Climate Shift Index Alerts
Using our Climate Shift Index (CSI) system (including Ocean CSI and Tropical Cyclone CSI), we issue alerts when select extreme weather events — such as heat waves, hurricanes, or wildfires — are made more likely by human-caused climate change.
Explore the log below to see a sampling of recent events linked to climate change, and use the CSI and Ocean CSI map tools to investigate daily conditions in your area.
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Climate change is driving widespread marine heat waves across the globe
The Pacific is experiencing a historic marine heat wave — but it’s far from alone. Every major ocean basin across the globe is currently experiencing unusually warm sea surface temperatures driven by climate change.
Pacific Ocean
The Pacific continues to host the world’s largest marine heat wave, now covering 63 million square kilometers — about 17% of Earth's oceans — an area larger than North and South America combined. A strengthening El Niño is contributing to some of this warming in the eastern Pacific.
Climate change is driving the vast majority of this event: 86% of the marine heat wave area would not have occurred without human-caused warming.
Since January, approximately 94% of the Pacific has experienced marine heat wave conditions, with the most persistent hotspots in the North Pacific remaining in marine heat wave conditions for more than 180 consecutive days.
Mediterranean
The Mediterranean marine heat wave has intensified following repeated heat waves over Europe, with 82.9% of the basin now experiencing marine heat wave conditions. About 85% of the current marine heat wave area is due to human-caused warming.
Sea surface temperatures have climbed into the mid-80s to low 90s °F (29-32°C), while large areas of the western Mediterranean are running 9-10°F (5-6°C) above normal.
One hundred percent of the basin has experienced at least one day this year under marine heatwave conditions.
Atlantic Ocean
Marine heat waves are less widespread across the Atlantic than in the Pacific or Mediterranean, with 23.3% of the basin currently affected. However, tropical sea surface temperatures largely remain in the upper 70s to upper 80s°F (24-32°C). Broad areas of the Atlantic are 2-5°F (1-3°C ) above normal compared to the 1991-2020 climatology.
Climate change is driving nearly all of the existing marine heat wave area: 81% would not have occurred without human-caused warming.
Gulf of Mexico
Marine heat waves encompass the southern Gulf of Mexico and the northwestern region of the Caribbean, as in some of the other basins, with 39.7% of the region currently experiencing marine heat wave conditions. Of the area experiencing marine heat wave conditions, however, 98% is attributable to climate change.
Sea surface temperatures are broadly in the 80s°F (27°C), with the hottest waters approaching 90°F (32°C) around Florida.
Record-hot nights grip much of the U.S. as climate change intensifies extreme heat
Record-warm nights are spreading across much of the U.S. this week, Aug. 12-14, offering little relief from extreme daytime heat and putting millions at greater risk of heat-related health impacts. Human-caused climate change made the extreme overnight temperatures at least three times more likely across more than 60% of the contiguous U.S., with the strongest influence across the West, South, and Southeast.
According to the National Weather Service, much of the Central and Southeastern U.S. is “forecast to see their hottest temperatures so far this year or even in the past few years. There will be little nighttime relief from the heat, and urban areas may not cool below 80°F.”
Record high minimum temperatures — the warmest daily low temperatures on record — were set across 20 states from California to Kentucky and West Virginia on Aug. 10 and 11. All-time and top-five records were also set in Florida, Georgia, South Carolina, and North Carolina.
From Wednesday, Aug. 12 through Friday, Aug. 14, low temperatures are forecast to only fall to the mid-to-upper 70s from Kansas to Texas and expanding into the Southeast U.S. Cities like Tulsa, OK; Dallas, TX; Little Rock, AR; New Orleans, LA; and Memphis, TN are not expected to fall below 80°F. Additional record high minimums are expected.
Hot summer nights limit the body’s ability to cool down and recover from extremely hot days, increasing the risk of heat stress, disrupted sleep, and related health impacts.
Since 1970, the number of unusually warm summer nights has increased in 95% of the 243 major U.S. cities analyzed by Climate Central.
Climate influence:
Climate Shift Index (CSI) levels of 5 — the highest possible — are forecast for minimum temperatures across much of the lower 48, or contiguous U.S., with the highest concentrations in the West, South, and Southeast from Aug. 10 through Aug. 14, meaning human-caused climate change made this extreme heat at least five times more likely. This signals an exceptional climate-influenced event.
On Aug. 11, the contiguous U.S. set a new record for warm overnight temperatures, with 82% of the lower 48 experiencing the largest spatial extent of overnight heat with a CSI 1 or higher.
From Aug. 10 through 12, more than 201 million people across the western, southern, and southeastern U.S will experience at least one night with a low temperature reaching a CSI 3 or higher.
