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Trianon Scientific Communication

  • Writer's pictureDr Audrey-Flore Ngomsik

Tackling Global Warming: Exploring strategies beyond CO2 reductions

Tackling Global Warming: Exploring strategies beyond CO2 reductions

The world is getting hotter and all attempts to do something about it, or at least to curb CO2 emissions, seem sluggish at best. Can we change our world so that it heats up less, despite the greenhouse gases?


Summer fire
Summer fire

The world is getting hotter and all attempts to do something about it, or at least to curb CO2 emissions, seem sluggish at best. Can we change our world so that it heats up less, despite the greenhouse gases?




Physical drivers of climate change
Phisical drivers of climate change

Well, yes, theoretically at least.

The temperatures we experience on this goodly frame, our earth, result from the incoming radiation from the sun, and the radiation the earth emits back into space. CO2, the most important of the greenhouse gases (GHGs) absorbs some of the incoming radiation and transforms it into heat. The higher the concentration of CO2, the lower the amount of radiation emitted back into space.


That leaves two options of redressing the balance (i.e. reducing the CO2 concentration in our atmosphere to a level somewhere between today's and that of around 1850):

  • Sucking the CO2 out of the atmosphere or

  • Introducing some element which either reduces the incoming radiation or increases the amount of radiation emitted back into space.


The first one could be some kind of sunlight-deflectors in our earth's orbit; the second one could be the introduction of aerosols which reflect sunlight into our atmosphere.

 

Technical considerations aside, both approaches are truly gigantic tasks.


The idea of mirrors in space sounds like science fiction.


Telescopic mirrors
Telescopic mirrors

 

Indeed, until quite recently it has been just that. The reason for this is simple geometry: given the distance between the sun and the earth any object that is to deflect a significant amount of radiation from the earth would have to be either very big or very close to the sun. However, in practice any object in space, such as satellites, has to be placed at the point where the gravitational pull of the sun and that of the earth cancel each other out, the so-called Lagrange point - moving the object closer to the sun in order to increase the area of shadow it casts is simply not an option.


In 1999, parts of this science fiction scenario became reality when the Russian satellite Знамя-2 (Znamya-2) unfolded a solar mirror which measured twenty meters in diameter. This mirror produced a spot on the earth which was about eight meters in diameter. The brightness of this spot was reported to be close to that of a full moon. It should be noted that this serves as just an example of what is possible, even though in this case the objective was not to deflect sunlight away from the earth but rather to divert it towards it.


 


In general, the enormous surface area needed to achieve a modification of about 1% of the incoming radiation can be brought about in two ways, either by putting up one gigantic mirror up into space or by putting up a large number of smaller mirrors up there.


The other extreme would be to disperse clouds of small particulate matter in our atmosphere.


Overview of large clouds of aerosols around Earth (green: smoke, blue: salt, yellow: dust, white: sulfuric)
Overview of large clouds of aerosols around Earth (green: smoke, blue: salt, yellow: dust, white: sulfuric)

It is well known that the dust ejected into the atmosphere by volcanic eruptions exerts a cooling effect by reflecting incoming sunlight leading to lower temperatures in the affected areas. Members of the older generation may remember the term 'nuclear winter', which was in widespread use in the 80s and which describes a scenario in which the enormous amounts of fine dust generated by multiple nuclear weapons would lead to drastically decreased temperatures on earth.


However, this effect could be used to our advantage by spraying suitable materials (diatomaceous earth, alumina, calcite, salt, inorganic sulfates, etc.) from carrier air-crafts into the stratosphere. This is known as stratospheric aerosol injection.

 

The stratosphere is the zone around our planet stretching from about 12 to 50 km above sea level. Our weather, in particular precipitation like rain, originates from the troposphere, which extends from ground level to about 12 km above. This means, any aerosol that is injected into the stratosphere will remain there without getting washed down by the rain.



The different layesr of the atmosphere
The different layers of the atmosphere

 

Of course, such an approach is not without its own set of risks although at present these are highly speculative. There is simply not sufficient knowledge to accurately gauge such possible effects. Stratospheric aerosol injection may lead to ozone depletion.

Since aerosol particles absorb heat this might change circulation patterns in the stratosphere with completely unknown consequences for circulation patterns closer to the earth's surface.

In addition, reduced sunlight might have an effect on plant ripening and primary production. Again, no hard and fast knowledge regarding such possible effects exists.

Finally, reducing the incoming solar radiation or, more precisely, its intensity will also have an effect on the efficiency of photovoltaic power generation.


CCS/CCU



Right down here on earth, our climate could also be engineered, namely by adjusting our atmosphere. In a way, the current global warming is also the result of an engineered atmosphere, albeit a mis-engineered one. The concept goes by the two acronyms CCS and CCU, standing for Carbon Capture and Storage and Carbon Capture and Utilisation, respectively.

 

CCS/CCU would solve the biggest obstacle towards renewable energy: cost. It would enable us to continue using our existing fossil fuel infrastructure.


If it were possible to use fossil fuels without warming up the climate (and without acidifying the oceans) that would be just marvellous, wouldn't it?

 

Not quite, because while it is technically quite feasible to so, it would generate enormous amounts of CO2. All this captured CO2 would have to be stored somewhere and in such a manner that it cannot escape. While CO2 is per se non-toxic, air which contains too much CO2 is still dangerous simply because it doesn't contain sufficient amounts of oxygen any more.

 

The captured CO2 could be pumped into exhausted oil or gas wells. However, that requires shipping it to wherever it could be pumped underground which would make the process unfeasible.

 

And if we 'suck' the CO2 out of the ambient air at the storage point? This is known as Direct Air Capture (DAC) and it is being tried on a larger scale. While still expensive, this technology is not nearly as costly as any space-based solutions described above.




 

This is where the second acronym (CCU) comes into play.

 

Now that I've got all that carbon, what do I do with it?

 

The problem with CO2, as a useful molecule is that it is energetically 'dead', which is to say that it requires a lot of energy to turn it back into something useful, something that is reactive and whose reactivity can be steered towards synthetically desirable outcomes.

 

However, there are 'non-chemical' uses for CO2. In terms of volume, the biggest one would be enhanced oil recovery. Some of the captured CO2 could also be used in controlled environment agriculture, where atmospheres enriched in CO2 are used to increase yields. A third use could be the carbonation of soft-drinks.

 

To sum things up, any self-respecting space scientist will call the space-based ideas outlined at the beginning of this article as something possibly nice for the years 2100 and later.

However, something needs to be done here and now. Ideas like stratospheric aerosol injection are much cheaper, however, the associated risks are poorly understood, if at all.

Capturing CO2, either at the point of generation (coal-fired power stations, cement kilns etc.) or straight out of the atmosphere is possible but raises questions regarding the security of the CO2-deposits.

Also, it does require some investment, however, far less so that mitigating the consequences of global warming.

 

The most promising and most sensible thing to do remains to reduce the generation of CO2 as much as possible.


In weighing the options to tackle climate change, we've seen ambitious ideas alongside practical challenges. Whether it's space mirrors or carbon capture, each solution presents its own set of possibilities and hurdles.

But one thing is clear: cutting CO2 emissions is non-negotiable.

We need to act now by embracing sustainable practices, switching to renewable energy, and rethinking our reliance on fossil fuels.

There's no silver bullet here. Instead, it's about combining innovation with practicality. We must work together globally, be resourceful, and stay committed to protecting our planet for the future. It's not just one solution; it's a concerted effort that holds the key to a sustainable tomorrow.

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