Search Climate Insights Directory

Between December 2025 and February 2026, human-caused climate change significantly influenced global temperatures, with more than one in six people daily experiencing temperatures at least twice as likely due to climate change. In the United States, a sharp divide occurred: western states saw record-breaking warmth, with nine states experiencing their warmest December-February on record and Casper, Wyoming, recording the highest temperature anomaly globally among 960 analyzed cities. Conversely, the eastern U.S. faced below-average temperatures and cold snaps that the Climate Shift Index (CSI) indicates were made less likely by climate change. The record warmth in the west has led to low snowpack in Oregon, Colorado, and Utah, threatening water supplies and increasing wildfire risks.

The document explains how a warming atmosphere and oceans fuel more powerful thunderstorms, leading to stronger straight-line winds and a shift in 'Tornado Alley' toward the Eastern US. It highlights the economic toll, noting that severe weather accounted for 91% of billion-dollar disasters in the US in 2025, and encourages newsrooms to use attribution studies and local data to illustrate these climate connections.

In February 2026, the United States experienced an average temperature anomaly of 2.1°F across 192 cities. While the Northeast was the coldest region with an average anomaly of -3.4°F, the Northern Rockies and Plains were the warmest, exceeding normal temperatures by more than 8.4°F. Long-term data indicates that 173 of the 192 analyzed cities have warmed since 1970, with Albany, Georgia, showing the greatest increase at 8.4°F. Climate attribution analysis using the Climate Shift Index (CSI) found that San Juan, Puerto Rico, had 16 days where temperatures were at least five times more likely due to climate change.

March 2026 was the warmest March on record for the contiguous U.S., characterized by a historic snow drought in the West and extreme heat that increased cooling energy demand. Globally, the month was the second-warmest on record, with Arctic sea-ice reaching a near-record low maximum. In the U.S., severe drought affected 77% of the contiguous region, while Hawaii experienced record-breaking precipitation due to Kona lows.

The document is a comprehensive glossary designed to bridge the communication gap between the scientific and legal communities in the context of climate litigation. It defines key terms across seven thematic areas: foundational scientific concepts, measurement and data methods, climate and environmental science, risk and impact, public health, Indigenous Knowledge, and socioeconomic policy. The guide emphasizes the distinctions between scientific and legal interpretations of terms like 'bias', 'significance', and 'uncertainty', and explains how attribution science and climate modeling can be used to establish causation and responsibility in court.

A study by World Weather Attribution on the impact of nine named storms in the western Mediterranean, finding that while evidence is uncertain, there is a trend toward increased intensity of extreme heavy rainfall events, particularly in northern regions, exacerbated by urban development in floodplains.

Analysis by Climate Central indicates that all 25 analyzed coffee-producing countries, representing 97% of global production, experienced an increase in 'coffee-harming heat' (temperatures above 30°C) between 2021 and 2025 due to carbon pollution. The top five producers—Brazil, Vietnam, Colombia, Ethiopia, and Indonesia—saw an average of 57 additional days of such heat annually. Brazil, the largest producer, experienced 70 extra days of coffee-harming heat per year on average. These conditions threaten both arabica and robusta coffee varieties, with arabica being more sensitive to heat. The report warns that land suitable for coffee farming could decrease by 50% by 2050 without adaptation, potentially leading to deforestation as farmers move to higher elevations.

In January 2026, severe wildfires affected central-southern Chile and northern Patagonia in Argentina, driven by temperatures above 38°C, drought, and winds of 40–50 km/h. The fires destroyed at least 1,000 homes in Chile, killed 23 people, and burned over 109,000 hectares across both countries, impacting the UNESCO world heritage site Los Alerces National Park. An attribution study using the hot-dry-windy index (HDWI) found that these conditions, typically 1-in-5-year events, were made more likely by human-induced climate change by a factor of approximately 3 in Chile and 2.5 in Patagonia. Additionally, fire-season rainfall intensity decreased by about 25% in Chile and 20% in Patagonia. The study highlights that nonnative monocultural pine plantations increased flammability and that natural variability, such as La Niña and the Southern Annular Mode, further enhanced the hot and dry conditions.

In January 2026, the United States experienced an average temperature anomaly of -1.2°F, with 133 cities recording cooler-than-average conditions. Despite this national trend, the western U.S., particularly the Northern Rockies & Plains, saw significant warming, with Helena, Montana, recording the highest anomaly at 9.1°F. Long-term data indicates that 191 of the 194 analyzed cities have experienced warming trends since 1970, with Great Falls, Montana, showing the largest increase of 9.6°F. Climate attribution analysis using the Climate Shift Index (CSI) highlighted that San Juan, Puerto Rico, had 24 days where temperatures were at least five times more likely due to climate change.

February 2026 was the fifth-warmest month globally on record, with the contiguous U.S. experiencing its second-warmest winter in 132 years. A critical 'snow drought' affected the western U.S., where snow-covered areas in January were only 34% of normal, threatening water supplies for agriculture and energy. Climate Central's analysis indicates that human-driven climate change significantly influenced winter temperatures, particularly in the Southwest, and is the primary cause of spring warming in 98% of 241 examined U.S. cities.

