How Earth's Climate System Works: Energy and Connections

How does Earth's climate system work?

Earth's climate works through energy exchange: sunlight is absorbed or reflected, and the planet emits infrared energy to space. The atmosphere, ocean, ice, land and living things interact to store and redistribute energy. A persistent imbalance changes the system's heat content. Human greenhouse-gas emissions have caused global warming by changing this system's energy balance.

Think of two questions as you follow the system: how much energy is Earth gaining or losing, and where is that energy going? They describe different things. Moving heat from one region to another changes regional conditions; changing the planet's total energy inventory requires a net gain or loss across its boundary. The mechanisms below connect those questions. NASA CERES describes these energy flows; the IPCC assesses human-caused warming.

What enters and leaves the climate system?

Sunlight arriving at Earth has two possible destinations: some is reflected back to space, while the rest is absorbed by the atmosphere and surface. Earth also emits thermal infrared radiation, energy associated with its temperature. Reflected sunlight and emitted infrared are separate outgoing flows.

At the top of the atmosphere:

Rate of energy gain = absorbed sunlight minus outgoing thermal infrared energy.

Absorbed sunlight already excludes reflection; subtracting reflected sunlight again would count it twice. When the two sides balance over time, the system is in radiative equilibrium. A positive difference adds energy; a negative difference removes it. This balance condition does not mean Earth is currently in equilibrium. See NASA's energy-budget explanation.

Why can a small persistent imbalance matter?

Distinguish a rate from an accumulated amount. A watt is one joule per second: watts measure power, while joules measure energy. Climate diagrams often express power per square metre, written W/m².

Here is an illustrative calculation, not an estimate of Earth's present imbalance. Suppose an area gains one extra joule each second for a full day:

• Assumed net gain: 1 W/m².
• Duration: 24 × 60 × 60 = 86,400 seconds.
• Accumulated energy: 1 × 86,400 = 86,400 joules per square metre.

For comparison, an assumed 10 W/m² gain lasting one hour adds 36,000 joules per square metre. The smaller rate operating longer adds more energy in this example. Neither calculation gives a temperature rise: that would also require knowing what absorbs the energy and how its state changes. The arithmetic illustrates why both the magnitude and duration of an imbalance matter.

What does the atmosphere do besides move air?

Greenhouse gases, including carbon dioxide and water vapour, absorb and emit infrared radiation. Together with clouds, they alter energy exchange between the surface, atmosphere and space. Their presence keeps the surface warmer than it would otherwise be. Energy still escapes to space; the greenhouse effect does not mean that every outgoing ray is permanently confined.

Clouds affect both sides of the radiation balance: they reflect sunlight and interact with infrared radiation. Their net effect depends on their properties, including height. A cloud therefore cannot be classified as warming or cooling simply because it contains water. These processes are explained by NASA's CERES science team. Our greenhouse-effect explainer follows that mechanism in more detail.

How does atmospheric circulation redistribute heat?

Uneven solar heating helps drive large-scale air movement. Atmospheric circulation is the recurring pattern of that movement, which transfers heat and moisture. The familiar three-cell diagram describes Hadley, Ferrel and Polar cells in each hemisphere; it summarises average circulation rather than tracing every day's weather.

In the Hadley circulation, trade winds converge toward the equator, where air rises in a zone of frequent thunderstorms. Higher up, air moves poleward before sinking in the subtropics. That pattern helps explain the contrast between equatorial rainfall and subtropical dry regions.

Earth's rotation also matters. The Coriolis effect deflects moving air to the right in the Northern Hemisphere and left in the Southern Hemisphere. High-altitude jet streams help guide weather systems. Heat transport consequently follows structured, changing routes rather than flowing straight from the equator to each pole. The Met Office describes these circulation patterns.

Why is the ocean central to climate?

The ocean stores heat and transports it through currents. Surface winds are an important driver of currents; temperature and salinity differences, Earth's rotation and tides also contribute. Salinity means the amount of dissolved salt in water. Water moving between regions carries heat with it, helping moderate the uneven heating of the planet. NOAA describes the ocean's climatic role.

Water has a high heat capacity, meaning it can absorb substantial energy without the temperature response being the same as in air. Ocean heat content therefore supplies information that a surface-air temperature reading cannot provide. Warming seawater also expands, contributing to sea-level rise. NASA's ocean-warming indicator explains heat storage and thermal expansion.

The IPCC's assessment assigns 91% of the observed energy increase during 1971–2018 to ocean warming. That is a share of the climate system's accumulated energy increase, not a claim that the ocean warmed by 91% or received 91% of all sunlight. The period and denominator matter. See IPCC Working Group I, Chapter 7, Section 7.2.2 and Table 7.1.

