I. Introduction and Motivation

2024 was the warmest year on record; a record that was just set by the previous year.1 In 2023, the National Oceanic and Atmospheric Administration (NOAA) reported that the United States was hit with a record number of inflation-adjusted billion-dollar extreme weather and climate events—such as severe storms, floods, and wildfires2 —leaving many to wonder whether climate change had something to do with them.

As described in the module, Drawing the Causal Chain: The Detection and Attribution of Climate Change, questions like these often can be answered with attribution science. Attribution science refers to four areas of scientific inquiry that together can provide the “causal chain” that links greenhouse gas (GHG) emissions to the impacts of a changing climate. These four areas are: source attribution, climate change attribution, event attribution (inclusive of both extreme weather events and those that are more subtle but still influenced by climate change), and impact attribution.3 Source attribution research first seeks to characterize or quantify the GHG emissions resulting from a given source like a state, industry, or company. Evaluating the effects of GHG emissions on global climate through, for example, an increase in global mean surface temperature or a reduction in Arctic sea ice, is the domain of climate change attribution. Of note, the line between source attribution and climate change attribution can sometimes be blurry in scientific exercises that investigate the relationship between the emissions of a particular source and a change in the climate system. Event attribution research attempts to isolate the influence of human-caused climate change on a particular weather event or class of events, such as a specific flood or heatwave (or floods or heatwaves generally). And, the final link of this causal chain is impact attribution, which characterizes the additional harm of a phenomenon due to climate change, such as the number of excess deaths that resulted from a climate change-fueled flood. By attempting to draw this causal chain, attribution science is a field that is shaping up to be increasingly relevant to litigation.

Attribution literature has skyrocketed over the last two decades (Figure 1). While Drawing the Causal Chain was released in 2023, much of its content is drawn from resources published in 2021 and earlier. From 2021 through 2023, however, data from Columbia Law School’s Sabin Center for Climate Change Law indicate that 332 new attribution resources (primarily peer-reviewed scientific articles and reports) were published. Put differently, over half of the total body of attribution science literature at the time of writing was published over these three years alone. Impact attribution research represents the largest area of scientific interest, followed by climate change attribution, event attribution, and source attribution in descending order (Figure 1).

Figure 1

Figure 1. (left) Number of attribution resources (primarily peer-reviewed scientific articles and reports) published per year from 1965 to 2023. (right) Breakout of attribution research by category. Data were retrieved from the Climate Attribution Database maintained by Columbia University’s Sabin Center for Climate Change Law in March of 2024 (available at https://climateattribution.org/-->).

One publication that deserves special attention is the federal government’s Fifth National Climate Assessment, released in November 2023.1 The National Climate Assessment is a policy-neutral consensus report2 about climate change and its impacts throughout the United States. This congressionally mandated report, which is intended to be released at least every four years, is coordinated by scientists from 15 federal agencies, including the National Aeronautics and Space Administration (NASA), the U.S. Department of Defense, and the Smithsonian Institution.3 The Fifth National Climate Assessment was reviewed by the public, scientists inside and outside of government, and a committee of the National Academies of Sciences, Engineering, and Medicine.4 The report represents the federal government’s best and latest understanding of how climate change is affecting and will affect the United States.

The next section of this paper synthesizes the Fifth National Climate Assessment’s major takeaways relevant to attribution science. Then, key legal and scientific developments related to attribution science are discussed. The first of these legal updates involves the status of three cases, ongoing at the time of this writing, that feature event attribution as part of the plaintiff’s argument—of a heat wave in County ofMultnomah v. Exxon Mobil Corp.,5 and of the 2017 hurricane season in a pair of cases filed in Puerto Rico.6 The second legal update is a discussion on emerging state “climate superfund” bills, which are incorporating attribution science as a way to apportion alleged responsibility for climate change to industry.

The first scientific development discussed here concerns an ongoing NOAA initiative to develop a framework for conducting “rapid” attribution analyses of extreme temperature and drought events,7 which could be transformative for both attribution science and related litigation. The second scientific update describes a new interagency satellite mission, Tropospheric Emissions: Monitoring of Pollution (TEMPO), that is designed to measure air pollution from space and could be used to better characterize the effects of climate-related extreme events, like wildfires, on air quality conditions.8 As attribution studies increase in number and the scientific methods of attribution become standardized—or even routine—and as data quality improves, scientists and legal scholars suggest that litigation could increase.9 The ongoing litigation highlighted here might therefore be only the very beginning of a wave of cases to come.