The report finds that while December 2025 temperatures in the U.S. were evenly split between warmer-than-average and cooler-than-average cities, long-term trends show nearly all analyzed cities have warmed since 1970. The Southwest was the most unusually hot region, with Casper, Wyoming, recording the highest anomaly. Climate signal (CSI) was minimal nationwide, though San Juan, Puerto Rico, saw 10 days where temperatures were at least five times more likely due to climate change.

January 2026 was the fifth-warmest January on record globally, characterized by significant temperature anomalies in the U.S. West and record-low snowpacks in several states. The document highlights the transition of NOAA to the Relative Oceanic Niño Index (RONI) to better account for climate change in ENSO tracking. Attribution analysis using the Climate Shift Index (CSI) indicates that extreme warmth in the northern U.S. and specific cities like San Juan and Honolulu was strongly driven by carbon pollution.

A World Weather Attribution study examines the role of climate change and natural variability in the devastating floods of November 2025 across Sri Lanka and the Malacca Strait. While observational data indicate a significant increase in the intensity of extreme 5-day rainfall events—up to 160% in Sri Lanka and 50% in the Malacca Strait due to a 1.3°C rise in global temperatures—climate models failed to consistently capture these trends, preventing a definitive quantitative attribution. The study also notes that La Niña and a negative Indian Ocean Dipole contributed between 5% and 13% to the rainfall in the Malacca Strait, while rapid urbanization and infrastructure failures exacerbated the humanitarian impact.

The document introduces attribution science as a method to measure how human-caused climate change affects the likelihood, frequency, and intensity of weather events by comparing current observations with simulated 'counterfactual' worlds. It details Climate Central's specific tools, such as the Climate Shift Index (CSI) for air and sea surface temperatures and the Tropical Cyclone CSI for hurricane wind speeds. The guide distinguishes between different types of attribution—event, trend, source, and impact—and notes that while temperature-related events are highly quantifiable, other severe weather like tornadoes remains an active area of research.

In November 2025, the United States experienced an average temperature anomaly of 2.1°F across 194 analyzed cities, with the western half of the country seeing exclusively above-average temperatures. The Southwest, South, and Northern Rockies and Plains were the most unusually hot regions, with anomalies exceeding 4.8°F. Waco, Texas, recorded the highest anomaly at 7.5°F. Long-term trends show 183 of 194 stations have warmed since 1970, with El Paso, Texas, seeing the greatest increase of 6.9°F. Climate attribution via the Climate Shift Index (CSI) highlighted San Juan, Puerto Rico, with 27 days at CSI 5, meaning temperatures were at least five times more likely due to climate change.

In 2025, the contiguous U.S. experienced its fourth-warmest year on record and 23 billion-dollar weather and climate disasters, totaling $115 billion in damages. Globally, 2025 was the third-warmest year since 1850, with NOAA data indicating it was approximately 1.3°C warmer than the pre-industrial average. The year was marked by record-breaking December heat in the U.S. Southwest and devastating atmospheric river flooding in Washington and Oregon.

The document reports that November 2025 was the third warmest on record globally and the fourth warmest for the contiguous U.S. It highlights a long-term trend of warming winters in the U.S., where the coldest day of the year has warmed by approximately 7°F since 1970. The briefing also notes significant regional anomalies, such as extreme warmth in Texas and heavy rainfall in southern California, while discussing the ongoing La Niña advisory and its expected impacts on weather patterns through early 2026.

An event attribution study on the October 2025 floods in eastern Mexico found that the onset of La Niña heightened the likelihood and intensity of heavy rainfall. While climate models and observational datasets showed conflicting trends regarding the long-term impact of climate change on regional rainfall, the study emphasizes that vulnerability was amplified by rapid urbanization, informal settlements, and chronic underinvestment in indigenous and rural communities.

In October 2025, the United States experienced an average temperature anomaly of 2.0°F across 192 analyzed cities, with the Ohio Valley seeing the most unusual heat at 4.89°F above normal. Fairbanks, AK, recorded the highest individual city anomaly at 7.1°F. Long-term data indicates that 190 of 191 analyzed stations have shown positive warming trends since 1970, with Wheeling, WV, experiencing the fastest increase at 7.8°F. Climate change influence was particularly strong in San Juan, PR, which had 29 days at a Climate Shift Index (CSI) of 5, and Honolulu, HI, where both cities saw at least two weeks of CSI values of 2 or higher.

The analysis shows that 161 of 192 analyzed U.S. cities experienced hotter-than-average temperatures in September 2025, with an average anomaly of 1.5°F. The Northwest region saw the most unusual heat, averaging 3.42°F above normal, while Spokane, WA, recorded the highest individual city anomaly at 7.8°F. Long-term trends indicate widespread warming since 1970, with Reno, NV, showing the fastest increase at 10.8°F. Climate Shift Index (CSI) data highlighted strong climate change influence in several cities, most notably San Juan, PR, which had 22 days at CSI 5.