Climate change and land use: Repairing centuries of damage

Since the industrial revolution, misuse and overuse of non-urban land has contributed greatly to climate change. Between now and mid-century, ecosystems damage must be halted and reversed if we are to succeed in hitting global net zero targets.

Throughout history, land has been the source of the food and energy that powers human flourishing. The very birth of civilisation is linked to the development of agriculture, the key change in the way our ancestors used land that allowed them to transition from nomadic hunter-gatherers to sedentary farmers. Without our capacity to work the land and extract its resources, modern human society would simply not exist. Beside the means for agriculture, terrestrial ecosystems provide us with a range of essential services – estimated to be roughly equivalent in value to annual global GDP[1] – as well as multiple intangible benefits of a cultural, spiritual and recreational nature.

Since land is finite, extracting its resources without depleting them beyond the natural capacity for regeneration is key to sustainable long-term human development. The way we allocate land to different uses directly affects the quantity and quality of resources and ecosystem services we can enjoy, and how we positively – or negatively – impact on natural environments. Currently, 29% of global land surface is occupied by relatively barren areas such as glaciers and deserts. Freshwater bodies amount to only 1%, while 34% is covered by natural vegetation (shrubs, 8%, and forests, 26%). The rest (35%) is directly affected by human activities and largely focused on food production, with 27% dedicated to sustaining livestock (through grazing and feed crops) and 7% to agricultural crops. The built environment (villages, cities and infrastructure) occupies only 1%. Estimates on land use in the past centuries indicate a steady but very slow growth of cropland and grazing land until the 18th century, followed by exponential growth until the second half of the 20th century. In the last 50 years, this growth has slowed down considerably, while the expansion of built-up land has become more noticeable.[2]

The spread of cropland and grazing land, which brought immense benefits in terms of food availability and variety across the world, has taken place – and continues to do so – mostly at the expense of vegetated areas. In ecological terms, converting forest into farmland means a loss in carbon absorption and oxygen release capacities, as well as an increase in greenhouse gas (GHG) production caused by farming and livestock emissions. In fact, about a quarter of global GHG emissions are directly linked to deforestation and agriculture.[3] In addition, deforestation and the transformation of other natural habitats leads to biodiversity loss and the degrading of ecosystem services, such as natural flood protections. Although at global level the expansion of agricultural land at the expense of natural habitats continues to be a problem, this is now mostly occurring in developing countries, while in the ‘global North’ (e.g. Europe and North America) the trend has started to reverse.[4] This does not necessarily mean that developed countries have become more virtuous, since much of their environmental burden has been shifted onto developing countries through the growth of international trade.[5]

In contrast, the trend of urbanisation continues across the world, albeit at different paces in developed and developing countries. In the last decades, global urban population doubled while rural population grew only by 40%.[6] Around 55% of global population now lives in urban areas, and this is expected to rise to almost 70% by 2050.[7] While this population lives in that small fraction of global land occupied by the built environment, three-quarters of global GHG emissions are generated in urban areas.[8] This highlights how decarbonising the built environment is essential to address the climate crisis.

However, significant GHG reductions can be achieved also by changing the way we use non-urban land. As the global population grows, demand for food follows and threatens to continue fuelling the expansion of agricultural land at the expense of natural habitats. It is now clear that a shift towards a more plant-based diet is necessary to establish a sustainable food supply and decrease its GHG emissions.[9] By reducing our need for crop feeds and grazing land for livestock, we can restore and expand natural habitats that provide carbon sequestration and storage. This does not necessarily mean leaving vast areas entirely void of human activities – although rewilding on a large scale is also needed[10]. A range of practices can be adopted to extract economic value from land while protecting its natural functions. Sustainable forestry is an obvious example, as it allows resource generation while keeping the multiple benefits of forested land, including carbon sequestration. GHG emissions savings can also be achieved by simply allowing water levels to rise in agricultural peatland used for grazing. Researchers estimated that in the UK alone, this practice could save 500 million tonnes of CO2 per year, equivalent to 1% of global annual emissions [11]

Restoring natural processes which were the norm before the advent of intensive agriculture can also provide multiple benefits. For example, leaving crop residues like stalks and leaves to rot in the field can extend the natural capability of the soil to store carbon.[12] Mixing crop cultures across fields, thus creating a biodiverse environment more similar to natural ecosystems, can regulate water balance, maintain soil fertility and even increase productivity.[13] Agroforestry practices that integrate natural vegetation into agricultural systems increase carbon sequestration and biodiversity, and mitigate floods and soil erosion.[14]

Far from being a simple return to traditional practices, sustainable land use for human activity can integrate tradition with innovation. Researchers in Oregon have compared conventional open pastures for sheep grazing against pastures partially covered with solar photovoltaic panels. Forage from the latter system was found to be lower in volume but higher in quality than forage from conventional pastures, which resulted in lambs gaining similar weight across the two systems. Thus, conventional pastures provided an annual return of US$1,046 per hectare against the US$1,029 provided by PV-integrated pastures. This second figure does not account for potential additional economic returns linked to solar energy generation.[15]

Overall, there could be plenty of land on the Earth for all animal and vegetal species to thrive. It remains to be seen whether human intelligence and empathy are enough to reverse the dangerous effects of our short-sightedness.

