From the poles to the tropics, from the oceans to our cities, we have mapped the temperature fluctuations that are leading to a climate crisis.
But strangely, little attention has been paid to the circadian landscapes of the world at night and day. And a new study shows that our nocturnal environment is actually warming up at a faster rate than our surroundings during the day, which may prove too much for many species.
After analyzing more than three decades of daily temperature data from around the world, researchers at the University of Exeter concluded that there is an asymmetry in our planet’s warming as it rotates on its axis.
The climate records spanned from 1983 to 201
In some places, the days have noticeably warmed up while the nighttime temperatures barely stirred. There were also periods of notable cooling for some environments.
But the bigger picture was surprising. Over more than half of the planet’s Earth’s surface, the average annual temperature rise during the night was a quarter of a degree Celsius higher than during the day.
A fraction of a degree each year might seem tiny, but over time these heat gains could add up to have a significant effect on ecology.
“Species that are only active at night or during the day will be particularly affected,” says ecologist and lead author Daniel Cox of the University of Exeter.
To get a better understanding of the environmental forces at work, the team also collected a range of data on other related climate factors such as humidity and rainfall.
They also compared regional differences in vegetation growth.
Putting it together, something as simple as increased cloud cover could easily explain the imbalance in warming.
Global warming traps extra amounts of energy near the planet’s surface, encouraging the atmosphere to retain moisture which then condenses into clouds. There is no real secret there.
We also know that clouds do a great job of reflecting certain wavelengths of light, both in space and downwards.
During the day, this can help shield the surface from full blast of sunlight by keeping a little lid on temperatures. Without this shading effect, we might expect our planet’s surface to roast.
At night, the process is reversed. Heat radiating from the ground has a harder time making it into space, keeping the surface a touch warmer.
We’ve all felt the chill of a cloudless winter night to understand the underlying mechanism, but having hard data can help us better model what we might expect in the coming years.
Putting aside the variations in temperature at different locations over time, the variations in temperature between night and day could have a profound impact on rainfall, which in turn determines the degree of plant growth.
Even with a general increase in rainfall, extra cloudiness during the day risks reducing the amount of light needed by plants for photosynthesis.
“The warming of asymmetry has potentially significant implications for the natural world,” says Cox.
‘We have shown that increased night warming is associated with wetter climate, and this has been shown to have important consequences for plant growth and how species, such as insects and mammals, interact.’
Understanding the full implications of daily fluctuating temperatures and cloud formation will require far more research.
Clouds can be surprisingly complex phenomena, especially when we take into account greenhouse gases, the influence of dust levels and even less the variables related to the Earth.
Knowing how much they will help or hinder our efforts to limit the rise in temperatures is not an easy question to answer.
This research was published in Biology of global change.