Climate change is not something that occurs overnight.
The atmosphere consists of roughly 78% nitrogen, 21% oxygen, 1% argon – and just 0.04% carbon dioxide [CO2]. In this section, we’ll see how this ridiculously small percentage of CO2, along with other greenhouse gases [GHGs] in the atmosphere, can have remarkable consequences at the global scale.
The Earth’s Energy Balance
For the following section, think of radiation as energy or heat contained in a ray of light.
The Sun emits light as shortwave radiation. The Earth heats as it absorbs some of that radiation, before sending a portion of that back towards space as longwave radiation. Unfortunately, the longwave type of radiation can be absorbed by CO2 and other GHGs. These gases then re-emit this energy in all directions. Here’s the issue: the energy that was supposed to be sent back to space is now partially redirected towards the Earth’s surface – which effectively traps heat in our atmosphere.
What we’ve just explained here is the famous greenhouse effect. It has been taking place since our atmosphere formed billions of years ago and has played an important role in keeping the Earth warm, but now it’s making it a tad too hot – way too fast. We’ve recently released GHGs in the atmosphere in such quantities that the previously stable energy balance is now tilted in favor of heating the Earth.
Global Warming and Climate Change
All the additional heat trapped in our atmosphere has been increasing our average global temperature. In fact, during the 2011-2020 period, global surface temperatures had increased by roughly 1.09°C compared to the 1850-1900 period. This shows once again that global warming is real and it began well over a century ago.
Scientific consensus is very clear that the atmosphere’s GHG content has been increasing rapidly because of human activity. Since 1750, atmospheric concentrations have risen by 47% for CO2, 156% for methane [CH4], and 23% for nitrous oxide [N2O]. In 2019, atmospheric CO2 concentrations were higher than at any point in the past 2 million years, and we’ve emitted more CO2 since.
Unfortunately, there are far more GHGs than just CO2 – and much more powerful ones too. For equal emissions [by mass], CO2 is 28 times less greenhousy than methane and 22,800 times less greenhousy than sulfur hexafluoride [‘greenhousy’ describes the global warming potential of a gas – here, taken over 100 years]. However, we’ve been producing so much more CO2 in the past few centuries that it’s still the largest contributor to global warming, with methane not too far behind.
From Global Warming to Climate Change
The Earth’s atmospheric and oceanic temperatures are 2 major reasons that our climates are the way they are. They play extremely critical roles in the global water and carbon cycles, dictate precipitation patterns, and help shape many of the world’s oceanic current systems. Unfortunately, that means that any slight variations in temperature can have devastating consequences at the global scale – notably by changing many climates at once.
Climate change literally means changes in climate patterns and events. Cyclones, storm surges, heat waves, droughts, and extreme precipitations are all destructive climate events that are occurring more frequently and/or more intensely as a result of global warming.
For example, global warming increases the atmosphere’s capacity to hold water vapor. In turn, this can cause more/bigger clouds to form, which can lead to more intense precipitation events – potentially causing floods. This corroborates the projection that extreme daily precipitation events will intensify by roughly 7% for every +1°C of global warming, according to the Intergovernmental Panel on Climate Change [IPCC]. That may not sound significant, but we have to keep in mind that long-term global temperatures are projected to reach +3.3-5.7°C under the “very high GHG emissions scenario”. So all the 7% intensifications can add up real fast if emissions aren’t curbed soon.
Alas it’s much worse than that. Global warming and climate change are driving many long-term ‘irreversible’ effects that will have significant consequences worldwide. In particular, the IPCC has outlined the following points:
- Mountain and polar glaciers are projected to continue melting for decades or centuries. Even if we were to drastically reduce our emissions in the coming decades [to limit warming to +1.5°C over the 21st century], the Arctic would still likely experience at least one sea-ice-free summer before 2050. And unsurprisingly, uncontrolled emissions in the near future would lead to far more occurrences of sea-ice-free summers in the Arctic.
- GHGs contained in permafrost [i.e. grounds that are completely frozen] will irreversibly be released into the atmosphere during permafrost thaw, at centennial timescales. Preventing permafrost thaw as much as possible by reducing our own emissions will be key to reduce the amount of GHGs released naturally by the environment.
- The Greenland Ice Sheet will keep melting and the Antarctic Ice Sheet will likely do the same, although the total amount of ice loss remains to be seen. In Greenland, total ice loss will be heavily influenced by the amount of GHGs we emit in the next few decades.
- Sea level will continue to rise for hundreds to thousands of years, after which it will maintain its elevation for additional thousands of years. Over the next 2000 years for example, the average global sea level is expected to rise by roughly 2-3 meters if we limit global warming in 2100 to +1.5°C, by 2-6 meters with a +2°C limit, or by 19-22 meters at +5°C . And there’s a possibility that sea levels continue to rise after those 2000 years have passed, especially if we keep increasing the amount of GHGs we release every year. In the short term, the average global sea level rise will likely be contained between 0.28-2 meters by 2100, depending on if we limit warming to +1.5°C or +5°C over the 21st century.
Unfortunately, there are too many consequences to global warming and climate change to list them all here. However, a few of them can help us understand how humans will be directly impacted by these changes – notably by threatening global food and water security, increasing the likeliness and intensity of extreme weather events, and forcing climate migration on hundreds of millions of individuals around the globe.
Sadly, many indirect effects will also drastically impact human lives, like biodiversity loss.
Global warming isn’t all due to GHG emissions, at least not directly. Interestingly, climate change has its own impacts on the Earth’s energy balance, known as ‘climate feedbacks’. We’ve seen a few examples of climate feedbacks already – between the release of permafrost GHGs, the melting of ice sheets and glaciers [which reflect radiation back toward space], and the increasing concentrations of water vapor in the atmosphere [a potent GHG]. In these examples of positive climate feedbacks, initial warming causes climate change, which itself amplifies the initial warming – which then induces additional climate change.
Climate vs. Weather
It’s important to note that global warming and climate change don’t imply that every day will be hotter than the last. Weather is not the same as climate. Weather describes short term events and temperatures that don’t really mean anything on their own – since weather is subject to internal and natural variability [i.e. a certain level of randomness].
On the other hand, climate is approximately weather averaged out over longer periods of time. As such, climate change is responsible for increasing the likeliness of extreme weather events – but can’t guarantee that they will take place at any given moment. Similarly, a single record-breaking temperature could not confirm climate change is real, nor could a freezing temperature refute it.
That being said, when year after year we measure record-breaking daily, weekly, monthly, and annual temperatures [or extreme weather events] in very different parts of the world, it becomes pretty clear that global warming and climate change are already here. It’s no longer the future generation’s problem.