Image credit: Pixabay, scholty1970

Climate scientists have found that there is only so much carbon dioxide our atmosphere can take, before we start to see higher risks of severe consequences.

They call this the carbon budget, and it’s currently being spent rapidly.

The solution? Many say it’s ‘net zero’. But why do we need to cut emissions so drastically?

Why ‘net zero’ rather than ‘just less’?

Net zero means that the amount of greenhouse gasses that we pump into the atmosphere is equal to the amount that we take out.

Sometimes we also use ‘carbon dioxide net zero’ i.e. the amount of carbon dioxide that we pump into the atmosphere is equal to what we take out.

This is due to the large role that carbon dioxide plays (more on this later).

So, why do we want carbon dioxide at net zero rather than just carbon dioxide at way less than it is now?

Well, slowing down our net output still has us spending our carbon budget. Once it’s spent, it’s spent.

If we reach net zero for carbon dioxide by 2050, then we are predicted to keep our average global temperature to 1.5°C above what it was before the industrial revolution.

Scientists have noted that there is a positive correlation between the average global carbon dioxide atmospheric concentration and the average global temperature.

So, not only do we need to reach net zero, but we also need to taper off our carbon dioxide emissions in the years leading up to 2050, in order to have sufficient impact.

Reaching global CO2 net zero by 2050 should give us just over a 50% chance of staying within the 1.5°C limit, according to the mathematical models.

Note that even as our net emissions are declining, the atmosphere continues to warm up, due to everything we already released in the preceding years. The effect is cumulative.

By achieving net zero, people hope to slowly stabilise the average global temperature. It won’t cool things down, but hopefully it will stop the situation escalating beyond our control.

How is our atmosphere similar to a giant greenhouse?

When certain, so called ‘greenhouse gasses’ enter the atmosphere, they contribute to it heating up.

The visible short wavelength radiation from the sun is absorbed by the Earth’s surface and then re-emitted as infra-red radiation which is ‘trapped’ by these gasses.

In fact, it is absorbed, and re-emitted over and over again in all directions.

There are a number of different gasses that contribute to this effect; carbon dioxide, methane, nitrous oxide (N2O), halocarbons (CFCs and HFCs) and water vapor being the main players.

Positive feedback loops

Research into positive feedback loops is creating some concern.

For example, when ice melts, the ground underneath reflects less of the Sun’s energy and instead absorbs it.

This energy is later emitted as infrared, which interacts with greenhouse gases leading to greater warming, and even more ice melting.

Eventually, there is the potential for this non-linear process to reach a tipping point where it becomes self-sustaining.

Water vapor is another example. We are not pumping out water vapor which warms the atmosphere, but rather, we release carbon dioxide which causes some warming, which causes evaporation of water, which then further warms the air.

There are a number of processes like this.

To some degree they interact with one another.

Unfortunately, they may currently be having a significant impact on local atmospheric temperatures and they have the potential to do a lot of damage when it comes to the average atmospheric temperature in the future.

To explore these feedback loops further, check out my article ‘Pernicious Positivity’.

Which gases are the biggest contributors?

CFCs (chlorofluorocarbons) and HFCs (hydrofluorocarbons) are both part of a group known as halocarbons, and can be found in things like propellants.

Unfortunately, both types of molecule contribute to the greenhouse effect, with for example one molecule of CFCl3 being 12,400 times stronger than one molecule of CO2 when it comes to the greenhouse effect.

The only saving grace is that they currently exist in our atmosphere in relatively low concentrations.

It’s also worth noting that carbon dioxide sticks around in the atmosphere for a long time.

Methane, while contributing much more powerfully to the greenhouse effect per molecule, will degrade after around 9-12 years.

In fact, reducing methane emissions could be considered a sort of mini quick win for this reason.

I thought I’d create a little graph showing how long each gas sticks around.

You’ve got your nitrous oxides lasting around 110 years and CFCs a little less at 52-93 years, but then after further research I realised carbon dioxide is actually hundreds to thousands of years.

