Earth’s energy budget is the balance between the energy our planet receives from the Sun and the energy it sends back out to space. About 340 watts per square meter of solar energy reaches the top of the atmosphere on average, and in a stable climate, roughly the same amount of energy leaves. Right now, that balance is slightly off: Earth is absorbing more energy than it releases, which is why the planet is warming.
How Energy Arrives and Gets Distributed
The Sun delivers its energy as shortwave radiation, mostly visible light and ultraviolet. While the total output hitting the sunlit side of Earth is intense, spreading that energy across the entire globe (including the night side) averages it out to about 340 watts per square meter at the top of the atmosphere. That number is the starting point for everything else in the budget.
Not all of that energy makes it to the surface. About 29% is immediately reflected back to space by clouds, bright surfaces like ice and snow, and the atmosphere itself. This reflective property is called albedo, and Earth’s average albedo sits at roughly 0.30, meaning 30% of incoming sunlight bounces away without warming anything. If the planet were entirely covered in ice, that number would jump to about 84%. If it were covered in dark forest, it would drop to around 14%. The remaining energy, about 240 watts per square meter, gets absorbed by land, oceans, and the atmosphere.
What Happens to the Absorbed Energy
The roughly 240 watts per square meter that Earth absorbs doesn’t just sit still. It moves through the system in several ways before eventually leaving as heat radiation. The atmosphere directly absorbs some incoming sunlight: gases take in about 19 units of energy and clouds absorb another 4 (using a simplified 100-unit scale that NOAA uses to map the budget). The rest reaches the surface, where land and water soak it up.
The surface then transfers energy back to the atmosphere through two invisible but powerful processes. Evaporation is the bigger one. When water evaporates from oceans, lakes, and soil, it carries energy upward as what physicists call latent heat. That energy gets released when the water vapor condenses into clouds. The second process is direct heating of the air through contact with the warm ground, called sensible heat. Together, evaporation and direct heating move a large share of surface energy into the atmosphere without any radiation involved.
How Energy Leaves the Planet
Earth can’t lose energy through evaporation or convection into space, since space is essentially a vacuum. The only way energy escapes is as infrared radiation, the same type of invisible heat you feel radiating from a hot sidewalk. The surface, the atmosphere, and clouds all emit this infrared energy upward.
Here’s where it gets interesting. The surface radiates a huge amount of infrared energy, but most of it never reaches space directly. Greenhouse gases like water vapor and carbon dioxide absorb that radiation and re-emit it in all directions, including back toward the ground. Only about 12% of incoming solar energy’s worth of surface radiation passes straight through the atmosphere and escapes to space through what scientists call the “atmospheric window,” a narrow range of infrared wavelengths that greenhouse gases don’t absorb well.
The bulk of the outgoing energy, equivalent to roughly 59% of incoming sunlight, leaves from higher in the atmosphere. Gases emit about 49 units of longwave radiation to space, and clouds contribute another 9 units. So most of Earth’s cooling happens not at the surface but from the atmosphere itself radiating heat upward.
The Role of Clouds
Clouds play a dual role that makes them one of the trickiest parts of the energy budget. On one hand, their bright white tops reflect sunlight back to space, cooling the planet. On the other hand, they trap outgoing infrared radiation like a blanket, warming it. Measurements from NASA’s Earth Radiation Budget Experiment put numbers on this tug-of-war: clouds reflect about 44.5 watts per square meter of solar energy (cooling effect) but trap about 31.3 watts per square meter of heat (warming effect). The cooling wins. On balance, clouds have a net cooling effect on Earth of roughly 13 watts per square meter.
This net cooling is one reason why changes in cloud cover matter so much for climate. A shift toward fewer low, bright clouds or more high, thin clouds could reduce the cooling effect and amplify warming, even without any change in greenhouse gas levels.
Why the Budget Is Currently Unbalanced
In a perfectly stable climate, energy in would equal energy out. That’s not the case today. As greenhouse gas concentrations rise, more outgoing infrared radiation gets trapped in the atmosphere before it can escape. The result is an energy imbalance: Earth absorbs more energy than it emits.
Between 1971 and 2020, this imbalance averaged about 0.48 watts per square meter. That might sound tiny compared to the 340 watts coming in, but spread across the entire surface of the planet, it adds up to an enormous amount of extra heat. And the imbalance is growing. For the period from 2006 to 2020, it rose to about 0.76 watts per square meter, confirmed independently by multiple research teams using different methods.
Where does all that extra energy go? The vast majority, over 90%, is absorbed by the oceans. The rest warms the land, melts ice, and heats the atmosphere. This is why ocean temperatures are rising and ice sheets are shrinking: the energy budget tells you not just that the planet is warming, but exactly how much extra energy is driving that warming and where it ends up.
Why the Energy Budget Matters
The energy budget is more than an accounting exercise. It’s the framework scientists use to understand every aspect of climate. Changes in any part of the budget, whether it’s more greenhouse gases trapping outgoing heat, less ice reflecting incoming sunlight, or shifts in cloud cover, ripple through the entire system. When you hear that adding carbon dioxide to the atmosphere causes warming, the energy budget is the mechanism. More CO₂ means less infrared radiation escaping to space, which means the imbalance grows, which means the planet accumulates heat until a new, warmer equilibrium is reached.
Satellite measurements since the late 1970s have allowed scientists to track each component of the budget with increasing precision. These observations show that the imbalance is real, measurable, and accelerating, providing one of the clearest lines of evidence for human-driven climate change.