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How Would SRM Affect Plants?
Plants need sunlight, water, and carbon dioxide (CO2) to photosynthesise. They also need nutrients and the right climate conditions to grow well. Climate change affects these factors, as would sunlight reflection methods (SRM), also known as solar geoengineering, though in different ways.
Key takeaways
- Rising atmospheric CO2 contributes to plant growth, but climate change impacts such as high temperatures can dampen it in some regions.
- SRM would decrease temperatures but would also reduce incoming sunlight a small amount and make the sky a little hazier.
- The potential impacts of SRM and climate change on plants are highly uncertain, regionally variable, and sensitive to other factors such as access to nutrients.
Since the 1980s, scientists have noted increased plant growth around the world – a phenomenon known as “greening” – and have attributed this growth to rising atmospheric CO2 and land-use changes.1 However, the accelerated plant growth has been slowing due to rising temperatures and related disturbances such as drought, fires, and insect outbreaks.2
SRM has the potential to decrease temperatures and related extreme events that contribute to plant mortality, but it cannot offset all aspects of climate change.3 How would plants respond to a world with higher CO2, lower temperatures, and a little less sunlight?
CO2 and plants
Plants use sunlight to convert water and CO2 from the atmosphere into food in a process called photosynthesis. Elevated CO2 due to burning fossil fuels has contributed to increased photosynthesis since 1900.4 This phenomenon is known as the CO2 fertilisation effect.
Though rising CO2 has contributed to increased plant growth, there are several limitations that affect plants differently depending on location. For example, at high latitudes, forest and plant growth are typically limited by cold temperatures. In those cold regions, forests have generally become more resilient over time, benefitting from warmer temperatures and higher atmospheric CO2.5
In the rest of the world, however, the harm caused to forests by rising temperatures often outweighs the benefits of increased CO2. In these regions, forests are becoming increasingly vulnerable to water limitations – which results from rising temperatures – and extreme weather brought on by climate change.5
Access to nutrients, such as nitrogen and phosphorus, can also limit plant growth despite higher atmospheric CO2.6 In fact, computer models estimate that low access to nutrients will limit the degree to which plant growth can increase as atmospheric CO2 levels rise.7
While high levels of CO2 in the atmosphere can stimulate plant growth, it can also greatly decrease the nutritional value of crops.6 The reason this happens is unclear, but it may be related to the way plants with access to more CO2 bring soil water, and accompanying nutrients, into their tissues.
How plants create food
Plants use energy from the sun to make themselves food by converting CO2 from the air to sugar via photosynthesis. Plants release oxygen and lose water when they take CO2 from the atmosphere.
Sunlight
Inputs
Photosynthesis requires CO2, sunlight, water, and minerals.
Water
and minerals
Cross section of a leaf
Glucose
Oxygen
CO2
Water
OUTputs
Plants produce glucose and oxygen via photosynthesis.
Source: SRM360
How plants create food
Plants use energy from the sun to make themselves food by converting CO2 from the air to sugar via photosynthesis. Plants release oxygen and lose water when they take CO2 from the atmosphere.
Inputs
Photosynthesis requires CO2, sunlight, water, and minerals.
Sunlight
Cross section of a leaf
Glucose
Water
and minerals
Oxygen
CO2
Water
OUTputs
Plants produce glucose and oxygen via photosynthesis.
Source: SRM360
How plants create food
Plants use energy from the sun to make themselves food by converting CO2 from the air to sugar via photosynthesis. Plants release oxygen and lose water when they take CO2 from the atmosphere.
Inputs
Photosynthesis requires CO2, sunlight, water, and minerals.
OUTputs
Plants produce glucose and oxygen via photosynthesis.
Sunlight
Glucose
Cross section of a leaf
Oxygen
Water and minerals
CO2
Water
Source: SRM360
SRM impacts are relevant for plants
SRM strategies aim to slow rising temperatures by reflecting sunlight. In addition to counteracting global warming, SRM would have impacts on rainfall patterns around the world. These impacts are some of the least certain physical consequences of SRM.8
Studies suggest that reflecting about 1% of incoming sunlight could lower temperatures globally by about 1°C.9 By lowering temperatures, which decreases plant respiration – the amount of energy plants spend maintaining themselves – SRM could increase plant growth through much of the world.10 At high latitudes, however, cooler temperatures would likely decrease plant growth, including crops.10
Significantly for plants, SRM strategies such as stratospheric aerosol injection (SAI) would increase the amount of diffuse (scattered) light that reaches the surface while decreasing direct sunlight.11
Although more light in general benefits plant growth, diffuse light is better than direct light. Diffuse light can reach deeper into canopies and be absorbed by shaded leaves rather than those that are over-saturated.12 The increase in diffuse light largely makes up for the decreased light overall, overcompensating in some cases.13
Following the eruption of Mt. Pinatubo in 1991 – a natural example of the reflective power of stratospheric aerosols – photosynthesis increased, largely due to the increase in diffuse light.14
Plant growth response to SRM is highly uncertain and would vary by region
Researchers have begun to use computer simulations to study the impacts of different SRM ideas on plants but there is still more work to do.15
Results depend on how the SRM study is designed: for example, whether the sunlight is dimmed uniformly – similar to space-based SRM – or if there is a higher proportion of diffuse sunlight after some sunlight is reflected – similar to SAI.16 Another consideration is plant access to nutrients such as nitrogen.10
Regardless of study design, there are some consistent results across studies. SRM would counteract warming, which would likely decrease the problems caused by high temperatures in most of the world – especially those related to water limitations.17 Conversely, cold regions where rising temperatures have increased forest resilience and crop yields would likely see reduced plant growth under SRM than under climate change alone.10
Open questions
- How would climate change and SRM affect natural carbon sinks and “nature-based” carbon dioxide removal?
