April 2024 Science Summary

Hello,

Just three articles this month: how wetland restoration affects climate mitigation, how climate change is affecting seasonality of river flow, and a summary of how people use plants around the world.

If you know someone who wants to sign up to receive these summaries, they can do so at http://bit.ly/sciencejon (no need to email me).

CLIMATE CHANGE:
Schuster et al. 2024 reviews the net climate impact of wetland restoration, considering carbon, methane, and nitrous oxide. Their headline is that it takes 525 years for restoring peat to result in net climate cooling (b/c short-term methane increases offset the carbon gains), and 141 years for non-peat wetlands (marshes, riparian wetlands, and swamps). They argue other more positive estimates have left out nitrous oxide. BUT they are looking just at the restoration over time NOT comparing restored wetlands to the baseline of degraded wetlands (since drained peat also emits methane and lots of CO2, the time would be a lot shorter to be net climate cooling. Some other papers I've read (e.g., Richardson et. al 2022 on pocosin) found minimal methane emissions making restoration a clear winner even in the short term. I asked a couple experts about this paper and they also flagged that while in the short term we should be worried about methane, it's also true that: the alkalinity export from peat could make them MORE cooling than we think, and that there are other ecosystem services to consider.

FRESHWATER:
Wang et al. 2024 looks at how climate change has changed the seasonality of river flow (how much it varies month to month, including frequency of droughts and floods). They found that ~14% of long-term river gauges show changes in seasonality over the last 50 years that isn't driven by changing annual precipitation. The surprise is that seasonality is mostly DECREASING counter to the narrative of more floods and droughts (see Fig 1 for a map of results, and Fig 2 which adds detail). In their figures brown means less seasonality (more even flow): "L+" means low flows become higher flows (NOT higher frequency of drought) while "H-" means floods see lower flood volume (again NOT lower frequency of flood events). You'll see most of North America, most of Europe, and some of Russia have seen reduced seasonality in recent decades. Blue means MORE seasonality, focused in: SE Brazil, some European countries, and in the US the SE and some of the Rocky Mountains. The explanation is worth reading in full, but in brief: 1) snow melting earlier means less runoff from snow at the same time as spring rains, 2) early spring greening means more water gets transpired, 3) it's more complicated in places not dominated by snowmelt.

PEOPLE AND NATURE:
Pironon et al. 2024 is a global analyis of plants used by humans (directly or indirectly - medicinal uses dominate but they look at nine other types of use, see Fig 2). See Fig 1a for a map of how many plant species are used around the world. They find 1) people use more plant species in places where most plant species exist, 2) Indigenous lands use slightly fewer species than neighboring non-Indigenous regions, and 3) protected lands use slightly fewer species than non-protected lands. These are correlations - they don't control for income or many other covariates. And from a conservation perspective we may not want all species to be used, especially rare ones!Note there are some problems with the data, e.g., Figure S1 shows how poor the sampling density is outside of the US, Central America, Europe, and Australia. Finally, they only found 971 species of plants that provide food to bugs we use (honeybees, silkworms, lac insects, and grubs) which seems really low. There's an article about this at: https://www.unep-wcmc.org/en/news/plants-and-their-contributions-to-people-are-insufficiently-protected-globally

REFERENCES:
Pironon, S., Ondo, I., Diazgranados, M., Allkin, R., Baquero, A. C., Cámara-Leret, R., Canteiro, C., Dennehy-Carr, Z., Govaerts, R., Hargreaves, S., Hudson, A. J., Lemmens, R., Milliken, W., Nesbitt, M., Patmore, K., Schmelzer, G., Turner, R. M., van Andel, T. R., Ulian, T., … Willis, K. J. (2024). The global distribution of plants used by humans. Science, 383(6680), 293–297. https://doi.org/10.1126/science.adg8028

Schuster, L., Taillardat, P., Macreadie, P. I., & Malerba, M. E. (2024). Freshwater wetland restoration and conservation are long-term natural climate solutions. Science of The Total Environment, 922(August 2023), 171218. https://doi.org/10.1016/j.scitotenv.2024.171218

Wang, H., Liu, J., Klaar, M., Chen, A., Gudmundsson, L., & Holden, J. (2024). Anthropogenic climate change has influenced global river flow seasonality. Science, 383(6686), 1009–1014. https://doi.org/10.1126/science.adi9501

Sincerely,
 
Jon
 
p.s. This photo is of a sculpture at the Kennedy Center by ByeongDoo Moon called "I have been dreaming to be a tree"

November 2022 science summary

Greetings,

Happy belated Halloween!

