Climate change has increasingly adverse effects on cycling, especially in relation to climate-sensitive hazards such as heatwaves, natural disasters, and air pollution [1]. Modal shifting from cars to bikes is an evidence-based strategy for reducing local greenhouse gas emissions and air pollution in cities [2]. The development of connected and secure cycling infrastructure and improved accessibility to cycle-sharing programs have contributed to an increase in daily cycling trips. Bike supportive policies have further boosted cycling in the US, China, Europe, South America, and Asia [3]. For instance, Amsterdam saw a 15% increase in cycling following infrastructure improvements, while Sevilla and Bogotá had 10% gains, and Vancouver and Paris saw smaller (~5%) increases [3]. Despite the progress, climate change and climate-sensitive hazards increasingly threaten bike use in cities [1]. Here, we summarize current evidence on the effects of heatwaves, natural disasters, and air pollution on urban cycling, highlighting the critical threat to its use. Investigating conditions facilitating the climate resilience of cyclists, defined as their ability to bounce back from climate-sensitive hazards, is essential [4].

As global temperatures continue to rise, the occurrence of climate-sensitive hazards is expected to increase [2]. This is expected to lead to a rise in the intensity, duration, and number of heatwaves, especially in urban areas [2]. Similarly, the frequency of natural disasters, including tropical cyclones and wildfires, is projected to increase with global warming [2]. The risk of wildfire is expected to rise in regions like Australia, Canada, USA, and the Mediterranean [2]. Heatwaves and wildfires worsen air pollution by increasing the concentration levels of ozone (O₃) and particulate matter (PM_10-2.5). Smoke from wildfires considerably raises PM_2.5 concentration levels both locally and in cities located thousands of kilometers away. Therefore, as heatwaves and wildfires are expected to increase, and co-occur more often with climate change and variability, air pollution will worsen.

Together, climate-sensitive hazards adversely impact cycle use [1]. Turning our attention to these impacts, it is crucial to note that many of the studies discussed here rely on mobility data from cycle-sharing systems. These data serve as a proxy for overall cycling behavior and offer valuable insights into trip frequency and duration during such climate-sensitive hazards. An investigation examining 40 cities worldwide has shed light on how temperature impacts cycle-sharing usage [5]. The results show an increase in usage with rising temperatures up to a tipping point between 19°C and 33°C, beyond which usage declines [6]. A negative effect of extreme temperature (≥32°C) on cycle-sharing usage was also observed in New York City (USA), however in some areas cycle-sharing usage remained unchanged despite the heat [7]. Within-city variations in cycle use are influenced by differences in shading and socioeconomic disparities. Shading provided by trees, canopies, and buildings contributes to a cooling effect, reducing thermal discomfort for cyclists and encouraging usage [7]. In San Francisco (USA), low-income individuals and those without access to cars disproportionately reliant on cycles compared to high-income individuals or car owners [8]. These differences in cycle usage within a city during extreme heat events underscore the role of the built environment while also reflecting social inequalities.

Given the harmful effects of extreme heat exposure on human health, many cities have implemented heatwave alert systems. They may also influence their cycle use. For instance, heatwave alerts in Buenos Aires (Argentina) are associated with a 20% decrease in the number of daily rider trips among elderly users [9]. A negative specific gender effect has been also reported (reductions of 16% for younger and 25% for older women). Finally, in the case of two consecutive days of heatwave alerts, the decrease of daily rider trips is no longer observed, indicating that heatwave alerts are only effective on the first day.

Heatwaves are not the only threats cyclists face. Current academic literature provides valuable insights regarding the impact of rising air pollution levels on cycle use. Research in Seoul (South Korea), examined the relationship between particulate matter PM_2.5 and PM₁₀ concentrations and cycle-sharing usage, revealing that usage decreased when particulate matter levels exceeded the World Health Organization’s recommendations [10]. Conversely, research estimated the effect of O₃ on cycling speed in London (United Kingdom), demonstrating that low O₃ levels were associated with a lower cyclist speed [11]. This is the first study to highlight that O₃ concentrations below the World Health Organization’s recommendation can negatively affect cycling behavior.

Air pollution alerts have also adverse effects on cycling usage. A cycle trips decrease by 14–35% following a one-time alert was found in Sydney (Australia), while a second consecutive day of alerts results in only a 5% reduction [12]. This evidence suggests that air pollution alerts reduce cycling usage, but primarily on the first day, as the impact declines quickly by the second day.

Shifting the focus to natural disasters, and their impact on cycling behavior, to our knowledge, only two studies have examined this relationship. Cycle data from Houston (USA) showed that cycling usage took six weeks to recover to pre-Hurricane Harvey levels [13]. Another investigation revealed a decrease in cycle trips during wildfire smoke events, with the magnitude of impact correlated with PM_2.5 concentration levels in Seattle (USA) [13]. Post-event patterns showed variations across studied areas, with some experiencing a slow return to pre-event levels of physical activity, likely due to lingering health effects from the smoke (e.g., respiratory issues) [13]. These studies further highlight a delay between the end of a natural disaster and the resumption of cycling habits, with duration varying across areas.

In conclusion, we emphasize that climate-sensitive hazards have both immediate and delayed impacts on cycling. These hazards not only reduce bicycle use during such events but, in some cases, for a period afterward. Structural, policy, and individual factors may influence the ability to recover from these events, commonly referred to as climate resilience. Additionally, gender and social inequalities may be exacerbated during climate-sensitive hazards. Future studies combining cycling with climate-sensitive hazard databases present a unique opportunity to identify factors that promote urban bike-use resilience and assess the impacts of other climate-sensitive hazards such as flash floods, dust storms, or torrential rain.