Core Viewpoint - An international study led by the Spanish National Research Council indicates that nighttime high temperatures may lead to an increase in global mortality rates, highlighting a significant health risk associated with this phenomenon [1] Group 1: Research Findings - The study analyzed over 14 million death records from 178 cities across 44 countries between 1990 and 2018, using hourly temperature data and statistical models to assess the relationship between nighttime high temperatures and mortality [1] - Nighttime high temperatures are positively correlated with increased mortality rates in all regions except Northern Europe, indicating that nighttime heat itself is a health risk factor [1] - Nighttime high temperatures hinder the body's recovery from daytime heat stress, affect sleep quality, and may exacerbate cardiovascular, respiratory, and neurological diseases [1] Group 2: Impact on Vulnerable Populations - Urban areas with strong heat island effects, such as Mediterranean cities like Barcelona and Valencia, experience higher frequencies of nighttime high temperatures, posing greater risks to vulnerable groups [1] - The most affected populations include the elderly, individuals with chronic illnesses, and residents in poorly ventilated or air-conditioned environments [1] Group 3: Recommendations - Researchers advocate for the inclusion of nighttime high temperatures in early warning systems, the development of urban climate shelters, and the increase of green spaces to mitigate health risks [1] - Ensuring adequate cooling conditions in homes, hospitals, and nursing homes is also recommended to protect vulnerable populations from the adverse effects of nighttime heat [1]

Group 1 - The phenomenon of "nighttime high temperatures" is caused by cloud cover that traps heat, preventing nighttime cooling [1][3] - Human activities, such as urbanization and transportation, contribute to higher nighttime temperatures due to heat retention in concrete and asphalt [3][4] - Global climate change factors, including increased greenhouse gases and water vapor, exacerbate nighttime warming [3][4] Group 2 - Nighttime high temperatures pose health risks, particularly for vulnerable populations such as the elderly, who have a reduced ability to regulate body temperature [4][6] - Recommendations for coping with nighttime high temperatures include improving air circulation indoors, staying hydrated, and being cautious about outdoor activities [4][6] - Special attention is needed for elderly individuals with heart conditions, as they may require careful management of fluid intake to avoid exacerbating health issues [6]

Core Viewpoint - The phenomenon of "nighttime high temperatures" is increasingly prevalent due to various atmospheric conditions and human activities, leading to health risks, particularly in urban areas [1][3][5]. Group 1: Atmospheric Conditions - Strong daytime solar radiation heats the ground, which then releases heat at night through long-wave radiation, but the cooling rate is influenced by atmospheric conditions [3]. - Increased cloud cover at night can trap heat, preventing effective cooling and resulting in slower temperature drops [1][3]. Group 2: Human Activities - Urban environments with dense buildings and limited vegetation act as "heat storage" systems, exacerbating nighttime temperatures [3][5]. - Human activities such as traffic and air conditioning contribute to elevated nighttime temperatures, making urban areas significantly warmer than rural ones [3][5]. Group 3: Health Risks - High nighttime temperatures can lead to health issues, including heatstroke and cardiovascular diseases, particularly in high-humidity conditions [5][6]. - Vulnerable populations, especially the elderly, are at greater risk due to their reduced ability to regulate body temperature [6]. Group 4: Recommendations - To mitigate the effects of nighttime high temperatures, it is advised to improve air circulation indoors and stay hydrated, regardless of thirst [5]. - Special attention should be given to vulnerable groups, such as the elderly, who may not perceive temperature changes effectively [6].