November 2024 science summary

Howdy,

I've got summaries of articles on carbon credits, wetlands and climate mitigation, and the Pantanal (drought, fire, and habitat loss).

But first - two quick notes on the use of artificial intelligence (AI):

1. When I mention AI tools I should say this every time: a) assume that any information you put into an AI may be shared in ways you don't want, so never put in sensitive / non-public information. b) that also means be wary of putting in copyrighted materials! Some publishers like Elsevier and New York Times have a blanket ban on using their publications in AI tools, and others allow some uses but not others!
2. I'm continuing to find Elicit a really helpful tool to find and summarize or extract info from science papers. If you have questions or want to chat about it let me know. If you register for a free account I can send you links to my custom notebooks to show how some cool features work.

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).

CARBON CREDITS
Trencher et al, 2024 is an analysis of the quality of credits on the voluntary carbon market. They focus on the 20 companies retiring the most credits between 2020-2023 (134 million metric tons CO2e), which is 20% of all global retirements on the three registries (see Fig 1 for company list). They found 87% of credits have a high risk of not providing real additional reductions (6% were low risk, most of the rest was medium), and 97% of credits focused on avoiding emissions rather than removal. Note that they classified all REDD+ (reducing deforestation and/or degradation) as high risk given that they have often 1) overestimated additionality, 2) not stopped deforestation, and/or 3) displaced deforestation elsewhere (aka 'leakage'). They also classify large-scale renewable energy as high-risk, since the price of credits is not typically the decisive factor in those projects (they are often built w/ or w/o credits) and they are often build in countries w strong government support for renewable energy. They also found that companies strongly prefer the cheapest credits (which creates demand for lower-quality offsets) often from older projects, although some companies have paid a lot more for REDD projects. The authors call for more regulation of the voluntary market, and for companies not using voluntary credits to support claims of offsetting emissions.

Blanchard et al. 2024 is a short opinion piece arguing that to fund nature conservation, we should pivot from an "offset" model (where companies buy credits to support assertions of lower net emissions and/or being carbon neutral) to a "contributions" model (where the financial contributions are recognized, but not taken as equivalent to reducing gross emissions). The authors say that 1) all entities should prioritize their own direct emissions reduction before seeking to pay others to do that, 2) we need to use the best science to pick what investments are most likely to lead to durable climate mitigation (considering reversibility, other GHGs, albedo, etc.), and 3) independent scientists should audit any quantitative claims made about the benefits of contributions to climate mitigation.


WETLANDS AND CLIMATE CHANGE MITIGATION
Arias-Ortiz et al. 2024 estimate how much methane different kinds of marshes in the U.S. emit each year. They found that warm freshwater marshes (>25.6C mean annual high temperature) produce the most methane by far (172 g CH4/m2/yr = 48.2 t CO2e / yr), followed by other freshwater marshes at low or medium elevation (producing ~1/3 that on average). Across all marshes the average is much lower (26 g CH4/m2/yr = 7.3 t CO2e / yr), and saltier marshes emit less methane. They report mangroves emit roughly twice as much methane flux as marshes, but seagrasses only emit 10% as much as marshes. Predicted methane was really close to measured methane (at least once they calibrated their estimates)


PANTANAL:
Marengo et al. 2021 is a review of the severe drought in the Pantanal in 2019 and 2020. The key direct cause was less warm humid air coming from Amazonia leading to much less rain across the Paraguay river basin, which in turn led to very low water levels in rivers and other wetlands, which reduced shipping goods by river (and economic losses) and enabled widespread fires. Previous studies looking at Pantanal rainfall trends have found only a small overall decrease but with a lot more variation each year. There are more days with no rain, the dry season has gotten drier, the Ládario river has been dropping ~3 cm / yr for 30 years, but the flooding in 2018 was unusually extensive. Part of the issue may be that the Pantanal has been relatively wet since roughly 1970, making a return to severe droughts that have not been seen for decades feel more unusual (see Fig 3). El Niño does not seem to be a driver of drought, nor do various climatic indices correlate well w/ drought years. But in 2019-2020 a strong South Atlantic Convergence Zone caused a shift in dominant winds to the Pantanal coming from drier and colder higher-latitude air.

Guerra et al. 2020 looked at the drivers of predicted habitat conversion in the Upper Paraguay River Basin (including the Pantanal, some of the Cerrado, and a bit of the Amazon) between 2008-2016 (broken into four 2-year periods). Key drivers in the Pantanal were unprotected status and existing land cover, with much weaker impact from elevation (higher means more loss), and in half the time periods there was also an influence of distance to roads (closer means more loss) and cattle (presence leading to more loss). Oddly there was LESS conversion near annual cropland which is very unusual except in dense fully converted ag landscapes. They only saw more habitat loss on land with good ag potential near rivers in the Pantanal from 2010-2012, which could be related to cropland moving closer to water due to the 2012 drought. Note that this model assumes deforestation expands from where it has already happened, rather than modeling other factors (economic, population modeling, commodity prices, planned roads, etc.) to look for what might change in the future.

