Removing CO2 from the atmosphere using land-based mitigation strategies is central to nearly every country’s net-zero target.

To mitigate global climate change, land-use and land-management sectors need to reduce greenhouse gas emissions and remove carbon from the atmosphere.

Protecting ecosystems and dedicating more land to nature-based solutions and climate-smart agricultural practices are promising ways to do so.

To date, there has been little work looking at where, specifically, these strategies may be in conflict with one another.

Our research, published in Global Change Biology, assesses opportunity costs among 19 different land-use strategies for climate mitigation.

We find that roughly 8.5bn hectares of land around the globe are suitable for at least one land-based mitigation strategy – representing about 60% of the Earth’s land surface.

However, almost 40% of this land is suitable for more than one mitigation strategy, presenting decisionmakers with a choice as to which strategy or strategies they should deploy.

Land-based mitigation

To achieve global climate targets in a timely manner, some studies call for up to 10% of Earth’s terrestrial surface to undergo a land-cover change.

But is there actually enough land to make this happen? And if there is, how can projects be scaled up strategically to maximise the mitigation benefits while minimising negative impacts on humans and biodiversity?

Disciplinary silos and practical uncertainties have previously made these questions hard to answer.

For instance, nature-based solutions, including habitat conservation and restoration, are often differentiated from other climate-motivated land-use practices, such as bioenergy cropping and afforestation. Yet, both types of practices can have significant trade-offs for biodiversity and for agriculture.

Although controversial, these types of climate-specific land-use changes are proposed in many national climate mitigation plans. As these plans are put in motion, the trade-offs that could result from increasing the land dedicated to certain strategies over others need careful consideration.

In our study, we assess land-use opportunity costs across a portfolio of 19 different strategies for climate mitigation.

Broadly speaking, these strategies can be classified into four main approaches to mitigation: maintaining or protecting ecosystems, modifying forestry or agricultural management practices, restoring ecosystems and converting land to increase biomass.

Of these, certain approaches and strategies can be used to avoid emissions, while others can be used to sequester carbon.

Among the strategies we studied are the protection and restoration of forest, wetland, peatland and grassland habitats, various approaches to climate-smart cropland and forestry management (including biochar and silvopasture), bioenergy cropping with carbon capture and storage and afforestation.

We used global datasets on forests, croplands and other habitat types alongside data on environmental conditions such as temperature to estimate how much of the global land area is suitable for each strategy.

Then, we created global maps at a one kilometre resolution that identify areas that could be considered for these measures.

Land potentials

We find that some strategies had large regions of suitability.

For example, deforestation and other types of habitat loss are a large contributor to greenhouse gas emissions from the land-use sector. Maintaining grassland and forest habitat types to prevent losses can be done anywhere that such loss is occurring.

Maintaining the carbon stored in ecosystems that are currently unprotected accounts for more than 3bn hectares of the land we estimate as suitable for land-based climate mitigation – equal to about 20% of the Earth’s land surface.

Other strategies, including peatland restoration and silvopasture, had much more restricted areas of suitability across the globe.

For peatland restoration, priority areas are primarily distributed in the boreal zone – the high-latitude northern hemisphere, just south of the Arctic. Cropland expansion has led to widespread peatland loss in this region over the past several decades.

For silvopasture – a type of livestock farming that integrates tree cover with grazing – suitability is primarily constrained by environmental limits on tree growth. Here, factors such as water availability determine in which regions traditional pastoral systems could be converted to silvopasture.

The figure below shows the 19 mitigation strategies we studied and the area of the Earth that is suitable for each, in millions of hectares. The three maps on the right show example distributions for (from top to bottom) enhanced chemical weathering, bioenergy with carbon capture and storage (BECCS) and integrating trees into croplands.

Conflict potential

When summing the suitable area across all the 19 strategies we examined, we find that a huge area of Earth – almost 60% of its land surface – is theoretically suitable for land-based climate mitigation.

However, the majority of this area captures regions where more than one mitigation strategy is suitable.

In some cases, these overlapping land potentials involve mitigation strategies that can be deployed jointly, such as increasing the carbon stored in soils at the same time as increasing the carbon stored in aboveground biomass.

One example of this is the potential to collectively implement enhanced chemical weathering and improved plantation management, which have a combined land suitability of 348m hectares.

(Enhanced chemical weathering involves spreading ground-up silicate rocks onto farms or other land. This speeds up natural chemical processes and removes CO2 from the atmosphere, while also improving crop yields.)

However, suitable areas for compatible strategies were rare, compared to the area where conflicts between strategies could occur.

For instance, large portions of the US, Europe and China are suitable for both ecosystem restoration and climate-smart agriculture.

In these regions, societies face a choice between restoring grassland, forest and wetland habitats, or continuing to manage the land for agriculture, where climate-smart practices could still be implemented to decrease greenhouse gas emissions or sequester more carbon.

Because the choice between large-scale restoration and climate-smart agriculture may involve a trade-off between restoring habitat for biodiversity or maintaining land use for people, we avoid making any recommendations about which land-use practices to implement.

Rather, our paper highlights areas where these trade-offs could occur – places in which large-scale top-down planning could conflict with local priorities for land-use.

More research is needed to map local constraints and management costs so that the choice between mitigation strategies aligns local needs with national and global targets for climate mitigation.

Opportunity costs

So, with these potential overlaps and conflicts, is there enough land to meet climate targets?

The answer is yes, in theory – the summed area we estimate as suitable for climate mitigation is more than double the amount of land that has been pledged for transformation by UN member countries in their pledges to meet the goals of the Paris Agreement.

However, the pace of on-the-ground implementation lags far behind the degree of land-use change needed to limit warming by 2050. And high-level constraints, such as meagre financing or a lack of political incentives, will continue to stall progress.

Given these choices and constraints, land-use opportunity costs should be considered when planning policies that may incentivise certain types of mitigation practices that could inadvertently displace opportunities for others.

As plans to reach net-zero continue to develop, the atlas of maps for mitigation practices – and the exploration of opportunity costs – can guide pathways for scaling up land-based mitigation to address climate change.

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The post Guest post: The conflicting practices in using land to tackle climate change appeared first on Carbon Brief.

Guest post: The conflicting practices in using land to tackle climate change