Climate, Trees, and Carbon


Where Will Everyone Go?

ProPublica and The New York Times Magazine, with support from the Pulitzer Center, have modeled how climate refugees might move across international borders.

By Abrahm Lustgarten, ProPublica

Read in English     Leer en Español

The human climate niche

The warming projected by most climate scientists will render the red areas on the map below less suitable for human settlement, the green ones more suitable. Chi Xu and colleagues have projected massive human climate-driven migrations, billions of people, necessitated by increased warming, especially at low latitudes. (Xu et al. PNAS. 2020).

How can IGC and geodesign impact climate change and climate-driven migration?

As designers, our intentions are to improve human and environmental conditions. What are the impacts of our designs on the conditions we want to improve, and are our impacts big enough to lead to the global improvements we dream about?

For IGC 2021 we invite teams to participate in advancing IGC's goal on two fronts – to continue to strengthen our understanding of IGC processes, and to explore global design processes and implications in the context of a coordinated assessment of a current global initiative - the Trillion Trees Initiative,


To advance such global thinking, we propose that each IGC 2021 project explicitly address projected changes in the Human Climate Niche (described above) and include an assessment of how each project could contribute to carbon sequestration, for slowing climate change, and as a facet of that, to the Trillion Trees initiative – a vision embraced by the World Economic Forum, the United Nations, and numerous national governments as an important way to capture carbon.

Climate change and the Sustainable Development Goals

The impacts of global climate change threaten achievement of the UN Sustainable Development Goals (McIntyre, Ivanaj, and Ivanaj 2018).

Climate change and climate-driven migration

The United Nations International Organization for Migration (IOM) is the leading UN migration agency. IOM’s objectives concerning migration, environment and climate change are:

  • To prevent forced migration that results from environmental factors to the extent possible;

  • To provide assistance and protection to affected populations when forced migration does occur in situations of environmental and climate change, and to seek durable solutions to their situation;

  • To facilitate migration in the context of climate change adaptation and enhance the resilience of affected communities.

Sustainable development is integral to this approach, implemented through disaster risk reduction, climate change adaptation and environmental sustainability measures. IOM and the European Union have collaborated on a series of maps summarizing the climate-related changes that will drive human migration patterns. The detailed maps and narrative are available at:

Notes on geodesign for migration
Carl Steinitz


The Center for Global Development ( has mapped areas of high vulnerability to climate change impacts and the Migration Policy Institute has projected the destination countries for international migration (

The United Nations High Commissioner for Refugees Handbook is a critical guide for designers. Click on handbook cover image or access

To slow migration, first slow climate change


Natural Climate Solutions

  • Natural Climate Solutions offer a powerful set of options for improving soil productivity, cleaning our air and water, and maintaining biodiversity (Griscom et al. 2017).

  • In contrast to capturing CO2 in permafrost or the oceans, tree protection or tree planting are readily understood and already widely accepted as a key means to offset anthropogenic carbon (Escobedo et al. 2010; Jarvis 1995).


The Trillion Trees Initiative (

  • The Intergovernmental Panel on Climate Change (IPCC 2018) suggests that an increase of 1 billion hectares of forest will be needed to limit global warming to 1.5℃ by 2050, leading to a global initiative to grow and restore 1 trillion trees by 2030 (World Economic Forum 2020).

  • Crowther et al. (2015) mapped trees worldwide and found 3.07 trillion trees, 1.3t in tropical and sub-tropical forest, 0.66t in temperate regions, 0.74t in boreal regions.

  • Bastin et al. (2019) mapped global potential tree coverage and found room for 0.9 billion hectares, enough for 1 trillion trees.

Existing global tree cover

Potential global tree cover, alternative models

Tree planting must also off-set continuing loss of forest cover


Growing a Trillion Trees the Right Way

TerraMatch, backed by The World Resources Institute, is an online platform and mobile app that combines private sector and global movement expertise to restore degraded and deforested land.
By Aaron Minnick and Will Anderson, WRI
Read the article

Do Forests Grow Better With Our Help or Without?

