Understanding the complex relationship between land and climate

How much can land contribute to mitigation?

Land use plays a very important role in the climate system and is presently an overall contributor to global climate change. Agriculture, forestry, and other land-use changes are responsible for 23% of global greenhouse gas emissions. This means that radical changes in the ways we use land are needed if we are committed to a Paris Agreement compatible pathway. Up to around a quarter of the mitigation pledged in countries’ Nationally Determined Contributions is expected to come from land-based mitigation options. Possible solutions such as sustainable food production, soil organic carbon management or sustainable forest management offer synergies with efforts to achieve the Sustainable Development Goals and could help combat land degradation and desertification, and improve food security.

However, certain circumstances also involve difficult trade-offs. For instance, most pathways that keep warming below 1.5°C by the end of the century rely on negative emissions such as from bioenergy with carbon capture and storage (BECCS). This is to make up for highly insufficient emissions reductions to date, as well as for any residual emissions from sectors such as agriculture or industry that are difficult to mitigate in the near- to medium term. Although the Integrated Assessment Models (IAMs) used to develop pathways often consider BECCS as being a cost-efficient option in the future, over-reliance on BECCS would use a great amount of land, thereby potentially threatening food security (SDG2) and biodiversity (SDG15). Managing the sustainability challenges, risks and trade-offs inherent in large-scale carbon dioxide removal efforts requires extremely careful consideration.

There is not one single pathway to achieve the 1.5°C target, but all those that limit warming to 1.5°C require very rapid emissions reductions and deep changes in all sectors. These include phasing out fossil fuels, renewable electrification, increased energy efficiency, lower levels of meat consumption, slower global population growth, as well as restoring forests at scale.

If effectively combined and deployed according to local conditions and capacities, these changes would complement and reduce the reliance on BECCS and other negative emissions technologies (NETs) for climate mitigation. This shows that we do not face a clear-cut dilemma between the repellent consequences of either climate change or large-scale BECCS deployment, although many of the mitigation scenarios produced by models – often due to limitations in computational capacity – may have suggested it.

More generally, the diversity of 1.5°C-compatible pathways clearly indicates that the faster carbon emissions are reduced, the less negative emission technologies (such as BECCS, direct air capture and storage, reforestation and afforestation) will be needed to stick to the temperature limit of the Paris Agreement. This is important as major uncertainties remain regarding the ability of land use practices to effectively store carbon in the long term, particularly as the impacts of climate change on ecosystems through droughts, heatwaves, floods or wildfires will become even more obvious.

One objective of the European LAMACLIMA (LAnd MAnagement for CLImate Mitigation and Adaptation) project is to conduct dedicated experiments with Earth System Models (ESMs) in order to refine these uncertainties to help assess the actual carbon storage potential of three land management practices – reforestation and afforestation, wood harvesting and irrigation – while keeping in sight their implications for other environmental criteria, including climate adaptation.

How much can land contribute to adaptation?

Changes in land cover or land management affect local energy and water cycles, and therefore the local climate. Scientists have shown that through these biogeophysical effects, deforestation for agricultural expansion has increased the risk of local heat extremes in North America and Eurasia. At the same time, changes in agricultural management practices such as irrigation or cropland intensification have dampened it.

One study has even suggested that changes in temperature extremes due to future land cover changes could be comparable in magnitude to changes arising from half a degree of global warming. However, climate models still strongly disagree on the magnitude – and in some circumstances even the direction – of these effects. This means there is a need to better understand how they would play out in the context of mitigation-driven land cover or land management changes, and then to take them into consideration when planning adaptation strategies.

Within LAMACLIMA, satellite observations combined with Earth System Models (ESMs) will be employed to help refine this understanding, with the final objective to better represent these processes and how they could influence land-use decisions in the IAMs used to derive global land use pathways.

Limitations of the models and how LAMACLIMA intends to address them

Even in a future where effective mitigation strategies limit the pressure on land, it will remain a limited resource and we will be left with trade-offs when deciding how to use it. Several types of models are typically employed to quantify those trade-offs; however, it is crucial here to be mindful of their current limitations. For example, the representation of irrigation in ESMs only considers constraints on water availability in a very limited way.

IAMs have been used to highlight that competition for land and subsidies for bioenergy crops can reduce land for food production and therefore lead to an increase of food prices, but as of now they cannot properly weigh this risk against the threat extreme events would pose to food production in the absence of sufficient emission reductions. While IAMs provide essential guidance for policymakers on technically and economically feasible pathways to achieve specific climate and sustainable development goals, they are only one component in the evaluation of mitigation options to meet climate targets. Relying solely on current IAMs provides an incomplete view of the costs of climate change and underestimates the benefits of mitigation measures.

Similarly, current biodiversity models are only able to represent options such as BECCS, reforestation and afforestation in a coarse way. Therefore, they may well overestimate the negative impacts of the deployment of these negative emission technologies and underestimate their benefits, because the potential of these options for combating land degradation is not adequately captured.

The LAMACLIMA project aims to address these model limitations using several approaches. First, it contributes to improving the representation of physical processes such as irrigation in Earth System Models. Then, the results of ESM experiments will be used to improve how physical risks from climate impacts are considered as well as the potential benefits from changes in LCLM in economic models and IAMs.

The project will also include webinars and workshops involving stakeholders from various backgrounds that are representative of key sectors addressed in the project. Their role will be to incorporate their unique perspective on the issues and their knowledge of the local environmental and socio-economic conditions to help critically assess the model results in light of the mentioned limitations. Through the interdisciplinary nature of its consortium, the LAMACLIMA project intends to build an integrated approach to tackling land-related issues in the context of climate change that can effectively incorporate important social and environmental factors.