Climate Change Transforms Ecosystems
This week I'm going to take a break from my series of shallow dives into specific climate technologies in my ClimateTech Market Map to write about climate change and global ecosystems. While much has been written about how climate change will affect the human environment (wildfires, flooding, extreme heat waves and sea level rise) there are few summaries of the consequences of climate change for the natural world. I hope this helps fill the gap.
Climate Change and Ecosystems - The TL;DR
Under the 2-4 °C of warming that we're currently tracking toward, the future natural world will look a lot different than our current one. Although there are significant uncertainties in the modeling, notable predictions from forecast models include:
The Basics of Biomes & Climate Change
In order to understand ecosystem shifts, it's important to understand some fundamentals about vegetation and climate change.
As shown above in the picture lede, vegetation types and their associated species traditionally fall into nine different categories of "biome" based on average temperature and rainfall that were defined by Robert Whitaker in his seminal 1970 text. (Latitude and seasonal patterns also matter - but I'll stick to the basics here.)
Average temperatures below zero create tundra (or ice) while temperatures above 22°C create tropical forest, savanna or hot deserts where vegetation doesn't require frost-tolerance adaptations. Between those extremes are the temperate biomes. Woody vegetation generally needs at least 20-60cm of rainfall per year depending on temperature. Below that amount, grasslands adapted to lower water conditions dominate.
Climate change is affecting both temperature and precipitation patterns. Global average surface temperatures have already increased by 0.85 ℃ between 1880 to 2012, with land temperature increasing disproportionately in northern high latitudes. Climate models project that temperatures will increase by an additional 1.2℃ by 2100 (RCP 4.5 emissions pathway), with continuing disproportionate warming in the arctic and near-arctic. As shown below, northern Canada is on track to experience an average 6℃ of temperature rise by 2100.
Precipitation is also changing, although precipitation models generally have more uncertainty than temperature because of the difficulties of modeling sea surface temperatures which have large influences on precipitation. Nevertheless, the CMIP5 model, the basis for the IPCC’s AR5 report, projects an overall increase in global precipitation because of increased temperatures, and predicts that precipitation changes will be distributed unevenly.
Key zones that are likely to be hit with big rainfall decreases include the Mediterranean, central and north-central South America, southern Africa and Australia. On the other hand, South East Asia, China, central Africa and northeastern North America are likely to experience higher precipitation (1).
While individual models within the CMIP5 ensemble can vary, predictions for a drier Mediterranean, Southern Africa, (some part of the) Amazon basin, and some share of Australia are reasonably consistent. (These predictions remained consistent in the more recent CMIP6 ensemble.)
Modeling Global Vegetation
Once temperature and precipitation forecasts are established, researchers can use a set of models called "Dynamic Global Vegetation Models" (DGVM) to predict what will happen to global vegetation zones. Here I'll summarize three of the papers that set out to simulate future global biomes: Ostberg et al. (2013), Leesman and Eickhout (2004) and Gonzalez et al., (2010).
Ostberg’s global simulations predict that about one fifth of total land surface will experience at least moderate ecosystem change if overall warming is limited to 2℃; and about half of total land surface will experience moderate ecosystem change under 3.5℃ (below)
The most affected biome is tundra: 80% of which converts to a new biome (mostly boreal forest). Warm savanna/scrubland and temperate coniferous forest also face large shifts: 40% of existing areas convert to a different biome. Other biomes experience moderate change: some boreal forest converts to temperate broadleaf forest; and some grassland desertifies.
The net effect - as can be seen above - is an intimidating mosaic of shifting ecosystems that affects India, Southern Africa, Australia and the near arctic substantially.
Leesman and Eickhout also predict changes in the northern latitudes. As shown below, they predict a shift from tundra to boreal forest in the near arctic and a shift from boreal to temperate forest in the mid northern latitudes. However, many regional differences exist between their predictions and Ostberg's. For example, Ostberg predicts large shifts for the north east of the Indian subcontinent, but Leesman predicts no changes there, but some desertification in northwest India. Their predictions also diverge for South America, Europe, and the American north east.
