this study, designed with the initial purpose of exploring pathways to climate neutrality, is that the Australian red meat industry is already climate neutral, with its RF footprint in absolute decline since 2019.The industry has made an historical contribution to the increase in radiative forcing that has led to change in the climate system.However, since 2019, the industry's contribution to climate change has not increased, and, indeed, has retracted marginally.That said, radiative forcing management is necessary to avoid future increases in RF that are incompatible with climate stabilization.In Australia, the expectation is that flock and herd numbers will increase over the coming decade (Table 1).Under a business-as-usual scenario, increasing livestock numbers are projected to push the RF footprint higher (Figures 1A, 2A and 3A), thereby not maintaining the current climate-neutral status.However, a combination of climate actions (Table 2), if successfully implemented, have the potential to allow increased production while also allowing further unwinding of the industry's historical climate impact.An important conclusion is that the industry has the potential to expand its role as a food producer, contributing to needed increases in food production [51,52] while operating within the constraints of climate stabilization.
There is considerable uncertainty associated with the pace at which new technologies and supplements to reduce livestock methane emissions can be developed and adopted [35].The Australian sheep and beef cattle sectors are diverse, including a wide range of intensive and extensive systems spanning temperate and tropical zones.High-impact feed additives that require daily administration are most feasibly implemented in feedlots and perhaps other production systems where farmers have a high degree of control over feed intake.Delivery techniques to enable implementation in grazing systems are a current research focus [53].In this study, the approach used was to assume realistic, yet conservative, estimates of adoption and efficacy (Table 2).Overall, feed additives contributed slightly less than 15% of the 2030 reduction in RF footprint compared to business-as-usual (Table 3).This outcome depended substantially on the deployment of feed additives in grazing systems, as the benefit of deployment in feedlots alone is important but limited (Table 3), as shown previously [22].In comparison, improved herd and flock management was found to contribute more than 26% of the RF footprint reduction in 2030 (Table 3).These measures are closely linked to productivity improvement and as such are expected to have a high rate of adoption.More than 50% of the RF footprint reduction in 2030 was related to vegetation management, especially tree planting on farms (Table 3).In Australia, the livestock industry manages a vast area of land, including more than 280 M ha of grazed native vegetation, more than 40 M ha of grazed modified pastures, and additional areas where mixed farming and crop/pasture rotations are practiced [54].The potential is therefore enormous, but the carbon sequestration rates are also variable, from shrub and fodder crops with a sequestration potential in the order of 0.7 t CO 2 /ha/y to trees planted in higher rainfall areas that might achieve between 2 and 4 t CO 2 /ha/y [55].The challenge will be to integrate vegetation strategies in a way that enhances overall farm productivity and profitability.Within the 2030 time horizon of this study, breeding for lower enteric methane emissions made little contribution (Table 3).Taken together, the modelled GHG mitigation and sequestration interventions were more than sufficient to achieve climate neutrality, with the projected RF footprint lower in 2030 than in 2020.As such, RF footprint stabilization is likely, even if not all interventions reach the modelled levels of efficacy and adoption.
The RF footprint reports present radiative forcing from current year emissions together with the radiative forcing from historical emissions remaining in the atmosphere [20].This approach differs from most other approaches to GHG emission reporting and management in that historical emissions are included.The time series approach also provides transparency with respect to the climate impacts of short-lived and long-lived GHGs over time (Figures 1-3).This is one of the main criticisms associated with the application of the GWP100 climate metric in the livestock industry.The result obtained using the GWP100 metric describes the integral of radiative forcing over a future 100-year horizon, obscuring the near-and long-term implications [7][8][9]12].As discussed in the Introduction, the IPCC states that to stabilize the climate, it is necessary to reach net zero CO 2 emissions, but the same cannot be said for short-lived biogenic methane [2], where a more or less steady emissions profile is consistent with climate stabilization.The implications for the ruminant livestock industries are enormous.Climate actions that mitigate livestock methane emissions at the expense of increasing CO 2 and other long-lived GHG emissions may appear to be beneficial when the GWP100 climate metric is used.However, while such strategies might reduce radiative forcing in the near term, they are adding to long-lived atmospheric CO 2 stocks and making the goal of climate stabilization more difficult [14,22].The RF footprint shares some similarities with the GWP* [23,24,56] and CGTP [57] climate metrics in that it is the rate of change of methane emission that is assessed rather than a pulse.However, a major drawback in the practical use of GWP* and CGTP is the need to discern what is a permanent rate of change in methane emission.The developers of GWP* suggest use of a 20-year time interval, arguing that this smooths out short-term fluctuations in emission rates that may not reflect permanent change [23].However, in practice, this approach has still been found to present challenges for performance tracking as results can deviate sharply from year to year, complicating interpretation and communication with stakeholders.
For this study, a target of zero increase in RF footprint was used, meaning that the industry no longer contributes to the further development of radiative forcing of the Earth's atmospheric system, which is contributing to the progression of climate change [58].However, the RF footprint approach can equally be used to manage industry GHG emissions toward any chosen RF target.In 2011, the total anthropogenic radiative forcing was estimated to have reached 2.3 W/m 2 [46].The RF footprint approach could be used to manage industry radiative forcing in a manner that is consistent with any global radiative forcing target, such as 1.9, 2.6, or 3.4 W/m 2 .The choice of RF target is ultimately a political decision and separate from the RF footprint calculation methodology.A further consideration is that of equity.It has been argued that climate metrics that are based on the rate of change of methane emissions favour countries that established their herd long ago, and disadvantage new entrants [59].However, this argument is founded on the assumption that RF management targets need to be identical for all industries and countries and introduces the notion of a fair share of the total global radiative forcing budget.However, equity is a consideration that goes beyond science.As pointed out by Cain et al. [60], climate metrics only exist to inform decision making and policy options.What matters for existing industries is that radiative forcing is managed to avoid escalating climate risks and impacts.

