Hot days may last up to four hours longer by 2100 under a high-emissions scenario, according to a study published in Nature Climate Change. Scientists from Sun Yat-sen University in Guangzhou, China, analyzed global hourly temperature data and climate projections to assess the potential increase in extreme heat duration.
The study found that land areas currently experience an average of 269 hours of extreme heat each summer. However, projections suggest that by 2070-2099, each hot day could include more than four additional hours of extreme heat compared to present-day levels. A significant concern is that these extended heat hours are anticipated to occur at night, diminishing the traditional relief period from daytime temperatures.
'The health implications by HHEs [hourly heat extremes] are profound,' the researchers stated. 'Nighttime has been traditionally regarded as a relief from daytime heat, yet this is not the case under abnormally warm nights. The rise of uninterrupted heat exposure throughout the night undermines this cooling window, increasing the risk of heat-related morbidity and mortality, especially among vulnerable populations.'
The research highlights that the impact of heat exposure is not uniform globally, with low- and middle-income countries disproportionately affected by both current and future hourly heat extremes, despite contributing less to historical emissions.
These findings come as Western Europe recently experienced its hottest June-July period on record, with average temperatures 2.79°C above the monthly average. This follows the continent's fourth successive heatwave. The Paris Agreement, established in 2015, aims to limit global average temperature increase to well below 2°C above pre-industrial levels, with an ambition to keep it at 1.5°C. Previous research suggests that reaching the 1.5°C goal is critical, as exceeding it could lead to significantly drier conditions in 25% of the world.
The study's authors advocate for further research into the specific mechanisms behind hourly heat extremes, such as heat bursts or flash heat events. They suggest that a better understanding of short-term heat events on an hourly scale could enhance early warning systems, health risk assessments, and adaptation strategies for a warming climate.