This month I have four articles on different facets of climate change (drought, ecological adaptation, and mitigation through peatlands), plus one big new global paper on the environmental impact of food.

If you know someone who wants to sign up to receive these summaries, they can do so at http://bit.ly/sciencejon

FOOD / AGRICULTURE:
Halpern et al. 2022 is the latest paper to try and compare the global environmental footprint of almost all foods (both aquatic and terrestrial), using greenhouse gases (GHGs but excluding land use change), "blue" water consumption (from irrigation), nutrient pollution (N&P, excluding crop N fixing), and land use. Note that blue water consumption excludes rainfall, and focuses on evaporation & transpiration as opposed to "water use" (the amount pumped out) much of which returns to surface and ground water. This lets us compare the impact of different foods, look at which foods have the most total impact (and thus offer the most opportunity to improve via changes in practice or biology), and see which countries have the most environmental impact from food (India, China, the U.S., Brazil, and Pakistan - see Figs 2, 3, and especially 4). Spend some time with Fig 4, it's dense and interesting. For example, you can see that India has slightly more total impact than China, but produces substantially less food by all 3 metrics (calories, protein, and mass). Most of the data here are similar to what we've seen before, but still interesting (e.g., U.S. soy is 2.4 times more efficient than Indian soy). Reporting "cumulative" impacts can be confusing - wheat and rice have similar total impact in Fig 5, but Fig 6 shows that rice is far more inefficient per tons of protein produced). Fig 5 and 6 would be useful in looking at which crops and livestock species to focus on improved genetics or practices to have the most impact. But if you want to know "what should I eat" this paper makes it really hard to find that (Fig 6 is closest, or look at Supplementary Data 3 for country-specific "total environmental pressure" data using the food key from Table S6). So for example they find goats have a higher impact than cows, and in the US soy is the most environmentally efficient source of protein while sugar beets are the most environmentally efficient source of calories.


CLIMATE CHANGE & DROUGHT:
Cook et al. 2015 estimates the likelihood of summer droughts (June through August) in the American Central Plains and Southwest between 2050 and 2100. Their findings are striking, even under the RCP 4.5 climate scenario (which they put in the supplement, focusing instead on the much less likely RCP 8.5 scenario). They predict the following chances of a decadal (11 year) or multidecadal (35 year) drought: decadal ~94% Central Plains and ~97% Southwest, multidecadal ~73%  Central Plains and ~80% for Southwest (see Fig S13 on the past page of the supplement). That's pretty scary, and they further note this is drier than even the historically dry period from the years 1100-1300. However, this is a lot more pessimistic than the IPCC (as the authors acknowledge), and I'm not qualified to go deep enough in the methods to weigh in as to how likely this is. But as we have already seen out West, droughts lasting multiple years have very different implications both for communities and agriculture. Tree crops will be increasingly untenable as the risk of multi-year droughts increase, and farmers may have to switch to very different crops to make it through these dry periods.


CLIMATE ADAPTATION (ECOLOGICAL):
Moore and Schindler 2022 is an opinion piece arguing that more diverse strategies are needed to help prepare ecosystems for climate change. They argue that conservation needs to adapt to shifting ecosystems and unpredictable futures by maintaining complexity, especially by promoting enhanced gene flow and facilitating the ability of habitat to shift to new places as climate changes. Given uncertainty in climate changes and ecosystem response, they argue that refugia may not be as robust as promoting climate corridors and habitat heterogeneity. Local conservation work to address current stresses and future threats is another important aspect of improving resilience: by working on known threats we can make ecosystems more able to withstand the unknown. Finally, as ecosystems and populations shift, resource management needs to adapt to these new realities rather than sticking to long-term plans.


