A study published in Nature Climate Change suggests a way forward for reconciling the different methods currently used to measure land-based greenhouse gas emissions, addressing a limit also acknowledged in the IPCC special report on 1.5oC, published on 8 October 2018.
The Paris Agreement calls for global warming to be limited to "well below 2oC" and for greenhouse gas (GHG) emission “neutrality” to be achieved by the second half of this century.
In order to achieve GHG neutrality, the emissions caused by human activities must be balanced by the removal of carbon dioxide (CO2) from the atmosphere. Forests play a key role in reaching this GHG neutrality.
"Forests act as an important CO2 'sink', i.e. globally they absorb nearly one third of the total CO2 emissions caused by human activities. They are currently by far the most important CO2 sink that humans can manage, although new technologies to remove CO2 from the atmosphere will be eventually needed", explains JRC researcher Giacomo Grassi.
Conceptual gap in GHG reporting
Forests play an important role in the assessment of the collective progress towards the goals of the Agreement. However, unlike emissions from fossil fuel use and industry, emissions and sinks from forests are difficult to measure.
The JRC-led publication highlights a gap that currently exists in the global forest CO2 flux estimates included in the GHG inventories of the participating countries and the methodologies used by the independent global modelling community to measure progress.
The gap corresponds to up to 10% of the current anthropogenic CO2 emissions, which is relevant when assessing the progress towards the Paris Agreement's temperature objectives and our collective pathway towards GHG neutrality.
This gap is also reflected in the Intergovernmental Panel on Climate Change (IPCC) special report on 1.5oC, which acknowledges that "(forest CO2) estimates reported here are not necessarily comparable with countries’ estimates".
The study demonstrates that the discrepancy in estimates stems from conceptual differences in estimating what we mean by "anthropogenic" forest CO2 sinks.
Both the methods used by countries and by the global modelling community can be justified, but the differences make it difficult to track progress towards the goals of the Paris Agreement.
Learning to speak the same language
The study shows how the discrepancy can be reconciled and makes practical recommendations.
For instance, countries should provide more transparent and complete information on what is included in their GHG inventories, e.g. what they consider to be "managed".
In parallel, the study highlights a pragmatic way forward for the global carbon modelling community, through an ex-post disaggregation of model results which would increase their comparability with countries’ inventories.
"Our suggested approach facilitates a deeper understanding of model-inventory differences and allows for a more transparent analysis of forest-based mitigation contributions. An increased collaboration between the different scientific communities is important when assessing the collective progress towards the goals of the Paris Agreement", concludes Giacomo Grassi.
IPCC Special Report: Global Warming of 1.5 °C
IPCC Special Report: Summary for Policymakers
- Publication date
- 9 October 2018