How Climate Change Is Intensifying Heat Waves in South Asia

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South Asia is experiencing an unprecedented climate crisis as heat waves become increasingly frequent, severe, and deadly. Climate change has doubled the number of days of extreme heat in 195 countries and territories, with South Asia emerging as one of the most vulnerable regions on the planet. The combination of rising temperatures, changing weather patterns, and dense populations creates a perfect storm that threatens the health, livelihoods, and future of over 1.8 billion people living in this region.

The situation has reached critical levels in recent years. 2025 began with the hottest January on record, continuing a trend that shows no signs of abating. Events like the April 2025 heatwave were 4°C higher over the past 30 years than the average between 1950 and 1986, demonstrating the dramatic acceleration of warming in the region. What makes this particularly alarming is that the weather extremes took place during a neutral phase and not El Niño, which usually further boosts temperature rise.

The Science Behind South Asia’s Extreme Heat

Understanding Wet-Bulb Temperature

One of the most critical concepts for understanding heat waves in South Asia is wet-bulb temperature, which combines both temperature and humidity to measure the actual stress placed on the human body. Extreme heat is measured via “wet-bulb temperatures,” a combined measure of temperature and humidity. This metric is particularly important because humidity is an important factor in how high temperatures affect the human body, as sweating, the way for humans to cool themselves, becomes less effective at high humidity.

The implications are dire. A wet-bulb temperature of 35°C can be considered an upper limit on human survivability, and extremes of wet-bulb temperature in South Asia are likely to approach and, in a few locations, exceed this critical threshold by the late 21st century under the business-as-usual scenario of future greenhouse gas emissions. Even more concerning, projections indicate that by 2100, 70% of Indian, Pakistani, and Bangladeshi populations could be exposed to these extreme wet-bulb temperatures.

Geographic Vulnerability

Southwest Asia, South Asia, and Eastern China are among the regions most prone to extreme heat. Within South Asia, certain areas face particularly acute risks. The most intense hazard from extreme future heat waves is concentrated around densely populated agricultural regions of the Ganges and Indus river basins. These river valleys, which support hundreds of millions of people and serve as the agricultural heartland of the region, are experiencing some of the highest wet-bulb temperatures currently observed anywhere on Earth.

Findings reveal a shift in heatwave synchronization from western and central Asia before 1990 towards Pakistan, northwest India, and the southwestern Tibetan Plateau by the mid-21st century. This shift means that areas previously less affected by extreme heat are now becoming hotspots, requiring new adaptation strategies and infrastructure investments.

Atmospheric Drivers

The physical mechanisms driving these extreme heat events are complex and interconnected. This shift is primarily driven by increased surface sensible heat flux, which enhances atmospheric diabatic heating and strengthens the early-summer circumglobal teleconnection. Additionally, the circumglobal teleconnection (CGT) pattern is known to facilitate the propagation of Rossby waves and link weather extremes across continents, contributing thus to the synchronization of heatwaves in South Asia.

Local factors also play a significant role. Enhanced high-pressure influenced by tropical waves, moisture deficiency and strong land-atmosphere coupling are considered as the key drivers to extreme heatwave events. This land-atmosphere coupling creates a feedback loop where high temperatures dry the soil by increasing evaporation and plant transpiration, while drier soil intensifies surface warming by reducing evaporative cooling and increasing upward sensible heat flux.

Recent Record-Breaking Heat Events

The 2023 Southeast Asia Heat Wave

The April-May 2023 heat wave stands as one of the most extreme events in recorded history. Continental Southeast Asia was hardest hit, where all the countries broke their highest temperature records with measurements exceeding 42 °C, and Thailand set the region’s new record of 49 °C. 70% of all weather stations in Thailand, Laos, Cambodia, Myanmar, and Vietnam recorded daily maximum temperatures exceeding 42 °C.

Individual countries experienced unprecedented conditions. In Vietnam, temperatures reached 44.2 degrees Celsius (around 111.6 Fahrenheit) in the northern district of Tuong Duong – the highest temperature ever recorded in the country. In Bangladesh, Dhaka observed the highest maximum temperature recorded in decades of 40.6°C on 15th April, while in India, several northern and eastern cities recorded maximum temperatures above 44°C on 18th of April.

This study delivers a comprehensive examination of the “once-in-200 year” Southeast Asia heatwave event in April-May 2023, though climate scientists warn that such events are becoming far more frequent due to climate change.

