Our living planet is unique among all those we have been able to explore in the Universe so far. From our axial tilt preventing too many temperature extremes to our position in the golden loops zone, life on Earth depends on many finely balanced and interwoven cycles that combine to produce the exact circumstances we need to thrive.
One of these cycles is the Earth’s delicate energy system – the inflows and outflows of energy received from the Sun.
This cycle dictates all planetary climate systems. On Mars, the seasonal change in energy imbalance – around 15.3% between Mars seasons, compared to 0.4% on Earth – is thought to be behind the planet’s infamously epic dust storms.
For at least a time, before the 1750s, this fluctuating energy cycle on Earth was relatively balanced. But we have now created an imbalance that has recently doubled in just 15 years.
“The net energy imbalance is calculated by looking at how much heat is absorbed by the Sun and how much can be radiated back into space,” says atmospheric scientist Kevin Trenbergh of the National Center for Atmospheric Research.
“It is not yet possible to directly measure the imbalance, the only practical way to estimate it is by an inventory of energy changes.”
Trenberth and Chinese Academy of Sciences atmospheric physicist Lijing Cheng looked at data from all components of the climate system: land, ice, ocean and atmosphere between 2000 and 2019, to take stock of these changes.
Earth’s atmosphere reflects almost a quarter of the energy that strikes it, unlike the Moon which experiences the full impact of energy from the Sun, resulting in surface temperatures of around 100°C (212° F). Most of this energy is then absorbed by the Moon and radiated back into space as thermal infrared radiation, more commonly known as heat.
Again, it is the atmosphere that modifies this process here on Earth. Certain molecules in our atmosphere capture this heat before reaching space and continue to retain it. Unfortunately for us, it is greenhouse gases, which have effectively enveloped the planet in an overly cozy blanket at the top of the atmosphere.
This extra trapped energy not only changes where it ends up, but also impacts its surroundings on the way to its final destination, the researchers explain in their paper.
“Understanding the net energy gain, and how much and where heat is redistributed in the Earth system, is essential,” they write. “How much heat could be moved to where it can be purged from the Earth by radiation to limit warming?”
While everyone’s main focus has been on rising temperatures, that’s just a product of that extra energy. Only 4% of it goes to raising earth temperatures and another 3% to melting ice, Trenberth and Cheng calculated.
Nearly 93% is absorbed by the ocean, they found, and we are already witnessing the unpleasant consequences.
Although less than 1% of the excess energy swirls around in our atmosphere, it is enough to directly increase the severity and frequency of extreme weather events, from droughts to floods.
However, increased atmospheric turbulence can also be helpful.
“These weather events move energy around and help the climate system get rid of the energy by radiating it out into space,” the researchers explain.
Clouds and ice also help reflect solar radiation before it becomes long-wave heat that gases trap. But reflective clouds and ice are reduced by disturbances in this energy cycle.
There is still too much missing information for a comprehensive Earth system model that accurately predicts specific outcomes beyond the short term, say Trenberth and Cheng. But by incorporating their Earth Energy Imbalance framework that considers every component of the Earth system, this can be improved.
“Modelling Earth’s energy imbalance is a challenge, and relevant observations and their synthesis need to be improved,” Cheng concludes.
“Understanding how all forms of energy are distributed throughout the world and are sequestered or returned to space will give us a better understanding of our future.”
This research was published in Environmental Research Climate.
