- Why Local Food Systems Can Support Healthier Communities - September 8, 2025
- Lessons From the Past on Managing Water Wisely - September 7, 2025
- Cycles in Nature That Keep the Planet in Balance - September 4, 2025
The Water Cycle Under Stress
Air temperatures over land in 2024 were 1.2°C warmer than the average between 1995 and 2005, when the temperature was already 1°C higher than at the start of the industrial revolution, affecting about four billion people across 111 countries – half of the world’s population. The 2024 Global Water Monitor Report shows how these changes are driving the global water cycle to new climate extremes and contributing to ferocious floods and crippling droughts. Record-high monthly rainfall totals were achieved 27% more frequently in 2024 than at the start of this century, while record-lows were 38% more frequent. Climate change is likely causing parts of the water cycle to speed up as warming global temperatures increase the rate of evaporation worldwide, causing more evaporation which leads to more precipitation, on average.
Water-related disasters killed more than 8,700 people, displaced 40 million people and caused economic losses exceeding US $550 billion. Rainfall records are being broken with increasing regularity, with daily rainfall records achieved 52 per cent more frequently in 2024 than at the start of this century.
Carbon’s Double Life
Over the long term, the carbon cycle seems to maintain a balance that prevents all of Earth’s carbon from entering the atmosphere or being stored entirely in rocks, helping keep Earth’s temperature relatively stable, like a thermostat. Coal and other fossil fuels are a convenient source of energy, but when they are burned, the stored carbon is released into the atmosphere, altering the balance of the carbon cycle and changing Earth’s climate. Excess carbon in the atmosphere warms the planet and helps plants on land grow more, while excess carbon in the ocean makes the water more acidic, putting marine life in danger. It is significant that so much carbon dioxide stays in the atmosphere because CO2 is the most important gas for controlling Earth’s temperature, absorbing infrared energy emitted by Earth and re-emitting it.
Human activity is altering these cycles faster and more dramatically than nature can compensate, overwhelming the carbon cycle with greenhouse gases. Oceans are acidifying, forests are shrinking, and species are disappearing.
Nitrogen’s Transformation Under Ocean Acidification
Ocean acidification, arising from the influx of anthropogenically generated carbon, poses a massive threat to ocean ecosystems. When pH was experimentally reduced at multiple locations in the Atlantic and Pacific Oceans, microbial nitrification rates decreased in every instance, with experimental acidification decreasing ammonia oxidation rates by 38% at Bermuda and 36% at Hawaii. Ocean acidification could reduce nitrification rates by 3–44% within the next few decades, affecting oceanic nitrous oxide production and fundamentally altering nitrogen cycling in the sea. Diazotrophic nitrogen fixation is likely enhanced by 29% ± 4% under ocean acidification, while nitrification processes were reduced by a factor of 29% ± 10%.
Acidification of coastal waters can inhibit the rate of nitrification while promoting the production of nitrous oxide, a potent greenhouse gas that is over 300 times stronger in trapping heat than CO2. Increased loading of ammonium in estuarine and coastal waters alleviated the inhibitory effect of acidification on nitrification rates but intensified the production of nitrous oxide, thus accelerating global climate change.
The Oxygen Factory
Plants, algae, and cyanobacteria release oxygen during photosynthesis, while animals and other organisms consume it through respiration, converting it back into carbon dioxide. This cycle also involves the oceans, where tiny phytoplankton produce much of the Earth’s oxygen supply – more than all the forests combined. Deep in the Earth, oxygen interacts with minerals, and in the upper atmosphere, it helps form the ozone layer that shields life from harmful radiation. Disruptions to this cycle – such as deforestation, ocean acidification, and climate change – can reduce the planet’s oxygen-producing capacity.
Phytoplankton convert sunlight and carbon dioxide into chemical energy, forming the base of the aquatic food web and transferring about 10 billion metric tons of carbon from the atmosphere to the deep ocean annually. Despite being the most abundant element in Earth’s atmosphere, nitrogen is the limiting factor for phytoplankton growth in much of the ocean, especially in the Arctic Ocean.
Milankovitch’s Orbital Dance
A century ago, Serbian scientist Milutin Milankovitch hypothesized that long-term changes in Earth’s position relative to the Sun are a strong driver of Earth’s climate, with these cyclical orbital movements causing variations of up to 25 percent in incoming solar radiation at Earth’s mid-latitudes. Over time, the pull of gravity from Jupiter and Saturn causes Earth’s orbit to vary from nearly circular to slightly elliptical, with about 23 percent more solar radiation reaching Earth at our planet’s closest approach to the Sun each year. Currently, Earth’s eccentricity is very slowly decreasing and approaching its least elliptic state in a cycle that spans about 100,000 years. The angle Earth’s axis of rotation is tilted as it travels around the Sun is known as obliquity, and obliquity is why Earth has seasons.
Our lives literally revolve around cycles, including natural ones such as the change of the seasons, annual animal migrations or the circadian rhythms that govern our sleep patterns. Cycles also play key roles in Earth’s short-term weather and long-term climate.
