Every Breath is Shorter: Fossil Fuel Emissions and the Gut-Brain Nexus

According to a recent article by EuroNews, parts of Croatia, Poland, and Italy ranked among the top 10 cities for the worst air quality in the European Union (Frost, 2024). Earlier this year, the European metropolis Milan even consistently ranked among the top 5 cities for the worst air pollution in the world, next to Dhaka (Bangladesh), Lahore (Pakistan), and Chengdu (China) (Giuffrida, 2024). The common link between air pollution in Croatia, Poland, and Italy is fossil fuel-based energy production (i.e. coal), manufacturing industries (i.e. plastics), and fossil fuel consumption such as from vehicles (IQAir, 2024a, b, c). While the World Health Organization finds that fine particulate matter directly causes health issues such as asthma, stroke, and heart disease, recent research reveals deeper more concerning impacts on the gut-brain nexus (European Environmental Agency, 2024). Exposure to poor air quality and environmental pollutants can alter the gut microbiome through gut bacteria imbalances, affecting neurological and mental health, our diets, causing mental health and mood disorders, metabolism changes, shifts in aging processes, and immune system dysfunctions (Singh et al., 2022; Chakrabarti and Chattopadhyay, 2024; Gunawan et al., 2023). The gut-brain nexus is a rapidly evolving field of study that shows growing support as evidence in the global fight for climate action and sustainable development.

A smog plume covers the city of Milan, Italy. Image source: https://www.theguardian.com/world/2024/feb/20/milan-mayor-casts-doubt-on-citys-ranking-as-third-most-polluted-in-world

So how does air pollution caused by fossil fuel emissions impact the gut-brain nexus? Alongside carbon dioxide (CO2) emissions, burning fossil fuels emits nitrogen dioxide (NO2) and sulfur dioxide (SO2) all in the form of particulate matter at PM2.5 (2.5 micrometres in diameter – an average human hair is 70 micrometres for broader comparison). Fine inhalable particles of PM2.5 enter our digestive systems and food and mingle with our bodily bacteria – the good, and the bad, and they make things ugly. Recent research on the gut microbiome and the gut-brain nexus shows that the gut regulates our mental health, nervous system responses, hormonal and neurotransmitter balances, and further cognitive capabilities. Air pollution affects all of these functions.

Singh et al., (2022) find that gut dysbiosis (a reduction of microbial diversity) is associated with disruptions in the gut-brain axis. The disruptions increase inflammation and alter immune system responses, contributing to psychiatric conditions like anxiety, depression and cognitive decline (Tota et al., 2024). However, this inflammation is not area-specific or acute. The pollution induces oxidative stress and triggers chronic systemic inflammation and neuroinflammation in the gut and the brain, compromising the gut barrier, increasing gut permeability and facilitating the transfer of harmful substances into the bloodstream (Rio et al., 2024). Besides cognitive decline, this increases the risks of Alzheimer’s disease and exacerbates frailty, which is associated with ageing (Campolim et al., 2024; Gunawan et al., 2023). Through the heightened gut permeability, pollutants that enter the bloodstream directly affect brain function, such as the hypothalamic-pituitary-adrenal (HPA) axis, disrupting stress responses and altering the production of hormones and neurotransmitters, like serotonin and dopamine. Neurotransmitter imbalances create mood swings and disorders, leading to potential social and mental health instabilities (Singh et al., 2022).

Moreover, pollutants can also impair the gut’s ability to produce short-chain fatty acids (SCFAs) necessary to maintain mental health by regulating inflammation and neurotransmitter production (Chakrabarti and Chattopadhyay, 2024). In addition to SCFAs, leptin levels are affected. According to the US National Library of Medicine, leptin is a hormone responsible for the regulation of appetite, neuroendocrine function, and energy homeostasis, influencing processes such as metabolism, immunity, and endocrine regulation (Dornbush, 2023). Air pollution exacerbates leptin resistance, further contributing to obesity via the gut microbiome (Campolim et al., 2024).

How can we reduce fossil fuel emissions with innovative technologies? Besides the well-known and popularly advocated technologies such as wind, solar, hydro, and geothermal renewable energies and electric vehicles, there are often missed alternative solutions that are as essential for climate action.

Biofuels are liquid fuels and blending components produced from biomass materials. They can include methane, biogas, and hydrogen, used primarily in transportation but also for heating and electricity generation. The greatest climate cost benefit of biofuels is their use as blended fuel with fossil fuel sources, reducing emissions and mitigating the transition costs of switching vehicles from gas to electric sources. Brazil largely leads the biofuel industry, promoting its ethanol program using sugarcane. Canada, the U.S., South Africa, and Nigeria also produce biofuels and are exploring additional biofuels from agricultural waste and biogas.