PEATLANDS - CLIMATE MITIGATION:
Richardson et al. 2022 estimates the potential climate mitigation benefits of rewetting drained peatlands (specifically pocosin - a bog found in the SE US dominated by trees and/or shrubs). They measured water table depth, soil characteristics, dissolved organic carbon, and emissions of CO2 & methand & nitrous oxide at 5 sites (3 drained, 1 restored, 1 natural). The drained peatlands emitted a net of 21.2 t CO2e / ha (Table 2). They conducted additional detailed measurements on the drained peatlands, and combined the data into a model to predict how water table would impact emissions. Methane and nitrous oxide were excluded since CO2 was responsible for 98% of CO2e (Fig 3). Validation found the model to be conservative and w/in 18% of measurements out of the training sample. The pocosin always emit more carbon than they absorb in fall and winter, but re-wetting peat resulted in them being a net sink in spring and summer. Rewetting from a water table 60 cm deep tp 30 cm deep cut annual net emissions by 91% (abstract says 94% but see Table 2 for the correct numbers). Rewetting from to 20 cm deep switched the pocosoins from a carbon source to a sink, sequestering 3.3 t CO2e / ha / yr. Re-wetting also reduces the risk of peat fires which would increase emissions much more. Finally, Table 3 has their estimate of how much restorable peatlands (drained peatlands currently used for agriculture or forest plantations) could be re-wetted. Note that Evans et al. 2021 earlier found that raising the water table to these levels are likely to reduce crop yields (or require a switch to different crops and cultivars), but that raising the water level to the bottom of the root zone is a clear win-win.

Goldstein et al. 2020 looks at peat fires in Indonesia and what causes them, especially the sub-surface fires which cause the most air pollution and can burn for a long time. Their answer: it's complicated. They essentially find three requirements for sub-surface fires: 1) drainage lowers the water table and dries out the peat, 2) fire is ignited (for one of many reasons), and 3) enough fuel is present (like tree logs) that the fire burns long enough to reach deeper layers (dry weather also has a big influence). Much of the widespread use of fire does NOT result in these deep fires, b/c either the site isn't dry enough or it burns often enough there is insufficient fuel on the surface. The authors try hard not to blame anyone for these fires, but do argue that major drainage projects are likely a dominant factor.


REFERENCES:

Cook, B. I., Ault, T. R., & Smerdon, J. E. (2015). Unprecedented 21st century drought risk in the American Southwest and Central Plains. Science Advances, 1(1), 1–8. https://doi.org/10.1126/sciadv.1400082

Goldstein, J. E., Graham, L., Ansori, S., Vetrita, Y., Thomas, A., Applegate, G., Vayda, A. P., Saharjo, B. H., & Cochrane, M. A. (2020). Beyond slash‐and‐burn: The roles of human activities, altered hydrology and fuels in peat fires in Central Kalimantan, Indonesia. Singapore Journal of Tropical Geography, 41(2), 190–208. https://doi.org/10.1111/sjtg.12319

Halpern, B. S., Frazier, M., Verstaen, J., Rayner, P., Clawson, G., Blanchard, J. L., Cottrell, R. S., Froehlich, H. E., Gephart, J. A., Jacobsen, N. S., Kuempel, C. D., McIntyre, P. B., Metian, M., Moran, D., Nash, K. L., Többen, J., & Williams, D. R. (2022). The environmental footprint of global food production. Nature Sustainability. https://doi.org/10.1038/s41893-022-00965-x

Moore, J. W., & Schindler, D. E. (2022). Getting ahead of climate change for ecological adaptation and resilience. Science, 376(6600), 1421–1426. https://doi.org/10.1126/science.abo3608

Richardson, C. J., Flanagan, N. E., Wang, H., & Ho, M. (2022). Annual carbon sequestration and loss rates under altered hydrology and fire regimes in southeastern USA pocosin peatlands. Global Change Biology, July, 1–15. https://doi.org/10.1111/gcb.16366


Sincerely,
 
Jon
 
p.s. the photo was my attempt to make a Jack o 'lantern w/ bloodshot eyes

June 2021 science summary

 

Hi,

Hope cicadas or other issues aren't keeping you from getting back into the world as people get vaccinated and cases are going down (in most places at least). The cicada above is super fun and ready to play!

