New Delhi, Oct. 3 -- In the last article, we looked at how Earth's albedo was falling and its interplay with the rising heat uptake by the oceans, as well as the rising acidity of the oceans. In this part, we will discuss the work of various scientists in this regard.
Forcings versus feedbacks
This leads us to an important debate in climate science: that of 'forcings versus feedbacks'. 'Forcings' are simply anthropogenic activities, such as massive injections of carbon dioxide into the atmosphere or a rise in sulphur dioxide because of industrial emissions, which disturb the energy balance of the Earth. 'Feedbacks' are the reactions to these forcings, such as the melting of ice and warming of the oceans.
The connection between 'forcings' and 'feedbacks' has been revised by the research of various scientists, such as Bjorn Stevens and Piers Forster, Norman Loeb, Gunnar Myhre, Hodnebrog, Armour and Rugenstein.
Stevens versus Hansen
Stevens and Forster found that aerosols trigger an impact on clouds almost immediately, even before any global warming has occurred, and called it rapid adjustment or a non-linear impact. Stevens also found that the 'cooling' effect of aerosols was much less than that assumed in many climate models. This would mean that the 'warming effect' of greenhouse gases would also be much lower, implying that global warming is not as rapid as many think and can be managed. On the other hand, James Hansen, using palaeoclimatic data and observations following International Maritime Organization regulations - where stricter regulations on sulphur emissions by shipping lines were followed by an immediate rise in temperatures in the North Atlantic - has suggested the opposite: that the 'unmasking effect' of aerosols is actually huge and will lead to accelerated global warming.
Loeb, Myhre and Hodnebrog
Norman Loeb, the scientist leading NASA's CERES project, has been collecting data on the Earth's albedo for the past 25 years. Myhre and Hodnebrog are Norwegian scientists who have carried out chemical modelling of aerosols and, based on primary data, have analysed how different types of aerosols interact with clouds. In an article published in Science in June 2025, Myhre, Hodnebrog, Loeb and Forster argue that the findings of low-climate-sensitivity models - those that assume lower warming as a result of greenhouse gas emissions - are contradictory to the data collected by CERES. In other words, future warming is likely to be higher and stronger than low-climate-sensitivity models suggest, and urgent action is therefore needed.
Further, they argue that the forcings of greenhouse gases are global in nature, while those of aerosols are local and limited to the mid-latitudes of the Northern Hemisphere - North America, Europe and Asia. As a result, the interaction is with the local atmosphere, which changes the cloud cover. They concluded that an energy imbalance caused by aerosols will require a higher surface temperature change compared with such an imbalance caused by greenhouse gases. Interestingly, David Stainforth has commended this research by the Oslo group and used it to underline his policy prescription: if climate feedbacks are based on local geography, then past data often used in Global Climate Models cannot be used to predict the local climate. Hence, there is a need to focus more on localised issues rather than refining such global climate models to produce more precise probabilities.
Understanding pattern effects
Armour and Rugenstein echo the findings of Myhre, Hodnebrog et al. when they say that the effects of climate feedback are a local phenomenon. Rugenstein, using thousands of years of climate data, says that these feedbacks change over centuries and that short-term observations will lead to faulty estimations of long-run climate feedbacks. Armour and Rugenstein say that climate feedback loops and their strength, speed and direction depend on the geographical pattern of surface warming across the oceans.
They give the example of the East Pacific, which is naturally cooler and has sinking air and low stratocumulus clouds, and the West Pacific, which is naturally warm and has sinking air, water-laden clouds and rainfall. They say that if the East Pacific also warms up because of global warming, the temperature differential with the West Pacific will fall and air circulation will slow. This will cause the bright and reflective marine clouds over the East Pacific to dissolve, leading to a lower albedo and the ocean absorbing more heat, thus accelerating global warming. The opposite will result if the West Pacific warms more than usual.
Interpreting climate models
In earlier articles in this Climate Series, we saw the challenges faced in constructing climate models and the even greater difficulties in interpreting the results of climate model simulations. Specifically, we may recall that the modelling of local phenomena, such as clouds and aerosols, poses a challenge. In this two-part article, we looked at CERES data and other experiments, such as Argo floats. In the second part, we examined the work of scientists in interpreting the impact of clouds and aerosols on the Earth's albedo. Their work will help us interpret the output of climate models better.
Published by HT Digital Content Services with permission from Millennium Post.