An additional 138 million people will experience at least one night with a low temperature reaching a CSI 3 or higher on Aug. 13 and 14. A CSI 3 indicates a very strong influence of climate change.
Minimum temperatures made at least three times more likely by human-caused climate change are projected to affect approximately 1.9 million square miles (4.8 million square kilometers) — more than 60% of the contiguous U.S.
Climate change intensified dangerous heat across South Korea and Japan
An intense heat wave has brought prolonged extreme heat to the Korean Peninsula and Japan, with Climate Shift Index levels indicating human-caused climate change made the event at least five times more likely across much of the region. The heat has contributed to heat illnesses, deaths, and widespread impacts as dangerously hot days and nights continue.
Excessive heat has been affecting much of South Korea and Japan since mid- to late July, and is forecast to continue through the first week of August.
The heat wave is being driven by overlapping high-pressure systems — the North Pacific High near the surface and the Tibetan High aloft — which are acting like a heat dome over the region. Sinking air is suppressing clouds and rainfall, allowing strong sunshine and heat to build over several days.
Hot, humid air moving north from the surrounding seas is also keeping overnight temperatures elevated, while downslope winds are further intensifying the heat in parts of southeastern Korea.
Since July 27, temperatures reaching between 30°C and 40°C have affected much of the Korean Peninsula, with the highest temperatures along South Korea’s southern and western coasts.
Yangsan in South Gyeongsang recorded South Korea’s highest temperature since observations began in 1904, with temperatures reaching 42.5°C over the weekend. South Korea issued its first-ever severe heat wave warning, urging people to avoid all outdoor activities.
Similar hot conditions have affected western and southwestern Japan over this period, with temperatures ranging from 30°C to 38°C. In some regions, temperatures topped 40°C.
Nighttime has offered little relief across the region. Pyongyang in North Korea and Donghae, Samcheok, and Goseong in South Korea recorded five straight tropical nights — nights with temperatures at or above 25°C — while Seoul recorded 12 consecutive tropical nights as of Monday, Aug. 3.
High nighttime temperatures can prevent the body from cooling and recovering after daytime heat, disrupting sleep and increasing heat strain over consecutive nights.
This heat is forecast to continue through the end of the week, affecting most of the Korean Peninsula and southwestern Japan.
Climate influence:
Climate Shift Index (CSI) levels of 5 — the highest possible — are forecast across much of Japan and South Korea, with the highest concentrations in South Gyeongsang, North Jeolla, and western Japan from July 27 through Aug. 7, meaning human-caused climate change made this extreme heat at least five times more likely. This signals an exceptional climate-influenced event.
From July 27 through Aug. 8, more than 149 million people (86% of the population) across South Korea and Japan will experience at least one day with average temperatures reaching a CSI 3 or higher, indicating a very strong influence from climate change.
Temperatures made at least three times more likely by human-caused climate change are projected to affect approximately 319,000 square kilometers (123,000 square miles).
See this event on the Climate Shift Index map
Impacts:
This heat has affected both people and animals across the Korean Peninsula and Japan, resulting in more than 1,800 cases of heat illness and 14 heat-linked deaths during the latter half of July in South Korea.
Three lions at a Tokyo zoo and more than 30,000 farmed flatfish on Jeju Island have also died as a result of this ongoing heat wave.
This heat is complicating earthquake-recovery efforts in Kumamoto Prefecture following the magnitude 7.1 earthquake that struck last week.
Climate change fueling increase in wildfire days in the Pacific Northwest
Nearly 50 large wildfires are burning across Oregon and Washington, as of Monday, Aug. 3. The fires are fueled by hotter temperatures, record drought, and drier conditions that climate change is making more common.
Nearly 50 large wildfires are burning across Oregon and Washington, as of Monday, Aug. 3. The fires are fueled by hotter temperatures, record drought, and drier conditions that climate change is making more common.
In Oregon, 33 active wildfires have burned 1,812,608 acres — an area larger than the state of Delaware — while 16 fires in Washington have burned 344,000 acres. Fire weather days are becoming more common as wildfire seasons are lengthening and intensifying across the western U.S.
The Pacific Northwest has seen an increase in the combination of hot, dry, and windy days that allow for explosive wildfire growth.
In Northeastern Washington — in cities like Spokane, where the Autumn Lane, Old Trails, and Fairview Fires are burning — the region now experiences 21 more fire weather days than in the early 1970s. These high-risk wildfire conditions have increased from less than a week 55 years ago to now over three weeks.
A similar trend has occurred in south-central Oregon, where the region now sees 26 more fire weather days on average than in the 1970s.
These worsening conditions increase both the wildfire risk and smoke pollution, which can degrade air quality and impact health.
