Do you know the boundaries of the planet we call “home”?

This post is the official first of the series “Know your planetary boundaries”, and it’ll discuss one of the planetary processes known to us all: climate change. We’ll discuss what the transgression of the climate change planetary boundary means for the living biosphere and if and how we can return to a safe state. But before we go there, know there is much more to this topic; check out our previous posts for a short overview of all planetary boundaries and more information on climate tipping points & feedback loops, and the human climate niche.

Climate change: a planetary boundary

In the mid-2000s, a team of scientists united behind a single goal: define Earth’s boundaries for a “safe operating space for humanity”. They mapped nine processes essential to maintaining the Earth’s atmosphere, oceans and ecosystems in the delicate balance that has allowed human civilisations to flourish. One of these processes is known to us all, climate change, and it’s measured through the concentration of carbon dioxide (CO2) in the atmosphere and the amount of heat the Earth absorbs.

There is no denying that we have left the safe and just threshold of 1°C warming behind us and that Earth’s natural systems can no longer keep up with our demands. After decades of fossil fuel burning and careless disregard for the environment, we are now getting awfully close to crossing the tipping points of systems that regulate the state of our climate.

Two of these systems, the Greenland and Antarctic Ice sheets, play an essential role in cooling the planet but are rapidly disappearing due to global warming. Ice-core data suggests the planet was largely ice-free until atmospheric carbon dioxide concentrations fell below 450 ppm (±100 ppm – the number of carbon dioxide molecules per million molecules of dry air in the atmosphere), indicating a danger zone for ice sheets above 350 ppm and a high risk of collapse beyond 450 ppm. With the current CO2 level of 417 ppm, one thing is for sure: The world is on thin ice.

In addition to CO2, there are other human forces driving climate change – think greenhouse gas emissions such as methane (CH4) and nitrous oxide (N2O). Most emissions are transparent to incoming solar radiation but partially opaque to the infrared radiation the Earth’s surface emits back. With more energy incoming than outgoing, the Earth’s atmosphere warms up – this is called Radiative Forcing.

Earth’s systems have helped us immensely by taking up most of the heat we have generated, but it has come at a high cost; it has resulted in ocean warming, ice loss, sea level rise, permafrost thawing, forest die-back, biodiversity loss, and an increase in extreme weather events. We currently generate +2.91 W/m2 of radiative forcing (the energy imbalance averaged over the Earth’s surface) annually, but beyond +1.0 W/m2, carbon sinks already start to weaken. Yes, we’re clearly heading towards a hothouse state.

Earth’s hydrological cycle out of whack

It’s greenhouse gases like water vapour that prevent the Earth from turning into a giant ball of ice. But now that we have pushed the climate system out of balance and the Earth is heating up at an unprecedented rate, evapotranspiration is also increasing. As a result, atmospheric water vapour increases by 1 to 2% per decade, which, in turn, drives up global temperatures even more – it’s a positive feedback loop!

Climate change is wreaking havoc on the global water cycle, causing wet regions to become wetter and dry regions to become drier. Due to increased air humidity, more energy is stored in the atmosphere, leading to more frequent and intense extreme weather events. In most areas, wet-bulb temperatures rise, leading to more heat-related diseases and vegetation degradation. The knock-on impacts are endless.

Climate change is a water crisis

Climate change affects all regions globally, but the impacts are highly variable and unevenly spread. Projections show that some areas will suffer from more prolonged droughts, others from more frequent and intense storms and floods, and some will experience both. One thing is for sure: climate change is felt most directly through water.

Among the most dramatic evidence of climate change are the rivers and lakes that are drying up and the mountain glaciers that are disappearing. Due to rising evapotranspiration, a lack of precipitation, and the increasing demand for irrigation, the water table is decreasing in many areas. As a result, we see rivers and lakes seeping away, forests retreating, vegetation becoming more vulnerable to fire, biodiversity collapsing, land emissions increasing, and food production falling.

The future of the climate niche

As our planet heats up, animals (incl. humans) and plants (incl. crops) are pushed outside their climate niches. In many areas worldwide, conditions become too humid, hot or dry for human societies and ecosystems to thrive, as these conditions are associated with higher death rates and lower food production.

The area experiencing unprecedented heat (Mean Annual Temperatures, MAT ≥ 29°C) expands rapidly. Such high temperatures are linked to decreased labour productivity and cognitive performance, adverse pregnancy outcomes, increased spread of pests and infectious diseases, reduced crop yield, and increased migration, state fragility, conflict, morbidity and mortality. It’s more than a climate crisis;
it’s a polycrisis.

Oceans are our lifeline

The oceans and polar areas are not spared when the atmosphere heats up. In fact, they are actively buffering global warming, and as a result, we observe significant changes in perennial ice cover and the ocean’s chemistry and temperature. And when water warms and ice melts, the sea rises. Even a few centimetres of rise can devastate coastal communities and habitats through erosion, flooding, and (salt) contamination – but we’re facing much more than that.

Current temperature, chemistry, and sea level changes drive the degradation of mangroves, seagrasses, kelp forests, marches and coral reefs. These coastal ecosystems protect hundreds of millions of people against floods and storms, and together, they store more carbon than all terrestrial forests combined. Safeguarding and restoring these ecosystems is of vital importance.

Getting back into a safe operating space for humanity

Climate change is only one of the boundary systems that can potentially drive the Earth’s climate into a completely new state. We should call the climate crisis what it is: a planetary crisis. If we want to get out of this mess – and we should – we must look at the interconnectedness of planetary systems and their interactions because they can all have devastating knock-on effects on the living world.

The impacts of climate change have the potential to cause system-wide failure. If we want to address the climate emergency, rapid biodiversity loss, and the freshwater, nutrients and pollution crises, and at the same time solve social injustices, we will need to start thinking in systems and stop addressing Earth systems and well-being separately.

We need a better plan for our planet and everything living on it. It’s time for systemic change, to address the root causes instead of the symptoms of the problems we’re facing, and to start understanding the underlying patterns and dynamics underpinning them. We must get serious about the planetary crisis and stop focusing exclusively on Net Zero strategies. Yes, we need to reach Net Zero by 2050, but we must also drastically reduce our energy and resource consumption, radically rethink our food system and how we use land, do everything to keep the carbon stability in the ocean and terrestrial ecosystems intact, and adopt an economic system that is regenerative and distributive by design.

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Next up is the planetary boundary biosphere integrity!