Leesman's major prediction for Net Ecosystem Production (somewhat equivalent to ecosystem biomass) - is that tundra loses the most while tropical woodlands gain the most. Overall, Net Ecosystem Production increases by ~20% globally (which would represent a fairly large natural emissions offset).
Our third modeler, Gonzalez, predicts biome shifts under the A1B emissions pathway, roughly equivalent to 2-3 ℃ of temperature increase. Like Ostberg and Leesman, increased forest growth is caused by increased temperature, precipitation, and CO2 fertilization. However, in Gonzalez's models, wildfire effects are also a key driver of many shifts.
Gonzalez predicts that the Andes, the Baltic coast, the boreal northern latitudes, Himalayas, Iberia, the Great Lakes, northern Brazil and southern Africa will experience biome shifts. Across biomes, Gonzalez predicts that temperate mixed forest and boreal conifer forests will lose the highest percentages of their existing areas, while tropical broadleaf forests will lose the lowest percentage of existing area. Some biome boundaries shift dramatically, with latitude changes up to 400km.
While these three modeling groups come to conflicting conclusions for many regions, the overall takeaway is that we are on track to fundamentally alter the distribution of temperate and tropical trees and grasslands across the globe. But specific regional impacts for most regions are still uncertain.
DGVM Modeling & Dispersal Speed
One of the limitations of the DVGMs summarized above is that they predict the end-state of a biome and don't consider what these lands may look like while they are in transition state. For example, if a given grid unit looks best suited for boreal forest, then it is predicted to be boreal forest, even if the nearest seed source is hundreds of kilometers away and it may take centuries for that species to reach there.
However tree dispersal speeds, particularly for non-pioneer tree species, are surprisingly slow. Under optimal conditions for temperature and competition, fast-colonizing birch (temperate) and pine (boreal) can disperse by 450 meters and 210 meters per year respectively. But most other tree families are very poor migrants, with a dispersal speed of 18 to 95 meters per year (2).
Because of these migration speed differences, pioneers are likely to do very well, but slower species may struggle. Even worse, some species may be out-competed in their old range before they have a chance to spread to their new one. This dispersal risk is exacerbated by habitat fragmentation, with many species unable to hurdle landscape discontinuities to reach newly created habitat.
As a result of these and other issues, researchers have projected that 20% to 50% of endemic plant species may go extinct, as they lose the race to disperse before their existing niches disappear (3).
Insects, Amphibians & Birds
Whether a species can survive in a biome is a result of climate fit, dispersal/colonization abilities, and biological factors like food availability, predation, parasite load etc. While some species adapt to changed climate through body changes (phenotypical plasticity) or evolutionary response, these responses are often metabolically costly and therefore reduce species fitness, or they depend on high variability in the starting genetic pool.
In fact, the dominant response by species to climate change that exceeds their tolerance envelope is migration or local extinction, NOT adaption (4). Migration response and speed varies widely across species, so long established predator/prey or symbiotic relationships can break with unexpected consequences when climate changes.
20th century climate change has already caused shifts in species ranges and traits and these shifts are expected to continue as climate changes. And we can already see the fingerprints of the moderate climate changes to date in animal populations.
Root et. al, (2003) performed a meta-analysis of 143 plant and animal studies that examined species trait changes over a period of at least ten years. The meta-analysis found that 81% of species had experienced a trait change in the direction predicted for elevated temperature. For the 64 studies that analyzed Spring events, the authors found an average shift of 5.1 days earlier per decade for the species who did experience timing shifts. The magnitude of the time shift ranged from 24 days earlier (North American common murre, nesting date) to 6.3 days later (North American Fowler’s toad, breeding date). Shifts were greater at higher latitudes.
Another meta-analysis of 20th century range shifts by Parmesan and Yohe (2003) found a pole-ward range migration of 6.1km per decade across all species studied, although the methodology excluded species with stable ranges and abundances (approximately one third of the species set), producing a worst case for climate effects.