Air quality alerts are in effect for Idaho, Montana, Oregon, Washington, and Wyoming as Unhealthy to Hazardous conditions are expected Monday, Aug. 3 and Tuesday, Aug. 4. Shifting winds are forecast to push ground-level smoke into cities like Seattle, Tacoma, Olympia, Portland, Salem, Corvallis, and Eugene.
Increases in wildfire smoke since 2016 have either stalled or reversed decades-long air quality improvements.
The number of people in the U.S. experiencing at least one day per year with smoke-related fine particle pollution 3 times over the EPA standard has increased 27-fold over the last decade.
Climate change fuels dangerous heat as wildfires force mass evacuations across western Europe
Human-caused climate change is intensifying an exceptional heat wave across western and southern Europe, where temperatures up to 45°C (113°F) are forecast in parts of France, and Climate Shift Index levels of 5 indicate the extreme heat was made at least five times more likely. The heat overlaps with severe drought and active wildfires that have forced about 330,000 people to evacuate, including 220,000 in France.
As of Tuesday, July 28, roughly 330,000 people have been evacuated from homes and vacation sites due to ongoing wildfire activity along France’s Atlantic coast.
The Gironde Fire in France reportedly burned an area four times the size of Paris, forcing 220,000 people to evacuate.
High temperatures across western France and north/central Spain are forecast to reach 34°C to 39°C (93°F to 102°F) through Friday, July 31st. This excessive heat is 9°C to 12°C (16°F to 22°F) above normal for late July.
The peak, and most extreme, heat is expected Wednesday, July 29th, in western France between Tours and Toulouse, with highs up to 45°C (113°F) — as much as 15°C (27°F) above average.
According to the European Drought Observatory and Copernicus, much of the affected area is in the highest level “Drought Alert.”
Research shows that human-caused warming is boosting the atmosphere’s growing demand for water, an increasingly important cause of drought.
Climate influence:
Climate Shift Index (CSI) levels of 5 — the highest possible — are forecast across much of western and southern Europe, with the highest concentrations in Spain, France, and Italy from July 28 through July 31, meaning human-caused climate change made this extreme heat at least five times more likely. This signals an exceptional climate-influenced event.
The highest CSI values overlap with areas experiencing significant wildfire activity and severe drought, including western France and northern/central Spain, where hundreds of thousands of people have been evacuated.
From July 28 through July 31, more than 301 million people across western and southern Europe will experience at least one day with average temperatures reaching a CSI 5 or higher, indicating an exceptional influence from climate change.
Temperatures made at least five times more likely by human-caused climate change are projected to affect approximately 2 million square kilometers (772,000 square miles) — an area larger than all of Mexico.
Climate change fueled extraordinary heat across Africa in July
Human-caused climate change intensified widespread July heat across Africa, with Climate Shift Index levels of 5 spanning much of the continent. Nearly 94% of Africa experienced climate change's influence on extreme heat on July 22 — the largest continental footprint ever recorded.
Since the beginning of July, warmer-than-usual temperatures have affected much of the African continent. A persistent heat dome over North Africa and southwestern Europe has trapped hot air over the region and helped draw very hot, dry air north from the Sahara.
Across North Africa, portions of northern West Africa, northern Central Africa, and northern East Africa, temperatures reached between 38°C and 46°C (100°F and 115°F), up to 8°C (14°F) higher than usual. In Western Sahara and Morocco, temperatures of this magnitude were up to 12°C (22°F) above normal.
Some regions of Tunisia and Algeria experienced daily highs of nearly 50°C (122°F), up to 8°C (14°F) above normal for this time of year.
Slightly milder but still warmer-than-normal temperatures affected Central, Southeast, and Southern Africa throughout July. These conditions may be tied to the rapid development of a strong El Niño and unusually warm tropical ocean conditions. The World Meteorological Organization’s June-August outlook showed higher odds of above-normal temperatures across much of the tropical belt, particularly equatorial Africa and Southern Africa.
Across Central and Southeast Africa, specifically in the Democratic Republic of the Congo, temperatures reached between 27°C and 35°C (81°F and 95°F), up to 6°C (11°F) above normal.
Temperatures between 21°C and 29°C (70°F and 84°F) affected much of Southern Africa. Throughout July, temperatures were up to 8°C (14°F) above normal.
Climate influence:
Throughout July, Climate Shift Index (CSI) levels of 5 — the highest possible — were observed or forecast across much of the African continent, indicating that human-caused climate change made these extreme heat conditions at least five times more likely. This signals an exceptional climate-influenced event.
On July 22, 2026, Africa recorded its largest CSI extent on record. Nearly 94% of the continent experienced CSI levels of at least 1, marking the greatest continental footprint of climate change influence on extreme heat in the observational record. The day also set a record for the largest extent of the more severe CSI levels 2–5. Not only was climate change's influence nearly continent-wide, but its strongest signals were more widespread than ever before.
