In August 2023, residents of Juneau, Alaska, watched as the Mendenhall River swelled to historic levels in a matter of hours. The rushing water undercut the riverbank and swallowed whole stands of trees and multiple buildings.

The source for the flood was not heavy rainfall – it was a small glacial lake located in a side valley next to the Mendenhall Glacier.

Glacier-dammed lakes like this are abundant in Alaska. They form when a side valley loses its ice faster than the main valley, leaving an ice-free basin that can fill with water. These lakes may remain stable for years, but often they reach a tipping point, when high water pressure opens a channel underneath the glacier.

The rapid and catastrophic drainage of lake water that follows is called a glacial lake outburst flood, or GLOF for short. The flood waters race downstream over hours or days and often hit unexpectedly.

Glacial lake outburst floods have destroyed homes, infrastructure and human life around the world. They have killed hundreds of people in Europe and thousands of people in both South America and central Asia. Globally, an estimated 15 million people live downstream from these lakes, with those in Asia’s high mountains at greatest risk.

Flooding from a glacial lake in the Himalayas on Oct. 5, 2023, left dozens of people dead in India as water swept away bridges, damaged a hydropower station and flooded small towns. Satellite images showed that the lake level dropped markedly within hours.

I study Alaska’s glacial lakes and the hazards that glacier-dammed lakes in particular can create. Our latest research shows how these lakes are changing as global temperatures rise.

When glaciers hold back lakes

Some glacial lakes are dammed by moraines – mounds of rock and debris that are left behind as a glacier retreats. Too much pressure from extreme rainfall or an avalanche or landslide into the lake can burst these dams, triggering a devastating flood. Officials say that’s likely what happened when the Himalayas’ Lhonak Lake flooded towns in India in October 2023.

Glacier-dammed lakes, like Suicide Basin off of Mendenhall Glacier, are instead dammed by the glacier itself.

These glacial lakes tend to repeatedly fill and drain due to a cyclic opening and closing of a drainage path under the ice. The fill-and-drain cycles can create hazards every couple of years or multiple times a year.

How glacier lake hazards are changing in Alaska

In a new study, we identified 120 glacier-dammed lakes in Alaska, 106 of which have drained at least once since 1985.

These lakes have collectively drained 1,150 times over 35 years. That is an average of 33 events every year where a lake drains its contents, sending a pulse of water downstream and creating potentially hazardous conditions.

Many of these lakes are in remote locations and often go undetected, while others are much closer to communities, such as Suicide Basin, which is within 5 miles of the state capital and has frequently drained over the past decade.

Our study found that, as a whole, glacier-dammed lakes in Alaska have decreased in volume since 1985, while the frequency of outbursts remains unchanged. This suggests a regional decline in the potential hazards from glacier-dammed lakes because less stored water is available, a trend that has been documented for glacier-dammed lakes worldwide.

To better understand this trend, imagine a bathtub. The higher the sides of the tub, the more water it can hold. For a glacier-dammed lake, the glacier acts as a side of the bathtub. Warming air temperatures are causing glaciers to melt and thin, lowering the tub walls and therefore accommodating less water. That reduces the total volume of water available for a potential glacial lake outburst flood.

Smaller lakes, however, have had less significant change in area over time. As the August 2023 event clearly illustrated, even small lakes can have significant effects downstream.

Alaskans witnessed a new record of destruction in Juneau from the flood. The water reached nearly 15 feet at the Mendenhall River gauge – 3 feet above its previous record.

In summer 2023 alone, Alaskans saw record or near-record flooding from multiple glacier-dammed lakes near populated areas or infrastructure, such as Suicide Basin, near Juneau; Skilak Glacier-Dammed Lake, which affects the Kenai River; and Snow Lake, which impacts the Snow River. These lakes have remained about the same volume but have produced some larger floods in recent years.

One possible explanation is that with a thinner and weaker ice dam, the water can drain much more quickly, though further research is needed to understand the mechanics. Regardless, it’s a reminder that these lakes and events are unpredictable.

How will rising temperatures affect these lakes?