II. Where Attribution Science Stands: Perspective of the Fifth National Climate Assessment

A. Source Attribution and Climate Change Attribution

The atmospheric concentrations of the three main greenhouse gases—carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)—are each increasing due to human activity. From 1850 to 2020, CO2 has increased from 280 parts per million (ppm) to 412 ppm, CH4 from 700 parts per billion (ppb) to 1,878 ppb, and N2O from 270 to 333 ppb.10 Notable human activities contributing to this increase include fossil fuel energy use, agriculture, and deforestation. While today China is the largest source of annual CO2 emissions derived from fossil fuel use and industry, the cumulative emissions of the United States and European Union (EU) countries over the last 170 years dwarf those of other high-emitting regions (Figure 2). Because CO2 is long-lived in the atmosphere, these historical emissions contribute to the warming of today and will continue to do so for centuries (see, e.g., What Is Causing Climate Change?). The Fifth National Climate Assessment reports that cumulative U.S. emissions are responsible for about 17% of global warming, whereas China and the EU are responsible for about 12 and 10% respectively. In stark contrast, the 47 least-developed countries are responsible for a meager 6% of warming. Despite contributing such a trivial fraction to climate disruption, these least-developed countries tend to experience the most severe climate impacts (see, e.g., Climate Justice).

  • 1Alexa K. Jay et al., Fifth National Climate Assessment, U.S. Global Change Research Program (2023), available at https://nca2023.globalchange.gov/ (hereinafter NCA5).
  • 2For more on consensus reports in climate science, see Confidence in Climate Science: How Consensus Emerges in the Scientific Community, People Places Planet Podcast (Feb 8. 2024), available athttps://share.transistor.fm/s/0c8f9c3c.
  • 3U.S. Global Change Research Program, Member Agencies, https://www.globalchange.gov/agencies (last visited Jan. 28, 2025).
  • 4NCA5, supra note 4, at “About This Report,” available at https://nca2023.globalchange.gov/chapter/front-matter/.
  • 5County of Multnomah v. Exxon Mobil Corp., No. 3:23-cv-01213-YY (D. Or., June 10, 2024).
  • 6Municipalities of Puerto Rico v. Exxon Mobil Corp., No. 3:23-cv-01550 (D.P.R., 2022); Municipality of San Juan v. Exxon Mobil Corp., No. 3:23-cv-01608 (D.P.R., 2023).
  • 7Joseph J. Barsugli et al., Development of a Rapid Response Capability to Evaluate Causes of Extreme Temperature and Drought Events in the United States, 103 Bull. Am. Meteorological Soc’y S14 (2022).
  • 8U.S. EPA, TEMPO: A New Era of Air Quality Monitoring From Space, U.S. EPA: Science Matters (May 19, 2020), available at https://www.epa.gov/sciencematters/tempo-new-era-air-quality-monitoring-space.
  • 9See, e.g., Rupert F. Stuart-Smith et al., Filling the Evidentiary Gap in Climate Litigation, 11 Nature Climate Change 651 (2021) (arguing “that greater appreciation and exploitation of existing methodologies in attribution science could address obstacles to causation and improve the prospects of litigation as a route to compensation for losses, regulatory action and emission reductions by defendants seeking to limit legal liability”).
  • 10NCA5, supra note 4, at Chapter 2, Table 2.1.
Figure 2

Figure 2. (left) annual CO2 emissions by country or region and (right) cumulative CO2 emissions by country or region. This is an example of source attribution. Source: NCA5, supra note 4, at Figure 2.1.-->