Conclusions
In summary, this study has demonstrated, through RF footprint quantification, that it is possible for the Australian red meat industry to continue as a supplier of high-quality protein and even increase output while also managing GHG emissions in a manner consistent with climate stabilization.The increase in production is contingent on successful GHG mitigation and carbon sequestration actions beyond current business-as-usual practices.With projected increases in sheep and beef cattle numbers of 18% and 13%, respectively, the successful implementation of GHG mitigation and sequestration actions has the potential to lower the overall RF footprint by 3.6%.These findings relate to the Australian red meat industry and may not be representative of livestock industries in other regions.In addition, the study only considered radiative forcing and not other environmental or social aspects.In conclusion, greater use of the RF footprint is recommended to inform climate action in the livestock industry.This will avoid unnecessary curtailment of the contribution of livestock to global food systems based on net zero emission strategies, which are applicable to long-lived GHG emissions but fail to represent the radiative forcing characteristics of short-lived GHG emissions like methane.

Methane 2024, 3 ,Figure 1 .
Figure 1.Australian red meat industry radiative forcing (RF) footprint (mW/m 2 ) under (A) a business-as-usual scenario, and (B) with the adoption of GHG mitigation and sequestration actions.Historical data 2005 to 2020.Projected data from 2021.Each annual RF footprint comprises RF from current year emissions along with RF from historical emissions that are remaining.

Figure 1 .
Figure 1.Australian red meat industry radiative forcing (RF) footprint (mW/m 2 ) under (A) a business-as-usual scenario, and (B) with the adoption of GHG mitigation and sequestration actions.Historical data 2005 to 2020.Projected data from 2021.Each annual RF footprint comprises RF from current year emissions along with RF from historical emissions that are remaining.

Figure 2 .
Figure 2. Australian sheep meat sector (mutton, lamb) radiative forcing (RF) footprint (mW/m 2 ) under (A) a business-as-usual scenario, and (B) with adoption of GHG mitigation and sequestration actions.Historical data 2005 to 2020.Projected data from 2021.Each annual RF footprint comprises RF from current year emissions along with RF from historical emissions that are remaining.

Figure 2 .
Figure 2. Australian sheep meat sector (mutton, lamb) radiative forcing (RF) footprint (mW/m 2 ) under (A) a business-as-usual scenario, and (B) with adoption of GHG mitigation and sequestration actions.Historical data 2005 to 2020.Projected data from 2021.Each annual RF footprint comprises RF from current year emissions along with RF from historical emissions that are remaining.

Figure 3 .
Figure 3. Australian beef cattle sector (including feedlot finishing) radiative forcing (RF) fo (mW/m 2 ) under (A) a business-as-usual scenario, and (B) with adoption of GHG mitigati sequestration actions.Historical data 2005 to 2020.Projected data from 2021.Each annual R print comprises RF from current year emissions along with RF from historical emissions t remaining.

Figure 3 .
Figure 3. Australian beef cattle sector (including feedlot finishing) radiative forcing (RF) footprint (mW/m 2 ) under (A) a business-as-usual scenario, and (B) with adoption of GHG mitigation and sequestration actions.Historical data 2005 to 2020.Projected data from 2021.Each annual RF footprint comprises RF from current year emissions along with RF from historical emissions that are remaining.

Table 1 .
Livestock and production forecasts for the Australian red meat industry.

Table 3 .
Contribution to projected RF footprint reduction in the Australian red meat industry.

Table 3 .
Contribution to projected RF footprint reduction in the Australian red meat industry.

Table 4 .
Contribution to projected RF footprint reduction in the Australian sheep meat sector.
3.3.Beef Cattle Sector RF FootprintConsidering the beef cattle sector of the Australian red meat industry (including feed-2

Table 4 .
Contribution to projected RF footprint reduction in the Australian sheep meat sector.

Table 5 .
Contribution to projected RF footprint reduction in the Australian beef cattle sector

Table 5 .
Contribution to projected RF footprint reduction in the Australian beef cattle sector.