Glacier loss in Alaska is accelerating as temperatures rise. Due to the large volume of glaciers and the many intersecting valleys filled with ice in Alaska, there is a high probability that new lakes will develop as side valleys deglaciate, introducing new potential hazards.

Many of these lakes are likely to develop in remote locations, and their presence may only be noticed in satellite images that reveal changes over time.

Given the abundance of glacial lakes and their potential threat to human lives, early warning and monitoring systems are worryingly sparse. Efforts are underway, such as those in the Himalayas and Chile, but further research is needed to develop reliable, low-cost monitoring systems and to improve our understanding of these evolving hazards.

Brianna Rick received funding from The National Science Foundation.

Lego, the world’s largest toy manufacturer, has built a reputation not only for the durability of its bricks, designed to last for decades, but also for its substantial investment in sustainability. The company has pledged US$1.4 billion to reduce carbon emissions by 2025, despite netting annual profits of just over $2 billion in 2022.

This commitment isn’t just for show. Lego sees its core customers as children and their parents, and sustainability is fundamentally about ensuring that future generations inherit a planet as hospitable as the one we enjoy today.

So it was surprising when the Financial Times reported on Sept. 25, 2023, that Lego had pulled out of its widely publicized “Bottles to Bricks” initiative.

This ambitious project aimed to replace traditional Lego plastic with a new material made from recycled plastic bottles. However, when Lego assessed the project’s environmental impact throughout its supply chain, it found that producing bricks with the recycled plastic would require extra materials and energy to make them durable enough. Because this conversion process would result in higher carbon emissions, the company decided to stick with its current fossil fuel-based materials while continuing to search for more sustainable alternatives.

As experts in global supply chains and sustainability, we believe Lego’s pivot is the beginning of a larger trend toward developing sustainable solutions for entire supply chains in a circular economy. New regulations in the European Union – and expected in California – are about to speed things up.

Examining all the emissions, cradle to grave

Business leaders are increasingly integrating environmental, social and governance factors, commonly known as ESG, into their operational and strategic frameworks. But the pursuit of sustainability requires attention to the entire life cycle of a product, from its materials and manufacturing processes to its use and ultimate disposal.

The results can lead to counterintuitive outcomes, as Lego discovered.

Understanding a company’s entire carbon footprint requires looking at three types of emissions: Scope 1 emissions are generated directly by a company’s internal operations. Scope 2 emissions are caused by generating the electricity, steam, heat or cooling a company consumes. And scope 3 emissions are generated by a company’s supply chain, from upstream suppliers to downstream distributors and end customers.

Currently, fewer than 30% of companies report meaningful scope 3 emissions, in part because these emissions are difficult to track. Yet, companies’ scope 3 emissions are on average 11.4 times greater than their scope 1 emissions, data from corporate disclosures reported to the nonprofit CDP show.

Lego is a case study of this lopsided distribution and the importance of tracking scope 3 emissions. A staggering 98% of Lego’s carbon emissions are categorized as scope 3.

From 2020 to 2021, the company’s total emissions increased by 30%, amid surging demand for Lego sets during the COVID-19 lockdowns – even though the company’s scope 2 emissions related to purchased energy such as electricity decreased by 40%. The increase was almost entirely in its scope 3 emissions.

As more companies follow in Lego’s footsteps and begin reporting scope 3 emissions, they will likely find themselves in the same position, realizing that efforts to reduce carbon emissions often boil down to supply chain and consumer-use emissions. And the results may force them to make some tough choices.

Policy and disclosure: The next frontier

New regulations in the European Union and pending in California are designed to increase corporate emissions transparency by including supply chain emissions.

The EU in June 2023 adopted the first set of European Sustainability Reporting Standards, which will require publicly traded companies in the EU to disclose their scope 3 emissions, starting in their reports for fiscal year 2024.

California’s legislature passed similar legislation requiring companies with revenues of more than $1 billion to disclose their scope 3 emissions. California’s governor has until Oct. 14, 2023, to consider the bill and is expected to sign it.

