Carbon removal beyond the trees

Another of our projects found similar tendencies around the world. We ran a survey in 30 countries, and focus groups in urban and rural areas in 22 countries, with randomly-recruited members of the public using quotas to ensure socio-demographic representation. The countries chosen represented a roughly even split between Global North and Global South, with every continent represented. Here, afforestation and reforestation was explicitly included, alongside six other carbon removal methods in the survey (see Fig. 1) and four others in the focus groups. Efforts were similarly made to mitigate the well-known naturalism bias, for example by avoiding the un-contextual use of “natural”, and emphasising dynamic socio-environmental interactions in plain language.

Levels of support for different carbon removal methods, from a survey in 30 countries (n = 30,284)¹⁶. Significant differences (p < 0.01) between levels of support in Global North versus Global South were identified using nonparametric independent-samples Mann Whitney U testing for six of the technologies: afforestation and reforestation was the exception (p = 0.497). Support was assessed on a 1-5 scale (1 = Strictly reject; 3 = Neither support nor reject; 5 = Fully support), along with a “don’t know” option, which was coded as a missing value. Support refers to overall support consisting of three types of activities: research, small-scale field trials, and broad deployment. Boxes show interquartile range and median. Whiskers show either minimum/maximum values in the sample population, or 1.5 times the interquartile range, whichever is closer to the median. Circles show outliers within 1.5 times the IQR.

Survey participants were significantly more likely to express familiarity with afforestation and reforestation¹⁶. Compared to evaluations and preferences for most carbon removal options, those for afforestation are more likely to be stable and informed by actual experiences and discussions. Afforestation and reforestation were also the most strongly supported of all the carbon removal options in the survey (Fig. 1) and participants perceived this option to have the most positive balance of benefits to risks. Interestingly, afforestation was the only option without significant differences between Global North and Global South countries, potentially echoing greater familiarity, and indicating broader alignment on perceptions of afforestation around the globe.

The survey did not experimentally test for the impact of including afforestation or reforestation on the perceptions of the other techniques; we refer to the data here solely as an illustration of general baseline preferences for afforestation and reforestation, and the Global South/North comparison. For indications that a biasing effect may occur, we turn to the qualitative data from this study.

Focus group participants tended to perceive biological carbon removal as tangible, distributed, and permissive of proactive behaviour, allowing individuals to make sense of and engage with a systemic problem^17,18. This applied to all approaches that relied upon biological sinks – but was especially strong for tree-planting. Indeed, the positive application of naturalism, feasibility, and agency to tree-planting was the only universal perspective identified in the study, represented in all 22 countries¹⁷.

Crucially, as we show in Table 1, participants often compared tree-planting favourably in relation to engineered carbon removals, such as Direct Air Capture, which were seen as costly, resource-intensive, and leveraging the same industrial processes that were perceived to be the root causes of climate change and unsustainability.

Participants highlighted a host of co-benefits associated with tree-planting that spanned biodiversity, health and air quality, flood prevention and soil erosion¹⁷, often conditioned by experiences of climate or environmental risk¹⁹. Yet the benefits were sometimes over-stated, or assumed to be so systemic that support could border on the simplistic: for example, commonly stating that “everyone” would tangibly benefit from afforestation efforts. Participants did not intuitively grasp nuances between afforestation, reforestation, and avoided deforestation, and there was very little discussion of different kinds of trees, their permanence, differences in carbon sequestration and suitedness to different areas – all of which have difficult carbon accounting and policy implications.

We should be cautious about overstretching the interpretation of our data. Favouring tree-planting was not always one-dimensional or overly enthusiastic, especially in the focus groups. The sense that trees distract from other types of carbon removal was common – but not universal. Participants also recognized risks in tree-planting, including land-use trade-offs, climate impacts from non-permanent biological carbon stocks, questions over potential impermanence, and perverse profit motives.

Techniques such as Direct Air Capture also maintained a significant degree of public support, especially in countries with more faith in innovation and/or state-owned industry sectors (India, China, Saudi Arabia, Norway, Switzerland). Nevertheless, there is clear evidence that tree-planting takes up a disproportionate space in the public imagination of carbon removal.