Nations are pledging to plant billions of trees to grow new forests. A new study shows that natural forest regrowth to absorb carbon from the atmosphere and fight climate change may be greater than can be achieved by planting.
By Fred Pearce, YaleEnvironment360
Read the article

What trees should be grown, and where?

Is it feasible to grow so many trees?

  • Although embraced by numerous national and international agencies, not all agree that planting a trillion trees would be wise, or effective (Rogers 2019, Guariguata and Brancalion 2014).

  • Many objections relate to local conditions – in snowy climates the reduced albedo of forest cover might accelerate warming, not slow it; climate stress might contribute to insect predation and fires; social needs might outweigh carbon storage priorities.



Carbon storage strategies for geodesign
(based on Ontl et al. 2020)

Ontl et al. is valuable guidance for geodesign for carbon sequestration strategies, but the physical design must be part of a comprehensive and multi-sectoral geodesign process that accommodates and supports the people who depend on the forest for its full range of ecosystem services, whether they are local or distant urban citizens. “Restoration is about more than what gets planted in the ground; it’s about forests, but it’s really about people. They are the agents of restoration.” (Robin Chazdon quoted by Cernansky 2018).


The boldface strategies are detailed below. For detail on other strategies, refer to the pdf linked above.

Strategy 1: Maintain or increase extent of forest ecosystems

Strategy 2: Sustain fundamental ecological functions

Strategy 3: Reduce carbon losses from natural disturbance, including wildfire

Strategy 4: Enhance forest recovery following disturbance

Strategy 5: Prioritize management of locations that provide high carbon value across the landscape

Strategy 6: Maintain or enhance existing carbon stocks while retaining forest character

Strategy 7: Enhance or maintain sequestration capacity through significant forest alterations

Strategy 1. Maintain or increase extent of forest ecosystems

  • Avoid conversion to non-forest

    • Forests are generally the largest carbon sinks – 172 MMT C (U.S.)

    • 90% of land-based sequestration in the U.S.

    • 70% of carbon stock is in live and dead trees

    • 25% carbon stored in soil organic matter, 5% in litter

    • Loss of canopy results in degradation of soils and their sequestration capacity

    • Conversion to row-crop agriculture results in largest losses

  • Reforestation

    • Reforestation of under-stocked land could add 13.3 MMT C (Sample et al. 2017)

    • Reforestation could add 13-21 MMT C via soils (Nave et al. 2018)

    • In 2015, nearly half of carbon sequestered by reforestation on former crop lands (Post and Kwon 2000)

  • Increase forest cover in urban areas

    • Large potential for significant sequestration (Nowak et al. 2013)

    • Sequestration rates can be higher – more foliage, less crowding, better care

    • Reduce energy demands by shading and wind protection

  • Increase or implement agroforestry

    • Agriculture-dominated landscapes sequester 73-84% less carbon than forests (Liu et al. 2014)

    • Agroforestry can include trees and shrubs in pastures, protection belts and cover for shade-tolerant crops

    • Agroforestry is more adaptive to changing climate, protecting soils, conserving soil moisture
      (1) silvopasture, (2) alley cropping, (3) forest farming, (4) windbreaks, and (5) riparian buffers

Strategy 5. Prioritize locations that provide high carbon value

  • Prioritize low vulnerability locations

    • Retain large-diameter trees on sites free of drought stress

    • Protect large un-fragmented sites

    • Maintain redundancy of high value sites

  • Establish reserves with high carbon density

    • Protect wetlands etc. with high underground stocks of carbon

    • Create reserves with high core:edge ratios

    • Restore/increase areas with little or no harvest activity

Strategy 6: Maintain carbon stocks, retain forest character

  • Retention of biological legacies

    • Oldest and most structurally complex forests have increased carbon storage

    • Retain survivors of pest outbreaks, fires, wind-throw events

    • Retain dead and downed wood, salvage material where fire, pest, and disease risks are low