At the federal level, the U.S. Securities and Exchange Commission released a proposal in March 2022 that, if finalized, would require all public companies to report climate-related risk and emissions data, including scope 3 emissions. After receiving significant pushback, the SEC began reconsidering the scope 3 reporting rule. But SEC Chairman Gary Gensler suggested during a congressional hearing in late September 2023 that California’s move could influence federal regulators’ decision.

This increased focus on disclosure of scope 3 emissions will undoubtedly increase pressure on companies.

Because scope 3 emissions are significant, yet often not measured or reported, consumers are rightly concerned that companies that claim to have low emissions may be greenwashing without taking action to reduce emissions in their supply chains to combat climate change.

At the same time, we suspect that as more investors support sustainable investing, they may prefer to invest in companies that are transparent in disclosing all areas of emissions. Ultimately, we believe consumers, investors and governments will demand more than lip service from companies. Instead, they’ll expect companies to take actionable steps to reduce the most significant part of a company’s carbon footprint – scope 3 emissions.

A journey, not a destination

The Lego example serves as a cautionary tale in the complex ESG landscape for which most companies are not well prepared. As more companies come under scrutiny for their entire carbon footprint, we may see more instances where well-intentioned sustainability efforts run into uncomfortable truths.

This calls for a nuanced understanding of sustainability, not as a checklist of good deeds, but as a complex, ongoing process that requires vigilance, transparency and, above all, a commitment to the benefit of future generations.

The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.

Climate change is affecting communities nationwide, but Florida often seems like ground zero. In September 2022, Hurricane Ian devastated southwest Florida, killing at least 156 people and causing an estimated US$113 billion in damages. Then Hurricane Idalia shut down the Florida Panhandle in September 2023, augmented by a blue supermoon that also increased tidal flooding in southeast Florida.

Communities can adapt to some of these effects, or at least buy time, by taking steps such as upgrading stormwater systems and raising roads and sidewalks. But climate disasters and sea-level rise also harm local governments financially by increasing costs and undercutting their property tax bases. Local reliance on property taxes also can discourage cities from steering development out of flood zones, which is essential for reducing long-term risks.

In a newly published study and supporting online StoryMap, we present the first-ever municipal fiscal impact assessment of sea-level rise in Florida and combine it with a statewide survey of coastal planners and managers. We wanted to know how sea-level rise would affect municipal tax revenues and whether coastal planners and managers are accounting for these fiscal impacts.

Our study finds that over half of Florida’s 410 municipalities will be affected by 6.6 feet of sea-level rise. Almost 30% of all local revenues currently generated by these 211 municipalities come from buildings in areas that will become chronically flooded, potentially by the end of the century. Yet, planners and managers remain largely unaware of how much climate change will affect local fiscal health. Some communities with the most at risk are doing the least to prepare.

Property tax and climate change: A Catch-22

Property taxes are critically important for municipal governments. Nationwide, they provide 30% of local revenues. They are one of the few funding sources that local governments control, and climate change directly threatens them.

As climate change warms ocean waters, it fuels hurricanes and increases their reach and intensity. Climate change also is raising sea levels, which increases coastal flooding during both storms and high tides, often referred to as sunny-day flooding. Unlike storms, sea-level rise doesn’t recede, so it threatens to permanently inundate coastal lands over time.

Property tax revenues may decline as insurance companies and property markets downgrade property values to reflect climate impacts, such as increasing flood risks and wildfires. Already, a growing number of insurance companies have decided to stop covering some regions and types of weather events, raise premiums and deductibles and drop existing policies as payouts rise in the wake of natural disasters. Growing costs of insuring or repairing homes may further hurt property values and increase home abandonment.

Climate change also makes it more expensive to provide municipal services like water, sewage and road maintenance. For example, high heat buckles roads, rising water tables wash out their substructure, and heavier rains stress stormwater systems. If cities don’t adapt, increasing damage from climate-driven disasters and sea-level rise will create a vicious fiscal cycle, eroding local tax bases and driving up services costs – which in turn leaves less money for adaptation.