References

1. P.R. Shukla, J. Skea, R. Slade, R. van Diemen, E. Haughey, J. Malley, M. Pathak, J. Portugal Pereira (eds.) Technical Summary, 2019. In: Climate Change and Land: an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems
2. https://ourworldindata.org/land-use#total-agricultural-land-use
3. P.R. Shukla, J. Skea, R. Slade, R. van Diemen, E. Haughey, J. Malley, M. Pathak, J. Portugal Pereira (eds.) Technical Summary, 2019. In: Climate Change and Land: an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems
4. Winkler, Karina; Fuchs, Richard; Rounsevell, Mark D A; Herold, Martin, 2021. Global land use changes are four times greater than previously estimated. Nature Communications, 12 (2501)
5. S. Giljum and N. Eisenmenger, 2004. North-South Trade and the Distribution of Environmental Goods and Burdens: A Biophysical Perspective. The Journal of Environment & Development, Vol. 13, No. 1, pp. 73-100
6. Monica Crippa, Diego Guizzardi, Enrico Pisoni, Efisio Solazzo, Antoine Guion, Marilena Muntean, Aneta Florczyk, Marcello Schiavina, Michele Melchiorri, Andres Fuentes Hutfilter. Global anthropogenic emissions in urban areas: patterns, trends, and challenges. Environmental Research Letters, 2021; 16 (7): 074033
7. https://www.un.org/development/desa/en/news/population/2018-revision-of-world-urbanization-prospects.html
8. Monica Crippa, Diego Guizzardi, Enrico Pisoni, Efisio Solazzo, Antoine Guion, Marilena Muntean, Aneta Florczyk, Marcello Schiavina, Michele Melchiorri, Andres Fuentes Hutfilter. Global anthropogenic emissions in urban areas: patterns, trends, and challenges. Environmental Research Letters, 2021; 16 (7): 074033
9. Hayek, M.N., Harwatt, H., Ripple, W.J. et al. 2021. The carbon opportunity cost of animal-sourced food production on land. Nat Sustain 4, 21–24. https://doi.org/10.1038/s41893-020-00603-4
10. https://www.theguardian.com/environment/2021/jun/03/rewild-on-massive-scale-to-heal-nature-and-climate-says-un-decade-on-ecosystem-restoration-aoe
11. C. D. Evans, M. Peacock, A. J. Baird, R. R. E. Artz, A. Burden, N. Callaghan, P. J. Chapman, H. M. Cooper, M. Coyle, E. Craig, A. Cumming, S. Dixon, V. Gauci, R. P. Grayson, C. Helfter, C. M. Heppell, J. Holden, D. L. Jones, J. Kaduk, P. Levy, R. Matthews, N. P. McNamara, T. Misselbrook, S. Oakley, S. Page, M. Rayment, L. M. Ridley, K. M. Stanley, J. L. Williamson, F. Worrall, R. Morrison. Overriding water table control on managed peatland greenhouse gas emissions. Nature, 2021
12. Kristina Witzgall, Alix Vidal, David I. Schubert, Carmen Höschen, Steffen A. Schweizer, Franz Buegger, Valérie Pouteau, Claire Chenu, Carsten W. Mueller. Particulate organic matter as a functional soil component for persistent soil organic carbon. Nature Communications, 2021; 12 (1)
13. Jianguo Chen, Nadine Engbersen, Laura Stefan, Bernhard Schmid, Hang Sun, Christian Schöb. Diversity increases yield but reduces harvest index in crop mixtures. Nature Plants, 2021
14. Stafford, R., Chamberlain, B., Clavey, L., Gillingham, P.K., McKain, S., Morecroft, M.D., Morrison-Bell, C. and Watts, O. (Eds.) (2021). Nature-based Solutions for Climate Change in the UK: A Report by the British Ecological Society. London, UK.
15. Alyssa C. Andrew, Chad W. Higgins, Mary A. Smallman, Maggie Graham, Serkan Ates. Herbage Yield, Lamb Growth and Foraging Behavior in Agrivoltaic Production System. Frontiers in Sustainable Food Systems, 2021; 5