Insects
Insects (terrestrial invertebrates) have many adaptive responses to persistently elevated temperatures, including de-melanization and body size reduction as well as migration to higher latitudes and altitudes. However, responses vary. A meta-analysis of mountain insect studies, showed that beetles (coleoptera) consistently shifted to higher altitudes in response to temperature, whereas other insects had inconsistent results. Ants, for example, were more likely to expand their range downward. Climate induced range shifting has been found in many other species including pine beetles, bottle flies, sand flies, cicadas, dragonflies, and damselflies. Insect range loss across all species except Dragonflies (odonata) is estimated to escalate sharply once climate change exceeds 2℃ (5).
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Amphibians
Amphibians are sensitive to climate change because they are both moisture and temperature sensitive, and have low dispersal speeds. An ensemble of species distribution models under 20 different climate scenarios were used to predict the effects of climate change on Western Hemisphere amphibians and found that precipitation changes in particular were likely to cause ~60% of species to lose existing range, with effects concentrated in areas of precipitation decline, such as the Andes and parts of Central America and Mexico (6). In addition, many species in southern Central America were projected to experience high rates of range restriction compared to their present range.
Birds
Birds have climate envelope ranges that have shifted during the 20th century, resulting in altered migration paths, with pole-ward shifts in temperate bird ranges and migration to higher altitude for tropical birds. Birds have the advantage that they can disperse faster than changing climate gradients, and as a result, while they will lose habitat as boundaries move, they will also be able to disperse into newly created habitat if food and resources are available. On average, global bird diversity is more threatened by tropical land-use change than climate change.
The Transformed World
While these models have many uncertainties, they do predict some specific future changes consistently. The arctic and near-arctic are likely to change radically by 2100, converting from tundra to boreal forest. Southern Africa and most of the Mediterranean littoral are going to get a lot drier and burn more frequently. On the other hand, some regions like the tropical African and Indonesian rain-forest will likely experience few impacts. For most other regions, the models aren't yet consistent enough to make predictions with high confidence.
Here, I've summarized some basics of how researchers are using temperature and precipitation models to predict future biome boundaries and species ranges. However there are other important factors that determine future ecosystems that I haven't covered such as changes to the soil microbiome, the CO2 fertilization effect, wildfires, disease and disease vectors, invasive species and even the ability of large herbivores to over-ride vegetation changes.
While the main focus of my writing here is to cover climate technologies, I may visit some of these topics in the future - particularly the CO2 fertilization effect which many people seem to mis-understand.
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Citations
(1) Herger, N., Abramowitz, G., Sherwood, S., Knutti, R., Angélil, O. & Sisson, S.A. 2019, "Ensemble optimisation, multiple constraints and overconfidence: a case study with future Australian precipitation change", Climate dynamics, vol. 53, no. 3-4, pp. 1581-1596.
(2) Snell, R.S., Huth, A., Nabel, J. E. M. S., Bocedi, G., Travis, J.M.J., Gravel, D., Bugmann, H., Gutiérrez, A.G., Hickler, T., Higgins, S.I., Reineking, B., Scherstjanoi, M., Zurbriggen, N. & Lischke, H. 2014, "Using dynamic vegetation models to simulate plant range shifts", Ecography (Copenhagen), vol. 37, no. 12, pp. 1184-1197.
(3) Thomas, C.D., Cameron, A., Green, R.E., Bakkenes, M., Beaumont, L.J., Collingham, Y.C., Erasmus, B.F.N., de Siqueira, M.F., Grainger, A., Hannah, L., Hughes, L., Huntley, B., van Jaarsveld, A.S., Midgley, G.F., Miles, L., Ortega-Huerta, M.A., Townsend Peterson, A., Phillips, O.L. & Williams, S.E. 2004, "Extinction risk from climate change", Nature, vol. 427, no. 6970, pp. 145-148.
(4) Huntley, B. 1991, "How plants respond to climate change; migration rates, individualism and the consequences for plant communities", Annals of botany, vol. 67, no. 1, pp. 15-22.
(5) Warren, R., Price, J., Graham, E., Forstenhaeusler, N. & VanDerWal, J. 2018, "The projected effect on insects, vertebrates, and plants of limiting global warming to 1.5°C rather than 2°C", Science (American Association for the Advancement of Science), vol. 360, no. 6390, pp. 791-795.