The 2024 Heat Crisis

The following year brought little relief. Throughout April and continuing into May 2024, extreme record-breaking heat led to severe impacts across the Asian continent, with large regions from Israel, Palestine, Lebanon and Syria in the West, to Myanmar, Thailand, Vietnam and the Philippines in the East experiencing temperatures well above 40°C for many days.

Heat indices peaked at 53 °C (127 °F) in Iba in the Philippines on 28 April 2024, reaching levels classified as “extremely dangerous” where maintaining body temperature becomes nearly impossible. Cambodia faced the highest temperatures in 170 years, with the ministry forecasting that temperatures in most parts of the country could reach up to 43C (109F).

2025 and Beyond

The pattern has continued into 2025 and 2026. Jakarta, Indonesia and the Manila region in the Philippines experienced a period of extended and unusual heat between December 2024 and February 2025. Another worrying trend is that early-season heatwaves are getting more frequent and dangerous, with scorching heat extremes occurring earlier, in spring, and lasting longer.

Looking ahead, NOAA and WMO say El Niño is increasingly likely from mid-2026, raising concern over heat and drought in Southeast Asia, with the world possibly heading towards a powerful El Niño later this year. Some scientists warn this could become an exceptionally strong event, potentially creating what has been termed a “climate double-whammy” for the region.

Climate Change Attribution

The Human Fingerprint

The connection between these extreme heat events and human-caused climate change is unequivocal. Both studies found that human-induced climate change influenced the events, making them around 30 times more likely and much hotter. Studies on recent extreme heat events in East Asia have found that human-caused climate change drastically increased their likelihood and severity, with heat being the weather hazard most straightforwardly attributed to global warming.

Observations and models both show a strong increase in likelihood and intensity of April humid heat events similar to that of 2023. The scientific evidence is overwhelming that without greenhouse gas emissions from human activities, these deadly heat waves would be extremely rare or would not occur at all.

The likelihood of intense heatwaves in South Asia is increasing due to climate change, highlighting the need to understand their evolving spatiotemporal patterns. Extreme heat in South Asia during the pre-monsoon season is becoming more frequent, creating longer periods of dangerous conditions before the monsoon rains arrive.

Extreme heat in Southeast Asia has increased in recent years, with heatwaves becoming more frequent, lasting longer, and exhibiting greater severity, as climate change is intensifying these conditions through increases in temperature and changes in humidity. This represents a fundamental shift in the region’s climate baseline, with conditions that were once exceptional becoming the new normal.

Health Impacts and Human Toll

Direct Health Consequences

The health impacts of extreme heat in South Asia are severe and multifaceted. Heatwaves are arguably the deadliest type of extreme weather event and while the death toll is often underreported, hundreds of deaths have been reported already in most of the affected countries, including Palestine, Bangladesh, India, Thailand, Myanmar, Cambodia and the Philippines.

Heat stress is the world’s leading cause of weather-related deaths and can exacerbate underlying illnesses including cardiovascular disease, diabetes, mental health conditions, and asthma, with roughly 489,000 heat-related deaths occurring each year, with 45 percent of the deaths in Asia and 36 percent in Europe.

The danger extends beyond just the hottest hours of the day. For older adults with physical health problems, temperatures as low as 26.7°C (80°F) can pose significant danger, and when humidity is as high as 90 percent, even 25.6°C (78°F) can be hazardous, with nighttime heat being especially harmful for older adults whose homes lack air conditioning or who can’t afford to run their air conditioners for long periods.

Vulnerable Populations

This will pose severe health risks, especially for the elderly, outdoor laborers, and those in agriculture. The heat was particularly difficult for people living in refugee camps and informal housing, as well as for outdoor workers. These populations often lack access to cooling technologies, adequate hydration, and the ability to avoid outdoor exposure during the hottest parts of the day.

Low-income urban areas are most at risk, with dense housing made of heat-retaining materials, little access to cooling technology, and limited tree cover and green space, making these neighborhoods already several degrees hotter than wealthier areas, resulting in urban heat inequality. This environmental injustice means that those least responsible for climate change and least able to adapt are suffering the most severe consequences.

The World Bank estimates that today, 185 million people in the Asia-Pacific region live in extreme poverty, while over 260 million more could be pushed into poverty in the next decade, with poverty remaining highest in South Asia, and the poorest bearing the biggest brunt of extreme heat.

