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A Climate Central analysis of 241 U.S. locations shows that 195 (81%) have experienced an increase in the annual number of extremely hot days since 1970, with an average increase of 11 days. The report highlights that extreme heat is the leading cause of weather-related fatalities in the U.S. and disproportionately affects vulnerable populations, including children, the elderly, and people of color living in urban heat islands. Specific cities like Austin, Texas, and San Angelo, Texas, have seen significant increases of 47 and 39 additional extremely hot days annually, respectively.

The document argues that reporting on extreme weather without mentioning climate change is incomplete and potentially inaccurate. It provides specific phrasing and examples for connecting various weather phenomena—such as heatwaves, droughts, floods, and hurricanes—to global warming, while highlighting the role of attribution science in quantifying these links. It also recommends tools like the Climate Central 'Climate Change Index' and World Weather Attribution for real-time data.

The report finds that a three-day extreme heat event in Uttar Pradesh from June 14-16, 2023, was made at least two times more likely by human-caused climate change, with some areas seeing a three-fold increase in likelihood. The event resulted in at least 34 fatalities in Ballia and led to school closures in Bihar. The analysis highlights that the combination of extreme heat and high humidity increased the severity of the event, following a previous humid heat wave in April 2023 that was made over 30 times more likely by climate change.

The document outlines the critical role of scientific research in climate litigation, emphasizing how experts can help hold corporations and governments accountable for climate damages and disinformation. It identifies key research priorities—such as attribution science and the study of climate obstruction—and provides actionable ways for scientists to engage, including serving as expert witnesses, contributing to amicus briefs, and designing research specifically relevant to legal proceedings. The Union of Concerned Scientists (UCS) Science Hub for Climate Litigation is presented as a central resource to bridge the gap between the scientific community and legal practitioners.

The study analysed peak 48-hour rainfall in Te Matau-a-Māui and Te Tairāwhiti during February 2023. Historical weather station data (1979-2023) suggests the 2-day maximum rainfall is now approximately 30% more intense and four times more likely to occur than if the climate had not warmed by 1.2C. However, climate models showed a much smaller change in likelihood and intensity, creating a discrepancy that prevents the researchers from quantifying the overall role of human-induced climate change with certainty. The report notes that 225,000 homes lost power and the event caused multi-billion dollar damages, comparable to the 2011 Waitaha earthquakes.

The analysis finds that while the low rainfall during the October-December 2022 period in Central South America cannot be attributed to climate change and is partly driven by La Niña, human-induced climate change likely reduced water availability by increasing temperatures and evapotranspiration. This exacerbates the agricultural drought, which has already caused severe crop losses in Argentina and water shortages in Uruguay.

The report finds that majorities in all 73 surveyed low-emission areas have experienced extreme weather, with unusually hot weather being the most common hazard. Most respondents attribute these events to climate change, yet significant gaps in individual and household preparedness exist, particularly in South America and Europe. Recovery times vary widely, with some populations in Central Asia and the Balkans expecting recovery to take a year or more.

The document explains attribution studies—which use climate models to determine if and how much human-induced climate change affected a specific event—and provides guidance on reporting various extreme phenomena. It details how global warming increases the probability and intensity of heatwaves and heavy precipitation globally, while the effects on droughts, wildfires, and tropical cyclones vary by region or specific metric. It emphasizes that while climate change influences the risk and intensity of these events, human factors like land use and water management also contribute to whether an event becomes a disaster.

The 2022 rainy season in West Africa saw above-average rainfall and devastating floods, particularly in Nigeria and Niger, where fatalities reached at least 612 and 195 respectively. An attribution study found that climate change made the seasonal rainfall over the Lake Chad region approximately 80 times more likely and 20% more intense, while the 7-day maximum rainfall over the lower Niger Basin became about twice as likely and 5% more intense. Beyond climate change, the flooding was driven by the release of the Lagdo Dam in Cameroon and exacerbated by high poverty rates, political instability, and the location of infrastructure and settlements on flood plains.

World Weather Attribution (WWA) reports on its activities from October 2021 to October 2022, during which it published eight rapid analyses and several peer-reviewed papers. These studies examined the role of human-induced climate change in events such as heatwaves in India, Pakistan, and the UK, as well as flooding and droughts in various regions. The organization emphasizes that while climate change is a major driver for heatwaves, its role in other events like tropical cyclones can be less clear, often compounding with high levels of vulnerability to increase human impacts.