(6) Lawler, J.J., Shafer, S.L., Bancroft, B.A. & Blaustein, A.R. 2010, "Projected Climate Impacts for the Amphibians of the Western Hemisphere", Conservation biology, vol. 24, no. 1, pp. 38-50.
Bibliography
Gonzalez, P., Neilson, R.P., Lenihan, J.M. & Drapek, R.J. 2010, "Global patterns in the vulnerability of ecosystems to vegetation shifts due to climate change", Global ecology and biogeography, vol. 19, no. 6, pp. 755-768.
Harvey, J.A., Tougeron, K., Gols, R., Heinen, R., Abarca, M., Abram, P.K., Basset, Y., Berg, M., Boggs, C., Brodeur, J. and Cardoso, P., 2023. Scientists' warning on climate change and insects. Ecological monographs, 93(1), p.e1553.
Jetz, W., Wilcove, D.S. & Dobson, A.P. 2007, "Projected impacts of climate and land-use change on the global diversity of birds", PLoS biology, vol. 5, no. 6, pp. 1211-1219.
La Sorte, F.A. & Jetz, W. 2010, "Avian distributions under climate change: Towards improved projections", Journal of experimental biology, vol. 213, no. 6, pp. 862-869.
Leemans, R. & Eickhout, B. 2004, "Another reason for concern: regional and global impacts on ecosystems for different levels of climate change", Global environmental change, vol. 14, no. 3, pp. 219-228.
McCain, C.M. & Garfinkel, C.F. 2021, "Climate change and elevational range shifts in insects", Current opinion in insect science, vol. 47, pp. 111-118.
Ostberg, S., Lucht, W., Schaphoff, S. & Gerten, D. 2013, "Critical impacts of global warming on land ecosystems", Earth system dynamics, vol. 4, no. 2, pp. 347-357.
Parmesan, C. & Yohe, G. 2003, "A globally coherent fingerprint of climate change impacts across natural systems", Nature (London), vol. 421, no. 6918, pp. 37-42.
Root, T.L., Price, J.T., Hall, K.R., Schneider, S.H., Rosenzweig, C. & Pounds, J.A. 2003, "Fingerprints of global warming on wild animals and plants", Nature (London), vol. 421, no. 6918, pp. 57-60.
Salazar, A., Rousk, K., Jónsdóttir, I.S., Bellenger, J.P. and Andrésson, Ó.S., 2020. Faster nitrogen cycling and more fungal and root biomass in cold ecosystems under experimental warming: a meta‐analysis. Ecology, 101(2), p.e02938.
Sánchez-Guillén, R.A., Córdoba-Aguilar, A., Hansson, B., Ott, J. & Wellenreuther, M. 2016, "Evolutionary consequences of climate-induced range shifts in insects: Evolutionary consequences of range shifts", Biological reviews of the Cambridge Philosophical Society, vol. 91, no. 4, pp. 1050-1064.
Skelly, D.K., Joseph, L.N., Possingham, H.P., Freidenburg, L.K., Farrugia, T.J., Kinnison, M.T. & Hendry, A.P. 2007, "Evolutionary Responses to Climate Change", Conservation biology, vol. 21, no. 5, pp. 1353-1355.
Snell, R.S., Huth, A., Nabel, J. E. M. S., Bocedi, G., Travis, J.M.J., Gravel, D., Bugmann, H., Gutiérrez, A.G., Hickler, T., Higgins, S.I., Reineking, B., Scherstjanoi, M., Zurbriggen, N. & Lischke, H. 2014, "Using dynamic vegetation models to simulate plant range shifts", Ecography (Copenhagen), vol. 37, no. 12, pp. 1184-1197.
Whittaker, R.H., 1970. Communities and ecosystems.
Writer / Director / Founder -- 2024 Rockefeller Foundation Resident -- former Pixar and Apple, spinning up the RyzoSphere
1moMichael - I really adore this series. Excited to read. (I know that is a weird word to use in the face of climate issues)