Climate crisis: Increased temperature between day and night affects life on Earth

In a recent study, researchers have found alarming shifts in the balance between day and night temperatures due to climate change. While it's common knowledge that days are warmer and nights cooler, this equilibrium crucial for life is being disrupted.

Day-night temperature gap is increasing

The study reveals a global trend where the temperature gap between day and night is widening. Climate change is causing an overall increase in average surface temperature, but this rise isn't uniform across day and night. As a result, the delicate balance necessary for ecosystems and living organisms is being thrown off.

This imbalance poses significant risks to all life forms. While the full extent of the consequences is yet to be fully understood, the implications are concerning. It underscores the urgent need for action to mitigate climate change and protect the delicate balance of our planet's temperature patterns.

Climate change, caused by humans, is making the world’s average temperature go up. But this increase is not the same during the day and night. In the second half of the 20th century, the temperature at night went up faster than during the day.

"We call this pattern of different warming rates during the day and night 'asymmetric warming'. Both human activities and natural events can cause it."

A new study in the journal Nature Communications looked at this pattern again. The researchers found that the pattern has changed. From 1961 to 2020, the temperature during the day has been going up faster, while the increase at night has stayed about the same. This change in the pattern has made the temperature difference between day and night bigger.

"We initially aimed to confirm the previously observed phenomenon of nighttime warming surpassing daytime warming. To our surprise, not only had the asymmetric warming trend ceased, but our analyses, based on state-of-the-art observation-based datasets, indicate a complete reversal of this original warming pattern over the past three decades," says Ziqian Zhong, a post-doctoral researcher at Chalmers.

Less clouds, more sun, warmer Earth

"A likely explanation to this change is a phenomenon called "global brightening," which has been observed since the late 1980s. It is a result of less cloud cover, which causes more sunlight to reach the Earth's surface, leading to higher daytime temperatures and, as a result, a broader difference between daytime and nighttime temperatures over the recent decades," says Ziqian Zhong.

Currently, significant uncertainty exists regarding the reasons behind the changes in cloud cover. A complex interplay between cloud-free and cloudy atmospheres may cause the "global brightening", as well as the effect of small particles in the atmosphere, known as aerosols.

Natural processes like sea spray and wildfires, as well as human activities like fossil fuel burning, can derive these aerosols, and they can profoundly affect many aspects of the environment. Besides the effects from global brightening, the researchers suggest another reason for the reversed asymmetric warming.

The increase in regional drought events and heatwaves suggests that the potential weakening of the cooling effect due to evaporation at the Earth's surface could result in a faster increase in daytime temperatures.

The researchers found that larger nighttime warming affected 81 per cent of the total land area from 1961 to 1990. However, a shift occurred in the subsequent period from 1991 to 2020, with larger daytime warming affecting 70 per cent of the observed land areas instead.

Bigger temperature gap, diverse impacts

The larger temperature difference between day and night could potentially affect crop yields, plant growth, animal well-being and human health.

"For example, we recognise an increased temperature difference between daytime and nighttime as one of the environmental stressors. This could lead to an elevated heart rate and blood pressure, subsequently increasing cardiac workload and the mortality and morbidity of cardiovascular and respiratory diseases."

"This indicates the need to adjust strategies in different areas affected by temperature variations between day and night, such as agriculture, public health, and forestry management, to address the challenges posed by this climate change," says Ziqian Zhong.

Certain tree species in humid areas might enhance their carbon sequestration capacity due to the increased temperature difference between daytime and nighttime.

However, the increased temperature difference between daytime and nighttime might prove disadvantageous for trees in dry regions, as higher daytime temperatures may increase evaporation, leading to a deficiency of soil water and unfavourable conditions for tree growth.

"In the upcoming research, we will further investigate the impacts of this reversed trend in asymmetric warming on tree growth and carbon cycle," says Ziqian Zhong.

The study also found that this change can help some types of trees in wet areas absorb more carbon. But in dry areas, the hotter days can slow down tree growth because they make the soil drier, which is bad for trees.

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