Martins et al. 2024 recommend priority areas for fire prevention and/or restoration in the Upper Paraguay River Basin, based on the number of fire-sensitive species present (along w/ factors like fire frequency and intensity, dry biomass, and time since the last burn). The relatively few top priority areas for fire management are in red on Fig 2, and occur in a triangle roughly between Paiaguás, Aquidauana, and Bodoquena. There are many more areas flagged as a priority for restoration, but their top focus is 1,206 km2 of forest high in both resilience and sensitive species. But they also note ~6,000 km2 of potential restoration priorities that hadn't been burnt until recently (2019-2022, Fig 5). The supplement also maps the most important places for fire prevention (Supplementary Fig 15).


REFERENCES:

Arias-Ortiz, A., Wolfe, J., Bridgham, S. D., Knox, S., McNicol, G., Needelman, B. A., Shahan, J., Stuart-Haëntjens, E. J., Windham-Myers, L., Oikawa, P. Y., Baldocchi, D. D., Caplan, J. S., Capooci, M., Czapla, K. M., Derby, R. K., Diefenderfer, H. L., Forbrich, I., Groseclose, G., Keller, J. K., … Holmquist, J. R. (2024). Methane fluxes in tidal marshes of the conterminous United States. Global Change Biology, 30(9). https://doi.org/10.1111/gcb.17462

Blanchard, L., Haya, B. K., Anderson, C., Badgley, G., Cullenward, D., Gao, P., Goulden, M. L., Holm, J. A., Novick, K. A., Trugman, A. T., Wang, J. A., Williams, C. A., Wu, C., Yang, L., & Anderegg, W. R. L. (2024). Funding forests’ climate potential without carbon offsets. One Earth, 7(7), 1147–1150. https://doi.org/10.1016/j.oneear.2024.06.006

Guerra, A., Roque, F. de O., Garcia, L. C., Ochao-Quintero, J. M. O., Oliveira, P. T. S. de, Guariento, R. D., & Rosa, I. M. D. (2020). Drivers and projections of vegetation loss in the Pantanal and surrounding ecosystems. Land Use Policy, 91(April 2020). https://doi.org/10.1016/j.landusepol.2019.104388

Martins, P. I., Belém, L. B. C., Peluso, L. M., Szabo, J. K., Trindade, W. C. F., Pott, A., Junior, G. A. D., Jimenez, D., Marques, R., Peterson, A. T., Libonati, R., & Garcia, L. C. (2024). Fire-sensitive and threatened plants in the Upper Paraguay River Basin, Brazil: Identifying priority areas for Integrated Fire Management and ecological restoration. Ecological Engineering, 209(1), 107411. https://doi.org/10.1016/j.ecoleng.2024.107411

Marengo, J. A., Cunha, A. P., Cuartas, L. A., Deusdará Leal, K. R., Broedel, E., Seluchi, M. E., Michelin, C. M., De Praga Baião, C. F., Chuchón Angulo, E., Almeida, E. K., Kazmierczak, M. L., Mateus, N. P. A., Silva, R. C., & Bender, F. (2021). Extreme Drought in the Brazilian Pantanal in 2019–2020: Characterization, Causes, and Impacts. Frontiers in Water, 3(February). https://doi.org/10.3389/frwa.2021.639204

Trencher, G., Nick, S., Carlson, J., & Johnson, M. (2024). Demand for low-quality offsets by major companies undermines climate integrity of the voluntary carbon market. Nature Communications, 15(1), 6863. https://doi.org/10.1038/s41467-024-51151-w

Sincerely,
 
Jon
 
p.s. these are jack o' lantern vegan quesadillas from our Halloween party

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

Soil carbon - what is it good for?

A while back I was on a soil carbon working group with the Science for Nature and People Partnership (SNAPP). Our recent journal article is about soil carbon and soil health. It’s a good read, and only 1,800 words: https://www.nature.com/articles/s41893-019-0431-y or https://rdcu.be/bWGfa if you don't have access.



The lead author did a phenomenal job getting the text to be clear and succinct, and the opening two lines actually sum it up very well:
"Soil-based initiatives to mitigate climate change and restore soil fertility both rely on rebuilding soil organic carbon. Controversy about the role soils might play in climate change mitigation is, consequently, undermining actions to restore soils for improved agricultural and environmental outcomes."

In other words: scientists disagree about how effective soil carbon is as a climate change mitigation strategy. We disagree a lot - more than you'd expect. Everything from "this is our best bet to start scaling up now" to "building soil carbon will not result in any net climate mitigation." So we argue about it a lot.

But that debate hides the fact that we generally strongly agree that rebuilding soil carbon is good for farmers and ranchers. Most agricultural soils have lost carbon over time. Regaining it can mean less erosion, better water retention, and better crop resilience to stress. With good management it can even mean less fertilizer use and cleaner water. How much carbon is ideal in different landscapes, and how to best increase it, varies. But it's worth remembering how strong the consensus is on the value of building soil carbon from an agricultural perspective.

Read the paper here: Soil carbon science for policy and practice
There's also a press release here: Building A ‘Solution Space’ for Soil