This month I am focusing on climate change and biodiversity articles.

If you know someone who wants to sign up to receive these summaries, they can do so at http://bit.ly/sciencejon

BIODIVERSITY:

Ellis et al. 2021 argue that protecting untouched or unmodified habitat from people is a fundamentally flawed framing, b/c most habitat on earth has been to some degree inhabitated by (and modified by) people for thousands of years). It's a good point that what we consider 'natural' is subjective and arbitrary (e.g. the grasslands of the Midwestern U.S. are a result of thousands of years of intentionally set fires and other impacts by indigenous people), and modified ecosystems may have higher species richness or other metrics. They have great data on how much habitats and land use have changed over time (check out all the figures for that), and make an excellent case about how wrong it is to depict human use of nature as a recent despoiling of human-free places. They further argue that current biodiversity losses come from "the appropriation, colonization, and intensifying use of the biodiverse cultural landscapes long shaped and sustained by prior societies" and that the solution lies in empowering the stewardship of indigenous people and local communities. I agree that opinions about which kind of ecosystem and land use is "good" are subjective, that there are good social and human rights reasons to support local autonomy, and that typically local and indigenous people use natural areas in a way more compatible with biodiversity than how people from elsewhere tend to. I think it's also worth recognizing that even indigenous people have consistently caused some extinctions (of large mammals in particular) when they first arrived to actually uninhabitated ecosystems, and that in some cases they currently support the same kind of intensification associated with colonialism. So local autonomy will not always be a recipe for maintaining ecosystems more or less as they currently are, although there are plenty of valid opinions about which human and ecosystem outcomes conservation organizations should work to support. I'd definitely recommend reading the paper, and I realize I have a lot of listening and learning to do on the subject of indigenous-led conservation.

Blankenship et al. 2021 is a good overview of the best available data for historical vegetation / land cover in the U.S. (which comes from LANDFIRE's Biophysical Setting [BpS] model), and how it was produced. It estimates habitat prior to European settlement of the Americas (but not prior to the arrival of Native Americans so not free of human influence). A LOT of data and expertise went into this, including expected natural succession of diferent ecosystems after disturbance, estimated fire frequency and severity, and more. I've used it to identify which areas are appropriate to reforest and which weren't forested to begin with (so shouldn't be a target of restoration in most cases). One bonus aspect of these data is that the team who manages them are incredibly helpful and willing to provide advice and guidance on how to apply them. There is a lot of helpful detail, caveats, and next steps in here for people who may want to use these data.

CLIMATE CHANGE:

Evans et al. 2021 estimated how to reduce greenhouse gases (GHGs) by raising water levels in peatlands which have been drained for agriculture. They found raising the water table by 10cm (re-wetting the peat) reduces net greenhouse gases (GHGs) by an average of 3 t CO2e/yr until it rises to a depth 30cm, from 30cm-8cm rising methane results in smaller net GHG benefits, and <8cm GHGs become net positive (see Fig 1). Cutting the water table depth in half globally (raising it to an average of 45cm in croplands and 25cm in grasslands) would cut emissions from drained peat by about 2/3 (from 786 Mt [aka MMT] CO2e/yr to 278 MT CO2e/yr). These are conservative estimates (leaving out N2O and reduced emissions from avoided deep fires), although the range of those estimates is huge (see Table 1). Alternatively re-wetting all peat up to 10cm would eliminate almost all peat emissions and likely even drive them slightly negative (15 Mt CO2e/yr). However, cutting water table depth in half would flood part of the root zone for most crops and regions, which would reduce yield. But raising the water table to just below the root zone could have big GHG benefits and potentially even improve crop resilience to drought. This is a big opportunity!

