Climate action may be hampered due to different land emissions accounting practices by scientists, countries: Study

A new study points to differences in how countries and scientists account for emissions from land use, land use change and forestry (LULUCF), hampering efforts to achieve global climate targets.

Globally, the difference in accounting between computer models and countries is around 4-7 gigatonnes of carbon dioxide, representing around 10 per cent of today’s greenhouse gas emissions, according to the study published in the journal Nature.

The discrepancy stems, more specifically, from a difference in what are considered anthropogenic carbon fluxes (emission and sequestration or removals), Thomas Gasser, senior research scholar at the International Institute for Applied Systems Analysis (IIASA) Energy, Climate and Environment Programme, told Down To Earth.

“A good analogy is to imagine you are driving a car with a speedometer in kilometres / hour but the speed limit on the road is in meters per hour. This makes estimating whether you're within the law difficult, and ideally, you want to express both speeds in the same unit,” he said.

The land-use sector covers the management of cropland, grassland, wetlands, forests and settlements. It also includes ‘land use change’ such as afforestation, deforestation or draining of peatland (a distinctive wetland type, characterised by the accumulation of partially decayed organic matter).

The United Nations Intergovernmental Panel on Climate Change (IPCC) uses direct and indirect fluxes in their computer models to calculate the global temperature response to anthropogenic emissions.

Direct fluxes come from direct human intervention, such as agriculture and forest harvest, while indirect fluxes are how the land responds to indirect human-induced environmental changes, such as an increase in atmospheric carbon dioxide or nitrogen deposition.

National inventories, too, consider direct and indirect fluxes. However, they do not include indirect fluxes from unmanaged land.

The paper assessed key mitigation benchmarks using the inventory-based LULUCF accounting approach. 

The 1.5°C long-term temperature goal of the Paris Agreement pathways needs Net Zero carbon dioxide emissions to be achieved one to five years earlier. It also needs emission reductions by 2030 to be 3.5-6 per cent stronger, and cumulative CO2 emissions between 55-95 gigatonnes CO2 lesser. 

“To achieve the Paris Agreement, it’s critical that countries aim for the correct target. If countries achieve model-based benchmarks using inventory-based accounting, they will miss the mark,” Matthew Gidden, senior research scholar from IIASA, said in a statement.

Benchmarks assessed by IPCC are based on scientific conventions to determine what LULUCF emissions are due to human activity. 

Mitigation benchmarks change when assessing IPCC scenarios from a national inventory perspective. 

Gidden explained that countries use a different approach, incorporating more land area and additional land removals due to climate change. “So if countries aim for IPCC-assessed benchmarks using their accounting approach, they may not reach the climate benchmarks they are shooting for,” the expert noted.

The researchers next plan to improve on their approach and methodology, further reduce uncertainties and support efforts to bring scientific and policymaking communities better understand these gaps in accounting emissions.

Further, the report comes ahead of the 28th Conference of Parties (COP28) to the United Nations Framework Convention on Climate Change, which will be held in Dubai between November 30 and December 12.

The findings, the researchers highlighted, could feed into the first Global Stocktake – a process that will enable countries and other stakeholders to see where they’re collectively making progress toward meeting the goals of the Paris Agreement and where they’re not. It will conclude at COP28. 

The researchers made a case for detailed national climate goals and recommended distinct targets for land-based mitigation.

“Agriculture, Forestry and Other Land Use sector, on average, was responsible for 13-21 per cent of global total anthropogenic greenhouse gas emissions between 2010-2019,” according to the IPCC sixth assessment report.

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