Heat Index and Danger Thresholds

The estimated heat index values exceeded the threshold considered as “dangerous” (41°C) over large parts of the South Asian regions studied, with a few areas nearing the range of “extremely dangerous” values (above 54°C) under which body temperature is difficult to be maintained. At these levels, heat-related illness becomes almost inevitable for anyone exposed for extended periods, regardless of their health status or fitness level.

Agricultural and Economic Impacts

Crop Failures and Food Security

Agriculture, which employs a significant portion of South Asia’s population and provides food security for billions, is under severe stress. The heat also had a large impact on agriculture, causing crop damage and reduced yields, as well as on education, with holidays having to be extended and schools closed in several countries, affecting millions of students.

The regional average daily maximum temperature reached its highest level since 1950, severely affecting people’s lives and properties, leading to unparalleled wildfires, and causing a substantial reduction in rice yields. Rice is the staple food for most of South Asia’s population, making these yield reductions a direct threat to food security and nutrition.

Water scarcity compounds agricultural challenges. Water levels at Lam Takhong Dam and Lam Mun river in Nakhon Ratchasima dropped sharply as drought and extreme heat caused the main water sources to run dry, sparking fears of water shortage. The Muda Dam in Kedah—a vital source for Malaysia’s “Rice Bowl”—has dropped to a critical 7.4% capacity, threatening the livelihood of over 50,000 farmers and necessitating expensive cloud-seeding operations that have so far yielded minimal results.

Economic Disruption

In multiple countries, extreme heat is disrupting daily life by keeping kids out of school and people out of work due to the risks of heat exposure, with the impact cutting into economic growth as well. The economic costs extend far beyond direct heat-related damages.

In some countries, the high heat has caused excessive energy demand, straining power grids and leading to blackouts in some areas. Vietnam’s state electricity company urged consumers to refrain from overworking their air-conditioning units, warning that electricity consumption has reached record highs in recent days.

Looking forward, a prolonged drought through late 2026 could lead to regional food price spikes of 15–20%, pushing millions back into poverty. This economic shock would reverse years of development gains and increase regional instability.

Infrastructure Stress

The extreme heat is testing infrastructure beyond its design limits. The heatwaves of April–May 2024 resulted in widespread school closures, agricultural losses, increased heat-related illnesses, and at least 40 reported fatalities. Millions of students across the Philippines were ordered to stay home, with the Department of Education ordering students of more than 47,000 public schools to switch to home-based, online lessons.

Monsoon Disruption and Water Resources

Changing Precipitation Patterns

The monsoon system, which billions of people depend on for water and agriculture, is being disrupted by climate change. Changes in monsoon patterns reduce rainfall in some areas while causing extreme precipitation events in others, creating a volatile situation where droughts and floods can occur in rapid succession.

The timing and intensity of monsoons are becoming less predictable, making agricultural planning increasingly difficult. Farmers who have relied on traditional knowledge about planting and harvesting times are finding that these patterns no longer hold, leading to crop failures and economic losses.

Water Scarcity

Areas around the Ganges and Indus river basins are on the frontline of an emergency, with extreme risks to humans increasing in these densely populated areas with limited access to cooling technologies. These river systems, fed by Himalayan glaciers and monsoon rains, are experiencing reduced flows during critical periods, threatening water supplies for drinking, agriculture, and industry.

Drought conditions affected over 75,000 families in the country, including 58,080 families in Sabah, with Papar District declared a drought disaster area in early March, as the drought was exacerbated by the heat wave, resulting in a severe water crisis for the district. These localized crises are becoming more frequent and severe across the region.

Urban Heat Islands and City Vulnerability

The Urban Heat Effect

Large cities are warmer by more than 2 degrees Celsius compared with the surroundings due to heat island effects, exacerbating heat stress conditions, with future warming causing more frequent temperature extremes and heatwaves especially in densely populated South Asian cities, where working conditions will be exacerbated and daytime outdoor work will become dangerous.

South Asia is experiencing rapid urbanization, with millions moving to cities each year. Its population, across its 11 constituent countries, has surged from approximately 215 million in 1960 to nearly 695 million today. This urban growth, combined with the urban heat island effect, creates particularly dangerous conditions in cities.

