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The emergency stopgap:
Is there a way to stop global warming if it becomes too large?

The answer is positive.

The consequences of a nuclear war would be a so-called nuclear winter - a large cooling caused by smoke, dust and ashes bloting out the sun for weeks. It has been argued that even a regional nuclear war could trigger global cooling and famine [6]. It follows quite automatically that mankind has the technical means to cause a global cooling.

A sufficiently harmless alternative:
Hydrogen bombs in a desert

Of course, to stop a too large global warming one would not have to start a nuclear war. There would be certainly less harmful ways to reach the same effect for the climate. But what would be an unwanted side effect of a nuclear war could be, without doubt, created intentionally with similar tools in a much less harmful way. Here we evaluate one particular idea how to reach such effects: To use nuclear fusion bombs in some inhabitable desert to transport large amounts of dust into the stratosphere. This dust would remain there some months, and lead to some cooling effect.

Given that one would use this possibility only as an emergency stopgap, it should not be completely harmless, without any negative side effects. All what is required is the following: It has to be efficient, thus, to reduce the temperature in a sufficiently large way. It should be realistic to do this. And, in comparison with the consequences of a further warming, the possible negative side effects would be acceptable as a lesser evil.

The side effects of the proposal seem sufficiently small to be acceptable: some possible contamination of areas which are inhabitable anyway, and dust in the stratosphere which does not have other important effects than the cooling. Let's note also that there will be a lot inhabitable deserts. If there would be none, the overall situation would have to be much better than today, thus, one would not even think about reducing temperature.

Instead of relying on hypothetical scenarios about a nuclear winter, which are speculative and may appear wrong, it seems better to rely on the influence of volcano eruptions on the climate. There have been volcano eruptions in history which have had a global cooling effect, and, moreover, for recent volcano eruptions these effects have been studied in some detail, thus, one can say that they are well understood and supported by empirical evidence.

What causes the cooling effect of volcano eruptions

To influence the climate, a volcano eruption has to fulfill some preconditions. Most importantly, the cloud has to be able to reach the Stratosphere. "Only certain types of volcanic eruption will have an effect upon the climate. The eruption has to be of sufficient magnitude to emit very large quantities of material into the lower stratosphere (20-25km above the Earth's surface) and, for maximum impact, it should be in lower latitudes." [1].

The material itself plays also a role. A very important contribution comes from small particles of dust and ash, they shade sunlight and cause temporary cooling: "... the smallest particles of dust get into the stratosphere and are able to travel vast distances, often worldwide. These tiny particles are so light that they can stay in the stratosphere for months, blocking sunlight and causing cooling over large areas of the Earth." [3].

Then, there is the special contribution of sulfur dioxide. "Sulfur dioxide is much more effective than ash particles at cooling the climate. The sulfur dioxide moves into the stratosphere and combines with water to form sulfuric acid aerosols. The sulfuric acid makes a haze of tiny droplets in the stratosphere that reflects incoming solar radiation, causing cooling of the Earth’s surface. The aerosols can stay in the stratosphere for up to three years, moved around by winds and causing significant cooling worldwide." [3].

The size of the cooling effect by volcanoes

The eruption of the volcano Tambura in 1815 was the greatest volcano eruption known in human history. And it has caused a quite large cooling, namely of 3 degrees Celsius during 1816, which was named "a year without summer". So, the effect even of a single eruption is potentially large.

For more recent volcano eruptions, we have, of course, more accurate data, see for example the temperature curves for some volcano eruptions.

It follows that if nuclear explosions in a desert would be able to transport an amount of dust into the stratosphere similar to what volcano eruptions reach, this would be sufficient to create a sufficiently large global cooling effect.

Properties of nuclear bomb explosions

Are nuclear explosions able to reach effects comparable to large volcanos? Let's see:

Height of the mushroom cloud

The height of the mooshroom cloud has already reached much greater heights than the lower Stratosphere, it reached even the Mesosphere. The Tsar Bomba, which was tested on 30 October 1961, had a mushroom cloud which was about 67 km (42 mi) high [4]. Thus, the height of the mushroom cloud is not a problem.

Material

Given that dust and ashes are sufficient for effects of several months, the material is also not a problem. Essentially, any material on the ground will be sufficient to give a lot of dust.

But one could of course also search for locations where a nuclear explosion would create also a large amount of sulfur dioxide.

But independent of the possibility to create large amounts of \(SO_2\), nuclear fusion bombs have both qualitative abilities necessary to create at least some cooling for some months.

How many bombs would be necessary?

Once the qualitative characteristics are unproblematic, the only remaining question is how many such fusion bombs are necessary to reach the necessary cooling effect. Indeed, if we would need millions of them, this could be, in principle, become a decisive counterargument.

