Nights warming faster than days, shows research

New Delhi: Global warming is affecting daytime and night-time temperatures differently – and greater night-time warming is more common than greater daytime warming worldwide, shows new research.

According to University of Exeter scientists, who studied warming from 1983 to 2017, there was a difference in mean annual temperature of more than 0.25 between daytime and night-time warming in over half of the global land surface. Days warmed more quickly in some locations, and nights did in others – but the total area of disproportionately greater night-time warming was more than twice as large, found the research team. The paper is published in the journal Global Change Biology.

The study has shown that this phenomenon termed “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, believe the researchers.

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

“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.”

In an important insight, the researcher added that species that are only active at night (nocturnal) or during the day will be particularly affected.

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

They then looked at changes in vegetation growth and precipitation over the same period.

The study found that differences in daytime and night-time vegetation growth depended on rainfall. 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.