City-Specific Impacts

In Manila, the temperature hit 38.8°C (101.84°F) breaking a longstanding record, with the vibrant city of 14 million also seeing its hottest minimum temperature of 29.8°C (85.6°F). Large crowds sought relief in air-conditioned shopping malls in metropolitan Manila, the congested capital of more than 14 million people where the temperature soared to 38.8 degrees Celsius (101.84 degrees Fahrenheit), surpassing the record set decades ago.

The combination of high temperatures, humidity, and urban density creates particularly dangerous conditions. Cities built with heat-absorbing materials like concrete and asphalt, with limited green space and tree cover, can be several degrees hotter than surrounding rural areas, especially at night when temperatures should provide relief.

Mitigation Strategies and Emissions Reduction

The Imperative of Emissions Reduction

Addressing the root cause of intensifying heat waves requires urgent and substantial reductions in greenhouse gas emissions. Climate change, without mitigation, presents a serious and unique risk in South Asia, a region inhabited by about one-fifth of the global human population, due to an unprecedented combination of severe natural hazard and acute vulnerability.

The Paris Agreement’s goal of limiting global warming to 1.5°C above pre-industrial levels is critical for South Asia. Every fraction of a degree of additional warming translates to more frequent and severe heat waves, with potentially catastrophic consequences for the region’s population. Current emission trajectories suggest the world is heading toward 2.5-3°C of warming by 2100, which would make large parts of South Asia periodically uninhabitable during heat waves.

Renewable Energy Transition

South Asian countries are increasingly investing in renewable energy, particularly solar and wind power. India has set ambitious targets for renewable energy capacity, aiming to reach 500 GW of non-fossil fuel capacity by 2030. This transition not only reduces emissions but also helps address the energy security challenges that heat waves create through increased cooling demand.

However, the pace of this transition needs to accelerate dramatically. Continued reliance on fossil fuels, particularly coal, undermines climate goals and locks in decades of future emissions. International cooperation and financial support for developing countries in South Asia are essential to enable a rapid and just energy transition.

Nature-Based Solutions

Protecting and restoring natural ecosystems can play a significant role in both mitigation and adaptation. Forests, wetlands, and other natural areas absorb carbon dioxide from the atmosphere while also providing cooling effects and water regulation services. Reforestation and afforestation programs, when done with native species and community involvement, can provide multiple benefits.

Urban green spaces, including parks, street trees, and green roofs, can significantly reduce urban heat island effects while improving air quality and providing recreational spaces. Cities across South Asia are beginning to recognize the value of green infrastructure, though implementation often lags behind planning.

Adaptation Measures and Resilience Building

Early Warning Systems

Effective early warning systems can save lives by giving people time to prepare for extreme heat events. These systems need to be accessible to all populations, including those in rural areas and informal settlements, and must be communicated in local languages through multiple channels including radio, mobile phones, and community networks.

One solution is to inform frontline communities with the latest climate projections from sophisticated models describing evolving climate phenomena such as deadly heatwaves and destructive cyclones. However, warnings are only effective if people have the means to act on them, including access to cooling centers, adequate water supplies, and the ability to avoid outdoor work during dangerous periods.

Heat Action Plans

Cities and regions across South Asia are developing heat action plans that outline specific measures to protect populations during extreme heat events. These plans typically include:

  • Establishing cooling centers in public buildings where people can seek relief
  • Adjusting work schedules to avoid the hottest parts of the day
  • Ensuring adequate water distribution in vulnerable areas
  • Training healthcare workers to recognize and treat heat-related illnesses
  • Coordinating emergency response services
  • Communicating heat safety information to the public

Ahmedabad, India, pioneered one of the first comprehensive heat action plans in South Asia following a deadly 2010 heat wave. The plan has been credited with reducing heat-related mortality and has served as a model for other cities in the region and around the world.

Water Management and Conservation

Improving water management is critical for building resilience to heat waves and associated droughts. This includes:

  • Modernizing irrigation systems to reduce water waste
  • Implementing rainwater harvesting at household and community levels
  • Protecting and restoring watersheds and aquifer recharge areas
  • Developing drought-resistant water supply systems
  • Improving water storage infrastructure
  • Implementing water pricing and allocation policies that encourage conservation

Traditional water management practices, such as stepwells and community ponds, are being revived in some areas, combining indigenous knowledge with modern engineering to create more resilient water systems.

Agricultural Adaptation

Developing heat-resistant and drought-tolerant crop varieties is essential for maintaining food security in a warming climate. Agricultural research institutions across South Asia are working on breeding programs and genetic modification to create crops that can withstand higher temperatures and water stress.