Linking the amount of emissions from a source to global warming or another change in the climate system is not as straightforward as it might appear. This is because the amount of carbon that resides in the atmosphere over time is affected by the amount of carbon emissions from human activity and the exchange of that carbon throughout different parts of the planet (its surface and deep ocean, for example). Scientists must use climate models that faithfully represent the carbon cycle to uncover the relationship between emissions of a source at a given period of time and the effect of those emissions on global warming and other changes in the climate system, such as sea-level rise. As noted above, the Fifth National Climate Assessment apportions emissions to their country of origin; it also apportions them to the sector from which they originate. Figure 3 depicts such trends since 1990, and highlights that transportation, electricity generation, and industry represent the largest sources of U.S. emissions. Figure 3 also depicts, in the dashed line, a trajectory of emissions reduction that is consistent with achieving the nation’s goal of “net-zero” emissions by 2050. Importantly, net zero does not require all activities that emit GHGs to cease after 2050, but rather that any such emissions must be offset by actions that store carbon in “carbon sinks,” such as planting trees and other vegetation that can remove additional carbon from the atmosphere. This carbon sink is represented as negative emissions on the figure. But actions taken to expand carbon sinks without reducing emissions are insufficient to achieve net zero.

Figure 3

Figure 3. U.S. sector-specific emissions trends and a pathway to net-zero emissions. Source: NCA5, supra note 4, at Figure 32.1.-->

So, how do total GHG emissions from human activity stack up against other potential drivers of climate change? Such a question, as previously indicated, is one of climate change attribution. The Fifth National Climate Assessment reports that, between 2010 and 2019, the planet has warmed by about 2 degrees Fahrenheit (°F) compared to the late 1800s (Figure 4a). However, all available scientific evidence indicates that human GHG emissions could have warmed the planet by up to 3.5 °F (Figure 4b)! What accounts for this discrepancy? Other human activities that have altered the concentrations of aerosols and ozone in the atmosphere and land use changes have worked together to reduce the effects of warming by an equivalent of around 1.5 °F. The result is net warming of about 2 °F.

Figure 4

Figure 4. (a) Global mean surface temperature increase observed over the 2010-2019 period relative to an 1850-1900 baseline and (b) summary of the parsing of human-caused and natural factors that influenced global mean surface temperature during this interval. This is an example of climate change attribution. Source: Modified from NCA5, supra note 4, at Figure 3.1.-->

While source and climate change attribution research might also explore the result of emissions from nongovernmental actors such as individual companies,1 the Fifth National Climate Assessment does not cover this topic. Because this research is at the heart of the lawsuits discussed in Section 3.A., more attention will be given to it in that section.

B. Event Attribution

The attribution of weather events, including extreme events, to climate change is a critical step in linking climate-related harms to emissions, and the science has come a long way since Myles Allen’s 2003 thought experiment about this field described in Drawing the Causal Chain. As indicated in the main text of that module, scientists working in this area attempt to determine the connections, if any, between human-caused climate change and the likelihood and/or severity of the event in question. As in other areas of climate science, confidence is highest when multiple independent lines of evidence point to the same conclusion—in other words, when a consilience of evidence from different models, methods, and observations highlight the same role for climate change in driving increased precipitation during a flood, confidence in that finding is high2 (see also How Climate Science Works).

One ongoing challenge to event attribution research is the coarse spatial resolution of global climate models, which are generally not constructed for the kinds of high-resolution regional and local analyses that the attribution of certain events operating on relatively small scales require.3 Nevertheless, significant progress has been made in the United States and around the world in the attribution to climate change of certain classes of events, such as extreme temperature and precipitation events. In fact, the high level of confidence that scientists now have in their ability to attribute some particular events within these classes has inspired the scientific community to begin to consider “operationalizing” their attribution. That is, they aspire to move these kinds of analyses, which can sometimes be done rapidly after the event or even in real time, outside the academic setting and into public-facing institutions, such as in weather prediction centers. Operationalizing the process in this way would allow for the attribution of a larger number of events and a wider applicability of this work.4 More attention will be given to a NOAA-led effort to standardize event attribution analyses in Section 3.C.

One “rapid” attribution study led by scientists of the Royal Netherlands Meteorological Institute (KNMI), the Dutch national weather service, investigated the role of climate change in the unprecedented 2021 Pacific Northwest heatwave, which was estimated to be responsible for nearly 300 deaths in the United States and over 600 deaths in British Columbia, Canada.5 The analysis, which used a combination of models and temperature data, explored the effects of climate change on both the severity of the heatwave and the likelihood of the event occurring. These scientists found that the event would have been “at least 150 times” less common6 without human-induced climate change,” and that an event of similar likelihood would have been between 2 and 4 °F cooler without climate change.7