How does the water cycle carry energy?

Evaporation changes liquid water into water vapour. It requires energy and removes heat from the surroundings. Oceans, lakes, rivers and other wet surfaces supply water to the atmosphere this way; boiling is not required. The US Geological Survey explains evaporation and its cooling effect.

When vapour becomes liquid again, condensation releases heat into the atmosphere. Rising air can cool enough for cloud droplets to form. Water changing state therefore transfers energy as well as moving moisture. This energy associated with a change of state is called latent heat. The USGS condensation explanation describes the release of heat as droplets form.

Follow the sequence carefully: taking energy from a wet surface during evaporation and releasing it during condensation are different stages. A statement that evaporation itself heats the surface reverses the local effect. Likewise, water vapour is a gas; the visible droplets in a cloud are liquid water, a different state of the same substance.

How do ice and snow affect absorbed sunlight?

The cryosphere is the frozen part of the Earth system. Its bright surfaces matter because of albedo, the proportion of incoming sunlight a surface reflects. Sea ice reflects more sunlight than the darker ocean exposed when it melts.

This creates a feedback: initial warming can reduce sea ice; the exposed water absorbs more sunlight; that additional absorption contributes to further warming. Positive feedback means amplification of the initial change. The word positive describes the direction of the response, not whether the outcome is desirable.

The National Snow and Ice Data Center explains this ice–albedo feedback. The important connection is that ice responds to temperature while also changing how much sunlight is absorbed. Treating ice only as an indicator of warming misses its active role in the energy budget.

What roles do soil, vegetation and carbon play?

Land cover changes the way the surface exchanges energy and moisture with the atmosphere. Vegetation and soil influence reflection, infrared emission and evaporation. Soil moisture affects surface temperature, while the shape and roughness of the land influence wind. These are physical connections, even before considering carbon. The Met Office's account of the climate system explains how the atmosphere, water, frozen regions, land and biosphere interact. Biosphere means living organisms and their place in that system.

The carbon cycle adds another connection. Plants take in carbon dioxide through photosynthesis, using sunlight to build organic material. Respiration, decomposition and burning return carbon to the atmosphere. Carbon also moves between the atmosphere and ocean and is stored in soils, organisms and rocks.

Burning fossil fuels transfers carbon from long-standing geological stores into the active cycle. Clearing forests also changes stored carbon. Vegetation is consequently neither a passive backdrop nor an unlimited solution to added carbon dioxide: plant growth also requires water and nutrients. NASA's carbon-cycle explanation follows those transfers and constraints.

What changes the system, and what responds to change?

A radiative forcing is a disturbance to the radiation balance, such as one caused by changing greenhouse-gas concentrations. A feedback is part of the system's response that changes the subsequent energy balance. Keeping these concepts separate helps distinguish an initiating influence from an amplifying or damping response.

Warming also increases the planet's emission of infrared energy, a stabilising response. Other responses, including changes in water vapour, ice and clouds, modify how much warming follows a given forcing. The IPCC assesses these processes together; recognising an amplifying feedback does not establish unlimited warming. See Chapter 7's assessment of forcing and feedbacks.

The existence of natural processes does not make the cause of recent global warming unresolved. The IPCC's 2023 Synthesis Report identifies human activities, chiefly the release of greenhouse gases, as the unequivocal cause of global warming. Its assessment distinguishes warming from greenhouse gases, cooling from other human influences, natural drivers and internal variability. These influences can operate together; they are not interchangeable explanations. Our climate-change and global-warming guide clarifies the terminology.

How do scientists check that these connections are real?

Different measurements address different parts of the system. NASA's CERES observations track radiation flows and help evaluate climate models. Ocean observations track stored heat; NASA describes combining in-water instruments, satellite measurements and models to study the ocean. Our climate-model guide explains how observations test simulations.

When reading a climate claim, ask three specific questions. Does it describe an energy flow or an accumulated amount? Is it about the whole planet or one region? Does the reported number include a time period and a clearly named quantity? Those checks help distinguish a circulation change, an energy imbalance and a measured warming trend without confusing one for another.

Sources

• NASA: Climate and Earth's Energy Budget.
• NASA CERES: Science.
• Met Office: Global Circulation Patterns.
• NOAA: Ocean, Climate and Weather.
• NASA: Ocean Warming.
• IPCC AR6 Working Group I: Chapter 7.
• USGS: Evaporation.
• USGS: Condensation.
• NSIDC: Why Sea Ice Matters.
• Met Office: What Affects Global Climate?.
• NASA: The Carbon Cycle.
• IPCC AR6 Synthesis Report: Summary for Policymakers.