The Science Stuff
CO2 - The Boogeyman
By Jesse Armstrong
Goods and services have always had traditional measures of value: their financial cost, their labour requirements, their inherent usefulness. The escalation of the climate crisis has added a new metric to this list – the carbon footprint. The past century of industrial activity has released extraordinary quantities of carbon dioxide (CO2) into the planet’s atmosphere, giving this humble, ubiquitous gas bizarre and unparalleled notoriety. The drive to reduce carbon emissions is now a key talking point at everything from international summits for world leaders to school classrooms. This two-part post will look at where this carbon has come from and why it’s posing such a problem, highlighting aspects of the CO2 issue that are often overlooked.
Since 1850, human activity has released 375 billion tonnes of carbon dioxide, with more than a quarter of this occurring post the year 2000. Carbon dioxide is an example of a ‘greenhouse gas’. These are key components of our atmosphere that play an essential role in supporting life on Earth by trapping the sun’s warmth. However, the recent rapid increase in the concentration of CO2, coupled with other greenhouse gases such as methane, has caused an unprecedented degree of climatic change in recent times. In 1850, the atmosphere contained around 285 parts per million (ppm) of CO2. By 2021, this has risen to 410ppm. Methane concentration has also risen by a factor of 2.5, and whilst this is still a tiny proportion of the atmosphere, methane is 80 times more warming than CO2. The consequences of this do not sound overly dramatic: an average warming of around 1℃ from 1880 to the present day. However, this slight change is already having a big impact. Scientists have predicted that without mitigation, we are currently on track for a 4℃ increase in global average temperatures, with devastating consequences. The last time CO2 levels were this high was 3 million years ago, and the earth looked very different. Temperatures were between 2 and 4 degrees warmer and sea levels were 15-25 metres higher.
Anthropogenic CO2 emissions come from a variety of sources, but the lion’s share, 87%, comes from the combustion of fossil hydrocarbons like coal, oil, and gas for transport, heating, and energy supply. The remaining 13% comes from agriculture, changes in land use such as deforestation and the destruction of peatland, and industries such as the processing of limestone for cement production. Fossil hydrocarbons and sedimentary rocks have held trillions of tonnes of carbon stably locked up for millions of years. These stores were deposited by a natural carbon cycle, which has been steadily sequestering CO2 on a geological timescale since life first evolved, gradually establishing the temperate climate we are accustomed to. This cycle protects against drastic changes in CO2 concentration through a combination of the ocean’s buffering against rises in atmospheric concentration by absorbing CO2, and the conversion of gaseous carbon into living matter by photosynthesising life forms including land plants, marine plants, algae, and other microorganisms. Marine algae and forest biomass are the primary contributors to the continued creation of new carbon stores. When these organisms and their consumers die, some of that carbon is released once more by the microbes which break down their cells, but much remains captured, either geologically through fossilisation or sedimentation, or in the cells of other living organisms. This system has in-built flexibility in the form of the photosynthesizers: when CO2 concentrations increased, their growth increased as well to compensate. So why is our current situation so concerning?
CO2 concentration in the atmosphere has fluctuated greatly throughout the Earth’s ancient history, mostly because of volcanic activity. During periods when concentrations were high the planet’s climate was extremely different to today, but life still flourished in healthy robust ecosystems. It’s not that higher CO2 concentrations and warmer temperatures are bad for living organisms, it’s that they must be adapted to these conditions, and this requires time. The species which lived in these periods could do so because they had time to evolve to suit their environments over millions of years, continuously adapting to suit the slowly shifting conditions. The issue is therefore not so much the amount of CO2 being released, but the speed at which it has been released. For the last several hundred thousand years, small CO2 fluctuations have been comfortably compensated for through this carbon-sequestering system, maintaining an atmospheric CO2 concentration within a stable margin. Humans have totally changed that. All the volcanoes on earth now produce just 1/100th of the CO2 released by human activities and the natural systems for removing it simply cannot hope to keep up. This is the crux of the CO2 issue; anthropogenic climate change is occurring at a pace that wild species simply don’t have the capacity to adapt to. With changes taking place in tens of years instead of tens of thousands of years, we risk losing countless unique species and despite our undeniable ingenuity, our own infrastructure and societies are also fragile and vulnerable. This is a crisis for all species, including us.
When we talk about climate change and CO2 levels, the buzzword issue is global warming, as has been alluded to throughout this post. The potential consequences of this phenomenon are without a doubt the main reason we need to address this problem, but a topic of that size requires a separate post. This will be discussed in part 2, where I will break down the different ways that rising temperatures will change our lands, oceans, weather, and climate. The remainder of this post will instead look at some of the subtler impacts that the rising CO2 concentration is having on wildlife, independently of warming.
98.1% of the CO2 on earth resides in the oceans. When dissolved, CO2 forms HCO2 – formic acid. As the name implies, this acidifies the oceans, severely affecting the growth of hard coral species. The lower ocean pH reduces the availability of key building materials used by coral polyps to create their aragonite skeletons. Corals are the cornerstone species in reef habitats. Without corals, none of the other fish and invertebrate species can survive. As some of the most diverse ecosystems on earth, the loss of reefs would be a huge blow to global biodiversity.
Plants are also under increasing pressure. Many plant species have experienced very different temperatures and CO2 concentrations throughout their evolutionary history. As temperatures and atmospheric composition have changed through this time, plants have had to adapt to these varied conditions, and of course, different species have adopted different strategies to do this. Consequently, different plant species have retained very varied abilities to cope with, or capitalise on, higher CO2 availability. As conditions change, there will inevitably be a disparity in how these species can respond. Within an ecosystem, some will flourish, whilst others may suffer and run the risk of being outcompeted. This could lead to a big shift in the balance of plant species within a habitat, and as plants are the primary food source for all ecosystems, this will have a ripple effect, impacting other species throughout the food web. There are other complications as well; higher CO2 levels can leave plant species more vulnerable to disease. For example, the increase in atmospheric CO2 concentration in the last few decades has led to many hardwood deciduous trees becoming up to a third more productive in terms of biomass per growing season. This sounds like a successful adaptation to the changing conditions, however, the faster-grown wood in these trees is less dense and more aerated, leaving them more vulnerable to fungal infections and less able to withstand difficult conditions, so forests are in fact weakened. We are only just beginning to understand the multitude of impacts climate change is having on these delicately balanced ecosystems.
In the grand scheme of things, the extinction of a species is just an opportunity for a new species to evolve and fill its niche. However, such a rationalisation is of very little comfort to those species living now, including us, a species with an average lifespan of just 73 years. We won’t be around to see those new species arrive. Our climate crisis doesn’t risk life on earth, but it risks our experience of life on earth, and that of future generations. The mass extinction looming on the horizon could leave our ecosystems on the verge of collapse, and could forcibly reshape our entire society. We owe it to ourselves and all life on earth to do what needs to be done.
BIBLIOGRAPHY
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