More muggy evenings as study finds that nights are warming faster than days

Climate change is causing more muggy evenings, scientists have found, as data shows nights are warming at a faster rate than days.

A new study by the University of Exeter, published in Global Change Biology, found that nights from 1983 to 2017 warmed at an average rate of 0.25 degrees more than the days in more than half of the areas surveyed.

The research shows this "warming asymmetry" has been driven primarily by changing levels of cloud cover.

Increased cloud cover cools the surface during the day and retains the warmth during the night, leading to greater night-time warming. Whereas, decreasing cloud cover allows more warmth to reach the surface during the day, but that warmth is lost at night.

The areas in which the days were warming at a faster rate than nights had less cloud cover, but in general clouds are increasing due to climate change.

Warmer nights tend to be wetter, scientists explained, warning that this could have impacts on plant and invertebrate life.

"Warming asymmetry has potentially significant implications for the natural world," said lead author Dr Daniel Cox, of the Environment and Sustainability Institute on Exeter's Penryn Campus in Cornwall.

"We demonstrate that greater night-time warming is associated with the climate becoming wetter, and this has been shown to have important consequences for plant growth and how species, such as insects and mammals, interact."

Scientists also found that drier conditions in the day meant that animals could die of heat stress or dehydration.

Dr Cox said: "Conversely, we also show that greater daytime warming is associated with drier conditions, combined with greater levels of overall warming, which increases species vulnerability to heat stress and dehydration.

"Species that are only active at night or during the day will be particularly affected."

However, warming, whether in day time or at night, caused fewer plants to grow.

Increased night-time warming led to less vegetation growth where it rained more, likely due to increased cloud cover blocking the sun. Whereas, vegetation growth was limited by water availability due to less rainfall where the days warmed more.

The global study examined hourly records of temperature, cloud cover, specific humidity and precipitation.

The authors modelled the different rates of change of daytime maximum and night-time minimum temperatures, and mean daytime and mean night-time cloud cover, specific humidity and precipitation.

Uncomfortably hot nights are on the rise in the UK, the Met Office said earlier thi syear.

During the summer heatwave, we saw 16 'tropical nights' above 20 degrees. This was previously an uncommon phenomenon. While the 30 years between 1961 and 1990 seeing 44 tropical nights, this almost doubled in the years between 1991 to 2020, when 84 such nights were recorded.