Global Shading: A New Trail for MIT to Blaze

A proposition to controllling a rise in global temperatures

It’s going to get hotter for the rest of your life. Probably a lot hotter. What can be done about this? Specifically, is there anything that MIT scientists and engineers could do? 

In October 2022, The Tech published a letter from us which posited that global temperatures and their accompanying effects such as drought and flooding will continue to rise for the rest of this century given our current approaches. To illustrate this, we cited MIT’s own En-ROADS model using the example of maximal world-wide incentivization of renewable energy and vehicle electrification.  

It elicited a response in the following issue by an MIT Sloan School professor asserting that we were “ignoring the many other actions we can take now with existing technologies,” and that the correct approach was “silver buckshot” --  in other words, everything, everywhere, all at once. 

Well, we tried that. Ignoring political reality, we used En-ROADS to explore maximal world-wide disincentivization of coal, oil, and natural gas usage, as well as deforestation, along with maximal incentivization of renewable energy, vehicle electrification and efficiency, nuclear energy, bioenergy, new zero-carbon energy, and building electrification and efficiency.  

We even threw in a 50% reduction in methane – which is especially unrealistic, because most methane emissions come from wetlands and agriculture, from which methane cannot easily be reduced – and the temperature in the year 2100 would go from today’s almost 1.5 degrees C above pre-industrial times to 2.0 degrees C. This is because adding CO2 is like piling on blankets; reducing the rate at which more blankets are added does not make you cooler. 

But the reality is much worse than our highly idealized scenario, because China, Russia, India, and the rest of the world outside the US and the EU will not implement these changes any time soon, and warming will be much greater than the model’s predicted 0.5 degrees C. If you think that things are bad now, imagine what it will be like in 50 years. 

There is, however, something that can be done that would have a near-term effect -- global shading. The earth’s temperature is quite sensitive to the amount of received sunlight, and reducing that by a few tenths of a percent can make a significant difference. We know this from the observed effect of major volcanic eruptions that spewed significant amounts of ash into the upper atmosphere. For example, worldwide temperatures were reduced by about half a degree for two years after the 1991 eruption of Mount Pinatubo. And it snowed in Virginia on the 4th of July in 1816 after the 1815 eruption of Mount Tambora. 

Unfortunately, ejecting ash and chemicals into the atmosphere has adverse health and environmental effects, so this approach is a non-starter. But other means of shading could work. For example, scientists at MIT and elsewhere have looked at giant barriers in space between the earth and the sun. But apart from the cost and complexity, these suffer from an irredeemable obstacle: They would probably require the permission of every nation on earth. Global warming reduction talks have been going on for over 30 years and we have yet to establish hard limits for most of the countries on earth. How long would it take to agree on a totally new concept?

Fortunately, there is a way to approximate that with a system that is environmentally friendly and scalable, and that can be implemented globally or regionally. Deploying a very large but achievable fleet (a few million) of very large (approximately 100 meters in diameter) balloons over the US Southwest would reduce temperatures there by a degree or two and as the cooler air mass travels eastward, providing some benefit for much of the rest of the country.  

To make it cooler, you’d add more balloons. If implemented solely within US airspace, this would not require permission from any other nation. And after seeing how this works, other countries might well decide to do the same, until eventually an international compact could be obtained. 

The balloons would fly in the stratosphere, well above any aviation, and they would be roughly geo-stationary. This capability was demonstrated in Google’s Project Loon

This is not to say that existing CO2 reduction proposals should not be implemented. They should. But they will benefit your grandchildren, not you. Actual reductions in temperature in the immediate term will provide these other approaches much-needed time to become effective. 

What is needed is an optimized scientific and engineering approach to this undertaking. Project Loon demonstrated balloon lifetimes of almost a year. Can this be extended to multiple years? NASA’s ASTHROS balloon is over 130 meters in diameter -- but it is expensive. Can this be made cheaply and mass produced? Optimized balloon fleet management can undoubtedly result in greater effectiveness, but how and how much? 

These are the kinds of questions that MIT could help to resolve. President Kornbluth has announced the MIT climate initiative which includes a category called “wild card” ideas. What fits that definition better than this? And what could members of the MIT community do that could have a greater potential impact than blazing a new trail to provide a near-term solution to the climate problem?  

— Tom Hafer ’70, Henry Miller ’69