  • Increase stocking, minimize mortality, where possible

    • Underplant underrepresented and climate range tolerant species

    • Harvest poorly-stocked and even-aged forest and replace

    • Lengthen harvest rotations, retain bigger trees

  • Species mix

    • Minimize less tolerant and less adapted species

    • Manage for species and genotypes with high moisture/temperature tolerance

    • Promote structural and genetic diversity for carbon storage

Strategy 7: Enhance capacity through forest alterations

  • Design for future, not current, conditions

    • Favor species, genotypes suited to future conditions

    • Alter forest composition (species, age, size) to maximize carbon stocks

    • Promote species with higher carbon density (e.g., incorporate or favor hardwoods vs. conifers where appropriate)

    • Introduce species, genotypes expected to be adapted to future conditions (e.g. drought-tolerant for drying locations, flood-tolerant for those prone to flooding)


This report on Good Practice Guidance for Land Use, Land-Use Change and Forestry (GPG-LULUCF) is the response to the invitation by the United Nations Framework Convention on Climate Change (UNFCCC) to the Intergovernmental Panel on Climate Change (IPCC) to develop good practice guidance for land use, land-use change and forestry (LULUCF).


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  • Awaworyi Churchill, Sefa, John Inekwe, Kris Ivanovski, and Russell Smyth. 2018. "The Environmental Kuznets Curve in the OECD: 1870–2014." Energy Economics 75: 389-399.

  • Bastin, Jean-Francois, Yelena Finegold, Claude Garcia, Danilo Mollicone, Marcelo Rezende, Devin Routh, Constantin M. Zohner, and Thomas W. Crowther. 2019. "The Global Tree Restoration Potential." Science  365 (6448): 76-79.

  • Belčáková, Ingrid, Małgorzata Świąder, and Małgorzata Bartyna-Zielińska. 2019. "The Green Infrastructure in Cities as A Tool for Climate Change Adaptation and Mitigation: Slovakian and Polish Experiences." Atmosphere 10 (9): 552.

  • Bernal, B., Murray, L.T. & Pearson, T.R.H. Global carbon dioxide removal rates from forest landscape restoration activities. Carbon Balance and Management 13, 22 (2018).

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  • Cernansky, Rachel. 2018. ”How to Rebuild a Forest." Nature (London) 560 (7720): 542-544.

  • Cook-Patton, Susan C., Sara M. Leavitt, David Gibbs, Nancy L. Harris, Kristine Lister, Kristina J. Anderson-Teixeira, Russell D. Briggs, Robin L. Chazdon, Thomas W. Crowther, Peter W. Ellis, Heather P. Griscom, Valentine Herrmann, Karen D. Holl, Richard A. Houghton, Cecilia Larrosa, Guy Lomax, Richard Lucas, Palle Madsen, Yadvinder Malhi, Alain Paquette, John D. Parker, Keryn Paul, Devin Routh, Stephen Roxburgh, Sassan Saatchi, Johan van den Hoogen, Wayne S. Walker, Charlotte E. Wheeler, Stephen A. Wood, Liang Xu & Bronson W. Griscom. 2020. "Mapping carbon accumulation potential from global natural forest regrowth". Nature 585, 545–550.

  • Crowther, T. W., H. B. Glick, K. R. Covey, C. Bettigole, D. S. Maynard, S. M. Thomas, J. R. Smith, et al. 2015. "Mapping Tree Density at a Global Scale." Nature (London) 525 (7568): 201-205.

  • Domke, Grant M., Sonja N. Oswalt, Brian F. Walters and Randall S. Morin. 2020. “Tree planting has the potential to increase carbon sequestration capacity of forests in the United States.” Proceedings of the National Academy of Sciences 202010840; DOI:10.1073/pnas.2010840117.

  • Endreny, Theodore A. 2018. "Strategically Growing the Urban Forest Will Improve our World." Nature Communications 9 (1): 1160-3.

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  • Griscom, Bronson W., Justin Adams, Peter W. Ellis, Richard A. Houghton, Guy Lomax, Daniela A. Miteva, William H. Schlesinger, et al. 2017. "Natural Climate Solutions." Proceedings of the National Academy of Sciences - PNAS 114 (44): 11645-11650.

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