Why you should care about climate change#

Living in France, where the reality of climate change is broadly accepted, I've never really tried to convince people about it.
However, recent events have made me realize that, even when people have accepted climat change, they do not necessarily realize how much of a threat it could be for us as individuals or as a civilisation, and for every living thing on the planet.

Because of this, it seems that people in general, and politics or industrials in particular, believe that they can just wait for scientific progress to make everything cleaner and solve all the problems without them having to make the slightest effort. Well, big news: we can afford that way of thinking!

Why is that? Because of two scary-looking adjectives that characterize climate: nonlinear and chaotic!
Now you might think that this is just some stupid jargon used by a scientist to impress and manipulate people. But what is implied by these two adjectives is actually very simple and has been well-known and well-understood by physicists for decades or even centuries.

So let's explain what nonlinear and chaotic means, then we'll use it to understand why we cannot take the risk of waiting for things to "resolve on their own".

Nonlinear and chaotic systems#

Nonlinear systems respond very differently depending on the sollicitation#

This is probably the easiest things to explain. Most people have learned only about linear systems at school: if you send a ball twice as hard against the ground, it will roughly bounce back twice as high.
Because of this, we usually expect things to change at the same pace all the time. In the case of climate change, this means that we expect the temperature to increase in a linear way as the emission that we reject in the atmosphere increase.

However this is not how nonlinear systems work: if you throw the ball twice as hard, it could come back ten times higher!
A very simple example of nonlinear systems can be seen in the response of objects to stress. They usually have a linear behavior for small levels of stress, then a strongly nonlinear response for higher levels.
Take a paper wall, for instance: if you lean on it lightly, it will bend (let's say by 3 centimeters) but it can bear the pressure and allow you to stay upright; however, if you rely on it twice as heavily, it will not bend by two additional centimeter: it's going to tear and you'll end up on the ground with people around laughing and the owner of the paper wall screaming at you for breaking it.
So there you have it: for a nonlinear system, the response can change greatly depending on the sollicitation.

Below is the example of how the length of polymer clay will change when you pull on it: it first elongates slowly, then thins and elongates faster and faster, then breaks. This is another simple example of a nonlinear response.

For climate change, this means that as our emissions pile up in the atmosphere, the rate at which the earth warms up (or the sea levels rise, or the extreme weather events occur) does not remain constant, it increases!
(see last paragraph for details and scientific articles)

Nonlinear systems can "remember" what happened before#

An interesting phenomenon, called "hysteresis", happens in some nonlinear systems: their state does not only depend on an external cause, but also on how this cause evolved in the past. This means that such systems will remember what happened to them before and change accordingly.
In a way, this means that once you've done something, you can't just go back on your tracks to undo it, you'll need to do more!
In fact, this is exactly what I described in the previous paragraph: once you put too much stress on a material, it's going to tear or bend irreversibly, and you cannot just stop pushing or unbend it to get it back to normal... it needs repairing!

Now for climate change, this means that once we reach +2 °C on the average temperature, it might not be that easy to revert back to the initial temperatures... it could even prove a bigger challenge that stopping the previous increase.

As an example, here is a simple model of magnetic hysteresis, showing how the magnetic field B of a magnet changes when you try to force it to either increase or decrease. Go on and try to demagnetize the magnet: reach the origin where the axes cross, in (B, H) = (0, 0)! For that, you can use the slider which allows you to change the value of the field H that is applied on the magnet. If you want to know what would happen in reality, let's say you would be using electricity to create a magnetic field in which you would put the magnet, progressively changing the value of the magnetic field to demagnetize the magnet.

If you tried it, you should understand how challenging it could be to bring Earth temperature back to its initial value now that we have changed it...

The dynamics of a chaotic system depends heavily on the initial conditions#

This is the last property that we need in order to understand what's so fearsome about climate change: its unpredictability.
Climate is actually a system for which we can rather accurately predict the behavior, though it is very costly in terms of the amount of data and computation that is required. But well, we have our weather forecast, don't we? And usually they are not that bad...

One thing they are not good at, however, is predicting the weather in the long run, let's say more than 5 or 7 days.
But this is not because they don't understand what is going on with the wind, the water and the clouds, it's just because unless you know exactly the speed of the wind, the temperatures humidity everywhere, it's impossible to predict what is going to happen after some time.

This incredible importance of very small changes is what is usually known as "the butterfly effect". What is means is simply that systems that differ very slightly at a given time will become very different after some time if they are chaotic.
You can find some nice videos showing this effect on the double pendulum here for a computer simulation and here for an actual experiment. So just imagine, if a simple pendulum leads to such complicated motions, how incredibly difficult it is to predict precisely what's going to happen next in a weather forecast! Yet we do it every day!

So what does this means for climate change?
Well, it means that, supposing that if we stop our carbon emissions by late 2018, we stick to +2 °C, if we end up stopping them by early 2019, we could reach +3 °C instead!
Remember: tiny changes can lead to huge differences after some time.