Energy’s Endless Flow
Every natural cycle on Earth is ultimately driven by energy – from the sun and from within the Earth, with the energy cycle making all the others possible. Sunlight powers photosynthesis and drives the water cycle, while geothermal energy stirs the mantle and fuels volcanic activity. Sunlight is the primary driver of Earth’s climate and weather, with roughly 342 watts per square meter of energy from the Sun reaching Earth on average. About one-third of that energy is reflected back into space, and the remaining 240 watts per square meter is absorbed by land, ocean, and atmosphere, with the exact amount depending on the reflectivity of the atmosphere and surface.
Energy flows, not recycles – once used, it disperses. The way energy moves through ecosystems – from the sun, to plants, to herbivores, to predators, and finally to decomposers – shapes the very structure of life.
The Arctic’s Complex Nitrogen Web
Although the Arctic Ocean is small, its shallow shelves and highly productive coastal waters make it an important component of global biogeochemical cycling, especially of nitrogen. Among the most important sources of nitrogen to the Arctic Ocean are horizontal flows of water from other oceans – most notably the Atlantic, which transports almost 4 times as much water into the Arctic as the Pacific. Nitrogen takes many forms in the ocean, including numerous organic and inorganic species that can be either dissolved or particulate, with dissolved nitrate being the primary form on the Arctic surface in early spring before phytoplankton consume it and turn to recycled ammonium later in the season. More frequent Arctic wildfires will mean greater carbon and nitrogen emissions, while rising ocean CO2 levels contribute to ocean acidification that is likely to affect nitrification.
When Droughts Meet Floods
While some parts of the world experienced major flooding in 2024, others endured crippling drought, with record low river levels in the Amazon Basin cutting off transport routes and disrupting hydropower generation. Wildfires driven by hot and dry weather burned through more than 52,000 square kilometres in September alone, releasing vast amounts of greenhouse gases. In southern Africa, a severe drought reduced maize production by more than 50 per cent, leaving 30 million people facing food shortages as farmers were forced to cull livestock. Warmer temperatures have led to increased drying of the land surface in some areas, with the Palmer Drought Severity Index showing that the Sahel region of Africa has been experiencing harsher drought conditions from 1900 to 2002.
With more evaporation, there is more water in the air so storms can produce more intense rainfall events in some areas. Global climate change will affect the water cycle, likely creating perennial droughts in some areas and frequent floods in others.
The Planck Response Safety Valve
Scientists have long known that as Earth warms, it is able to restore its temperature equilibrium through a phenomenon known as the Planck Response, which is an overall increase in infrared energy that Earth emits as it warms. The response acts as a safety valve of sorts, allowing more of the accumulating heat to be released through the top of Earth’s atmosphere into space. Their work reveals in new detail how Earth cools itself back down after a period of natural warming. Natural climate cycles alone are insufficient to explain the global warming observed over the last century.
Greenhouse Gas Thermodynamics
Globally, thermodynamics explains an increase in atmospheric water vapor with warming of around 7%/°C near to the surface, while global precipitation and evaporation are constrained by the Earth’s energy balance to increase at roughly 2-3%/°C. Thermodynamic increases in atmospheric moisture fluxes amplify wet and dry events, driving an intensification of precipitation extremes, with the rate of intensification deviating from simple thermodynamic response due to in-storm and larger-scale feedback processes. Changes in atmospheric circulation in response to radiative forcing and evolving surface temperature patterns are capable of dominating water cycle changes in some regions. The direct impact of human activities on the water cycle through water abstraction, irrigation, and land use change is already a significant component of regional water cycle change.
Nature’s Survival Systems at Risk
Natural cycles are Earth’s survival systems that depend on balance, having kept the planet habitable for millions of years through ice ages, asteroid strikes, and tectonic upheavals. But today, something different is happening as human activity is altering these cycles faster and more dramatically than nature can compensate. The water cycle is thrown off by melting ice and changing rainfall, while nitrogen and phosphorus cycles are overloaded by agriculture. We are not separate from these cycles – we are part of them. Every breath, every bite of food, every drop of water we use connects us to Earth’s natural rhythms.
Climate Feedback Loops Intensify
New research indicates that a positive feedback loop will likely occur, with international teams conducting field and laboratory experiments to determine how ocean acidification affects nitrification processes and nitrous oxide emissions in estuarine and coastal waters. Both ammonia-oxidizing archaea and bacteria produced more nitrous oxide when stimulated by acidification, with metagenomics research indicating that microbes may adjust gene expression under acidification stress, reducing nitrification rates and increasing nitrous oxide production. Further acidification in estuarine and coastal waters may alter the nitrogen cycle and accelerate global warming by stimulating nitrous oxide emissions. Even if we stopped releasing greenhouse gases today, the planet would continue warming for decades, but by acting now we still have time to avoid the worst impacts.
These intricate natural cycles that have sustained life on Earth for billions of years now face unprecedented pressure from human activity. Each disruption creates a ripple effect through interconnected systems, threatening the delicate balance that has made our planet a haven for life. Understanding these cycles isn’t just academic curiosity – it’s our roadmap for survival in an era of rapid environmental change.