C. Impact Attribution

As described in The Impacts of Climate Change, the impacts of climate change are diverse and manifest differently across different regions of the country—and across the world. One of these impacts is on human health. Perhaps the clearest way in which climate change affects human health comes from the direct effects of excess heat on morbidity and mortality. One impact attribution study conducted by 70 scientists from around the world used epidemiological data and counterfactual climate model simulations to isolate the effect of climate change on heat-related deaths during the four consecutive warmest months between 1991 and 2018 across 43 countries, including the United States.8 The authors found that just under 40% of these heat-related deaths in the United States were caused by climate change. Another study led by scientists at the University of Nebraska Medical Center looked more broadly at the role of climate change in heat-related emergency room visits in North Carolina.9 The authors reported that about 15% of heat-related emergency room visits were caused by climate change from 2011 to 2016, and they note that this proportion is expected to increase under future warming scenarios.

Characterizing climate change-driven declines in air quality and its consequences for people is another area of interest in health-focused impact attribution research. Wildfire smoke, which has a growing reach partially due to climate change,10 is composed of extremely fine particulate matter pollution. The fraction of particulate matter that is less than 2.5 micrometers (or 0.00025 centimeters) in diameter is called “PM2.5,” and can cause a variety of respiratory and heart problems for those who inhale it.11 One study, led by Stanford University scientists, found that wildfire smoke contributes to up to about half of all PM2.5 pollution in some parts of the western United States.12 However, the impacts of PM2.5 pollution are not limited to the American West, as wildfire smoke can travel long distances, including to more populated areas in the eastern parts of the country. Indeed, an analysis jointly performed by atmospheric scientists and health scientists found that, between 2006 and 2018, approximately three-fourths of the country’s mortality events and asthma morbidity attributable to smoke plumes occurred outside of the western U.S.13

Scientists and economists have also produced a robust body of literature around attributing financial costs to climate change, some of which are connected to these same health-related climate challenges. For example, Duke University scientists estimated that declines in labor due to extreme heat cost $1.7 billion annually from 2006 to 2016.14 They found that the southern regions of the country, from California to Florida, are particularly sensitive to these losses. The economic impacts of climate change-driven increases in wildfire smoke,15 flooding,16 and many other climate hazards have also been explored.17

  • 1See, e.g., Brenda Ekurzel et al., The Rise in Global Atmospheric CO2, Surface Temperature, and Sea Level From Emissions Traced to Major Carbon Producers, 144 Climatic Change 579 (2017).
  • 2NCA5, supra note 4, at Chapter 3, Key Message 3.
  • 3Id.
  • 4See, e.g., Michael F. Wehner & Kevin A. Reed, Operational Extreme Weather Event Attribution Can Quantify Climate Change Loss and Damages, 1 PLOS Climate 2 (2022).
  • 5Sjoukje Y. Philip et al., Rapid Attribution Analysis of the Extraordinary Heat Wave on the Pacific Coast of the US and Canada in June 2021, 13 Earth Sys. Dynamics 1689 (2022).
  • 6Later studies reduced this estimate but still concluded that climate change contributed to the heatwave. See, e.g., Likun Zhang et al., Leveraging Extremal Dependence to Better Characterize the 2021 Pacific Northwest Heatwave, J. Agric., Biological & Env’t. Stat. (2024).
  • 7Philip et al., supra note 18; and NCA5, supra note 4, at Chapter 2.
  • 8Anna Maria Vicedo-Cabrera et al., The Burden of Heat-Related Mortality Attributable to Recent Human-Induced Climate Change, 11 Nature Climate Change 492 (2021).
  • 9Jagadeesh Puvvula et al., Estimating the Burden of Heat-Related Illness Morbidity Attributable to Anthropogenic Climate Change in North Carolina, 6 GeoHealth 11 (2022).
  • 10NCA5, supra note 4, at Focus on Western Wildfires.
  • 11U.S. EPA, Health and Environmental Effects of Particulate Matter (last updated July 16, 2024), available at https://www.epa.gov/pm-pollution/health-and-environmental-effects-particulate-matter-pm.
  • 12Marshall Burke et al., The Contribution of Wildfire to PM2.5 Trends in the USA, 622 Nature 761 (2023).
  • 13Katelyn O’Dell et al., Estimated Mortality and Morbidity Attributable to Smoke Plumes in the United States: Not Just a Western US Problem, 5 GeoHealth 9 (2021).
  • 14Yuqiang Zhang & Drew T. Shindell, Costs From Labor Losses Due to Extreme Heat in the USA Attributable to Climate Change, 164 Climatic Change 35 (2021).
  • 15Mark Borgschulte et al., Air Pollution and the Labor Market: Evidence From Wildfire Smoke, Nat’l Bureau Econ. Rsch. (2022).
  • 16Frances V. Davenport et al., Contribution of Historical Precipitation Change to US Flood Damages, 118 Proc. Nat’l Acad. Sci. U.S.A. 4 (2021).
  • 17See generally NCA5, supra note 4, at Chapter 19, Table 19.1.