Climate Central's global analysis using the Climate Shift Index (CSI) found that 96% of the world's population—7.6 billion people—experienced daily temperatures made warmer by human-caused climate change between October 2021 and September 2022. The study identifies the strongest influences in regions near the equator and on small islands, with Lagos, Mexico City, and Singapore emerging as the highest hotspots of human exposure when accounting for urban population. The analysis also pinpointed peak continental CSI days, noting that these do not always coincide with major heat waves.

Summer 2022 was the third hottest on record for the contiguous U.S., with significant influence from climate change on both daytime and nighttime temperatures. Using the Climate Shift Index, the analysis shows that nearly half of the contiguous U.S. experienced 15 or more days where average temperatures were at least twice as likely due to climate change. The period was also marked by extreme precipitation in Missouri and Kentucky, widespread wildfires burning over 6.7 million acres, and severe drought affecting 94% of Hawaii and 85 consecutive weeks in Puerto Rico.

The 2022 monsoon rainfall in Pakistan, particularly in Sindh and Balochistan, resulted in catastrophic flooding that affected over 33 million people and caused damages likely exceeding US$30 billion. Attribution analysis indicates that 5-day maximum rainfall in Sindh and Balochistan is now approximately 75% more intense than it would have been without a 1.2C warming, while 60-day rain across the Indus basin is about 50% more intense. While high regional variability and model discrepancies make exact quantification of the human-induced role difficult, most models and observations show that intense rainfall has increased as Pakistan warmed, with future projections suggesting further significant increases in rainfall intensity at 2 °C of warming.

The analysis finds that human-caused climate change made the July 2022 UK heatwave, which saw record temperatures of 40.3°C, at least 10 times more likely. Observational data suggests such a heatwave would have been approximately 4°C cooler in preindustrial times, while model-based estimates suggest a 2°C difference in a 1.2°C cooler world. The event was extreme even in the current climate, with some 1-day maximum temperatures having return periods of 1 in 1000 to 1500 years.

An event attribution study found that human-caused climate change increased the likelihood and intensity of the extreme rainfall that hit eastern Northeast Brazil in May 2022, causing over 133 deaths and displacing at least 25,000 people. While the events were exceptionally rare—with a 1-in-500 to 1-in-1000 annual chance in the current climate—they would have been approximately 20% less intense in a world without human-induced warming. The study highlights that pre-existing structural vulnerabilities, such as unplanned urbanization in low-income neighborhoods and an infrastructure deficit, exacerbated the disaster's impact.

A collaborative scientific study found that human-induced climate change approximately doubled the probability of the extreme 2-day rainfall that caused devastating floods in eastern South Africa in April 2022, increasing the event's intensity by 4-8%.

A collaborative scientific analysis concludes that greenhouse gas and aerosol emissions contributed to the increased likelihood and intensity of heavy rainfall during Tropical Storm Ana and Tropical Cyclone Batsirai in early 2022. While Tropical Storm Ana was a rare event for Malawi and Mozambique (1 in 50 years), Cyclone Batsirai was more common for Madagascar (1 in 2 years). The study highlights that existing vulnerabilities, including prior flooding, conflict in northern Mozambique, and drought in southern Madagascar, exacerbated the humanitarian impacts.

The report outlines critical research needs across natural sciences, social sciences, and legal analysis to support climate litigation. Key gaps include the need for localized attribution science, investigations into corporate disinformation and internal knowledge (including non-fossil fuel industries), and the quantification of economic damages. It also emphasizes the necessity of 'translational work' to bridge the communication gap between scientists, legal practitioners, and judges, particularly regarding legally relevant timeframes and standards of evidence.

The document outlines the escalating impacts of human-induced climate change on humans and ecosystems, emphasizing that the most marginalized populations are hit hardest. It highlights the role of 'attribution literature' in linking extreme weather to human activity and discusses the critical need for transformative adaptation and nature-based solutions. The briefing warns that the costs of inaction far exceed those of mitigation and adaptation, noting significant GDP losses in vulnerable nations and the potential for mass migration and biodiversity loss.

The document explains 'event attribution' as a scientific method to determine how much human-induced climate change affects the probability and intensity of specific weather extremes. It provides a detailed breakdown of how climate change influences heatwaves, floods, tropical cyclones, snowfalls, droughts, and wildfires, while cautioning against oversimplifying these events as having a single cause. The guide emphasizes that while some trends (like heatwaves) are globally certain, others (like floods or droughts) vary by region and are influenced by local human factors such as land use and water management.