Has Global Warming Stopped?

Since industrialization began 100 years ago, the amount of carbon dioxide in the Earth’s atmosphere has steadily grown, and this is thought to be the primary cause of global warming. In contrast to the brisk warming of the late 20th century, the observed global mean atmospheric temperature stabilized throughout the first decade of the 21st century. This phenomenon, also known as the “atmospheric warming slowdown” or “global warming hiatus,” has received a lot of attention from scientists throughout the world since it appears to refute the hypothesis that global warming is caused by humans.

The changes in ocean heat content might have a tight relationship with the atmospheric warming slowdown. Dr. Changyu Li, Prof. Jianping Huang, and their colleagues, a group of researchers from the Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, had their findings published on October 7, 2019, in Advances of Atmospheric Sciences. 

In their paper, they explore the energy redistribution between the atmosphere and ocean at different latitudes and depths by using observational data as well as simulations of a coupled atmosphere-ocean box model. 

The greenhouse (GHG) effect caused by CO2 and other GHG gases acts as a “pump,” feeding more and more energy into the Earth system. Most of this energy is ultimately stored in the ocean, and the warming rate of the atmosphere is affected by the air-sea energy transport. Credit: Jing Xu

“Imagine the energy transport in our climate system as a water flow,” Dr. Li says. “Let’s turn on a tap at the top of the system, the feed rate of which represents the top-of-the-atmosphere radiative imbalance caused by the greenhouse effect. A bucket below the tap can be an analog of our atmosphere, and its water level is analogous to atmospheric warming. There is also a sinking flow at its bottom, draining into a larger bucket (i.e. the ocean). Now, here comes the key point. Generally, the water level of the atmospheric bucket rises as a result of global warming. However, if the drain rate approximately equals the feed rate of the tap, the water level of the bucket will not increase (the occurrence of the warming slowdown). That’s the basic idea of our coupled box model.”

“A rapid increase in the global ocean heat content has been detected in observations during the warming slowdown period, at a rate of about 9.8 × 10²¹J yr⁻¹. That is, from the energy point of view, there is no slowdown in global warming if we take the ocean into consideration,” he adds. “Furthermore, the increase in heat content provides a worrisome picture of the ocean. This rapid oceanic warming could lead to serious degradation of marine ecosystems, eventually becomes a great threat to the ocean biodiversity.” 

Reference: “Atmospheric Warming Slowdown during 1998–2013 Associated with Increasing Ocean Heat Content” by Changyu Li, Jianping Huang, Yongli He, Dongdong Li and Lei Ding, 7 October 2019, Advances of Atmospheric Sciences.
DOI: 10.1007/s00376-019-8281-0