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Climate forcings &  Earth’s energy budget

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Summary

What’s in this page:

What are ‘climate forcings’?

The term ‘climate forcings’ comes from radiative forcing or RF. This is the difference between the amount of solar energy reaching Earth and the amount that escapes back into space via shortwave radiation. If incoming energy = outgoing energy, Earth’s energy balance is in equilibrium and average global temperature remain stable. If too much energy arrives than leaves, Earth’s energy becomes imbalanced, which causes global temperatures rise (Fig. 1). This is due to the Law of Conservation of Energy, a fundamental law of thermodynamics that states:

Energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another.

That is, solar radiation is transformed into heat, and what can’t escape back into space remains trapped on Earth.
Earth energy imbalance to 2025
Figure 1: Growing energy imbalance 2020-2025. The influence of heat energy is measured as Watts/square metre, expressed as Wm-2 or W/m2 in equations. The ups and downs in the graph reflect the fact that the process is not smooth. In 2023 the imbalance reached 1.8W/m2. The red and blue lines are the averages. Because global temperatures are rising, outgoing radiation (purple area) is increasing, but even more radiation is being retained (yellow area), hence the imbalance: 1 W/m2 = 0.8°C of retained heat. Image: Berkeley Earth; click here to be taken to Climate Tracker’s monthly updates.

Even small changes to one forcing can have a huge impact on Earth’s average temperature. But not all climate forcings heat the planet. For example, emissions from Mt. Pinatubo volcano in 1991 blocked some of the sunlight (incoming solar radiation). That helped cool the planet for the next year or two. 

Aerosols—pollution in the atmosphere that, paradoxically come from burning poorly refined fossil fuels—also block out some sunlight. But the cooling effect of these two climate forcings—volcanoes and aerosols—were not nearly enough to offset the rapid warming caused by an increasing volume of greenhouse gases in the atmosphere (Fig. 2).

Figure 2: Climate forcings contributing to increased temperatures (black line) 1850-2023. ‘Natural’ forcings (green line) include volcanic eruptions. Aerosol emissions are the blue area. When added together, all of the cooling climate forcings (amber line) weren’t enough to offset the largest warming forcing of all: greenhouse gases (grey line). Image: Climate Brink January 2025

Earth’s energy budget: where is all the extra heat going?

The imbalance leads to energy accumulation in the atmosphere, oceans and land, and melting of the cryosphere, resulting in increasing temperatures, rising sea levels, and more extreme weather. – Mauritsen et al 2025

About 89% of the excess heat prevented from escaping into space—23 Zettajoules annually—is absorbed by the oceans (Fig. 3). In 2025, the amount of heat was the equivalent of heat from 12 Hiroshima sized atomic bombs exploding in the ocean every second of every day.
Ocean heat content to 2024
Figure 3: Ocean heat content accumulation 1955-2021. Data: NOAA/NCEI World Ocean Database. Image: RCraig.
Water has a very high specific heat capacity, so the ocean can store massive amounts of this thermal energy with relatively small changes in temperature—although they are rising fast, contributing to extreme weather patterns including El Niño, and accelerating sea level rise.

As for the remaining 11% of excess heat, the cryosphere (ice caps, glaciers, permafrost) absorbed ~4%, which is why it’s rapidly melting and the land took up ~6%. This helped keep global air temperatures down because only 1% of excess heat stayed in the atmosphere.

These factors were included the IPCC AR6 (CMIP6) climate models that project warming to the year 2100. However:

Worryingly, the observed energy imbalance is rising much faster than expected, reaching 1.8 W/m2 in 2023—or twice that predicted by climate models—after having more than doubled within just two decades. –op.cit. (Fig. 2)

Then in late 2023 surface air temperatures abruptly jumped, leading to 2024 being the first year on record to exceed 1.5°C (Fig. 4). 

2025 global temperatures
Figure 4: Annual global surface air temperature anomalies (°C) relative to the 1850–1900 pre-industrial period. Image: Copernicus

This jump was partly due to El Niño, part of the natural cyclic ENSO phenomena that releases some of the heat stored in the Pacific Ocean into the atmosphere. This warming effect is known to cause temporary temperature spikes above ‘average’. And in the past, cooling La Niñas, the flip side of ENSO, brought temperatures back down.

