Sunrise from the ISS. (NASA/Reid Wiseman)
Our living planet is unique among all we’ve been able to explore in the Universe so far. From our axial tilt preventing too many temperature extremes, to our goldilocks zone position, life on Earth depends on many finely balanced, interwoven cycles that come together to produce the exact circumstances we need to thrive.
One of these cycles is Earth’s delicate energy system – the inputs and outputs of the energy received from the Sun.
This cycle dictates all planetary climate systems. On Mars, the seasonal change in energy imbalance – around 15.3 percent between Mars’s seasons, compared to 0.4 percent on Earth – is thought to cause the planet’s infamously epic dust storms.
For at least a while, before the 1750s, this fluctuating energy cycle on Earth was relatively balanced. But we’ve now created an imbalance that’s recently doubled in just 15 years.
“The net energy imbalance is calculated by looking at how much heat is absorbed from the Sun and how much is able to radiate back into space,” explains atmospheric scientist Kevin Trenberth from the National Centre for Atmospheric Research.
“It is not yet possible to measure the imbalance directly, the only practical way to estimate it is through an inventory of the changes in energy.”
Trenberth and Chinese Academy of Sciences atmospheric physicist Lijing Cheng reviewed data from all components of the climate system: land, ice, ocean and atmosphere between 2000 and 2019, to conduct a stocktake of these changes.
Earth’s atmosphere reflects almost one quarter of the energy that hits it, unlike on the Moon which takes the full impact of the Sun’s energy, leading to surface temperatures of around 100°C (212°F). Most of that energy is then absorbed by the Moon and radiated back out into space as thermal infrared radiation, more commonly known as heat.
width=”700″ height=”414″ allowfullscreen=”allowfullscreen”>
Again, it’s the atmosphere that changes this process here on Earth. Some molecules in our atmosphere catch that heat before reaching space and keep holding onto it. Unfortunately for us, these are the greenhouse gasses, which have effectively now enveloped the planet in a too-snug blanket at the top of the atmosphere.
That extra trapped energy not only changes the place it ends up in but also impacts its surroundings on the way to its final destination, the researchers explain in their paper.
“It is vital to understand the net energy gain, and how much and where heat is redistributed within the Earth system,” they write. “How much heat might be moved to where it can be purged from the Earth via radiation to limit warming?”
While everyone has mostly been focusing on increasing temperatures, that’s only one product of this extra energy. Only 4 percent of it goes into raising temperatures of land and another 3 percent goes into melting ice, Trenberth and Cheng worked out.
Almost 93 percent is being absorbed by the ocean, they found, and we’re already witnessing the unpleasant consequences.
Although less than 1 percent of the excess energy whirls around in our atmosphere, it’s enough to directly increase the severity and frequency of extreme weather events, from droughts to floods.
However, the increased atmospheric turbulence may also be helpful.
“Those weather events move energy around and help the climate system get rid of energy by radiating it to space,” explain the researchers.
Clouds and ice also help to reflect solar radiation before it becomes long-wave heat that the gasses trap. But both reflective clouds and ice are being reduced by disruptions in this energy cycle.
There’s still too much missing information for a comprehensive Earth system model that accurately predicts specific outcomes beyond the short term, Trenberth and Cheng say. But by incorporating their Earth energy imbalance framework that considers each Earth system component, this may be improved on.
“Modeling the Earth energy imbalance is challenging, and the relevant observations and their synthesis need improvements,” concludes Cheng.
“Understanding how all forms of energy are distributed across the globe and are sequestered or radiated back to space will give us a better understanding of our future.”
This research was published in Environmental Research Climate.