During the first decade of this century, specialist scientific groups around the globe met independently, but with common purpose. Their objective was to attempt to quantify the precise mess that we had got ourselves into with respect to our one-and-only planet. The outcome of these meetings was universal agreement on nine areas of significant concern (agreed c.2010), where human actions were impacting on the natural world and where immediate action was imperative. The groups sought and to define in specific mathematical terms what they called ‘sustainable planetary boundaries’ (SPBs).
Although the nine areas were separately defined and each assigned individual sustainable boundaries, there is considerable interaction between several of them. The groups analysed the extent of various impacts and produced precise and stark warnings. They indicated that urgent steps must be taken to avoid tipping points beyond which change would be inevitable and unstoppable. In some cases, they believed that such points had already been exceeded, and that only ‘firefighting’ could now prevent severe disasters.
In early 2025, six of those nine SPBs – climate change, chemical pollution, biodiversity, land usage, freshwater usage and the nitrogen and phosphorus cycles – have already been breached.
Climate change
Climate change includes primary features like the rises in each of atmospheric levels of greenhouse gases like carbon dioxide (CO2), average global air temperatures, oceanic temperatures, ocean levels and atmospheric pollution. Numerous secondary features are also implicated.
It would be perversely obstinate to deny the changes we have all seen in the last few decades, but some world leaders seem intent on meeting that description. Stories of wildfires and destructive floodings have dominated our news media, and the root cause of both is the same. As the atmosphere and the oceans warm, even very slightly, so climate consequences follow.
Warmer air can hold more water vapour; more vapour and warmer air lead to lower pressures, which in turn create more violent storms. The El Niño/La Niña cycles are disrupted and oceanic mixing currents have become unpredictable. The very latest data indicate that the oceans have warmed significantly more than we feared, and of course, warmer waters occupy greater volumes, and so sea levels inexorably rise.
Ocean acidification and the surprise success of tackling ozone depletion
Ocean acidification has been called the ‘evil twin’ of climate change, since it too is caused mainly by the increase in atmospheric CO2 levels. The gas dissolves in water where it produces a weak acid, carbonic acid (H2CO3), which lowers the pH value of sea water. This drop is quite small, but has caused significant changes in the ability of shell-forming creatures to deposit the calcium carbonate that largely makes up their shells. Without shells, they simply cannot survive, and food chains collapse.
Ozone depletion, however, can largely be seen as a success story, in that worldwide efforts have outlawed the production of the chemicals which caused it, and there is the possibility of a complete recovery of the ozone layer by the end of this century.
Nitrogen and phosphorus
Both nitrogen (N), and phosphorus (P), have been cycling through living organisms for as long as there has been life on earth. They are essential components of life, and especially of the proteins that constitute life. Phosphorus is present in minute quantities in some of earth’s rocks, but minute quantities are all that are needed for life.
Nitrogen is the principal component of the atmosphere. It is mostly converted into solid chemical form through being absorbed by bacterial species found, for example, living in nodules on the roots of leguminous plants.
Both these elements are incorporated into plant tissue and transfer to animals when the plants are eaten, or they are released into the soil when the plants die and rot. Thus, the two elements recycle continuously.
Early farmers soon realised that to collect animal (and human) waste to spread over their fields had the beneficial effect of increasing the next year’s crop yield. It harnessed and concentrated a naturally occurring process.
Industrialisation creates shortages
Problems began to arise with the massive social changes of the late 18th century, as millions of country dwellers were driven into the burgeoning industrial centres. These people needed food, which was brought in from the countryside. They also needed to dispose of their waste, but instead of this being returned to the land, it became a problem that was solved by the building of sewers, and by dumping the waste into our rivers and seas.
Having dumped so much natural nitrogen and phosphorous, there arose a serious and dire need to source artificial replacements. The current global usage of artificial nitrates exceeds 120 million tonnes. The planetary boundary committee felt that the maximum should be 35 million tonnes: thus the ‘safe’ limit has been exceeded nearly four-fold. For phosphorus. the current, although rapidly rising, usage is under 10 million tonnes, against a boundary limit of 11 million tonnes.
Global freshwater use
The world’s glaciers often act as summer freshwater reservoirs. Winter snow bulks them up and the summer’s slow melting allows for continuous supplies along the length of their rivers. Rapid melting has produced both uncontrollable flooding and, perhaps more significantly, left much-reduced water sources unable to meet traditional needs.
This is seen acutely in the Andes and the Himalayas. In Bangladesh, people at the ends of the rivers are presented with a monstrous challenge to their existence. Humans have only added to this problem by building dams upstream to harvest the scarcer supplies, exacerbating the crisis for those downstream.
A second natural source of fresh water lies in underground aquifers. These are generally vast tracts of porous rocks which may carry billions of tonnes of fresh water globally. This water is replaced naturally on an extremely long timescale of centuries or even millennia. Farmers desperate to irrigate their crops in times of drought, drill down into the aquifers and take what they need, but usually greatly exceeding the natural rainfall replacement rate.
