Systems Thinking: Unlocking A Complex Earth
July 28th, 2021
Earth is a complex, multi-system wonder! Just as the human body consists of multiple systems that all work in tandem to sustain human life, the Earth System is composed of multiple systems that sustain a vast quantity and variety of life forms. These subsystems are: the lithosphere, also called the geosphere (rocks, soil, molten rock, fossil fuels), the hydrosphere (oceans, rivers, lakes, groundwater, etc.), the atmosphere (tropo-, strato-, meso-, thermo-, magneto-, and exo-sphere), the biosphere (oceanic and terrestrial plants and animals), and some climatological conventions separate out the cryosphere (ice and snow).
To understand how the Earth System operates, we need to understand “systems thinking”. It helps to break Earth down into “stocks” (nouns) and “flows” (verbs). A stock/reservoir is any entity that can be filled or depleted, like a bathtub filling or draining. We just listed the Earth System stocks: the lithosphere, hydrosphere, biosphere, atmosphere, and cryosphere. We concern ourselves with how materials and energy flow throughout the system, i.e. how water, nitrogen, carbon, phosphorous, and other elements of key interest move throughout the different spheres. This means that the flows/fluxes are actions, or processes through which materials can move from one sphere to another.
Most of us confidently understand the hydrological cycle. Evaporation is the flux that moves water from the hydrosphere and lithosphere (in the form of soil moisture) up into the atmosphere. Precipitation is the flux that moves water back down from the atmosphere to the hydrosphere and lithosphere. Condensation is another flux/process in the hydrological cycle, but in this example, it does not transfer water from one sphere to another, but occurs solely within the atmosphere.
Systems Thinking also requires us to understand residence times and time lags, nonlinear relationships, as well as feedback loops. Residence times refer to how long a material remains within a stock. Sticking to our hydrological cycle example, here’s how long a water molecule stays, on average, within a given stock: Oceans/Seas (at a depth of 2,500 m) 4,000 years, Lakes/Reservoirs 10 years, Swamps 1-10 years, Rivers 2 weeks, Soil Moisture 2 weeks-1 year, Groundwater (120 m) 2 weeks-10,000 years, Ice Caps/Glaciers 10-1,000 years, Atmospheric Water 10 days, Biospheric Water 1 week (https://www.spokaneaquifer.org/the-aquifer/what-is-an-aquifer/residence-time-of-groundwater/).
For each of the cycles we’ll cover (rock, carbon, nitrogen, etc.) there will be different residence times for the material of interest. I cannot over-emphasize how important it is to consider the residence time of a given material. For some cycles, the residence time is hundreds of millions of years!
The lag time we experience every day is the diurnal (daily) temperature lag. Noon is when we receive the most sunlight, but peak daytime temperatures occur several hours after noon. That’s because air warms (and cools!) faster than water, dirt, and rock. The earth continues to radiate heat well past noon, maintaining warm temperatures. Another example is seasonal ocean temperatures: northern hemisphere oceans tend to reach their warmest temperature in August and September, 2-3 months after the summer solstice! (https://www.seatemperature.org/atlantic-ocean). This is due to the massive heat capacity of water: it takes 4,184 joules to warm 1 kilogram of water by 1°C (by comparison, it takes 385 joules to warm 1 kilogram of copper 1°C) (https://www.usgs.gov/special-topic/water-science-school/science/specific-heat-capacity-and-water?qt-science_center_objects=0#qt-science_center_objects). Thus, the ocean continues to warm well beyond the longest day of the year.
Exponential growth is the most crucial nonlinear relationship to understand in the Earth system. Human population is one example: it took about 12,000 years to reach 1 billion people (in the year 1800), and then it only took 120 years to grow to 7.9 billion (https://ugc.berkeley.edu/background-content/population-growth/).
Lastly: feedback loops. Positive feedback loops amplify or increase the effect of a forcing, negative feedback loops dampen or decrease the effect of a forcing. A positive feedback: as sea ice melts, dark ocean water is revealed. Dark ocean water absorbs sunlight (as opposed to reflective white ice and snow), and so absorbs more heat, which melts more ice, on and on and on. Right now, permafrost in the arctic is melting and releasing methane, a greenhouse gas 30 times more powerful than CO2 but with 1/10th the atmospheric residence time (https://royalsocietypublishing.org/doi/10.1098/rsta.2014.0423).
This heats the planet, which melts more permafrost, which releases more methane, etc. Same with wildfires: combustion moves carbon from the biosphere to the atmosphere, and the train runs away.
Canary in the coal mine? Or arctic tern on the burning permafrost graveyard . . .?
Image sourced from: https://ugc.berkeley.edu/wp-content/uploads/2016/01/Human-Pop-Growth-2019.jpg