Lenzen et al. 2018 estimate the global carbon footprint of tourism in 2013, and is a fascinating read but looks to me like it has some big errors. They find tourism is 8% of global emissions (much higher than other estimates, b/c they look at full supply chain emissions, which means this 8% cuts across several sectors). They helpfully summarize the results both by the countries where tourists reside, and the countries they visit (see Fig 1 and take a moment to read what it all means as it's fascinating). But some of their findings don't make sense to me. For example, they report that from 2009-2013 tourism spending went up by 88% while emissions only rose 15% (which seems very odd, and Fig SI2 on p21 of the supplement looks like spending only went up ~28%). Also, Fig 1 reports Canada as the top "net origin" by emissions but in Table 1 it seems like a huge net destination (with US travel to Canada by far the biggest flow globally). If anyone knows the paper and can point out if I'm missing something I'd appreciate it, otherwise this looks entertaining but unreliable.

Lipsett-Moore et al. 2018 finds that improved fire management in savannas could reduce a lot of greenhouse gas (GHG) emissions, especially in Africa (which has 77% of global potential, compared to 15% in South America and 8% in Austraila & PNG). The basic idea was piloted in Australia, and involves intentional burning in the early dry season to reduce fire (intensity, frequency, and scale) later on. The pilot roughly tripled the area burned early, while cutting the area burned late by 2/3, resulting in ~1/3 less GHG emissions over 7 years. This analysis uses remote sensing to estimate fire emissions and opportunities to reduce them. In South America the total emissions potential is much lower than Africa, but the relative change is larger (75% reduction). These changes count under Kyoto so can be used for carbon credits.

Milly and Dunne 2020 predict a roughly 9% decrease in flow in the Colorado River for every degree C increase in local temperature, due to evaporation increasing more than precipitation. Much of the paper is about different aspects of the model and how they corrected for some issues, but the core point that areas expecting more rain may still see rivers dry out was notable (especially in areas where snow cover is expected to decrease).

REFERENCES:

Blankenship, K., Swaty, R., Hall, K. R., Hagen, S., Pohl, K., Shlisky Hunt, A., Patton, J., Frid, L., & Smith, J. (2021). Vegetation dynamics models: a comprehensive set for natural resource assessment and planning in the United States. Ecosphere, 12(4). https://doi.org/10.1002/ecs2.3484

Ellis, E. C., Gauthier, N., Klein Goldewijk, K., Bliege Bird, R., Boivin, N., Díaz, S., Fuller, D. Q., Gill, J. L., Kaplan, J. O., Kingston, N., Locke, H., McMichael, C. N. H., Ranco, D., Rick, T. C., Shaw, M. R., Stephens, L., Svenning, J.-C., & Watson, J. E. M. (2021). People have shaped most of terrestrial nature for at least 12,000 years. Proceedings of the National Academy of Sciences, 118(17), e2023483118. https://doi.org/10.1073/pnas.2023483118

Evans, C. D., Peacock, M., Baird, A. J., Artz, R. R. E., Burden, A., Callaghan, N., Chapman, P. J., Cooper, H. M., Coyle, M., Craig, E., Cumming, A., Dixon, S., Gauci, V., Grayson, R. P., Helfter, C., Heppell, C. M., Holden, J., Jones, D. L., Kaduk, J., … Morrison, R. (2021). Overriding water table control on managed peatland greenhouse gas emissions. Nature. https://doi.org/10.1038/s41586-021-03523-1

Lenzen, M., Sun, Y.-Y., Faturay, F., Ting, Y.-P., Geschke, A., & Malik, A. (2018). The carbon footprint of global tourism. Nature Climate Change, 8(6), 522–528. https://doi.org/10.1038/s41558-018-0141-x

Lipsett-Moore, G. J., Wolff, N. H., & Game, E. T. (2018). Emissions mitigation opportunities for savanna countries from early dry season fire management. Nature Communications, 9(1), 2247. https://doi.org/10.1038/s41467-018-04687-7

Milly, P. C. D., & Dunne, K. A. (2020). Colorado River flow dwindles as warming-driven loss of reflective snow energizes evaporation. Science, 367(6483), 1252–1255. https://doi.org/10.1126/science.aay9187

Sincerely,

 

Jon