Specific examples in the case of climate change#

Accelerated heat production#

Because of it white color, the ice cap around the North Pole used to reflect a large amount of the light received from the Sun back into space. However, the increased melting due to warmer temperatures in these regions have thinned it to such an extent that large regions are no longer white (either because they have been replaced by sea water or because the ground is starting to show under it). These darker colors absorb a much larger amount of light, and thus heat up a lot more, worsening temperature increase.
This positive feedback is contributing to the system's nonlinearity: the more it heats up, the more ice melts, so the more energy is absorbed, leading to even higher heat, and so on, and so forth.

Read more:

Increased natural emissions#

Melting the ice cap and permafrost regions has another indirect effect on the temperature rise: these regions could have huge amounts of trapped carbon that are now being released.

This can be either under the form of preserved plants that now start decaying, or as large bubbles of methane, one of the most potent greenhouse gases.

Because of this,

Explore further:

Best and worst case scenarios#

So based on what we say, what could be the best and worst case scenarios, and what would it take for our future to switch from one to the other?

Best case scenario: emissions and temperature increases are contained#

If we actively try to limit our impact and if we are really lucky, the best case scenario is the following:

  1. we stop our emissions,

  2. natural emissions and temperature increase keep going for a little while because of the system's inertia, then emissions go down,

  3. temperatures stop increasing or even start to go down.

Worst case scenario: temperature increases suddenly and does not go down when emmissions do#

Even if do take actions to fight climate change, if we are unlucky, we might already be above the threshold where the strongly nonlinear effects kick in.

In that case, what would happen is the following:

  1. temperatures keep increasing,

  2. natural emissions skyrocket because of the increased heat,

  3. this leads to a sharp increase in temperatures,

  4. even after the emissions go down, the system has been significantly altered (e.g. desertification, deforestation, disappearance of major oceanic currents) and temperatures do not go down.

What separates these two scenarios?#

As far as I know, we don't really know which scenario is more likely, and as climate is a chaotic system, if we are not on track to the worst case scenario, we could be by next year, or even next month...

Indeed, as was mentionned before, you cannot know what will be the last straw, triggering drastic events such as the disappearance of the Gulf Stream. If there is a threshold on carbon emissions, a no-return point, we don't know where it is, so we could cross it in 10 years, tomorrow... or did we cross it yesterday?

My point is, not acting to stop climate change is kind of like making a bet, except one with insanely high odds.
So while I'm not against a small bet from time to time, I'm really not ready to play Russian roulette, and I really don't like being forced to! This is not a sensible game, so let's just stop playing... now.

What can we do to reduce our impact?#

There are plenty of scientific articles or documentaries that describe what can be done to help reduce our environmental impact.
Unfortunately, the best way to limit your impact is to not have children... but this is a bit much to ask (even for me), so let's just try to be reasonnable and not have much more than 2.

Apart from that, there are actually many things you can do to reduce your footprint. I listed some below, the order does not convey any particular meaning:

  • Avoid planes

  • Try to avoid using cars or motorbikes as much as possible.

  • Stop eating meat and diary products

  • If you don't do the previous item, at least stop beef and milk! Or eat a lot less! (once a month would be best)

  • Avoid palm oil (it could be bad for your health, but it definitely is for the environment)

  • If you skipped the previous items, you could at least try cooking vegetarian meals. There are many good ones and they are not more difficult than "standard" cooking (also they are cheaper!) and yes, I'm a crook, this is actually items 2/3 again ;P

  • Try not to buy things with too much plastic wrapping, avoid them entirely if you can (just kidding: if you're reading this, it's most likely you can't... but you can try! Just nkow this is really far from having the largest climate impact)

  • Be nice to people (OK, this does not actually help with climate change but it could help you be happier ;D)

As to why these items help reducing the impact we have on the environment, here are a few (you'll find many more articles if you look for them):

  • Cars and planes burn fossil fuels, which produces $CO_2$, but also a lot of particles that interact with your lungs, rain, etc. Furthermore, oil is incredibly useful to create plastics, various chemicals, etc, so it's really a shame to burn it...

  • Raising cattle or fish requires a lot of space to grow the crops that will then be used to feed the animals; this is actually one of the prime reasons deforestation in the world. What's more, cows generate huge amounts of methane, one of the most potent grenhouse gases, and require enormous amounts of water every day. Eventually, since animals (just like us) are a form of "biological machines", like every machine, they have a yield (an efficiency), which turns out to be fairly low... this means that it is a lot more efficient (ecologically and economically) to directly eat cereals and beans instead of first feeding the cow with them, then eating the cow!

  • Palm oil is pretty similar to cattle: most of it grows in regions where the rainforest was burnt to make space.

  • Plastic wrapping is pretty obvious: most of it is not recycled and just ends up getting burnt (in the best case, otherwise it ends up in the ocean, or pretty much everywhere as microplastic), and burning plastic is pretty much the same as burning oil in cars or planes...