Across July, more than 1.4 billion people (90% of Africa's population) experienced or are expected to experience at least one day when average temperatures are five times more likely due to climate change.
Temperatures made at least five times more likely by human-caused climate change are projected to affect, or have already affected, approximately 26 million square kilometers (10 million square miles) across the African continent. The extraordinary footprint spans more than 80% of the continent and represents about 17% of Earth’s total land area.
Climate change intensifies dangerous heat across the western and southern U.S.
Human-caused climate change is making an intense late-July heat wave across the western and southern United States significantly more likely, with exceptional Climate Shift Index levels forecast across much of the region. Millions of people face repeated days of dangerous heat, record-warm nights, and elevated health risks through early August.
Unusual temperatures:
At the start of the week, the National Weather Service issued Heat Advisories or Extreme Heat Warnings for more than 79 million people across more than a dozen states, primarily across the southern and southwestern United States. (Latest information: Heat.gov)
Repeated days of dangerous to extreme heat are expected, driven by a combination of hot days and warm overnight temperatures.
Highs between 95°F and 105°F are forecast, with locally higher temperatures of 115°F to 120°F in parts of the Desert Southwest — southwest California, southern Nevada, and western Arizona — especially between Friday, July 31 and Sunday, August 2.
The warmest daily low temperatures on record for late July and early August are forecast across Alabama, Florida, and Georgia on Wednesday, July 29. By late week and into early August, this record overnight warmth expands west into Louisiana, Texas, New Mexico, Arizona, and Southern California.
Parts of Arizona, Southern California, and Nevada may not drop below 88°F to 92°F each night through August 2. This excessive nighttime warmth is as much as 10°F above normal.
The Weather Prediction Center expects an “enhanced risk of Rapid Onset Drought for 2 areas in the Central states due to expected extreme heat, increased evapotranspiration, and mounting rainfall deficits.”
Climate influence:
Climate Shift Index (CSI) levels of 5 — the highest possible — are forecast across much of the western CONUS, with the highest concentrations in the Southwest from July 29 through August 2, meaning human-caused climate change made this extreme heat at least five times more likely. This signals an exceptional climate-influenced event.
From July 29 through August 2, more than 74 million people across the western and southern United States will experience at least one day with average temperatures reaching a CSI 5 or higher, indicating an exceptional influence from climate change.
Temperatures made at least five times more likely by human-caused climate change are projected to affect approximately 1.2 million square miles (3 million square kilometers) — more than 50% of the area west of the Mississippi River.
Climate change is intensifying an extreme and widespread U.S. heat wave.
Human-caused climate change is fueling dangerous heat across much of the United States as a prolonged heat wave spreads from the western U.S. eastward to the Midwest and South. Climate Shift Index levels of 5 — the highest possible — are forecast across large areas of the country through July 28, indicating that climate change made the extreme heat at least five times more likely. Over two dozen states are forecast to experience temperatures above 100°F (38°C).
How has climate change influenced this heat?
Climate Shift Index (CSI) levels of 5 — the highest possible — are forecast across much of the CONUS, with the highest concentrations in the Southwest, southern Plains, and parts of the central U.S. from July 23 through July 28, meaning human-caused climate change made this extreme heat at least five times more likely. This signals an exceptional climate-influenced event.
From July 23 through July 28, more than 101 million people across the western and southern United States will experience at least one day with average temperatures reaching a CSI 5 or higher, indicating an exceptional influence from climate change.
Temperatures made at least five times more likely by human-caused climate change are projected to affect approximately 1.5 million square miles (3.9 million square kilometers) — about 50% of the CONUS — an area larger than India.
How unusual is the forecasted heat?
Heat dome brings dangerous heat
From July 23 through July 28, a heat dome building across the United States will drive widespread hot and humid conditions. According to NWS, Moderate to Major HeatRisk is already present across parts of the southern half of the country and forecast to expand over much of the country, with areas of Extreme HeatRisk forecast to develop over the weekend and persist into next week.
Currently, 60.2 million people are under heat alerts — this number is expected to grow over the weekend and into next week.
Daytime temperatures
Widespread daytime heat is forecast across much of the contiguous U.S., with the hottest conditions focused across the Southwest, southern Plains, and parts of the central U.S. High temperatures above 90°F (32°C) are expected across a broad swath of the West, Plains, Midwest, and South, while many areas in the hottest portion of the event are forecast to reach or exceed 100°F (38°C).
Across much of the western U.S., daytime highs are forecast to be about 4°F to 11°F (2 to 6°C) above normal, while parts of the northern and north-central U.S. are expected to reach about 10°F to 20°F (6°C to 11°C) above normal.