Our consumption waste is another treasure trove of potential alternative energy. Municipal solid waste (paper, cardboard, wood), organic waste, food waste, and wastewater sludge can be converted into energy for electricity production. For example, waste-to-energy implementation is growing in Africa, the Middle East, and Asia, particularly in Ethiopia, South Africa, Japan, South Korea, the UAE, and Qatar. In Sweden and Finland, districts heat their homes using organic waste-powered biomass energy, meanwhile, Southeast Asia and India are turning to agricultural waste for biogas production.

Green hydrogen is a clean fuel obtained through electrolysis, a chemical process that uses renewable electricity to separate hydrogen from oxygen in water. This process generates hydrogen without emitting CO2 and can be an alternative fuel for vehicles. The U.S., Japan, South Korea, Germany, and Spain are investing heavily in green hydrogen to replace fossil fuels in transportation and industrial applications. Yet this technology can similarly be used for energy production.

Additionally, there are Carbon Capture and Storage (CCS) technologies. These hold larger marginal abatement costs, meaning that their capital and operating costs are still significantly high in terms of additional units of emissions reduced. They can be installed at fossil fuel emissions sites to directly capture and cycle CO2 emissions, or simply in an outdoor space to retrieve CO2 and store CO2 from the atmosphere. China, South Korea, Norway, Saudi Arabia, and the UAE use this technology for their industrial plants, capturing and repurposing CO2 such as for oil mining. The U.S. and Canada are advancing large-scale CCS and direct air capture projects to reduce emissions from their coal, and gas plants, and the atmosphere. However, the R&D budget is significantly lacking globally to make this technology cheaper and much more accessible.

Considering the dangers of air pollution and the possible technologies to reduce them, what are some regulatory outlooks towards fossil fuels across Europe? Quite frankly, the European Union is a world leader in the race for decarbonization (ClimateTrade, 2023). It has made tremendous recent gains in emissions reductions (Figure 1). The EU Emissions Trading System is the world’s largest carbon market. It sets a cap on emissions and allows companies to buy and sell emissions allowances, incentivizing industries to reduce emissions by adopting cleaner technologies. Certain cities, like London, Paris, and Berlin, have even implemented low emissions zones, by charging high-emission vehicles a fee in urban areas. Moreover, certain EU countries are determined to not only phase out fossil fuels but achieve 100% renewable electricity by 2050. This includes Germany, the largest EU fossil fuel-emitting electricity producer EU (Figure 2). The bold EU plans emerged particularly after the establishment of the European Green Deal in 2020, an overarching policy aim to make Europe climate-neutral by 2050.

Figure 2, source: European Commission

Figure 2, source: (Brown and Jones, 2024)

These are significant climate policy milestone achievements, but they are just as much at risk of being overturned. Climate policy is in danger with the rise of far-right politics across Europe.

For example, in Germany the AfD, which strongly opposes the government’s energy and climate measures, advocates for fossil fuels and nuclear power, rejecting wind energy. Moreover, they deny the anthropogenic (human-caused) cause of climate change (Pfeifer, 2023). There is also a growing sentiment of AfD supporter-led “greenlash” against climate policies and the Green Party – an anti-climate policy political backlash (Niranjan, 2024a).

In France, climate experts argue that with the victory of the National Rally, the country would witness “a big regression” on the climate agenda (Niranjan, 2024b). Their political campaign has barely featured climate action, although it has indicated that it plans to “overturn a 2035 ban on combustion engine cars, block new wind turbines, scrap low-emissions zones and rip up rules on energy efficiency” (Niranjan, 202b). As the second-largest economy in the EU, these actions pose a serious risk for the grander scheme of the European Green Deal (Jack and Camut, 2024).

Similar worries are visible across the rest of the European Union, such as in Poland, Italy, and the Netherlands, where political parties, populist movements, or even current governments are pushing back on the broader EU climate directives (van Rij et al., 2024; Berthelsen, 2023; Ocvirk and Guerout, 2024).

Conclusion

In conclusion, with increasing political resistance to climate policies, the fight against fossil fuel emissions and their dangerous effects on human health, particularly through the gut-brain nexus, is more critical than ever. Every breath is shorter as air pollution continues to rise, putting both our health and the planet's future at risk. Innovations in renewable energy and pollution reduction technologies offer hope, but the risk of setbacks is real as far-right political shifts threaten to reverse hard-won progress. Not only the health of our planet, but most importantly the well-being of our current and future generations, is at a tipping point. With so much at stake, the question remains: How long can we afford to wait before taking decisive action to protect both our environment and our health?