- Vegetation and the water cycle are closely linked – how would they be impacted by climate change and SRM?
- Which regions could expect greater plant productivity, and which could expect less in a future with and without SRM?
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Endnotes
- Chen X, Chen T, He B, et al. (2024). The global greening continues despite increased drought stress since 2000. Global Ecology and Conservation, 49. https://doi.org/10.1016/j.gecco.2023.e02791
- Liu Q, Peng C, Schneider R, et al. (2023). Vegetation browning: Global drivers, impacts, and feedbacks. Trends in Plant Science, 28(9), 1014–1032. https://doi.org/10.1016/j.tplants.2023.03.024
- Tye MR, Dagon K, Molina MJ, et al. (2022). Indices of extremes: geographic patterns of change in extremes and associated vegetation impacts under climate intervention. Earth System Dynamics, 13(3), 1233–1257. https://doi.org/10.5194/esd-13-1233-2022
- Haverd V, Smith B, Canadell JG, et al. (2020). Higher than expected CO2 fertilization inferred from leaf to global observations. Global Change Biology, 26(4), 2390–2402. https://doi.org/10.1111/gcb.14950
- Forzieri G, Dakos V, McDowell NG, et al. (2022). Emerging signals of declining forest resilience under climate change. Nature, 608(7923), 534–539. https://doi.org/10.1038/s41586-022-04959-9
- Dong J, Gruda N, Lam SK, et al. (2018). Effects of elevated CO2 on nutritional quality of vegetables: A review. Frontiers in Plant Science. Frontiers Media S.A. https://doi.org/10.3389/fpls.2018.00924
- Terrer C, Jackson RB, Prentice IC, et al. (2019). Nitrogen and phosphorus constrain the CO2 fertilization of global plant biomass. Nature Climate Change. Nature Publishing Group. https://doi.org/10.1038/s41558-019-0545-2
- Ricke K, Wan JS, Saenger M, et al. (2023). Hydrological Consequences of Solar Geoengineering. Rev. Earth Planet. Sci. 2023, 51, 447–70. https://doi.org/10.1146/annurev-earth-031920-083456
- Visioni D, Macmartin DG, Kravitz B, et al. (2021). Identifying the sources of uncertainty in climate model simulations of solar radiation modification with the G6sulfur and G6solar Geoengineering Model Intercomparison Project (GeoMIP) simulations. Atmospheric Chemistry and Physics, 21(13), 10039–10063. https://doi.org/10.5194/acp-21-10039-2021
- Cao L. (2018). The Effects of Solar Radiation Management on the Carbon Cycle. Current Climate Change Reports, 4(1), 41–50. https://doi.org/10.1007/s40641-018-0088-z
- Xia L, Robock A, Tilmes S, et al. (2016). Stratospheric sulfate geoengineering could enhance the terrestrial photosynthesis rate. Atmospheric Chemistry and Physics, 16(3), 1479–1489. https://doi.org/10.5194/acp-16-1479-2016
- Gu L, Baldocchi D, Verma SB, et al. (2002). Advantages of diffuse radiation for terrestrial ecosystem productivity. Journal of Geophysical Research Atmospheres, 107(5–6). https://doi.org/10.1029/2001jd001242
- Fan Y, Tjiputra J, Muri H, et al. (2021). Solar geoengineering can alleviate climate change pressures on crop yields. Nature Food, 2(5), 373–381. https://doi.org/10.1038/s43016-021-00278-w
- Gu L, Baldocchi DD, Wofsy, SC, et al. (2003). Response of a Deciduous Forest to the Mount Pinatubo Eruption: Enhanced Photosynthesis. Science, 299. Retrieved from https://doi.org/10.1126/science.1078366
- Zarnetske PL, Gurevitch J, Franklin J, et al. (2021). Potential ecological impacts of climate intervention by reflecting sunlight to cool Earth. Proceedings of the National Academies of Sciences, 118. https://doi.org/10.1073/pnas.1921854118
- Lee H, Muri H, Ekici A, et al. (2021). The response of terrestrial ecosystem carbon cycling under different aerosol-based radiation management geoengineering. Earth System Dynamics, 12(1), 313–326. https://doi.org/10.5194/esd-12-313-2021
- Dagon K, Schrag DP. (2019). Quantifying the effects of solar geoengineering on vegetation. Climatic Change, 153(1–2), 235–251. https://doi.org/10.1007/s10584-019-02387-9
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