• Alex Campbell

Global Warming Explainer (Part 1) - The trouble with temperature

Why are all the scientists freaking out about a couple of degrees of warming?


If you’ve spent more than a few days on planet Earth you’ll know that the temperature on its surface fluctuates - a lot. A cool change can blow into town and the mercury may drop by 20 °C in a matter of moments. Things warm up again with a few degrees of latitude or the first rays of sunrise. Temperature is vastly different between north and south, summer and winter, night and day, and is also influenced by solar flares, volcanic eruptions and cloud cover.


Temperature on our planet is a profoundly changeable thing. So why are all the scientists freaking out about a couple of degrees of global warming?


Well, despite all these fluctuations, the average temperature on the surface of planet Earth has, for quite some time now, actually been really consistent - at around 15°C. It has fluctuated around this average with the cycle of ice ages (dropping to about 11 °C ) and interglacial peaks (increasing to about 19 °C), but accounting for these fluctuations, for at least the last 800,000 years - until very recently - the average global temperature on the surface of Earth has been about 15 °C.


This thermal sweet spot has persisted for so long thanks to a beautiful coincidence between the particular chemical composition and ‘thickness’ of our atmosphere and our precise distance from the sun.


Atmospheres around planets work in a similar way to greenhouses, which we’ve used to grow fruits and vegetables in places far cooler than they would grow naturally, for at least the last 1000 years. Greenhouses (and atmospheres) work by allowing the Suns’ energy to pass through initially, then trapping it when it reflects and tries to escape. The energy that’s trapped inside warms up the interior of the greenhouse (or the surface of the planet).


The first scientist to formally compare our atmosphere to a greenhouse was John Tyndall in 1869 and from this work, the ‘greenhouse effect’ was born. Although it’s not a new idea, the importance of atmospheres in regulating planetary temperatures can be well illustrated by a quick, imaginary space jump to some of our nearest neighbours.


Mercury is the innermost planet in our solar system, which means it’s exposed to a lot more solar energy than everywhere else. Despite this, Mercury is not the hottest planet in our solar system. That’s because it has essentially no atmosphere. So although the sun’s rays completely bake whichever side of Mercury is facing it, when the planet rotates away from the sun, the heat quickly dissipates and the surface temperature plummets down well below freezing. Because it lacks an atmosphere, Mercury’s surface experiences the largest range of temperatures of any single body in the solar system and a toasty but surprisingly low (given its proximity to the sun) average temperature of about between 85 and 160 °C.


Jumping now from Mercury to Venus, where, despite being twice as far from the sun and receiving 4 times less solar energy, the average surface temperature is a staggering 420 °C. This average temperature is maintained because Venus has a very ‘thick’ atmosphere, which is composed of about 96% carbon dioxide (CO2) - a type of gas that’s very efficient at trapping the suns energy - keeping the surface of Venus intensely hot.


Because CO2 is so good at trapping heat and helping an atmosphere behave like a greenhouse, it’s called a ‘greenhouse gas’. Having lots of CO2 and other greenhouse gases in an atmosphere means that it will trap more heat, resulting in more warming at the surface.


Jumping back down to Earth now where, at the time of writing, our atmosphere had a much more modest measure of CO2 than Venus (a little over 0.03%). This chemical composition of our atmosphere, in combination with our precise distance from the Sun, is why Earth has maintained a warm but mild average global temperature of 15 °C – our thermal happy place - for millennia.


For a long time now, we’ve known that adding more greenhouse gases to the atmosphere would enhance its greenhouse effect and directly lead to warmer temperatures on the surface of our planet. In fact, it was way back in 1896 that a Nobel prize winning chemist, Svante August Arrhenius, outlined that very concept.


Since Arrhenius’s paper more than 120 years ago, the global average temperature has increased to 15.83 °C. This 0.83 °C rise might not sound like such a big deal for a planet whose temperature peaks and troughs by almost 5 °C with the ebb and flow of ice ages. But here’s the thing - in the past, it’s taken our planet about 5000 years to warm up or cool down by 5 °C.


Scientists are freaking out because the warming we’re observing now is happening more than 10 times faster than anything that’s occurred for the past 800,000 years. What has scientists even more worried are the predictions for the next 100 years, which project future global average temperatures anywhere between 2-6 °C higher than they are now. This warming would be between 20-120 times faster than anything that has occurred in the last 800 millennia.


The only convincing explanation for this sudden and rapid rise in global average temperature is a coincident and similarly sudden and rapid rise in levels of CO2 in our atmosphere.