III. Other Recent Developments and Items on the Horizon

A. Litigation in Focus: Extreme Events, Attribution, and Disputes

Scientific research linking individual extreme events to climate change has already come up in a handful of U.S. cases seeking to hold industry liable for harms caused by climate change. About two years after the 2021 Pacific Northwest heatwave described in Section 2.B., Multnomah County, Oregon, filed a lawsuit in state court against major energy companies, trade associations, and a consulting firm for their alleged role in contributing to the harms caused by this heatwave and other alleged climate change-induced harms, such as wildfires.1 Alleging claims of nuisance, fraud, negligence, and trespass, the county is seeking over $50 million in actual damages from the 2021 heatwave, $1.5 billion for future damages allegedly caused by climate change, and $50 billion for an abatement fund that is meant to support climate adaptation. Among other allegations, the county asserts that defendants had knowledge of the causes of climate change and its impacts, but they failed to disclose this information and warn the public. The county further argues that the rapid attribution analysis of the 2021 heatwave, in which scientists concluded that the extreme heatwave would have been “virtually impossible” without climate change,2 “corroborated” what defendants allegedly knew about the impacts of climate change.3 Other peer-reviewed scientific studies of the heatwave’s relationship to climate change4 and its impacts5 are also discussed in the complaint. An effect of climate change on the emergence of this event has been found by several peer-reviewed articles, relying on different methods and conducted independently of one another.6

Whether the plaintiffs can link their alleged harms to the defendants is already shaping up to be an issue in the case. In their complaint, plaintiffs cite research published in 2014 by Richard Heede of the Climate Accountability Institute,7 alleging that these companies are “directly responsible for the majority of global GHG emissions from 1965-present.”8

In August 2023, defendants removed the case to federal court, arguing among other things that pursuant to the U.S. Supreme Court’s 2011 decision in Am. Elec. Power Co. v. Connecticut,9 “Plaintiff’s claims are . . . based on global emissions that are impossible to trace to any particular source or time.”10 In October 2023, the county filed a motion to remand the case back to the state court in which it was originally filed, contesting each of the defendants’ arguments for removal. Then, in June 2024, the federal court remanded the case back to state court. Such procedural disputes are typical of these cases (see Overview of Climate Litigation).

Should this case reach the substantive issues, it could provide a unique window into how courts might respond to attribution science as evidence. While parties in climate cases have generally agreed upon the basic scientific facts of climate change (that climate change is real, caused by human activity, and will have adverse consequences on society), it is likely that source attribution research will continue to be disputed. It is also conceivable that this particular heatwave attribution analysis would become the subject of dispute between the parties.

In addition to the suit brought by Multnomah County, two others filed in Puerto Rico rely on event attribution science to support their allegations that energy companies bear responsibility for climate impacts.11 In Municipalities of Puerto Rico v. Exxon Mobil Corp. and Municipality of San Juan v. Exxon Mobil Corp., Puerto Rico municipalities filed lawsuits in federal court against a similar set of companies for their alleged role in causing climate impacts across the island, also referencing the research of Heede,12 to argue that defendants are responsible for 40.01% of industrial GHG emissions from 1965-2017.13 Plaintiffs argue that climate change made the impacts of two 2017 hurricanes—Hurricane Maria and Hurricane Irma—stronger and thus more damaging, citing an event attribution study of Hurricane Maria that found climate change likely contributed to the historic levels of rainfall associated with the hurricane.14 They allege 14 causes of action, which include negligence and fraud claims similar to those in County of Multnomah, but also four claims under the Racketeer Influenced and Corruption Organizations (RICO) Act. Defendants have filed several motions to dismiss, but they have been denied as of January 2024. While there are several other pending lawsuits brought by state and municipal governments that attempt to impose liability on energy companies for the impacts of climate change, the plaintiffs bringing these others have not to date cited formal event attribution studies like those brought by Multnomah County and Puerto Rico.