In 1000 years, you’d still expect 20-40% of the carbon dioxide to remain! So, no graph.

Because of this combination of the potency of each molecule and it’s ‘lifespan’ in the atmosphere, scientists will sometimes use a unit called CO2-equivalent, or CO2e.

This is the equivalent contribution that a greenhouse gas provides over a set period of time, compared to the contribution of carbon dioxide.

Take a look at this graph using data from way back in 1989, which shows the relative contributions of different greenhouse gasses to the overall warming of Earth’s atmosphere.

Relative contributions of different greenhouse gasses to global warming. Data from Hansen et al, 1989.

Hang on, you may be thinking!

It looks like water vapor and clouds are doing most of the warming here, and the sections we are contributing to (CO2 and ‘other’) are tiny in comparison!

Why is it that more modern sources tend to omit the clouds and water vapor?

The thing is, water vapor will move on up into cooler parts of the atmosphere and then condense into clouds which then rain.

The lifespan of water vapor is days.

And what makes the water evaporate in the first place?

Warming due to a combination of all the greenhouse gases.

Because both water vapor and clouds form part of the water cycle which involves rapid condensation and precipitation along with rapid evaporation in response to warming, you can think of these as knock on effects.

Because of this very short lifespan for water vapor and the fact that it’s considered a ‘feedback’ rather than a more direct cause, it isn’t even assigned a CO2e value like the other gases.

The train driver doesn’t represent much of the power behind the train as a whole, but if they are the one in the driving seat, they can control the whole train.

The carbon dioxide and ‘other’ gases are our drivers.

What’s the big problem?

Why is a 1.5°C rise even an issue?

If the temperature of the air around you rose by that much, I expect you’d barely feel the difference.

The problem is that even tiny increases in the global average temperature can cause knock on effects including ice caps melting, loss of habitat, sea level rise, changes in rainfall patterns leading to drought and food shortages, extreme weather events, the list goes on.

It’s not just a case of everyone feeling marginally warmer.

The problem has become so bad that the Intergovernmental Panel on Climate Change (IPCC) has said that the world should aim to reach ‘net zero’ by 2050.

Goal achieved

Let’s say we achieve our goal.

A 1.5°C change will still be sufficient to change local weather and rainfall patterns around the world, leading to a number of problems, however our best models predict that this will help us to avoid problems on a larger scale.

It’s also worth noting that it takes time for the sea and ice to absorb the heat from the atmosphere.

This means that even if atmospheric temperatures stabilise, the sea will continue to heat up.

The molecules of water will have more kinetic energy, causing the water to expand and take up more space (not to be confused with water increasing in volume due to hydrogen bond formation as it freezes).

This means sea levels will still rise, and continued melting of ice will add to this.

It seems fitting that, just as the industrial revolution had it’s roots in the UK and later became a world-wide phenomenon, the UK was one of the first countries to pledge a legally binding commitment to reach net zero by 2050.

But with the UK only contributing a miniscule proportion of global emissions, a coordinated international effort will be needed.

Anger and worry

Climate change is already in full swing, and the truth is that the future is uncertain.

Some of the most severely impacted places include what are referred to as Small Developing Island Nations.

As sea levels rise, freshwater rivers become flooded with seawater and coastal towns (sometimes entire islands) become submerged.

Fish populations decline and coral reefs suffer as the ocean acidifies as it takes on increasing levels of atmospheric carbon dioxide, which becomes carbonic acid in the water.

Many of these Island Nations have already made waves among international communities, with their calls to halt greenhouse gas emissions and protect what remains of their homelands.

Image credit: Pixabay, ThousandImages

Perhaps a more wide-reaching issue is that of food scarcity.

In the UK we get over half our calories from just four crops: wheat, maize, soy and rice.

Crops like these are mainly grown in just a few countries, the so called ‘breadbaskets’ of the world.

If these breadbaskets are hit by drought or a heatwave, there is the potential for food shortages on a huge scale.

A 2019 study by Gaupp and colleagues at Oxford looked at three crops with worldwide importance; wheat, soybean and maize.

