Cause and Effect | The undeniable and alarming increase in Earth's energy imbalance

The global mean temperature last year was 1.15 degree Celsius above the 1850-1900 average.The last eight years were the warmest since record-keeping began 173 years ago.The Arctic will witness ice-free Septembers by 2030-2040 even in a low-emissions scenario.These and similar conclusions have become more frequent, especially over the last decade, as science finds clear signs of an impending climate catastrophe.All these conclusions boil down to one thing: Earth's temperature has risen because of greenhouse gas emissions. In scientific terms, the phenomenon is known as Earth Energy Imbalance (EEI), which denotes how what was once a balance between the energy the Earth received from the sun and that it lost back to space has been upset.In a 2021 study, Satellite and Ocean Data Reveal Marked Increase in Earth’s Heating Rate, scientists from NASA and the National Oceanic Atmospheric Administration, said that the Earth is trapping nearly twice as much heat as it did in 2005.Describing the increase as "alarming", the scientists said the energy imbalance nearly doubled from 2005 to 2019."The two very independent ways of looking at changes in Earth's energy imbalance are in really, really good agreement, and they're both showing this very large trend, which gives us a lot of confidence that what we're seeing are a real phenomenon and not just an instrumental artifact, " Norman Loeb, lead author for the study and principal investigator for CERES at NASA's Langley Research Center in Hampton, Virginia, said in a statement at the time.The excess energy accumulates in the form of heat in different reservoirs in the climate system — the atmosphere, the land, the cryosphere, and the ocean. The imbalance can be estimated by an inventory of heat changes in these reservoirs, which, in effect explains climate change.A separate study, published in April this year, quantified the amount of heat that accumulated in the Earth's system.The study, Heat stored in the Earth system 1960–2020: where does the energy go, put this number at approximately 380 zetta joules.One Zetta Joule is 1,000,000,000,000,000,000,000 joules. It takes nearly 360,000 Joules to accelerate a standard one-tonne car to 60mph.Basically, the amount of heat being accumulated on the planet is so high, scientists, over time, started reporting it in a new measure, the ZJ.The EEI, or heating rate, was thus calculated to be 0.48±0.1 W m−2.A positive EEI means "the Earth system is gaining energy, causing the planet to heat up”, the Nasa statement said.The majority, about 89 %, of this heat is stored in the ocean, followed by about 6% on land, 1% in the atmosphere, and about 4% available for melting the cryosphere, the researchers, nearly 70 from dozens of institutes across 15 countries led by Karina von Schuckmann of Mercator Ocean International, found in the second study.The IPCC's sixth assessment report put the percentage of heat accumulation in the ocean at 91%.“The amount of heat we are putting into the oceans is equivalent to about five Hiroshima atom bombs of energy every second," John Abraham, a professor of thermal sciences, wrote for The Guardian.The next question then is: why is this heat increasing?The greenhouse gases (carbon dioxide, methane) let solar radiation pass, but not the radiation emitted by the Earth, thus trapping this energy – this is, simply, a greenhouse effect.Earth’s near-surface temperature, which is 14°C, would be around -19°C without the greenhouse effect, IPCC said in its fourth assessment report in 2007.The warming drives other changes, such as snow and ice melt. It also affects water vaporisation and cloud changes, which further enhance the warming.The positive EEI is a result of the net effect of these factors.The Nasa study also said that a "naturally occurring" shift in the Pacific Ocean from a cool phase to a warm one, called the Pacific Decadal Oscillation, probably had a significant role in amplifying this imbalance.Loeb said that it's not possible to predict with any certainty what the coming decades might look like for the balance of Earth's energy budget. But, he added in the statement, "Unless the rate of heat uptake subsides, greater changes in climate than are already occurring should be expected".The IPCC was grimmer in its conclusions.“Energy will continue to accumulate in the Earth system until at least the end of the 21st century, even under strong mitigation scenarios, and will primarily be observed through ocean warming and associated with continued sea level rise through thermal expansion,” the report said with “high confidence”.

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