B. State “Climate Superfund” Bills

The judiciary is not the only branch of government encountering attribution science. In 2024, New York and Vermont enacted “climate superfund” bills that aim to hold large GHG-emitting energy companies strictly liable for the costs resulting from climate change. Similar bills have been introduced in California, Maryland, and Massachusetts.

These bills are inspired by the federal government’s approach to cleaning up contaminated sites under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980. CERCLA, commonly known as Superfund, holds parties strictly liable for environmental contamination and establishes a fund into which those parties must pay that are used to clean up designated sites of contamination. Under these state climate Superfund bills, liability is intended to apply to entities that are deemed responsible for more than one billion metric tons of CO2-equivalent GHG emissions over a specified interval of time.15 These “responsible parties” will be required to pay into a state fund that is to be utilized for climate adaption projects. Attribution science is informing the costs associated with adapting to climate change, who is required to pay, and the amount each responsible party must pay pursuant to these laws.

The Vermont bill, which is intended to cover damages resulting from emissions between January 1, 1995, and December 31, 2024, was the first in the nation, but responsible parties are not yet identified and payments are not yet required.16

The Vermont bill does set a January 1, 2027, deadline for the state’s Agency of Natural Resources (ANR), in coordination with the State Treasurer, to adopt regulations that rely on “available science and publicly available data to identify responsible parties and determine their applicable share of” emissions.17 After that, ANR will issue cost recovery demands by July 2027 and administer the recovery fund. The law also requires ANR to develop a resilience implementation strategy that will help inform where to direct adaptation funds to boost climate resilience throughout the state.

As an initial step, the law required ANR, in consultation with the State Treasurer, to produce a feasibility report of the program, which was submitted January 15, 2025.18 This report notes that ANR sought information about the possible methods it might use to estimate the economic damages borne by Vermont and its residents that have resulted from climate impacts, as well as how to identify responsible parties and apportion costs among them. Several attribution scientists provided feedback, offering support for using Heede’s emissions accounting—the same accounting invoked in the litigation discussed above—as a basis for apportioning liability. The report also discussed the potential and limitations of event attribution and calculating damages associated with climate impacts, noting that the approach can be jurisdiction-specific and “[t]he analysis for flooding, Vermont’s largest climate hazard, has not yet been done, though respondents stated that it can be done in principle.”19

The New York bill was signed into law in December 2024, and likewise sets up a cost recovery program.20 First payments under the law are due no later than September 30, 2026. In contrast to Vermont, New York’s climate superfund law specifies $75 billion in damages, with responsible parties liable for a share equivalent to their share of covered emissions between January 1, 2000, and December 31, 2018. The was not predicated on an assessment of impacts; the bill’s legislative findings cite to a number of impact attribution assessments and note that “climate adaptation investments through 2050 will easily reach several hundred billion dollars . . . .”21

Over the course of 2025, the New York State Department of Environmental Conservation (NYSDEC) will promulgate regulations to adopt methodologies based on the “best available science” to identify responsible parties and what they owe. Similar to Vermont, regulations will also develop a procedure for identifying “climate change adaptive infrastructure” to be funded by the program. Specifically, the law calls for a statewide adaptation master plan to help guide funding decisions. It also includes numerous provisions related to labor standards and worker protection, and requires that at least 35%, with a goal of 40%, of program expenditures benefit disadvantaged communities.

