The Earth’s energy budget is the balance sheet of all energy coming into and leaving the planet. Energy arrives almost entirely as sunlight, and energy leaves as reflected light and heat radiated back to space. When these two sides balance, global temperatures stay stable. When more energy comes in than goes out, the planet warms. Right now, that balance is off by a small but significant amount.
How Energy Arrives
Nearly all the energy Earth receives comes from the sun, arriving as electromagnetic radiation across a range of wavelengths: visible light, ultraviolet, and near-infrared. At the top of the atmosphere, this solar energy delivers roughly 340 watts per square meter when averaged across the entire globe. (The actual solar beam is about four times stronger, but only half the planet faces the sun at any moment, and the curved surface spreads that energy out.)
Not all of that 340 watts reaches the ground. Some is immediately bounced back to space, some is absorbed by the atmosphere on the way down, and the rest is absorbed by land, water, and ice at the surface. Each of these pathways plays a distinct role in setting Earth’s temperature.
What Gets Reflected Away
About 30% of incoming solar energy never warms anything. It reflects straight back to space, a property scientists call planetary albedo. Satellite measurements confirm this 30% figure consistently. Clouds are the single biggest reflector, responsible for roughly half of the planet’s total reflectivity. The rest comes from bright surfaces like ice sheets, deserts, and snow cover, plus tiny particles suspended in the atmosphere such as dust and sulfate aerosols.
This means roughly 100 watts per square meter, out of the original 340, simply bounces away. The remaining 240 or so watts per square meter is the energy that actually enters the climate system and must eventually be radiated back out for temperatures to stay constant.
Where the Absorbed Energy Goes
Of the solar energy that doesn’t reflect away, the atmosphere itself captures a portion on the way down. Gases like ozone absorb ultraviolet light in the upper atmosphere, while water vapor and clouds together absorb additional energy in the lower atmosphere. NOAA estimates that atmospheric gases absorb about 19% of incoming solar radiation, with clouds absorbing another 4%. The rest, roughly half of the total incoming sunlight, reaches and warms the surface.
Once the surface absorbs that energy, it doesn’t just sit there. The surface loses energy back to the atmosphere through three main channels. First, the ground and ocean radiate infrared heat upward, the same kind of invisible radiation you feel standing near a hot road. Second, evaporation carries enormous amounts of energy into the atmosphere as latent heat: water molecules absorb energy when they evaporate and release it when they condense into clouds. Third, direct warming of the air in contact with the surface (sensible heat) transfers energy upward through convection. The global average sensible heat flux over land is around 39 watts per square meter, though it varies widely by region and season.
How Earth Radiates Energy to Space
Everything with a temperature emits radiation. Earth’s surface and atmosphere emit energy in the infrared range, often called longwave radiation. The total outgoing longwave radiation measured at the top of the atmosphere is about 235 to 239 watts per square meter, which in a balanced system would match the absorbed solar energy coming in.
Here’s the critical detail: very little of that outgoing radiation comes directly from the surface. Less than one-tenth of the total outgoing longwave radiation passes straight through the atmosphere without being intercepted. Most infrared energy emitted by the surface gets absorbed by greenhouse gases (water vapor, carbon dioxide, methane, and others) and by clouds, which then re-emit it in all directions. Some of that re-emitted energy heads back down toward the surface, warming it further. Some heads upward and eventually escapes to space, but from higher, cooler layers of the atmosphere.
This is the greenhouse effect in action. It’s not blocking energy from leaving entirely. It’s raising the altitude from which Earth effectively radiates to space, which slows the rate of energy loss and keeps the surface warmer than it would otherwise be. Without this natural greenhouse effect, Earth’s average surface temperature would be well below freezing.
The Budget Is Currently Out of Balance
For most of Earth’s recent history, incoming and outgoing energy were roughly equal, with small natural fluctuations. That’s no longer the case. Rising concentrations of greenhouse gases have made the atmosphere more effective at trapping outgoing infrared radiation, creating a persistent energy imbalance.
Measurements show this imbalance was relatively small, around 0.2 watts per square meter, through much of the mid-20th century. By the late 1990s it had intensified to roughly 0.8 watts per square meter. Satellite data from NASA’s CERES instruments, which have tracked Earth’s radiation budget continuously since March 2000, show the imbalance averaging around 0.6 to 0.7 watts per square meter during the 2000 to 2014 period. That may sound tiny compared to the 240 watts per square meter flowing through the system, but applied across the entire planet’s surface area, it adds up to an enormous amount of extra energy accumulating every second.
CERES data through early 2025 reveal that shortwave (solar) energy absorbed by the climate system has been trending upward, while outgoing longwave radiation has also increased but not enough to compensate. The net result is a continued surplus. In 2023, absorbed solar radiation hit unusually high levels, exceeding normal variability for most of the year, partly driven by conditions that reduced cloud cover and surface reflectivity.
Where the Extra Energy Ends Up
When more energy enters the system than leaves it, that surplus has to go somewhere. About 90% of the excess heat from planetary warming over the past century has been absorbed by the ocean. Water has an enormous capacity to store thermal energy, so the ocean acts as a massive buffer, absorbing heat that would otherwise warm the atmosphere and land surface much faster.
The remaining roughly 10% of excess energy goes into warming the atmosphere, heating the land surface, and melting ice. Ice loss is particularly significant because melting absorbs large amounts of energy without raising temperature, a process that simultaneously raises sea levels and reduces the bright, reflective surfaces that bounce sunlight away. As ice melts, darker ocean water or land is exposed underneath, which absorbs more solar energy, creating a feedback loop that amplifies warming.
The ocean’s role as a heat sink is why global surface temperatures haven’t risen as fast as the energy imbalance alone might suggest. But it also means the climate system has “committed warming” built in. Even if greenhouse gas concentrations stopped rising today, the ocean would gradually release stored heat back to the atmosphere, continuing to warm surface conditions for decades.
Why the Energy Budget Matters
The energy budget is the fundamental framework for understanding climate. Every climate phenomenon, from trade winds to hurricanes to ice ages, is ultimately driven by how energy moves through this system. When you hear that Earth is warming, what’s really being described is a persistent imbalance in this budget: more energy arriving than departing, with the surplus accumulating mainly in the oceans.
Tracking the budget with precision requires satellites like the CERES constellation, which has now established a continuous 25-year record of Earth’s radiation flows. That record is how scientists quantify not just whether the planet is warming, but how fast and through which specific mechanisms. Changes in cloud cover, ice extent, aerosol pollution, and greenhouse gas concentrations all show up as shifts in the budget’s individual line items, making it possible to diagnose what’s driving temperature changes rather than simply observing them after the fact.