Other agricultural adaptations include:

  • Shifting planting dates to avoid peak heat periods
  • Adopting conservation agriculture practices that improve soil moisture retention
  • Diversifying crops to spread risk
  • Implementing agroforestry systems that provide shade and improve microclimates
  • Improving access to weather information and climate forecasts for farmers
  • Developing crop insurance programs to protect farmers from climate-related losses

Building Design and Urban Planning

Adapting the built environment to extreme heat requires rethinking building design and urban planning. Traditional architecture in South Asia incorporated many heat-adaptive features, such as thick walls, high ceilings, courtyards, and natural ventilation, which modern construction has often abandoned in favor of air conditioning.

Heat-adaptive building strategies include:

  • Using reflective or light-colored roofing materials to reduce heat absorption
  • Incorporating natural ventilation and passive cooling designs
  • Installing green roofs and walls
  • Using heat-resistant building materials
  • Designing buildings to maximize shade
  • Implementing building codes that require heat-adaptive features

At the urban scale, planning strategies include increasing tree cover and green spaces, creating pedestrian-friendly streets with shade, preserving water bodies, and designing neighborhoods to promote natural ventilation through strategic building placement and orientation.

Social Protection and Equity Considerations

Protecting Vulnerable Workers

Outdoor workers, including agricultural laborers, construction workers, street vendors, and delivery personnel, face extreme risks during heat waves. Protecting these workers requires:

  • Implementing and enforcing regulations on maximum working temperatures
  • Requiring employers to provide shade, water, and rest breaks
  • Adjusting work schedules to avoid peak heat hours
  • Providing heat safety training
  • Ensuring access to healthcare for heat-related illnesses
  • Establishing compensation systems for heat-related work disruptions

Many outdoor workers in South Asia are in informal employment with limited legal protections, making enforcement of heat safety measures particularly challenging. Strengthening labor rights and extending social protection to informal workers is essential for heat resilience.

Addressing Heat Inequality

Heat impacts are deeply unequal, with poor and marginalized communities suffering disproportionately. Addressing this inequality requires targeted interventions including:

  • Prioritizing cooling infrastructure investments in low-income neighborhoods
  • Providing subsidized or free access to cooling centers
  • Ensuring affordable electricity for cooling
  • Improving housing quality in informal settlements
  • Expanding tree cover in underserved areas
  • Strengthening social safety nets to help vulnerable populations cope with heat-related economic shocks

Healthcare System Strengthening

Healthcare systems need to be prepared for the increasing burden of heat-related illnesses. This includes:

  • Training healthcare workers to recognize and treat heat-related conditions
  • Ensuring adequate supplies of intravenous fluids and cooling equipment
  • Establishing protocols for heat emergency response
  • Strengthening disease surveillance to track heat-related morbidity and mortality
  • Conducting public health campaigns on heat safety
  • Integrating heat health considerations into primary healthcare

Regional Cooperation and International Support

Cross-Border Collaboration

Heat waves do not respect national borders, and effective response requires regional cooperation. South Asian countries can benefit from sharing:

  • Climate data and forecasting capabilities
  • Best practices in heat action planning and implementation
  • Research on heat-resistant crops and adaptation technologies
  • Early warning systems and emergency response protocols
  • Water resource management strategies for shared river basins

Regional organizations like the South Asian Association for Regional Cooperation (SAARC) can play a coordinating role in facilitating this cooperation, though political tensions between some member states have limited the effectiveness of regional collaboration.

Climate Finance and Technology Transfer

Developed countries, which are historically responsible for the majority of greenhouse gas emissions, have a responsibility to support climate adaptation in vulnerable regions like South Asia. This support should include:

  • Providing adequate climate finance for adaptation projects
  • Facilitating technology transfer for renewable energy and climate-resilient agriculture
  • Supporting capacity building for climate science and adaptation planning
  • Addressing loss and damage from climate impacts that exceed adaptation capacity

The international community’s commitments on climate finance have often fallen short of what is needed and what was promised. Scaling up support for South Asian countries is both a moral imperative and a practical necessity, as climate impacts in this densely populated region have global implications for migration, security, and economic stability.

Research and Knowledge Gaps

Improving Climate Projections

While climate models have improved significantly, uncertainties remain about the precise magnitude and timing of future heat extremes in South Asia. The ECMWF exhibited limited forecast skills for the reduced soil moisture and failed to capture the land-atmosphere coupling, leading to a severe underestimation of the heatwave’s intensity. Continued investment in climate science and modeling is needed to provide more accurate and actionable information for decision-makers.