But that’s no longer happening:

“Cool” years are now hotter than the “warm” years of the past: tracking global temperatures through El Niño and La Niña. – Our World in Data, 2025

As of September 202, the 2026-2027 El Niño is shaping up to be far worse.

The carbon budget

So why has Earth’s energy imbalance (Fig. 1) suddenly increased so quickly? Was the IPCC modelling wrong?

Under the 2015 Paris Accord, the aim was to hold global warming to ‘well below 2°C’ above pre-industrial levels and to ‘pursue efforts to limit it to 1.5°C’. To do so required knowing how much additional carbon dioxide CO2 could still be emitted into the atmosphere before those limits were exceeded. The budget, created and monitored by Global Carbon Budget included how much CO2 was being emitted (‘spent’) and how much the planet was absorbing (‘saved’). This budget underpinned the Paris Accord as it underpinned the entire the global carbon trading market.

Most of the carbon market depended on plants, mostly trees, absorbing CO2. If not for plants, atmospheric CO2 and with it, temperatures, would be much higher (see Greenhouses gases and how they work). Plants on land and in the ocean (mostly algae) were absorbing 38% of the excess CO2 being emitted into the atmosphere (Fig. 5). Plants also store CO2 in the soil and the bottom of the ocean where it accumulates and is recycled over millions of years.

Natural carbon sinks Image: Project Drawdown
Figure 5: Natural carbon sinks totalled 38% on land while 62% stayed in the atmosphere Image: Project Drawdown

 

However, warnings of a tipping point being breached were made clear at COP26 in Glasgow in 2021:

The only reason why the IPCC provides the world with the remaining carbon budget of roughly 4-500 gigatonnes, is that the models assume that the carbon sink capacity of intact nature will continue. So not only are we assuming that biological systems will not cross tipping points, we’re also assuming that the stocks of carbon in forests in soils, in wetlands and permafrost, remain reasonably intact over the next 50 years. 

That is quite an optimistic assumption because it means we need to invest in conserving the remaining intact ecosystems. – Rockström, 2021 (YouTube)

Earth’s ability to absorb CO2 compromised

Then in 2023-24 the amount of CO2 in the atmosphere abruptly increased:

 Concentrations [of CO2] surged by a record 3.5 ppm from 2023 to 2024, the largest single-year jump since modern record-keeping began in 1957. – World Meteorological Association (WMO) 2025

Human emissions were still climbing in 2023-2024. Based on the IPCC modelling and the carbon budget, these emissions weren’t nearly enough to account for the increase in the energy imbalance (Fig. 1), the sudden jump in CO2 in the atmosphere, and the abrupt increase in temperatures (Fig. 4).

In 2026 a peer-reviewed paper by Dang et al showed that between 2014 and 2023 the land had been absorbing and average 3.22Gt/year of carbon. Then in 2024 the land suddenly stopped absorbing ~30% of the CO2 that it had done so over the previous 10 years of measurements. Dang et al also pointed out what Rockström and others had been saying for years but were ignored. The 6% of heat that the land had been taking up was driving up ground surface temperatures, increasing soil respiration, and triggering decomposition of soil organic matter—which releases CO2 in a positive feedback effect.

 ….the underlying mechanism for the reduction was caused by hotter and drier conditions leading to a larger increase in respiration than photosynthesis….These results challenge previous assumptions about the long-term stability of the terrestrial carbon sink. – Dang et al April 2026

The land has not just stopped absorbing as much CO2 as it once had. It’s now also emitting some of the ‘banked’ CO2 into the atmosphere through melting permafrost, drought, increasing wildfires, and the ongoing destruction of forests. 

The consequences

The goal to keep temperatures under 1.5°C was to avoid irreversible tipping points. By definition, there is no returning to the once stable climate that enabled and sustains our modern civilization. This was acknowledged by the U.N in September 2026. 

Limiting global warming to 1.5°C remains a cornerstone of the Paris Agreement, yet under current policies and alternative near-term trajectories, exceedance of 1.5°C is now widely assessed as unavoidable…There will be no going back to how things were. Some losses will be irreversible, which means returning to 1.5 doesn’t mean we return back to the same world we left. – United Nations 02 September 2026

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