Earth’s climate is determined by Earth’s energy budget, a delicate balance between how much of the Sun’s radiative energy is absorbed in the atmosphere and at the surface and how much thermal infrared radiation Earth emits to space.
With increasing greenhouse gases in the atmosphere, the Earth’s energy imbalance flows in and out of the earth system at the top of the atmosphere. The greenhouse gases increasingly trap more radiation and hence create global warming.
Significant issues for Earth from an energy perspective are the actual Earth’s energy imbalance.
Climate scientists have warned for a half-century that this imbalance results from the addition of too much carbon dioxide to the atmosphere. On the other hand, so-called climate deniers have suggested that the observed changes might result from natural variation.
A new study by Princeton University shed light on this. The study found that it is exceptionally unlikely less than a 1% probability that natural variations in the climate systems can explain this trend. It means there are less than 1% chances for the changes to occur naturally.
For the study, scientists used satellite observations from 2001 to 2020. The observations indicated that the Earth’s energy imbalance is growing.
Shiv Priyam Raghuraman, a graduate student in atmospheric and oceanic sciences (AOS) at Princeton, said, “Until now, scientists have believed that because of the short observational record, we can’t deduce if the increase in the imbalance is due to humans or climatic ‘noise.’ Our study shows that even with the given observational record, it is almost impossible to have such a large increase in the imbalance just by Earth doing its oscillations and variations.”
“We always think, Increasing greenhouse gases means trapping more infrared heat’ — the classic greenhouse effect becomes larger. This is correct, but the flip side is that the resulting warmer planet now radiates more infrared heat away to space, so the greenhouse gas heating impact is canceled. Instead, much of the imbalance increase comes from the fact that we are receiving the same amount of sunlight but reflecting backless because increased greenhouse gases cause cloud cover changes, less aerosols in the air to reflect sunlight — that is, cleaner air over the U.S. and Europe — and sea-ice decreases.”
Oceans store 90% of this excess heat. This close relation between the growing energy imbalance and ocean heating has a significant impact on marine health, sea-level rise, and the warming of the global climate system.
According to scientists, tracking the trends of this energy imbalance and understanding its components will improve the models of future climate change that drive policymaking and mitigation efforts.
Raghuraman said, “The satellite record provides clear evidence of a human-influenced climate system. Knowing that human activity is responsible for the acceleration of planetary heat uptake implies the need for significant policy and societal action to reduce anthropogenic greenhouse gas emissions to curb further increases in Earth’s energy imbalance.”
- Raghuraman, S.P., Paynter, D. & Ramaswamy, V. Anthropogenic forcing and response yield observed positive trend in Earth’s energy imbalance. Nat Commun 12, 4577 (2021). DOI: 10.1038/s41467-021-24544-4