Dear Evil Engineer: Could I plunge Earth into an eternal winter?

Dear Evil Engineer,

I am a resentful and wealthy polar bear. You can only imagine the trauma my species has experienced; it wasn’t long after the hunting stopped that our habitat started melting away into the ocean. We’re sick to the (very large) teeth with humans and it is finally time to exact revenge. Is it possible to engineer the climate to send Earth into a permanent winter?

Yours
A polar bear

Dear polar bear,

Whether you’re one of the dime-a-dozen evildoers heating Earth into a fiery wasteland or you’re aiming to freeze it into a planet-sized Pluto, your contribution to the villainous cause is valued. The industry is committed to diversity and inclusion.

The artificial cooling of Earth is more topical than usual; in March, the US National Academies of Sciences, Engineering, and Medicine called for a research programme to investigate geoengineering solutions to climate change. These approaches are all about increasing the proportion of sunlight reflected back into space and/or reducing the proportion of thermal radiation trapped within Earth’s atmosphere (the anti-greenhouse effect). The ratio of sunlight reflected vs. total sunlight (albedo) is measured on a scale of 0 to 1; 0 is a perfect black body absorbing all radiation falling on it while 1 is a surface reflecting all radiation. Cooling the Earth means increasing albedo; models suggest an increase of just 0.02 could halve the heating effect of doubling carbon emissions.

The anti-greenhouse effect occurs naturally on Earth alongside the greenhouse effect. It is most noticeable following massive volcanic eruptions which propel sulphurous gas and other substances into the atmosphere. The 1815 eruption of Mount Tambora in Indonesia threw enough material into the atmosphere to cause a “year without a summer” to follow. The lack of sunlight led to failed crops, mass food shortages, famine, violence, and typhus epidemics; it is estimated that fatalities were double that of average years. We workaday villains can only fantasise about causing such devastation.

In order to trigger something similar, you must burn sulphur or spray sulphur aerosols into the stratosphere; a cost analysis published in Environmental Research in 2012 estimates five million tons of sulphur dioxide must be delivered annually (such as by cannon, tethered balloon, or aircraft) to offset global warming, so that’s your starting point if you want a net reduction in temperature. Speaking in the most basic terms; the more sulphur dioxide added to the stratosphere, the more sunlight is reflected and the cooler Earth gets. Releasing tens of millions of tonnes of sulphur dioxide into the stratosphere sounds like a feat – and it is – but given the relative cheapness of the gas and the enormous potential for global disruption, it’s a pretty feasible approach to wrecking the world!

Sulphur particles also act as seeds around which cloud droplets form; that’s why you see clouds forming above shipping lanes. Clouds mostly reflect sunlight, so you get an indirect cooling effect through cloud formation. There are many other opportunities to cool Earth by tampering with clouds. Adding benign substances such as sea salt to clouds could make them brighter, increasing albedo and reflecting more sunlight. Cirrus clouds (those wispy, icy, high-altitude chaps) have a net warming effect but they could be reduced by seeding them with ice crystals to grow rapidly, encouraging more precipitation and shorter lifetimes. It is worth noting that there remains much to be understood about cloud formation, so if you approach the problem this way, be ready to expect the unexpected.

Humans from all across the spectrum of derangement have suggested more ostentatious approaches to global cooling, including but not limited to: putting a huge (1000km diameter) mirror in space; putting a huge diffraction lens in space; and putting as similarly huge sunshade in space (you get the idea, it’s all just putting huge things in space to block sunlight). You can take your pick if you are a theatrical villain, but none of these options will be cheaper or easier than the sulphur dioxide approach.

The drawback of filling the stratosphere with material to increase albedo is that the material falls over weeks or years and temperatures restabilise. Maintaining the cooling effect would require the continual emission of material into the stratosphere. If you are able to reduce the surface temperature far enough and for long enough, however, something extraordinary could happen.

The ‘snowball Earth hypothesis’ suggests Earth’s entire surface may have been frozen some time in history. A triggering event – such as a supervolcano or asteroid impact that blasts ash, dust, and gas into the atmosphere – would have caused enough cooling for ice (high albedo) to spread from the poles towards the equator. When Earth’s albedo reaches a critical point, a positive ice-albedo feedback loop begins. It would take about 1000 years to reach ‘snowball Earth’ (I’ve checked Google and polar bears don’t live quite that long, but you’d still have many years of enjoyment as Earth freezes, crops fail, and life struggles for survival). The most feasible artificial trigger is a nuclear war; this could lead to massive firestorms filling the stratosphere with soot and blocking sunlight.

An important caveat when talking about geoengineering – whether you are a hero or villain – is that we have a limited understanding of the anti-greenhouse effect due to limited direct observation opportunities; it is impossible to predict exactly what side effects will appear (but they may include holes forming in the ozone layer over polar regions: most inconvenient to you and other polar bears). Lawful-evil villains* will be apprehensive about this unpredictability, but it could give your evil plan a pleasing element of randomness!

Yours,
The Evil Engineer

*If you do not know what your villain type is, consider booking a D&D alignment indicator workshop.