What Is a Zettajoule? Understanding the Massive Unit Behind Climate Change
The term zettajoule has become increasingly important in discussions about climate change, yet most people are unfamiliar with it. Even scientists working on global climate systems find it difficult to fully grasp the scale it represents. A zettajoule is an enormous unit of energy used to measure the vast changes happening in Earth’s climate system.
What Is a Zettajoule?
A zettajoule (ZJ) has a huge amount of energy and equals 1 sextillion joules or 1 followed by 21 zeros (1,000,000,000,000,000,000,000). Since the zettajoule is such a big amount, scientists use it to gauge how much total energy is used by people throughout the World, as well as the total amount of heat that has been absorbed by all of Earth‘s oceans. As such, every year, the World consumes approximately 0.5 to 0.6 zettajoules of energy; however, in 2025, the oceans absorbed a record–breaking 23 zettajoules of excess heat (approx. equivalent to 11-12 atomic bombs the size of Hiroshima‘s dropping every second for a full year) or enough energy to boil approximately 3.4 billion Olympic swimming pools. We can determine just how powerful the zettajoule (ZJ) is by using an example that shows the amount of energy needed to increase the temperature of the Earth‘s atmosphere by 1°C, which requires about 2.2 zettajoules. In terms of climate science, the zettajoule is extremely important when it comes to monitoring Earth‘s energy imbalance, since about 90% of the heat being trapped because of greenhouse gases is being absorbed by the ocean and is therefore a better indicator of global warming than air temperature alone. The term zettajoule is constructed from the word “joule,“ named after physicist, James Prescott Joule, and the prefix “zetta,“ meaning a sextillion, i.e., a 1 and 21 zeros, illustrating the unbelievable volume of energy involved.
What is Zettajoules Role in Climate Change?
Zettajoules have gained popularity lately because they can measure Earth‘s heat imbalance. The World Meteorological Organization (WMO) states that Earth has an ever–growing imbalance with its energy; our planet is heating the oceans, land, and air dangerously fast. From 2005–2025, the energy imbalance of Earth grew about 11 zettajoules annually. If you combine this amount of energy with all other humans combined, it would amount to approximately 18 times greater than each other.
This heat imbalance primarily results from human activities like burning fossil fuels and cutting down trees. These activities release greenhouse gases (primarily CO2, CH4, and N2O), which capture heat in the atmosphere and cause temperature increases on Earth instead of allowing heat to leave through space, thereby contributing to increasing temperatures and worldwide extreme weather events [World Meteorological Organization, 2017].
How Fast Is Earth’s Energy Imbalance Growing?
We are seeing rapidly declining global climate conditions. The WMO report states that by 2025, ocean heat energy will be at a new high level equating to an additional 23 zettajoules. As the water absorbs over 90% of all solar radiation, the global oceans are critical contributors to Climate Change. John Kennedy, WMO of the WMO report: “This level of ocean [heating] energy absorbed equal to approximately 39 times U.S. annual energy use.” Researchers have made multiple analogs to explain the ocean heating energy buildup. For example, researcher John Abraham used the Hiroshima bomb comparison for heating energy absorbed by the ocean over a 1–second period. In 2020, the oceans were absorbing heat from the sun compared to approximately 5 atomic bomb detonations. In 2022, this number reached approximately 7 per second, and in 2025, it will be about 11 every second. Additionally, the Chinese Academy of Sciences has indicated that at prior levels of ocean heating, the accumulated energy would have boiled away approximately 2.3 billion Olympic size swimming pools worth of water; now, it would boil away approximately 3.4 billion Olympic size swimming pools worth of water.
How Did Energy Levels Reach Zettajoules?
The unit “joule” is named after James Prescott Joule, a scientist who studied energy in the 19th century. A single joule represents a very small amount of energy like the effort needed to lift an apple onto a table.
Over time, as human technology advanced, energy use increased dramatically. Scientists began using larger units such as kilojoules, megajoules, gigajoules, and beyond, eventually reaching zettajoules to describe global-scale energy changes.
However, while humans have become better at producing and using energy, less attention has been paid to where that energy goes after use. According to the basic law of physics known as the first law of thermodynamics, energy cannot be destroyed it only changes form or moves elsewhere. In the case of Earth, much of this excess energy remains trapped in the climate system.
Why This Matters for the Planet
The growing energy imbalance is a serious warning sign. As more heat gets trapped, it leads to rising global temperatures and increases the risk of extreme weather events such as heatwaves, storms, floods, droughts, and wildfires.
The scale of energy measured in zettajoules shows how severe and fast climate change is becoming. It highlights the urgent need for global action to reduce emissions and restore balance to Earth’s climate system.
Zettajoules may be difficult to understand, but they clearly show the scale of the climate crisis. The rapid rise in Earth’s energy imbalance reflects the growing impact of human activity on the planet. Unless action is taken to reduce greenhouse gas emissions, this imbalance will continue to grow, making the future more uncertain and challenging for all life on Earth.