The result is a dramatic depletion which often affects the very structure of the underlying rock layers. Earth tremors, landslides and land collapses result, with dire consequences for humanity and often a permanent loss of the resource.
Soil degradation and change of usage
Soil degradation is the subject of recent global studies highlighting our planet’s deterioration by the action of humanity. In 2016, the Intergovernmental Science Policy Platform on Biodiversity and Ecosystem Services (IPBES) released a global biodiversity study that warned that the human destruction of nature is rapidly eroding the provision of food and water, and the security of billions of people.
Species loss and species shift
Species have always ‘gone extinct’ but the rate of species extinction has rapidly increased over recent decades. This increase is purely due to the rapacious invasion by humans into previously untouched environments.
Before 1750 and Industrialisation, the natural rate of species loss was in the range of 0.1 to 1.0 species per million per annum. Scientists suggested that an SPB for this should be 10 species per million per annum. Shockingly, the current rate is actually 10 times that, at around 100 species per million lost every year – 1,000 times the natural rate.
Atmospheric aerosol loading
No ‘safe’ limits have been defined for aerosol loading because of the extreme complexity of this topic and the difficulty in making reliable measurements. Nevertheless, great concern has been expressed about the current levels of pollution in general and strenuous efforts need still to be made to reduce aerosol loading.
Paradoxically, some solutions to global heating actually propose releasing thousands of tonnes of specific aerosols, such as silver salts, into the upper layers of the atmosphere. Here, it is hoped, they would reflect the sun’s light and heat back into space, thus causing a small degree of planetary cooling. The process would need to be continued indefinitely, or perhaps even escalated, as artificial cooling would not address the urgency of the need to stop releasing CO2. Without that, the reliance on aerosols would only grow. Any currently unforeseen side-effects might cause the process to be halted, suddenly and disastrously releasing all the increased amounts of CO2.
Chemical pollution
Again, and for similar reasons as for aerosol loading, precise SPBs were not originally set, but the rough limits that were suggested have now been exceeded. The number of synthetic chemicals produced is in the tens of thousands. This does not include all the bizarre and largely unquantified compounds created as these chemicals interact, including high up in the stratosphere.
Even so, there can be no doubt that the spread of chemical pollution in the form of heavy metals, radioactivity and organic molecules represent one of the most serious threats to human, animal and plant life. Chemical pollution is one of the factors causing the much-increased loss of biodiversity.
The scourge of plastics is included in this category, including the microplastics readily ingested by the smallest of oceanic creatures, thereby becoming incorporated into every food chain. The dramatic reduction of the use of such materials in every walk of life is a vital necessity.
Other chemical pollutants include surplus pesticides draining into watercourses, and the spent drugs we metabolise and excrete. These find themselves in increasing concentrations in our water sources and our drinking water. These compounds share the potential to cause illness and damage to us and to all life on earth. Many of these substances are carcinogenic and others have been blamed for loss of fertility. In the wild, the inevitable result will be to increase the rate of extinction of species.
Conclusions and obligations
Climate change and other system changes do not happen in gradual, predictable steps. Rather, they take the form of sudden tipping points fed by positive feedback (or ‘amplifying’) mechanisms.
Polar ice is one area which should concern us most. As the ice disappears and is replaced by dark water, the poles heat up much more rapidly than the rest of the earth. Whether this will cause the great ice sheets to disappear completely is currently unknown. Should such a catastrophe occur, it will likely happen very fast, and ocean levels will rise too fast for humanity to do anything about it.
Warmer poles are causing the wholesale melting of vast areas of what has hitherto been permafrost. Some welcome this for releasing usable land, but under the permafrost lie possibly billions of tonnes of methane clathrates, which can be described as ice-cages containing methane. The melting of these will cause another disastrous tipping point as unimaginable amounts of methane will be released into the atmosphere. The volumes involved will make the belching of cattle seem trivial.
COP needs a more radical approach
The now yearly COP climate conferences have produced many long-term promises, but little by way of immediate deeds. Our leaders have demonstrated that they do not fully grasp what is at stake, nor how painful and difficult the decisions they must make. Anodyne promises and pious commitments are no longer sufficient. A radical rethink and a sustained, committed outcome to change traditional thinking and traditional practices is more vital than ever.
It is, of course, vital that we stop pumping CO2 into the atmosphere. We can only achieve this by stopping the use of fossil fuels. It is equally important that efforts should be redoubled to respect the SPBs, largely ignored by COP, in a criminally negligent and wasted opportunity.
Time to take action now
Many climate commentators have identified the 2020s as the most significant decade for action: what happens in the next few years will affect humanity for the long-term foreseeable future to extents greater than in any preceding decade.
The adverse changes and effects that we have instigated, and of which we are fully aware, will happen if we do nothing.
We simply cannot negotiate with the planet: we cannot bargain with nature. We cannot do deals to lessen these changes or lengthen timescales.
We have no choice but to act as our world tells us.
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