In the race against climate change, scientists are turning to the land beneath our feet for solutions, but at what cost?
Imagine a technology that could actively suck carbon dioxide out of our atmosphere, effectively reversing some of the damage done by centuries of industrial emissions. This isn't science fiction; it's the promise of Negative Emissions Technologies and Practices (NETPs). Under the Paris Agreement, nations are committed to preventing dangerous global warming, and most scientific pathways to achieve this now rely heavily on these technologies to clean up our atmospheric carbon mess 1 .
The most prominent strategies—afforestation (planting new forests) and Bioenergy with Carbon Capture and Storage (BECCS)—are land-hungry. They envision a future where vast tracts of land are used as carbon sinks.
But our land is already stretched thin, tasked with feeding a growing global population and sustaining the planet's precious biodiversity. This sets the stage for a critical conflict: the fight against climate change could come at the expense of sustainable land use, threatening food security and natural ecosystems 1 . This article explores how science and policy are co-producing this challenge and the new research revealing a potential path forward.
To understand how we arrived at this juncture, we need to look at the science that informs high-level climate policy. The process is more of a collaborative "co-production" than a one-way street 1 .
Powerful computer simulations that combine economics, energy systems, and climate data to chart the cheapest possible pathways to meet climate targets.
The heart of the controversy lies in feasibility. The modelled levels of land-based mitigation could reduce agricultural land and encroach on natural land 1 .
When models prioritize cost-effectiveness above all else, they may sideline other critical societal goals enshrined in the UN Sustainable Development Goals (SDGs), such as Zero Hunger (SDG 2) and Life on Land (SDG 15) 1 . The challenge is to move from a technocratic vision to a negotiated "serviceable truth" that openly acknowledges these trade-offs 1 .
So, is there a way to increase carbon sequestration without triggering a food and biodiversity crisis? A groundbreaking 2024 study published in Communications Earth & Environment provides a compelling answer: yes, if we are much smarter about the types of forests we plant 6 .
Researchers used an innovative framework that combined three models: an economic model to project regional land demand, a land-use allocation model to downscale this demand to specific geographic grids, and a terrestrial vegetation model to calculate the carbon sequestration potential of different forest types 6 .
The crux of the experiment lay in three different approaches to selecting trees:
Native Forest Type
The business-as-usual approach, planting forests native to the area.
Diverse, Ecologically-Conscious
Selecting the most carbon-intensive forest type from a variety of species that exist within the same agro-ecological zone.
Carbon-Maximized
Selecting the most carbon-intensive forest type from all possible types globally, without regard for native ecology.
The findings were striking. Compared to planting native forests (Aff-Cur), the ecologically-conscious selection (Aff-Div) slightly increased carbon sequestration. However, the carbon-maximized approach (Aff-Cmax) boosted global carbon sequestration by 25% by the year 2100 6 .
| Scenario | Description | Global Carbon Sequestration (GtCO₂ per year) | Change vs. Native Forest |
|---|---|---|---|
| Aff-Cur | Native forest type | 7.6 | Baseline |
| Aff-Div | Diverse species in same agro-ecological zone | 7.7 | +2% |
| Aff-Cmax | Most carbon-intensive type globally | 9.5 | +25% |
Source: Adapted from 6
This crucial metric measures how much carbon you get per unit of land. A higher LIC means you need less land to remove the same amount of CO₂, thereby reducing competition with agriculture.
Despite higher efficiency, afforestation generally had a lower LIC than BECCS. Relying solely on afforestation would require more land expansion, leading to higher food prices and increased risk of hunger 6 .
| Scenario | Key Technology | Impact on Global Cropland Area (vs. no policy) | Impact on Food Prices (vs. no policy) |
|---|---|---|---|
| No Climate Policy | N/A | Baseline | Baseline |
| Aff-Cur | Afforestation (Native) | Increase | Significant Increase |
| Aff-Cmax | Afforestation (Carbon-Maximized) | Moderate Increase | Increase |
| BECCS | Bioenergy with Carbon Capture | Lowest Increase | Lowest Increase |
Source: Adapted from 6
Understanding the trade-offs of NETPs requires a robust set of analytical tools. Here are some of the key "reagents" in the scientist's toolkit for quantifying and assessing these technologies.
| Tool / Concept | Function | Why It Matters |
|---|---|---|
| Life Cycle Assessment (LCA) | A comprehensive evaluation of all environmental inputs, outputs, and impacts of a product or system throughout its existence 2 . | It reveals the net carbon balance of a CDR technology, ensuring it removes more CO₂ than it emits across its entire supply chain. It also highlights trade-offs like water use or toxicity 2 . |
| Global Warming Potential (GWP) | A standardized metric that compares the warming effect of different greenhouse gases to that of carbon dioxide over a specific time frame 2 . | It allows scientists to express all greenhouse gas emissions in a common unit (CO₂-equivalent), providing a complete picture of a technology's true climate impact 2 . |
| Integrated Assessment Models (IAMs) | Computer models that combine economic, energy, and climate systems to project cost-effective pathways for meeting climate targets 1 . | They are the primary tools used to inform global climate policy, but their assumptions about land availability and technology feasibility are critically important to scrutinize 1 . |
| Land Intensity of Carbon (LIC) | The potential amount of carbon sequestered per unit area of land used 6 . | This is a crucial efficiency metric. Technologies with higher LIC put less pressure on land resources, reducing potential conflicts with food production and biodiversity 6 . |
LCA ensures we account for all emissions across the entire lifecycle of carbon removal technologies, not just during operation.
These tools help quantify the inevitable trade-offs between carbon removal, food security, and biodiversity conservation.
The journey to a stable climate is fraught with complex choices. The co-production of climate policy and negative emissions reveals that there are no perfect, frictionless solutions. Relying on vast tracts of land for carbon removal presents real and significant trade-offs for food security and biodiversity 1 .
Carefully selecting forest types can dramatically increase carbon sequestration efficiency 6 .
No single technology is a silver bullet. We need a diverse portfolio of NETPs 7 .
"The challenge is not just scientific; it is deeply social and political. It calls for transparent dialogue about the values and trade-offs embedded in our climate models and policies."
By acknowledging these complexities, we can co-produce a future that is not only climate-neutral but also sustainable and equitable for all.