Global Warming: Reversing the Trend

Last modified: 2010-04-10 12:10:21 UTC

© 2008~2024 Charles L. Chandler

 

A method of reversing the current global warming trend is proposed. The idea is to stop burning sulfur in the troposphere, as we currently do, where all it does is create acid rain, and start burning it in the stratosphere, where it will act as an icehouse gas. It will take the release of 20 million tons of sulfur dioxide (S0₂) into the stratosphere every year, for 5 years, to return the temperature to normal. After the desired global average temperature has been reached, some lesser amount of S0₂ would have to be released each year to maintain the desired temperature. Damage to the ozone layer by increasing the amount of S0₂ is an unmitigated problem, and is probably a show-stopper.

The Earth has been in a warming trend since the end of the Little Ice Age in the 1800's.¹ Some scientists believe that the burning of fossil fuels has accelerated the process by increasing the amount of carbon dioxide (CO₂) in the atmosphere. Others maintain that climate fluctuations are due to very different factors, and that CO₂ emissions play a neglible role.^2,3

Regardless, it might be possible to gain control over the global climate, and to prevent fluctuations in temperatures which could have catastrophic consequences for a world population that has so vastly expanded in the past several hundred years.

When Mount Pinatubo erupted in 1991, it released an estimated 20 million tons of S0₂ into the stratosphere.⁴ This had the effect of cooling the Earth 0.5° C.^5,6 This means that if we released 20 million tons of S0₂ into the stratosphere on purpose, then we would cool the Earth by 0.5° C on purpose. If we did this every year, in less than a decade we would return global temperatures to normal.

20 million tons sounds like an impossibly large volume of anything to handle on purpose, but this is approximately the amount of SO₂ that is released from power plants that burn fossil fuels in one year in the US alone.⁷ So this is certainly within the range of what humans can do. If we burned all of that sulfur in the stratosphere instead of the troposphere, we'd get the same amount of acid rain that we currently get, but we'd reverse the global warming trend.

So how do we burn that much sulfur in the stratosphere?

Commercial airliners frequently fly in the stratosphere, if the wind speeds and directions are right. A total of 7½ billion miles are flown by US airliners in a year.⁸ (Some percentage of that is actually in the stratosphere.) At approximately 5 gallons of fuel consumed per mile,⁹ that's 37½ billion gallons of fuel consumed per year, or over 100 million tons.¹⁰ If 20% of those miles are actually flown in the stratosphere, then that's 20 million tons of fuel being consumed, and we are already burning enough fuel in the stratosphere to fix global warming. But instead of burning kerosene, we would have to burn sulfur.¹¹

So we need to develop jet engines that can burn sulfur instead of kerosene, to be used once the airliners enter the stratosphere. The development and implementation of such engines would be a non-trivial task. If such development would take too long, or be too expensive, we could always burn the sulfur without bothering to use it for propulsion, but we would lose the economic benefit of burning it instead of kerosene during the stratospheric portion of the flight.

Then there's the additional cost of extracting the sulfur out of the fossil fuels so that we can burn it separately, in the stratosphere, instead of leaving it in the #6 fuel oil to be burned in power plants. Kerosene and sulfur would both come from the same refinery, so fuel shipping costs would not change. And sulfur extraction is already being done, to lower SO₂ emissions per EPA standards, and to produce sulfur to be sold to various process industries. But currently, plenty of sulfur is left in the #6 fuel oil, despite the environmental damage it causes, simply because of the cost of extracting it.

But all of these expenses would still be cheaper than the alternative (see "The Problem" above).

So OK, it's an idea, and it's got a chance at being feasible, so let's take a closer look.

First, the "20 million tons" number might be a little high. Some estimates for the total amount of sulfur dioxide released into the stratosphere by Mount Pinatubo are as low as 15 million tons. Not enough of a difference there to warrant recalculating the numbers. But another factor to be considered is that Mount Pinatubo also released CO₂, which is a greenhouse gas. Since we'd be leaving this out, it wouldn't take as much SO₂ to get the same cooling effect. Still looking for confident numbers on the amount of CO₂ released.

Another factor is that the cooling effect from the SO₂ lasted 3 years or so, with a total of a 0.5° C drop in temperature at the peak. If we released SO₂ into the atmosphere every year, we'd probably want to do so in quantities that would bring the temperature down slowly, so we could watch the effects closely, rather than shocking the world's climate with a dramatic change. And since the SO₂ will linger in the stratosphere for 2~3 years before falling out, we would take the year-to-year cumulative effect into account. This would further lower the amount of SO₂ required to do the job. How much lower needs to be calculated.

The statement about "20 million tons of fuel [currently] being consumed [in the stratosphere]" seems a little high. I would actually be surprised if ¹/10 of all airline miles were actually flown in the stratosphere. Currently trying to track down confident numbers on that.

The biggest problem with this proposal is that SO₂ in the stratosphere causes major damage to the ozone layer.¹² The result of this is more UV radiation making its way through the atmosphere and hitting the surface of the Earth. The severity of the effects needs to be calculated carefully, as it might be possible that we would do ourselves more harm than good in this respect.

Are there alternatives? Unfortunately, I'm having a hard time imagining that there could be any other possible solution to this problem. After all, any action taken on such a huge scale would only be conceivable if there was some way of knowing exactly what the effects were going to be. In the case of Mount Pinatubo, we know the effects. Since this happened so recently, it was well-studied with modern scientific methods. And since large-scale ecological issues were already a focus in 1991, scientists were looking for the short- and long-term effects across the world. And since 17 years have passed since that event, we have had a chance to study the lingering effects. And unfortunately, there hasn't been anything else that has ever been clearly identified as a single factor that lowered the temperature of the Earth. So any other method of attempting to reverse the effects of global warming would be an untried method.

Another issue is that if we relied on commercial airliners to release the SO₂, then it would be released wherever they happened to be flying. This would not necessarily provide an even distribution over the entire globe, and that could have effects of its own. The SO₂ from Mount Pinatubo was (obviously) released from a single source, and even though stratospheric winds distributed the SO₂ around the world, it did so in a relatively narrow band, more or less along the Equator. The result was an uneven cooling effect across the entire Earth, which impacted upper level convective currents. This raises interesting questions about how the effects would differ if the SO₂ was distributed more evenly, as would be the case with airliners doing the distribution. But since there are many more airliner flights in the Northern hemisphere than in the Southern, it raises other questions about hemispheric distribution. This whole line of questioning suggests other possibilities, such as releasing the SO₂ over the Poles, to concentrate the cooling effect there in the hopes of encouraging the expansion of the polar ice caps. Another idea along these lines is to release the SO₂ in the Northern hemisphere during its summer (June-July-August) and in the Southern hemisphere during its summer (December-January-February), where it would do the most good with the least amount of SO₂.

Other unanswered questions:

• What if we start releasing SO₂ into the atmosphere, and then there is another volcanic eruption, and then we get a double-whammy of SO₂?
• Is it really CO₂ that is causing the global warming, or could it be increased solar activity, or geothermal processes, that are doing the warming? What if these processes subside? During the period of 1940~1970, the Earth cooled down, instead of warmed up. Yet all the while, we were steadily increasing the production of CO₂. How sure are we that the current warming cycle won't be temporary as well?

These are all excellent questions.

The possibility of controlling the Earth's climate on a global scale has been considered before.^{13,14,15,16,17,18} But in the end, the only possible conclusion is that we cannot even begin to estimate the consequences of such strategies, given our existing understanding. If, in fact, we got ourselves into this mess by carelessly toying with the environment, it's hard to believe that frantically trying extreme measures to fix it, without fully considering the consequences, would actually make things better.