References

Air Pollution. European Environment Agency. (2024). https://www.eea.europa.eu/en/topics/in-depth/air-pollution

Berthelsen, R. G. (2023, September 26). Mounting discontent augurs badly for EU Green deal. POLITICO. https://www.politico.eu/article/discontent-eu-green-deal-climate-change-backlash/

Brown, S., & Jones, D. (2024, April 29). European Electricity Review 2024. Ember. https://ember-climate.org/insights/research/european-electricity-review-2024/

Campolim, C. M., Schimenes, B. C., Veras, M. M., Kim, Y.-B., & Prada, P. O. (2024). Air pollution accelerates the development of obesity and alzheimer’s disease: The role of leptin and inflammation - a mini-review. Frontiers in Immunology, 15. https://doi.org/10.3389/fimmu.2024.1401800

Chakrabarti, S. K., & Chattopadhyay, D. (2024). Understanding The Eco-Gut Link: How Climate Shapes Gut Microbiome and Human Health. Journal of Community Medicine and Public Health Reports, 5(11), 1–11. https://www.researchgate.net/publication/383495187_Understanding_The_Eco-Gut_Link_How_Climate_Shapes_Gut_Microbiome_and_Human_Health

Countries leading the world’s decarbonization. ClimateTrade. (2023, August 7). https://climatetrade.com/top-10-countries-leading-the-worlds-decarbonization/

Croatia Air Quality index (AQI) and Air Pollution Information. IQAir. (2024a). https://www.iqair.com/croatia

Dornbush, S. (2023, April 10). Physiology, leptin. U.S. National Library of Medicine. https://www.ncbi.nlm.nih.gov/books/NBK537038/  

European Commission, Official Website. European Commission. (n.d.). https://commission.europa.eu/index_en

Frost, R. (2024, September 2). Which European cities have the best and Worst Air Quality?. EuroNews. https://www.euronews.com/green/2024/09/02/uppsala-faro-reykjavik-which-cities-have-the-best-and-worst-air-quality-in-europe

Giuffrida, A. (2024, February 20). Milan mayor casts doubt on City’s ranking as third most polluted in World. The Guardian. https://www.theguardian.com/world/2024/feb/20/milan-mayor-casts-doubt-on-citys-ranking-as-third-most-polluted-in-world

Gunawan, W. B., Abadi, M. N., Fadhillah, F. S., Nurkolis, F., & Pramono, A. (2023). The Interlink between climate changes, gut microbiota, and Aging Processes. Human Nutrition & Metabolism, 32, 200193. https://doi.org/10.1016/j.hnm.2023.200193

Italy Air Quality index (AQI) and Air Pollution Information. IQAir. (2024b). https://www.iqair.com/italy

Jack, V., & Camut, N. (2024, July 5). Far-right France risks paralyzing EU’s green deal. POLITICO. https://www.politico.eu/article/far-right-france-risks-paralyzing-eu-green-deal/

Niranjan, A. (2024a, April 30). How climate policies are becoming focus for far-right attacks in Germany. The Guardian. https://www.theguardian.com/world/2024/apr/30/how-climate-policies-are-becoming-focus-for-far-right-attacks-in-germany

Niranjan, A. (2024b, July 3). Far-right win in French election could deal blow to climate policy, say experts. The Guardian. https://www.theguardian.com/world/article/2024/jul/03/far-right-win-french-election-could-deal-blow-climate-policy-experts

Ocvirk, M., & Guerout, C. (2024, March 28). Plowing under the EU Green Deal? climate policy and the European Parliament elections. Wilson Center. https://www.wilsoncenter.org/article/plowing-under-eu-green-deal-climate-policy-and-european-parliament-elections

Pfeifer, H. (2023, June 4). Germany’s far-right AFD profits from climate change spat. Deutsche Welle. https://www.dw.com/en/germanys-far-right-afd-profits-from-climate-change-spat/a-65797438

Poland Air Quality index (AQI) and Air Pollution Information. IQAir. (2024c). https://www.iqair.com/poland

Rio, P., Caldarelli, M., Gasbarrini, A., Gambassi, G., & Cianci, R. (2024). The impact of climate change on immunity and gut microbiota in the development of disease. Diseases, 12(6), 118. https://doi.org/10.3390/diseases12060118

Singh, S., Sharma, P., Pal, N., Kumawat, M., Shubham, S., Sarma, D. K., Tiwari, R. R., Kumar, M., & Nagpal, R. (2022). Impact of environmental pollutants on gut microbiome and mental health via the gut–brain axis. Microorganisms, 10(7), 1457. https://doi.org/10.3390/microorganisms10071457

Tota, M., Karska, J., Kowalski, S., Piątek, N., Pszczołowska, M., Mazur, K., & Piotrowski, P. (2024). Environmental pollution and extreme weather conditions: Insights into the effect on mental health. Frontiers in Psychiatry, 15. https://doi.org/10.3389/fpsyt.2024.1389051

van Rij, A., Benton, T., Butler, C., & Schröder, P. (2024, June 11). How will gains by the far right affect the European ... Chatham House. https://www.chathamhouse.org/2024/06/how-will-gains-far-right-affect-european-parliament-and-eu