Abstract
The goal of limiting mean global temperature rise to 1.5 °C, described in the Paris Agreement, depends upon urgent action to stabilize radiative forcing (RF). However, the contribution of different greenhouse gases (GHGs) to future RF is often obscured by the application of climate metrics, such as the 100-year global warming potential (GWP100). RF climate footprints are an alternative way of presenting emissions information relating to GHGs and other climate forcers. These footprints include RF from current emissions as well as the fraction of historical emissions that remain in the atmosphere. The profile over time can support the management of RF toward targets informed by climate stabilization goals. In a study involving Australian sheep production for meat, it was found that the sector’s contribution to RF has plateaued in recent years at 0.64 mW.m², and is projected to reach the point of net zero increase in 2020, a status that could be described as “climate neutral”. Further, on present emission trajectories, the sector’s contribution to RF will decline to 0.50 mW.m¯² in 2049, which represents a contribution to climate cooling consistent with the Paris Agreement. RF climate footprints clearly articulate the diverse climate impacts of short and long-lived climate forcers, avoiding the policy ambiguity that can arise when different climate metrics and different arbitrary time horizons are chosen. This new RF framework, soon to be supported by an international (ISO) standard, has relevance in aligning food systems with the aspirations of the Paris Agreement. However, the challenge of stabilizing and managing RF downward is applicable to all sectors and organisations.
Generated Summary
This research, presented as a Journal Pre-proof, investigates the application of radiative forcing (RF) climate footprints to the Australian sheep meat sector, focusing on the period from 1990 to 2017, with projections extending to 2050. The study’s methodology involves a sector-level analysis of RF, combining current and historical emissions data for carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) to assess the sector’s contribution to global warming. The primary goal is to explore the relevance of the RF framework in aligning food systems with the Paris Agreement, specifically its 1.5°C temperature target. The study quantifies the sector’s RF footprint and product-level footprints to assess the trajectory of emissions and their alignment with climate stabilization goals. The study provides insight into the need to address emissions from the livestock sector, particularly from methane, and its impact on climate change.
Key Findings & Statistics
- The goal of limiting mean global temperature rise to 1.5 °C, as described in the Paris Agreement, depends upon urgent action to stabilize radiative forcing (RF).
- In 2011, total anthropogenic radiative forcing was estimated to have reached 2.3 Wm² (Myhre et al., 2013).
- The sector’s contribution to global RF was plateauing at 0.64 mW.m-² (Fig. 1), with negligible additional contribution to RF occurring.
- Annual carbon dioxide emissions have trended progressively upwards by around 1.7% per annum, from 460 to 679 kt over the same period.
- The sector’s RF footprint is projected to be in decline, a situation that could be described as contributing to climate cooling.
- The Australian sheep meat sector needs to reduce its RF by 17.4% compared to the 2011 level.
- In 2011, current year emissions contributed 7% of the total RF footprint, with the remaining 93% the legacy of historical emissions.
- By 2050, it is projected that the contribution to the sector’s RF footprint from CH4 will have fallen from a peak of 0.58 mW.m² (over the period 2014 to 2021) to 0.39 mW.m² (Fig. 3A).
- By 2050 the total contribution from historical and current emissions reaches almost 0.07 mW.m² for N2O and almost 0.05 mW.m² for CO2 (Fig. 3B and 3C).
- In 2017, sheep and lambs for meat production were associated with 3.06 x 10-12 mW.m² of additional RF per kg of live weight produced (Table 2).
- The carbon footprint has decreased from 6.99 kg CO2e per kg LW in 1990 to 5.73 kg CO2e per kg LW in 2017.
- Projections indicate the carbon footprint decreasing further to 5.63 kg CO2e per kg LW in 2020 and 5.14 kg CO2e per kg LW in 2030.
- Based on emissions and production trends, the product-level RF footprint was projected to become negative after 2020, and reach -2.96 x 10-12 mW.m² per kg LW by 2030 (Table 2).
Other Important Findings
- The study found that the sector’s contribution to RF has plateaued in recent years and is projected to reach the point of net zero increase in 2020.
- The Paris Agreement contains the ambitious goal of limiting global mean temperature rise to 1.5 °C above preindustrial levels (well below 2 °C).
- RF climate footprints are an alternative way of presenting emissions information relating to GHGs and other climate forcers.
- The RF framework can articulate the diverse climate impacts of short and long-lived climate forcers.
- Actions to achieve net zero anthropogenic CO2 emissions are an essential response to the climate stabilization goal articulated in the Paris Agreement.
- Methane is a short-lived climate forcer with an atmospheric lifetime in the order of only 12 years (Myhre et al., 2013).
- The GWP100 climate metric establishes equivalence based on the cumulative radiative forcing over a future 100-year time horizon.
- The sector-level RF profile combines RF from current year emissions and RF remaining from historical emissions.
- Historical emissions of CO2 and N2O are highly important as they accumulate over time.
- The profile of RF over time informs about whether progress is being made toward RF stabilization, which is a requirement for climate stabilization, and can inform RF management actions.
- Other GHGs and non-GHG climate forcer emissions were excluded from the analysis due to insufficient timeseries data.
- The product-level RF climate footprints (mWm² kg¯¹) were quantified by dividing the annual change in sector-level RF (mW m² yr¯¹) by the sector-level annual output (kg yr¯¹).
- The greatest contribution came from historical CH4 emissions, at 86%.
- The study demonstrates a negative product RF footprint, indicating that a product arises from an industry or organisation that is managing its radiative forcing downward, which is necessary if climate targets described in the Paris Agreement are to be met.
- The transition to net zero CO2 emissions will need to become an increasingly important aspect of the overall emissions management strategy.
- The GWP* hinges on a permanent reduction in the rate of methane emission.
Limitations Noted in the Document
- The study primarily focused on the Australian sheep meat sector, and the results may not be indicative of systems elsewhere.
- The timeseries excluded GHG emissions related to changes in soil carbon stocks as well as land use change.
- Emissions of non-GHG climate forcers were excluded.
- The study relied on data from the Australian Greenhouse Emissions Information System (AGEIS).
- The study did not include uncertainty estimates in RF footprint calculations.
- The RF framework does not account for land use change impacts and carbon sequestration.
- The GWP100 metric does not simply translate into a GHG emissions reduction target.
- The study’s assessment of a new RF framework is limited by data and scope.
Conclusion
The study’s findings underscore the critical need to address the increasing imbalance in radiative forcing to stabilize the climate and prevent irreversible changes. The research provides a framework for assessing the impact of the Australian sheep meat sector’s activities, emphasizing the need for climate action, as the sector is a contributor to climate change. Using the RF climate footprint, strategies can be developed to avoid further increases in RF, thereby limiting the future progression of climate change, as well as to manage RF downward in alignment with climate stabilization targets such as the one expressed in the Paris Agreement. The plateauing and projected decline in the sector’s RF contribution, along with the potential for a negative product-level RF footprint, suggest the possibility of aligning the livestock industry with the Paris Agreement’s climate goals. The need to transition toward net zero anthropogenic emissions of CO2 and other long-lived climate forcers is clear, but the study shows the importance of the management of methane. The study shows the importance of considering the limitations of the GWP100 metric in favor of a more nuanced approach to measure emissions from livestock sectors. The research highlights the need to understand the various implications of the climate forcers. However, despite progress and the shift in the sector’s RF footprint, the need for a stronger management and reduction strategy remains, in accordance with the goals established by the Paris Agreement. The research emphasizes that avoiding further increases in RF is critical to stabilize the climate, posing a challenge for all sectors and organizations.