Note4Students
From UPSC perspective, the following things are important :
Prelims level: Heat Budget of Earth
Mains level: Read the attached story
The study published in the journal Earth System Science Data estimates that almost 90% of the warming that has occurred in the last 50 years has been absorbed by the ocean, with the remaining heat absorbed by the land, cryosphere and atmosphere.
Earth’s energy balance: A quick recap
- It is the balance between the amount of energy that Earth receives from the Sun and the amount of energy that Earth radiates back into space.
- It is also known as the radiation budget.
- The energy from the Sun that Earth receives is mainly in the form of visible light and ultraviolet radiation.
- This energy is absorbed by the Earth’s surface and atmosphere, which then radiate it back into space in the form of infrared radiation.
- The balance between incoming and outgoing radiation is crucial for maintaining the Earth’s temperature and climate.
- Any imbalance between the two can lead to global warming and climate change.
| Description | |
| Total incoming solar radiation | Approximately 342 W/m² reaches Earth’s atmosphere |
| Albedo | About 30% of incoming solar radiation is reflected back to space |
| Greenhouse effect | Remaining 70% of incoming solar radiation is absorbed by Earth’s surface and atmosphere, creating the greenhouse effect |
| Atmospheric heat | Atmosphere contains only 0.001% of Earth’s heat energy, but is crucial in regulating heat budget |
Key highlights of the Study: Heat Accumulation
- The study estimates that approximately 381 zettajoules (ZJ) of heat accumulated on the planet from 1971-2020 due to anthropogenic emissions.
- This roughly equals a heating rate of approximately 0.48 watts per square metre (Earth Energy Imbalance or EEI). EEI is the difference between incoming and outgoing solar radiation.
- According to the study, about 89% of the accumulated heat is stored in the ocean, 6% on land, a percent in the atmosphere, and about 4% available for melting the cryosphere.
Implications
(1) Land Heat Accumulation
- Heat accumulated on land drives up ground surface temperatures, which may increase soil respiration, releasing carbon dioxide in the process.
- Higher soil respiration will likely decrease soil water, depending on climatic and meteorological conditions and factors.
(2) Inland Water Bodies and Permafrost Thawing
- Heat storage within inland water bodies has increased to roughly 0.2 ZJ since 1960. For permafrost thawing, it was about 2 ZJ.
- The accumulation of heat in inland water increases lake water temperatures, making conditions ripe for algal blooms.
- Permafrost heat content could inject methane and carbon dioxide into the atmosphere, the researchers warned.
(3) Ocean and Troposphere heating
- The upper ocean (0-300 and 0-700 meters depth) has taken up a major fraction of heat, according to the new estimates.
- During 2006-2020, ocean warming rates for the 0-2,000 meters depth reached record rates of roughly 1.03 watts per square meter.
- The troposphere is also warming up due to increased heat accumulation.
(4) Cryosphere heating
- The cryosphere – the frozen water part of the Earth system – gained roughly 14 ZJ of heat from 1971-2020.
- Half of the uptake triggered the melting of grounded ice, while the remaining half is linked to the melting of floating ice.
- The Antarctic Ice Sheet contributed about 33% to the total cryosphere heat gain, while Arctic sea ice stood second, having contributed 26%.
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