So, let's start with the comparison of the energies released during volcano eruptions with those released during nuclear explosions. While the energy released by nuclear explosions is something well-known and reliable, the situation is unfortunately quite different for volcano eruptions. This starts with the problem that we can make estimates only after the eruption, by considering the results. Then, there is a lot of energy release which is not at all relevant for the problem. In particular, there is all the heat energy of the magma which simply flows out of the volcano, or is ejected but falls down immediately. There is the material of the old volcano which is thrown away by the explosion but does not reach the stratosphere, so that it does not cause any long time cooling.

Whatever, we can for a rough pessimistic estimate ignore these uncertainties, and compare the estimates about the energies released by volcano eruptions with those released by nuclear explosions.

The best what I have found up to now about the energies released by volcanoes is the following table below (sorry for the low quality). This is not optimal because it is only about heat energy. But heat energy could be dominated by the completely irrelevant magma which does not reach the stratosphere, and the energies relevant for the transport of dust into the stratosphere may be quite different.

Whatever, let's at first take these numbers as if they would be the relevant numbers, and then consider the question what would be the related systematic errors.

The table gives for the Tambura eruption \(2.8 \cdot 10^{26}\) to \(1.4\cdot 10^{27}\) erg. Nuclear weapons are usually described in the unit of Megatons TNT, and 1 Mt TNT is roughly \(4 \cdot 10^{22}\) erg, so that the Tsar bomba gives, with 50 Megatons, \(2\cdot 10^{24}\) erg. If these would be the relevant numbers, one would need 140 to 700 Tsar bombs to create the same effect as the Tambura eruption, which gave 3 degrees of cooling in the next year. This would be a large number, but certainly it would not make it impossible. Let's remember, the technology we talk about has been tested succesfully in 1961, and all what would have to be done is a mass production of such an old technology.

Why nuclear explosions are a much more efficient tool to transport dust into the stratosphere

In fact, the typical picture of a nuclear blast looks already much more appropriate for the aim we want to reach: to transfer a large amount of dust to a sufficiently large height. An ideal system of such transport would move all the dust, first, upwards, as direct as possible, and only if the optimal height has been reached, distribute it horizontally to increase the affected area. But this is exactly the picture of a mushroom cloud.

And, in fact, the physics behind the mushroom cloud explains that this is what is done. The main effect which creates the mushroom cloud is the very high temperature created at the place of the explosion. The air which has been heated up in such an extremal way goes up with a quite high speed, and the heat moves it directly upwards. The environment of this is a flow of air going upwards as well. Whatever dust comes up from the bottom will be immediately moved directly upwards too.

So, the very form of the mushroom cloud is essentially already what one would dream about if one wants to move a large amount of material to a well=defined height, namely the lower stratosphere. To optimize the energy of the fusion bomb so that it reaches the necessary height in an optimal way will, therefore, be easy. The Tsar bomba with 50 megatons TNT was, in this sense, too large, reaching 65 km when 20 km would have been sufficient.

There is also another parameter which can be easily changed: The height of the explosion. It may be helpful if the bomb explodes close to the ground. The reason is that what a nuclear explosion is doing with nearby material in underground tests is named "vaporizing" this material. That means, the result is that all the material is transformed into dust. But it is very thin dust which one wants to transport into the stratosphere. To create a lot of such very thin dust, moreover in a very hot state, at the place where the transport starts would be quite optimal.

The expectation that a nuclear explosion will be more efficient in transporting dust into the stratosphere is supported by the table itself too. What would be comparable to the Tsar bomba is, according to the table, the Vesuvius eruption of 1906. But this eruption 1906 is described as having thrown ashes only at a high of 1300 m, which is nothing in comparison with the 64 km height reported for the mushroom cloud of the Tsar bomba. So, while the Tsar bomba has obviously transported a lot of dust into the Stratosphere, the Vesuvius 1906 has done no such thing.

Negative side effects

Radioactive contamination?

Would radioactive contamination be a problem? No. First, if one uses fusion bombs, this will not create radioactive contamination in itself.

The classical design of a fusion bomb uses a small fission bomb to ignite the fusion bomb. The question is if this is really necessary, or if this is only a consequence of the particular military requirement that one has to transport the bomb via a plane or intercontinental rocket into an area controlled by the enemy. This problem, of course, requires to minimize the weight of the ignitor as much as possible, so that a fission bomb may be a good idea, and if the territory of the enemy will be additionally contaminated so what.

If one can, instead, ignite the fusion bomb on the ground, the weight of the ignitor would not be a problem at all, and this makes it quite plausible that a conventional way of ignition may be sufficient too.