Right now, the level of CO2 in Earth’s atmosphere is unprecedentedly high, having increased by at least 40% of pre-industrial levels. The consequence of this build-up of CO2 in the atmosphere is - just as Arrhenius predicted - a build-up of more and more heat on the surface of our planet.


In fact, the amount of extra energy that’s accumulated on our planet’s surface is phenomenal and describable only with units of measurement that sound like a creative invention from a 1970s sci-fi film. Between 1997 and 2016, the earth accumulated at least 150 zettajoules of extra energy. What is a zettajoule, I hear you ask? Well, it’s about 1 000 000 000 000 000 000 000 000 Joules (or, more scientifically, 25x10^22 J). A chilling (or rather, warming) analogy recently posited by physical scientists is that the amount of extra energy accumulated in the past 20 years or so is equal to the energy that would be released by the explosion of 2 billion Hiroshima-style atomic bombs. 2 billion!


Whilst this information is sobering, it’s downright terrifying to think that, up until now, most (at least 96%) of this energy has been absorbed by the oceans. So, for that matter, has at least 30% of the extra CO2 in the atmosphere. What will happen when the ocean becomes saturated with CO2 and reaches its capacity to absorb heat? I’m just going to leave that question here, for now.


There are plenty of other complexities, too, such as other types of greenhouse gases, which can sometimes be more potent than CO2 and persist in the atmosphere for different periods of time. Feedback loops are are horrendous situations where the impacts of warming further exacerbate warming (like, for example, the melting of ice which reduces heat reflection, leading to more warming, or the release of additional methane from the melting of permafrost, etc.). Our other actions can also reduce the planets resilience. Deforestation for example, reduces the amount of CO2 that can be absorbed by plants.


If you’re not convinced by the numbers, have a look at some historical images of glaciers and then check those same glaciers out online now. The disappearance of glaciers is for me, one of the most salient, confronting and clear pieces of visible evidence of global warming. In the (now somewhat ironically named) Glacier Park in the USA, the number of glaciers has dramatically dropped from 100 in 1912 to only 25 today and scientists predict that in the next 20 years, they’ll all disappear. In Alaska, more than 98% of some 700 glaciers studied are diminishing and, in the Himalayas, (which provide water to India and China), 95% of the 612 Tibetan glaciers are retreating.


But despite the numbers, the glaciers, the myriad of real, extant biological and human crises directly resulting from warming, the world continues to march on along the ‘worst case scenario’ and ‘business as usual’ pathways, unabated, undeterred. In 2018, we set a new record for the highest ever annual global emissions of CO2 - an increase of 1.7% from 2017 - to a new high of 33.1. billion tonnes of CO2. That’s 33.1 billion tonnes of greenhouse gas released into the atmosphere through the burning of fossil fuels an other activities in a single year.


The Intergovernmental Panel for Climate Change (IPCC) is a high-profile group of expert climate scientists, hand-picked from all over the world. Their job is to collate, compare, debate and synthesise all the data on climate change from all over the world. They write reports, make recommendations and in a special report released last year, the IPCC put the world on notice, warning that the changes we’ve already made to our atmosphere and our oceans will irreversibly impact on our climate systems, ecosystems and ways of life for hundreds or thousands of years.


Their new goal is to encourage leaders to commit to measures that will help limit warming to 1.5 °C, which will, essentially, just be ‘less bad’ than allowing temperatures to increase by 2 °C or more. This ambitious target will require global CO2 emissions to be reduced by 45% of 2010 rates by 2030, which will, of course, require big changes, policy backflips, real leadership and global cooperation. It’s already half way through 2019 which leaves us only 10.5 years until the 2030 deadline, by which time we’ll need to have our emission situation well and truly sorted. Otherwise, it will be impossible to avoid what the -traditionally conservative – IPPC warn will be ‘catastrophic warming’.


There is a solution and it’s renewable energy. Even with existing technology, it is possible to meet the world’s current energy demands with solar power alone. Sure, it will take some remodelling, it will be expensive and probably a bit inconvenient for a while, but technically at least, it’s possible. There is an alternative to what we’re doing now, which is just making everything worse.


I will admit that I swing like a pendulum between hope and despair on this matter. Despite our poor performance in 2018, right now I’m feeling hopeful. Appallingly, this is partly because the impacts of warming are no longer hypothetical or distant. They’re no longer just impacts on “the environment”. It’s no longer possible for us to ignore them. Global warming is here, it's already affecting our lives and we’re running out of time to debate it.



© 2023 by

A. H. Campbell

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