Forests not enough
IPCC’s special report asserts that land-based carbon sinks are not limitless and therefore not a panacea for the inevitable climate crisis
The carbon cycle is classically described in terms of 'sources' and 'sinks' of emissions. The electricity sector, which converts fossil fuels into light and heat, is a source (as are most human activities since the dawn of the industrial age).
Identifying sinks is trickier. We know that, as a general principle, more forest cover equals more carbon sequestration (or sink) potential. It is much more difficult to put a number on how much carbon forests can absorb.
The special report on Climate Change and Land released on August 8, 2019, by the Intergovernmental Panel on Climate Change (IPCC) illustrates this difficulty. It thus delivers a wake-up call for policymakers that aggressive forestry targets do not excuse cowardice in cutting emissions from fossil fuel use. To make this case, it explicitly identifies the limits of carbon sequestration by forests.
The report estimates the mitigation potential from reducing deforestation and forest degradation at between 0.4 and 5.8 gigatonnes of carbon dioxide per year. By comparison, the energy sector accounted for 33 gigatonnes of carbon dioxide in 2018; coal alone accounted for over 10 gigatonnes.
Headlines may continue to give the impression that planting forests is a panacea for the climate crisis, but scientists are much less sanguine in their projections.
The IPCC indicates that some land-based response options "take decades to deliver measurable results" because "adaptation and mitigation benefits from afforestation/reforestation depend on the growth rates of trees".
Besides, afforestation, reforestation and agroforestry "do not continue to sequester carbon indefinitely"—eventually "the net annual removal of CO2 from the atmosphere declines towards zero". The report also notes that any sequestration gains are "at risk from future loss (or sink reversal) triggered by disturbances such as flood, drought, fire, or pest outbreaks, or future poor management".
The long view on forestry stands in contrast with the report's statements on "Action in the near term". This section of the report's summary for policymakers makes clear that "the consequences of inaction on […] mitigating climate change exceed the costs of immediate action in many sectors".
It also makes clear the consequences for not acting immediately, stating that "[d]eferral of Greenhouse Gas emission reductions from all sectors implies trade-offs including irrevocable loss in land ecosystem services required for food, health, habitable settlements and production, leading to significant economic damage to many countries in many regions of the world". (emphasis ours)
The second type of magical thinking in the land-energy discussion centres on the question of bioenergy carbon capture and storage (BECCS). This is a technological solution to generate net-zero carbon energy which has firstly, not been tested at scale, and secondly, will require extensive tracts of land to implement. Nevertheless, it has emerged as a buzzword in climate innovation.
It is undeniable that all pathways that keep us below a 1.5°C threshold will require some amount of carbon capture and storage (CCS). However, there are other CCS technologies which are less land-intensive (but which do not generate energy).
Moreover, the IPCC is clear that BECCS should not be a preferred solution for land-based mitigation. In its attempt to inform policymakers, the report's summary explicitly divides such solutions into two categories:
Those which contribute positively to sustainable development and other societal goals, which can be applied without competing for land and which have the potential to provide multiple co-benefits. This includes improved management of cropland and grazing lands, improved forest management, and increased soil organic carbon content.
Those which increase demand for land conversion and which, if applied at scale, could have adverse side effects for adaptation, desertification, land degradation and food security. BECCS is the highlight of this category.
The report, as with all IPCC reports, is scrupulously even-toned. Yet, it brings home the seriousness of the land-based challenge (particularly in its observation that, since the 1850s, the land surface air temperature has risen nearly twice as fast as the global average temperature).
The report also clarifies the limits of land-based mitigation and differentiates risks associated with critical policy choices. Sustainable land management will remain an important counter-balance to carbon emissions. It must proceed hand-in-hand, however, with deep cuts to gross carbon emissions. DOWN TO EARTH
(The author is Deputy Programme Manager, Climate Change, Centre For Science and Environment, New Delhi. The views expressed are strictly personal)