The enactment of these bills, however, is not the final word. In December 2024, the U.S. Chamber of Commerce and the American Petroleum Institute challenged the Vermont Climate Superfund Act in federal court in Vermont, alleging that the law is unconstitutional and preempted by the Clean Air Act, and requesting that the court enjoin the law’s enforcement.22 Plaintiffs argue the law violates due process and the Commerce Clause, amounts to an excessive fine in violation of the Eighth Amendment, and effects a taking, among other things. Plaintiffs’ preemption argument relies on City of New York (see Overview of Climate Litigation), asserting that the Vermont law goes too far by extending liability to emissions from outside Vermont. As of this writing, defendants have yet to respond to the complaint. In early 2025, a coalition of 22 states, led by West Virginia, and a collection of industry associations filed Aa lawsuit challenging the New York law on similar constitutional and statutory grounds bill is likely.23

C. Toward Standardizing the Rapid Attribution of Extreme Events

One motivating factor for studying the links between climate change and extreme weather events is to better understand how these hazards are changing at the local, state, and regional scales so that policymakers, residents, and businesses can make informed decisions around climate adaptation in a timely manner. Recognizing this, an ongoing NOAA project aims to standardize these kinds of analyses to make them more widespread with easily comparable and publicly available results.24 This project focuses exclusively on extreme warm and cold temperature events—such as heat waves and cold snaps—and drought.

The underlying scientific objective of the project is to produce a standardized set of best practices and methodologies for rapid event attribution. As the field of event attribution currently stands, different methodologies can sometimes generate different conclusions about the role that climate change played in affecting the probability and/or magnitude of a given extreme weather event. While scientists agree that climate change will generally worsen certain classes of weather events (like extreme precipitation), individual attribution analyses might disagree on the role, if any, that climate change played in contributing to a specific event. And while a variety of methodologies is beneficial to advancing the field of research, conflicting conclusions can present a challenge for decisionmakers interested in developing a scientifically informed climate adaptation plan.

NOAA scientists have proposed five key iterative steps for rapid attribution analysis, although the approach is still evolving: (1) pre-event research and development to evaluate the kinds of datasets and model simulations needed for an attribution analysis, (2) event monitoring and triggering protocols to provide an objective definition of an “extreme event,” (3) initial observational analyses to characterize the event in quasi-real-time and assess it in a historical context, (4) detailed causal analysis to isolate the relative influence of human-caused climate change and natural factors on the probability of the event occurring and its magnitude, and (5) communication of results using clear language that is accessible to the public at large. These protocols are similar to those developed by other rapid attribution experts at the World Weather Attribution, a joint effort among scientists at Imperial College London, the Royal Netherlands Meteorological Institute, and the Red Cross Red Crescent Climate Centre.25

D. Measuring Air Pollution From Space: The TEMPO Mission

Other recent scientific developments may also influence attribution science and its appearance in the courtroom. In April of 2023, NASA, NOAA, the U.S. Environmental Protection Agency, and the Smithsonian Astrophysical Observatory launched a satellite mission to monitor air pollution from space.26 This mission, called Tropospheric Emissions: Monitoring of Pollution (TEMPO), relies on a satellite that orbits the Earth’s equator at the speed of its rotation—a class of satellites known as “geostationary” satellites. The satellite takes hourly measurements of the atmosphere at a fixed location that overlooks all of North America.27 In doing so, it provides the first space-based high-resolution picture of air pollutants, such as particulate matter and nitrogen oxides, over the contiguous United States. With such data also comes the opportunity to empirically evaluate the impacts of extreme weather events, such as wildfires, on air quality. These data could therefore be critical for future analyses that seek to characterize the impacts of extreme weather events on air pollution and, by extension, on human health.