However, if cities reduce development in vulnerable areas, their property taxes and other revenues will take a hit. And if they build more seawalls and homes fortified to withstand hurricanes and storms, they will induce more people to live in harm’s way.

In Florida, we found that these theoretical dynamics are already occurring.

Florida’s local revenues at risk

Our analysis shows that sea-level rise could flood properties that have a combined assessed value of US$619 billion and currently generate $2.36 billion in annual property taxes. Five million Floridians live in towns where at least 10% of local revenues comes from properties at risk of chronic and permanent flooding. For 64 municipalities, 50% of their revenues come from these risk zones.

Actual fiscal effects would likely be worse after accounting for other lost revenues, rising expenditures and the impacts of multiple climate hazards, such as hotter weather and more intense hurricanes.

These impacts are not evenly distributed. Municipalities with the greatest fiscal risks are geographically and demographically smaller, denser, wealthier and whiter. Lower-risk municipalities tend to be more populous, more diverse, lower-income and have larger land areas.

For instance, the 6,800 residents of the city of Treasure Island in southwest Florida are 95% white and have a median household income of $75,000. The town occupies 3 square miles of land on a barrier island. In our model, its potential lost revenues due to sea-level rise equal its entire municipal revenue stream.

In contrast, St. Petersburg, the nearest big city, has a population of 246,000 residents that is 69% white and a median household income of $53,800. It covers 72 square miles, with only 12% of its property tax revenues at risk from flooding.

Heads in the sand

We see our findings as a wake-up call for state and local governments. Without urgent action to adapt to climate change, dozens of municipalities could end up fiscally underwater.

Instead, many Florida cities are pursuing continued growth through infrastructure expansion. Even after devastating events like Hurricane Ian, administrative boundaries, service obligations and budgetary responsibilities make it hard for municipal leaders to make room for water or retreat onto higher ground.

Treasure Island, for instance, is allocating property taxes to upgrade the town’s causeway bridge. This protects against modest climate impacts in the short term but will eventually be overwhelmed by bigger storm surges, rising water tables and accelerating sea-level rise.

These dynamics can worsen displacement and gentrification. In Miami, developers are already buying and consolidating properties in longtime Black and lower-income neighborhoods like Little Haiti, Overtown and Liberty City that are slightly more elevated than areas along the shore.

If this pattern continues, we expect that inland and upland areas of cities like St. Petersburg, Tampa and Miami will attract more resilient, high-end development, while displaced low-income and minority residents are forced to move either out of the region or to coastal zones with declining resources.

Charting a different future

We don’t see this outcome as inevitable, in Florida or elsewhere. There are ways for municipalities to manage and govern land that promote fiscally sound, equitable and sustainable ways of adapting to climate change. The key is recognizing and addressing the property tax Catch-22.

As a first step, governments could assess how climate change will affect their fiscal health. Second, state governments could enact legislation that expands local revenue sources, such as sales or consumption taxes, vacancy taxes, stormwater impact fees and resilience bonds or fees.

Regional sharing of land and taxes is another way for small, cash-strapped communities to reduce development in vulnerable places while maintaining services for their residents. For example, New Hampshire passed a bill in 2019 to allow coastal municipalities to merge in response to sea-level rise.

Finally, state governments could pass legislation to help low-income neighborhoods gain more control over land and housing. Tested tools include limited equity cooperatives, where residents buy an affordable share in a development and later resell at below-market prices to maintain affordability; community land trusts, where a nonprofit buys and holds land title to keep land costs down; and resident-owned mobile home parks, where residents jointly buy the land. All of these strategies help communities keep housing affordable and avoid displacement.

Shifting away from a business-as-usual development model won’t be easy. But our study shows that Florida, with its flat topography and thousands of miles of coastline, faces cascading fiscal impacts if it continues down its current path.

Linda Shi receives funding from the National Oceanographic and Atmospheric Administration.

Tisha Joseph Holmes received funding from the Florida Department of Environmental Protection, the Robert Wood Johnson Foundation and the Center for Disease Control and Provention. She is affiliated with REfire Culinary.

William Butler received funding from the Florida Department of Environmental Protection in support of this research.