How Climate Change is Supercharging Heatwaves in the Northern Hemisphere

What is a Heatwave?

A heatwave is defined as a prolonged period of excessively hot weather, often accompanied by high humidity. While definitions vary, they typically involve temperatures above the 90th percentile for several consecutive days. Heatwaves can be deadly, especially in regions unaccustomed to extreme temperatures. Vulnerable populations such as the elderly, children, and outdoor workers face the highest risks. According to the Center for Climate and Energy Solutions (C2ES), heatwaves are one of the deadliest natural hazards in the United States. The frequency and duration of these events have increased, and cities with poor green coverage suffer disproportionately due to a lack of shade and limited cooling infrastructure (C2ES).

The Climate Connection

There is a strong scientific consensus that climate change is making heatwaves more intense and frequent. A 2020 article in Physics and Chemistry of the Earth explains that anthropogenic warming alters atmospheric circulation and increases the baseline temperature, thereby raising the likelihood of extreme heat events (Qui and Yan 2020). Simply put, a hotter world makes heatwaves more likely to occur. The Intergovernmental Panel on Climate Change (IPCC) notes that what used to be a once-a-in-50-year event may now occur every decade or less. Moreover, emissions of greenhouse gases have created a climate system in which heat extremes are more probable even during natural variability cycles.

Understanding Heat Domes

A heat dome forms when a high-pressure system traps warm air beneath it, preventing cooler air from circulating. This phenomenon creates a self-reinforcing cycle, where the ground heats the air and the air, in turn, further heats the ground. According to the BBC, this summer’s heat domes over the US and Europe have shattered temperature records. These systems can persist for days or even weeks, making them particularly dangerous. Heat domes are also linked to stagnating weather systems, which delay the arrival of cooler fronts. This delay exacerbates public health and agricultural impacts (Keith-Lucas 2025).

Heatwaves in the United States

In June 2025, New York City and much of the US Northeast sweltered under a heat dome that pushed temperatures above 38°C (100°F). The Associated Press reported widespread health alerts, blackouts, and overwhelmed emergency services. The heat-strained infrastructure caused road buckling and exposed urban heat island effects, which make densely built areas disproportionately hotter. Vulnerable communities suffered most, underlining long-standing social inequities. Additionally, subway systems experienced delays due to overheated tracks, and cooling shelters reported record footfall during the peak of the event (Borenstein 2025).

Europe: A Summer of Extremes

Europe also faced brutal temperatures in 2025, especially in Spain, Italy, and parts of France. Climate experts say Europe is warming at twice the global average, intensifying heatwave impacts. High nighttime temperatures are particularly hazardous as they prevent the body's ability to recover. Health systems came under pressure, and energy grids were stretched. According to Yale Environment 360, the continent’s ageing population and lack of widespread air conditioning exacerbate the risks. In Italy, municipalities deployed water tankers and emergency health services to combat dehydration, while France reinstated early warning systems that had been launched after the deadly 2003 heatwave (Yale E360 2023).

Japan: Weeks of Searing Heat

Japan is also experiencing a prolonged heatwave, with temperatures exceeding 35°C (95°F) in Tokyo and other cities. Bloomberg reports that the heatwave could last for several weeks, increasing energy demand and pushing the country’s power grid to its limits. Authorities have urged people to conserve energy and remain indoors during peak heat hours. The situation has reignited debates about nuclear power and renewable energy infrastructure. The government is also exploring emergency subsidies for electricity to reduce blackout risk and ensure that vulnerable populations can maintain safe indoor temperatures (Bloomberg 2025).

Urban Heat Islands

Urban areas are significantly hotter than surrounding rural regions due to the urban heat island effect. Asphalt, concrete, and buildings absorb and re-emit heat more than vegetation-covered areas. The BBC explains how cities like Paris and New York often experience temperatures several degrees higher than nearby suburbs, worsening health outcomes and increasing cooling costs. Mitigation strategies include increasing green spaces and using reflective building materials. Some cities have begun integrating heat-resilient planning into zoning codes, while others are investing in heat-mapping tools to identify priority cooling zones (Keith-Lucas 2025).

Energy Systems Under Strain

Heatwaves put immense pressure on energy systems. As demand for air conditioning surges, power grids face the risk of blackouts. In Japan and the US, authorities are issuing conservation notices and rationing electricity during peak hours. These challenges highlight the importance of modernizing grids and investing in renewable sources that can better withstand climate stresses. Energy utilities are also facing scrutiny over their preparedness and have begun exploring energy storage and battery deployment to stabilize load imbalances (Bloomberg 2025).

Agricultural Impacts of Heatwaves

Extreme heat can severely affect crop yields, soil moisture, and livestock health. In Europe, prolonged heat has scorched wheat and corn fields, with countries like Spain and Italy reporting harvests well below seasonal averages. Heat stress on crops reduces photosynthesis and accelerates ripening, often before full maturity, leading to lower nutritional quality and market value. Fruit and vegetable growers in Japan have seen substantial crop loss, particularly in strawberries and leafy greens, which are especially sensitive to high temperatures. Bloomberg reports that this has caused a spike in food prices and concerns over domestic food security (Bloomberg 2025).

Livestock are also at risk during extreme heat events. Heatwaves can lead to reduced feed intake, lower milk production, and higher mortality, especially among poultry and swine. Yale Environment 360 notes that heat-induced reductions in water availability further strain both crop irrigation and animal hydration. In regions where agriculture is already under pressure from drought, recurring heatwaves risk destabilizing entire rural economies and food supply chains (Yale E360 2025).

Heatwave Health Risks

Heatwaves can lead to dehydration, heatstroke, respiratory problems, and cardiovascular stress. Vulnerable populations such as the elderly, infants, and people with chronic illnesses are particularly at risk. The AP reports that hospitals in New York admitted hundreds of heat-related cases during the June 2025 heatwave. Public health campaigns and cooling shelters have become essential. Some cities are testing wearable temperature sensors and mobile alerts to identify at-risk individuals in real time and provide emergency interventions (Borenstein 2025).

The Role of Jet Streams in Heatwaves

Shifts in the jet stream, fast-moving air currents in the upper atmosphere, play a significant role in heatwave formation. Climate change is weakening these currents, allowing heat domes to linger longer. According to Qui and Yan (2020), this disrupted circulation pattern traps heat over large areas, worsening the duration and severity of heatwaves. Scientists are now exploring predictive models that combine jet stream data with ocean temperatures to improve early warning systems.

Heatwave Policy and Adaptation Strategies

Governments must adapt to a hotter world. Policies include setting heat action plans, expanding green infrastructure, and revising building codes. Some cities are piloting urban cooling strategies, such as reflective pavements and rooftop gardens. The C2ES stresses that climate adaptation must be equity-centered to protect the most vulnerable (C2ES). Examples include Spain's push to redesign public spaces with shade structures and India’s use of city-wide heatwave action plans tailored to local contexts.

Long-Term Outlook

Without drastic cuts to greenhouse gas emissions, heatwaves will continue to worsen. One study warns that by 2100, half of the world’s population could be exposed to life-threatening heat for 20 days or more each year (Qui and Yan 2020). The world is at a tipping point. Mitigation and adaptation must go hand in hand to ensure a livable future. Climate experts urge stronger international cooperation, increased funding for resilience infrastructure, and swift decarbonization of energy systems.

Zara Prew, Phd