But let's assume there is no such safer possibility. Nonetheless, the only purpose of using a dirty fission bomb is the ignition, thus, this part is small in comparison with the fusion bomb. Let's for simplicity assume that it would have to have the same size as the Hiroshima bomb. What would be the resulting contamination?

If the bomb explodes on the ground, there may be some of the contamination in the resulting crater and very close to it. This would be a very small area. Let's not forget that the area which could be contaminated in this way is located in an inhabitable desert. There will be a lot of such deserts, because there are already a lot of them today, and to use the emergengy stopgap would be reasonable only if the situation becomes worse than today.

Then there is the fallout - the part of the radioactive material blown up and falling down later, and possibly at other places. In the case of the fusion bomb, the dust which reaches the Stratosphere will be distributed over the whole world. In the case of Hiroshima, the fission bomb was all, it was not very large, the mushroom cloud was not very high, and therefore the fallout region was much less too. The size of that region is unclear, it was essentially the area covered by the black rain. As an order of magnitude, the area of the whole town, possibly together with some of its environment, seems a reasonable guess. This is, in comparison with the whole world, a very small area. Once we assume that the whole contamination is the same, the concentration of the contamination would be therefore much higher in Hiroshima and Nagasaki itself than what we would have to expect as the effect of the fusion bomb.

Nonetheless, this much higher fallout has not created any long term contamination. The radioactive contamination caused by a fission bomb is mainly a short time effect: Hiroshima and Nagasaki do not have problems with radioactivity today [7]. Nuclear reactor accidents like in Chernobyl or Fukusima are much more problematic, because they create over time a lot of isotopes with long halflife, which can contaminate the affected area for a very long time [8].

So, even if the use of a fission bomb as ignition would remain necessary (very questionable), and even if it would have to have the same size as the Hiroshima bomb (also very questionable), radioactive contamination by the fallout would not be a problem at all.

Conclusions

We conclude that with explosions of fusion bombs in inhabitable deserts one can reach, at moderate costs, local as well as global cooling effects over a short period of time. The side effects are sufficiently small - some contamination in some area which is inhabitable anyway. Comparison with effects of volcano eruptions show that the resulting cooling effect is large enough to stop or even revert a global cooling.

That means, mankind has an emergency stopgap which allows to stop global warming if it becomes too large or too fast. The technology for this exists already today. It follows that we should not be afraid of global warming becoming dangerous for the survival of mankind.

PS: Have there been climatic influences of the hydrogen bombs tested in the past?

In a discussion about this page, it has been claimed that the nuclear tests did not have influences on the climate. In fact, given the considerations above, I would not expect much influence, given that the mushroom clouds of a typical fission bomb would not reach the stratosphere, and that many tests have been done in the ocean, where what has been transported into the stratosphere is mainly water vapor, not dust.

The record cold in winter 1962/1963 following the Tsar bomba Oct. 1961

But there has been an obvious exception, namely the Tsar bomb. It was detonated on land, the quite big island Nowaja Semlja, on the 30. of Oktober 1961, and the mushroom cloud reached 64 km. If it had consequences on the climate, one would expect them in that near-arctic region during the next year.

And there was, in fact, a record cold in the following winter.

The picture shows the anomaly of surface temperature for the months December, January and February of the Winter 1962/63, compared to the average temperatures of winters 1949 to 1978. It reached up to some -5 degrees of Celsius, in particular it was the strongest winter of the century in Germany. The island Nowaja Semlja can be seen as localized inside the region of this extremal cold.

To postulate that the Tsar bomba has caused this cooling seems, therefore, quite plausible. In this case, already a single hydrogen bomb of the Tsar bomba size per year could lead to an essential cooling, sufficient to stop a climate change.

References

  1. David Viner & Phil Jones, Volcanoes and their effect on climate
  2. Kelly, P.M., Jones, P.D. and Jia Pengqun, 1996: “The spatial response of the climate system to explosive volcanic eruptions.” International Journal of Climatology 16(5), 537- 550
  3. University Corporation for Atmospheric Research: How Volcanoes Influence Climate
  4. Veselov, A. V., Tsar-bomba, Atompress, 2006, Nr. 43 (726), p. 7
  5. Peter W. Lipman, Donal Ray Mullineaux (eds.) The 1980 Eruptions of Mount St. Helens, Washington, p. 565
  6. C.Q. Choi (2011). Regional nuclear war could trigger global cooling and famine, National Geographic
  7. Are Nagasaki And Hiroshima Still Radioactive?
  8. Answer to Question #12228 Submitted to "Ask the Experts", 2016 Health Physics Society

Cooling effect of various volcano eruptions



Heat energy of various volcano eruptions