Humidity is more than just a weather term, it’s a key player in how we feel, how we live, and how climate change is reshaping our world
Humidity, a measure of the amount of water vapour in the air, plays a crucial role in shaping our weather, influencing rainfall, and affecting how we feel day to day. While often overshadowed by temperature in discussions about climate and comfort, humidity is a key factor in our experience of heat and has significant implications for human health, especially in a changing climate.
What is humidity?
Humidity refers to the concentration of water vapour in the air. It can be measured in several ways, including relative humidity (RH), specific humidity, and thermal humidity indicators such as dew point and wet bulb temperature. Relative humidity is the most familiar measure, indicating how close the air is to saturation at a given temperature. When RH reaches 100%, the air cannot hold any more moisture, making it feel particularly muggy and uncomfortable.
The heatwave continues across western Europe with temperatures 5 to 10°C above average for many regions🌡️
— Met Office (@metoffice) June 26, 2025
Maximum temperatures are widely reaching 30 to 35°C, with a few locations approaching 40°C pic.twitter.com/z3HbGRi8yn
READ MORE: Learn about humidity
How humidity affects human health
Humidity directly influences our body’s ability to regulate temperature. In hot and humid conditions, sweat does not evaporate efficiently, making it harder for the body to cool down. This can lead to heat stress, dehydration, and in severe cases, heatstroke or cardiovascular complications. Vulnerable populations, such as the elderly, children, and those with pre-existing health conditions, are particularly at risk.
During periods of high humidity, especially in summer, the air can feel heavy and oppressive. This not only affects physical comfort but can also impair mental wellbeing. Interestingly, some research suggests, a drop in humidity following rainfall often brings a sense of relief and has been linked to improved mood and energy levels, particularly in tropical regions where high humidity is a year-round feature.
Humidity also impacts productivity. High humidity can reduce physical performance, making it harder to carry out manual labour or exercise. This has implications for sectors such as agriculture, construction, and manufacturing, where sustained physical effort is required.
The role of humidity in climate change
As the climate warms, the atmosphere can hold more water vapour. This leads to an increase in specific humidity – the actual amount of water vapour in the air. However, relative humidity over land is decreasing, as land areas are warming faster than oceans, where most evaporation occurs. This paradox highlights the complex relationship between temperature and humidity in a warming world.
Water vapour is also a potent greenhouse gas. It amplifies warming by trapping heat in the atmosphere, contributing to the feedback loop that accelerates climate change. More water vapour also means more intense rainfall events, increasing the risk of flooding. This is already being observed in many parts of the world.
READ MORE: Humidity – the second pillar of climate change
Monitoring humidity in a changing climate
To better understand and track these changes, the Met Office, in collaboration with international partners, has developed datasets such as HadISDH.land and HadISDH.marine. These tools allow scientists to monitor surface humidity trends over land and ocean, assess climate model performance, and study the impacts of extreme humidity events.
Wet bulb temperature is a simple way to measure how heat and humidity affect the body. If it reaches 35°C, the same as human skin, sweating stops working because the air is too full of moisture to absorb more. This makes it impossible for the body to cool down, which can be life-threatening. Even healthy people struggle to stay active when wet bulb temperatures get close to this level. Research shows that parts of the tropics are already experiencing wet bulb temperatures above 31°C, highlighting the urgency of addressing heat and humidity together.
Humidity is more than just a measure of moisture in the air, it is a critical component of our climate system and a major factor in human health and wellbeing. As global temperatures rise, understanding and adapting to changes in humidity will be essential. Whether it’s planning for heatwaves, designing climate-resilient infrastructure, or protecting public health, humidity must be part of the conversation.
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