Particular research priorities include:

  • Better understanding of monsoon dynamics under climate change
  • Improved modeling of extreme heat events at regional and local scales
  • Enhanced understanding of compound extremes (heat combined with drought, air pollution, etc.)
  • Better quantification of tipping points and non-linear climate responses

Health Impact Assessment

Scientists have said the number of heat-related deaths around the world has been rising significantly in recent years along with temperatures, however, the trend in Asia so far is unclear, partly because of the question of how to classify deaths that appear to be heat-related. Improving surveillance and attribution of heat-related mortality and morbidity is essential for understanding the true health burden and targeting interventions effectively.

Adaptation Effectiveness

More research is needed on the effectiveness of different adaptation measures in South Asian contexts. This includes rigorous evaluation of heat action plans, building design interventions, agricultural adaptations, and social protection programs. Understanding what works, for whom, and under what conditions can help optimize limited resources and scale up successful approaches.

The Path Forward

Urgency of Action

Current projections suggest that South Asia will experience heatwaves that go well beyond what humans are able to tolerate, pushing public health systems to the brink and triggering waves of climate migration. Recent projections suggest that heatwaves will become more frequent and severe in western Bangladesh under the business-as-usual scenario, exceeding the extreme danger threshold defined by U.S. National Weather Service criterion, which has rarely been observed in the current climate.

According to experts, South Asia should brace for earlier, longer-lasting and hotter heatwaves going forward. The window for preventing the most catastrophic impacts is rapidly closing, making immediate and ambitious action essential.

Integrated Approaches

Addressing the heat wave crisis requires integrated approaches that combine mitigation and adaptation, address both immediate needs and long-term resilience, and tackle the underlying inequalities that make some populations more vulnerable than others. Siloed interventions that address only one aspect of the problem will be insufficient.

Successful responses will need to:

  • Integrate climate considerations into all aspects of development planning
  • Combine top-down policy interventions with bottom-up community-led initiatives
  • Address both climate change and other stressors like poverty, inequality, and environmental degradation
  • Balance short-term emergency response with long-term transformation
  • Engage all sectors of society, from government to business to civil society

Building Transformative Resilience

Southeast Asia is no longer “preparing” for climate change; it is surviving it, and as the region braces for the intensified heat of the coming months, the focus must shift from temporary school closures to permanent urban cooling, heat-resilient crop engineering, and a unified ASEAN response to the looming water and haze crisis.

True resilience goes beyond simply coping with heat waves to fundamentally transforming systems to be sustainable and equitable in a changed climate. This means reimagining cities, agriculture, energy systems, and social structures to be compatible with the climate reality of the 21st century.

For South Asia, this transformation is not optional—it is a matter of survival for nearly two billion people. The region’s response to intensifying heat waves will shape not only its own future but will have profound implications for global climate action, migration patterns, economic development, and human security.

Conclusion

Climate change is intensifying heat waves in South Asia with devastating consequences for human health, agriculture, water resources, and economic development. The scientific evidence is clear that these extreme heat events are becoming more frequent, more severe, and more deadly due to human-caused greenhouse gas emissions. Without urgent action to reduce emissions and build resilience, large parts of South Asia face a future where extreme heat periodically exceeds human survivability limits.

However, the future is not predetermined. Ambitious mitigation efforts can still limit the worst impacts, and comprehensive adaptation measures can protect vulnerable populations and build resilience. The choices made in the coming years—by governments, businesses, communities, and individuals—will determine whether South Asia can navigate the heat crisis or whether it becomes an unfolding catastrophe.

The heat waves affecting South Asia are a warning for the entire world. They demonstrate that climate change is not a distant future threat but a present reality that is already claiming lives and undermining development. They show that the most vulnerable populations, who have contributed least to causing climate change, are suffering the most severe impacts. And they make clear that the time for incremental action has passed—only transformative change at unprecedented speed and scale can avert the worst outcomes.

For more information on climate change impacts and adaptation strategies, visit the Intergovernmental Panel on Climate Change and the World Health Organization’s climate and health resources. To learn more about heat action planning, see resources from the C40 Cities Climate Leadership Group. For real-time climate data and analysis, explore Climate Central and World Weather Attribution.