They investigated five of the global ‘breadbaskets’ covering production of these crops.

The scientists took data about the climate from the atmosphere-only HadAM3P model, a computer model that was developed by the UK Met Office in order to predict the risks of what they refer to as ‘climatic extreme events’.

Gaupp found that after a 1.5°C rise in global temperature, the risks of such events leading to multiple breadbasket failures rose disproportionately.

Breaking this 1.5°C threshold was described as a ‘risk to global food security’.

The problems associated with global warming are too far reaching for this post and they extend beyond humanity.

What to do?

OK, so all we have to do is use our toolbox of carbon dioxide removal methods and we can keep pumping it out at the same rate, right?

Well, it turns out it’s actually pretty difficult to remove carbon dioxide from the atmosphere and the removal methods we have would never be able to outpace the speed that we are pumping it into the atmosphere.

Don’t forget that we’ve been doing this for years, so we’ve already accumulated a bunch of it in the atmosphere, as we blow through our carbon budget.

To make matters worse, as the air warms, some methods of CO2 removal actually become less effective.

Even the trusty ocean, which has absorbed most of the atmosphere’s excess heat and a big chunk of our anthropogenic carbon dioxide, will be less able to hold carbon dioxide as it warms up.

In a 2022 article, T.M. Gür described the problem of global warming on Earth’s ecosystems as ‘too real and imminent to be judged and driven only by economics.’

But the technologies which we have available right now are expensive.

Can we expect countries to put policies in place which are unaffordable? Can we sway the hearts and habits of millions of consumers enough to make a dent directly or pressure companies to go greener?

Can I sit here in my comfy home and say that others should turn off their heating or switch off their air con?

This will not be an easy hurdle.

Whether a combination of the above, along with further scientific research, can plug this gap, still remains to be seen.

‘Net zero’ was borne from a series of IPCC reports which cite thousands of scientific studies.

It isn’t just an arbitrary goal plucked out of the air by politicians.

Reaching this goal is what we all need, if we are to finally stop the temperature rising.

Wondering what the path to global net zero might look like? Look out for an upcoming article, where I will be discussing the road to net zero in more detail.

References

T.M. Gür (2022) Carbon Dioxide Emissions, Capture, Storage and Utilization: Review of Materials, Processes and Technologies. Progress in Energy and Combustion Science, Vol 89, March 2022

https://www.sciencedirect.com/science/article/abs/pii/S0360128521000630

Gaupp F, Hall J, Mitchell D, Dadson S (2019). Increasing risks of multiple breadbasket failure under 1.5 and 2 °C global warming. Agricultural Systems Volume:175 pp.34 – 45

https://www.climate.ox.ac.uk/publication/1003598/ora-hyrax

IPCC sixth assessment report – intergovernmental panel on climate change

https://www.ipcc.ch/assessment-report/ar6/

UK enshrines net zero target in law:

https://commonslibrary.parliament.uk/what-is-net-zero/

Effects of climate change on small developing island nations

https://www.unep.org/news-and-stories/story/small-island-states-fight-back-against-nature-loss-climate-change#:~:text=Many%20island%20nations%20are%20struggling,indeed%20are%20large%20ocean%20states.%22

Ramanathan, V. (1998) Trace-Gas Greenhouse Effect and Global Warming. Royal Swedish Academy of Sciences, Vol. 27, Issue 3.

https://ramanathan.ucsd.edu/wp-content/uploads/sites/460/2017/10/pr78.pdf#:~:text=First%2C%20was%20the%20demonstration%20in%201975%20(17),their%20concentrations%20were%20shown%20to%20be%20increasing.

Lifespans of greenhouse gasses:

https://science.nasa.gov/resource/graphic-major-greenhouse-gas-sources-lifespans-and-possible-added-heat/

Halocarbons article

https://www.sciencedirect.com/topics/earth-and-planetary-sciences/halocarbon#:~:text=2.5.&text=Halocarbons%20are%20another%20group%20of,Kieran%20Ohara