  • 1County of Multnomah v. Exxon Mobil Corp., No. 3:23-cv-01213-YY (D. Or., June 10, 2024).
  • 2Philip et al., supra note 18.
  • 3Complaint at 5, County of Multnomah v. Exxon Mobil Corp., No. 23CV25164 (Or. Cir. Ct. 2024).
  • 4Samuel Bartusek et al., 2021 North American Heatwave Amplified by Climate Change-Driven Nonlinear Interactions, 12 Nature Climate Change 1143 (2022); Emily Bercos-Hickey et al., Anthropogenic Contributions to the 2021 Pacific Northwest Heatwave, 49 Geophysical Rsch. Letters 23 (2022).
  • 5Rachel H. White et al., The Unprecedented Pacific Northwest Heatwave of June 2021, 14 Nature Comm. 727 (2023).
  • 6This heatwave has attracted wide scientific attention, resulting in several studies that have found a role of climate change in causing the event. See, e.g., Philip et al., supra note 18; Bartusek et al., supra note 34; Bercos-Hickey et al., supra note 34; Chunzai Wang et al., Unprecedented Heatwave in Western North America During Late June of 2021: Roles of Atmospheric Circulation and Global Warming, 40 Advances Atmospheric Sci. 14 (2023); and Nicholas J. Leach et al., Heatwave Attribution Based on Reliable Operational Weather Forecasts, 15 Nature Comm. 4530 (2024).
  • 7Richard Heede, Tracing Anthropogenic Carbon Dioxide and Methane Emissions to Fossil Fuel and Cement Producers, 1854-2010, 122 Climatic Change 229 (2014).
  • 8Complaint at 12, County of Multnomah, supra note 33.
  • 9American Electric Power Co. v. Connecticut, 564 U.S. 410, 418 (2011).
  • 10Notice of Removal at 43, County of Multnomah v. Exxon Mobil Corp., No. 3:23-cv-1213 (Dist. Or. 2023).
  • 11Municipalities of Puerto Rico v. Exxon Mobil Corp., No. 3:23-cv-01550 (D.P.R., 2022); Municipality of San Juan v. Exxon Mobil Corp., No. 3:23-cv-01608 (D.P.R., 2023).
  • 12Heede, supra note 37.
  • 13Complaint at 19, Municipalities of Puerto Rico v. Exxon Mobil Corp., No. 3:22-cv-01550 (D.P.R. 2023); Complaint at 16, Municipality of San Juan v. Exxon Mobil Corp., No. 3:23-cv-01608 (D.P.R. 2023).
  • 14David Keellings & José J. Hernández Ayala, Extreme Rainfall Associated With Hurricane Maria Over Puerto Rico and Its Connections to Climate Variability and Change, 46 Geophysical Rsch. Letters 2964 (2019).
  • 15Martin Lockman & Emma Shumway, State “Climate Superfund” Bills: What You Need to Know, Sabin Center: Climate Law Blog (Mar. 14, 2024), available at https://blogs.law.columbia.edu/climatechange/2024/03/14/state-climate-superfund-bills-what-you-need-to-know/.
  • 16Climate Superfund Act, No. 122, S. 259, 2023-2024 Sess. (Vt. 2024) (codified at 10 V.S.A. §§566-69). The law was enacted without the governor’s signature.
  • 1710 V.S.A. §599a(b)(1). A follow-on report is expected no later than January 15, 2026.
  • 18Report to the General Assembly: Climate Superfund Cost Recovery Program, Act 122 (Jan. 15, 2025), available at https://outside.vermont.gov/agency/anr/climatecouncil/Shared%20Documents/2025FeasibilityReportAct122.pdf?_gl=1*1eg7bqj*_ga*NzMxOTE0Nzg1LjE3MzcwNTkzMzk.*_ga_V9WQH77KLW*MTczNzA1OTMzOS4xLjEuMTczNzA1OTg5NS4wLjAuMA.
  • 19Id.
  • 20Climate Change Adaptation Cost Recovery Program, S. 2129B, 2023-2024 Leg. Sess. (N.Y. 2023) (codified at E.C.L. 76-0103), at 2, lines 18-24.
  • 21Id. at 2, lines 40-41.
  • 22Complaint, Chamber of Commerce of the United States of America v. Moore, No. 24-01513 (D. Vt. Dec. 30, 2024).
  • 23Complaint, West Virginia v. James, No. 25-00168 (N.D.N.Y. Feb. 6, 2025).
  • 24Barsugli et al., supra note 10.
  • 25Sjoukje Philip et al., A Protocol for Probabilistic Extreme Event Attribution Analyses, 6 Advances Stat. Climatology, Meteorology & Oceanography 177 (2020).
  • 26Smithsonian Institution & NASA, Tropospheric Emissions: Monitoring of Pollution, TEMPO, https://tempo.si.edu/ (last visited Jan. 28, 2025).
  • 27U.S. EPA, 2020 supra note 11.

IV. Conclusions

This paper provides an overview of select developments in climate attribution science, with a focus on key findings in the field between 2021 and 2024, and how these scientific concepts have begun to emerge in U.S. law and policy. It is clear that attribution science is developing quickly, and that the body of scientific research is already factoring into government decisions and showing up in court cases. As studies continue, policies develop, and cases evolve, attribution science will only become more important for informing climate adaptation, law, and policy.