First-year courses · Sciences

Intro environmental science: cycles, climate and energy

Environmental science flashcards: energy flow, carbon and nitrogen cycles, the greenhouse effect, IPCC findings, energy units and sustainability terms.

41 cards5 topicsAbout 15 minutes a roundTypical first-year introduction to environmental science

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About this deck

This deck is for students in a first-year environmental science or environmental studies course, and for science students taking one as an elective. It covers how energy moves through ecosystems, the carbon, nitrogen, phosphorus and water cycles, the physical basics of the climate system (greenhouse effect, albedo, radiative forcing and feedbacks), key observations summarized by the Intergovernmental Panel on Climate Change (IPCC), energy sources and units, and the vocabulary of sustainability and environmental assessment.

Climate figures in this deck come from the IPCC Sixth Assessment Report (AR6) Synthesis Report summary for policymakers, and the explanations follow the public science pages of NASA and the Government of Canada listed below. Assessment reports are updated over time, so check the latest report before quoting a figure in an assignment, and cite the report, not a flashcard.

You should know high school biology and chemistry: photosynthesis and respiration, the idea of a chemical cycle, and basic unit conversions. To study, draw each cycle from memory as a box-and-arrow diagram, labelling reservoirs and the processes that move material between them. For the energy cards, redo the arithmetic and keep units attached to every number.

Common mistakes: confusing weather (short-term conditions) with climate (long-term statistics); treating the greenhouse effect itself as a problem rather than a natural process that human emissions are strengthening; and mixing up power (kW) with energy (kWh).

Before you start: High school biology and chemistry, and comfort with unit conversions and percentages.

All 41 cards

Cover the definitions with a sheet of paper and test yourself, or use the study modes above.

Ecosystems and energy flow

Ecosystem: A community of living organisms interacting with each other and with their non-living surroundings, linked by energy flow and nutrient cycling.Example: A boreal wetland: mosses, insects, birds, water, peat and the microbes that decompose them.
Trophic level: An organism's position in a food chain: producers first, then primary consumers, secondary consumers and so on.Example: Grass (1), hare (2), lynx (3).
Ten percent rule: A rough guide that only about 10% of the energy at one feeding level becomes biomass at the next; the rest is lost mostly as heat.Example: 10,000 kJ in producers supports about 1000 kJ in herbivores and 100 kJ in carnivores that eat them.
Gross and net primary productivity: GPP is the total energy fixed by producers through photosynthesis; NPP is what remains after their own respiration, NPP = GPP - R.Example: GPP 2000 g C/m^2/yr minus respiration 800 gives NPP = 1200 g C/m^2/yr.
Biodiversity: The variety of life at the genetic, species and ecosystem levels.Example: A forest with many tree species and genetically varied populations rates highly.
Carrying capacity: The largest population of a species that an environment can support over the long term with its available resources.Example: A lake's fish population levels off as food and oxygen become limiting.
Ecosystem services: Benefits people receive from nature, including provisioning (food, water), regulating (flood control, pollination), cultural and supporting services.Example: Wetlands that store floodwater protect towns downstream.

Biogeochemical cycles

Carbon cycle: The movement of carbon among the atmosphere, oceans, living things, soils and rocks through photosynthesis, respiration, decomposition, ocean exchange and combustion.Example: Burning fossil fuels moves carbon stored for millions of years in rock into the atmosphere as CO2.
Carbon sink and source: A sink takes up more carbon than it releases over a period; a source releases more than it takes up.Example: A growing forest acts as a sink; the same forest burning in a wildfire acts as a source.
Nitrogen fixation: Conversion of unreactive atmospheric N2 into forms organisms can use, such as ammonia, by bacteria, lightning or the industrial Haber-Bosch process.Example: Rhizobium bacteria in root nodules of peas and clover.
Nitrification and denitrification: The first is bacterial conversion of ammonium to nitrite and nitrate; the second returns nitrate to N2 gas (and some N2O) under low oxygen.Example: Waterlogged soils lose nitrogen back to the air this way.
Phosphorus cycle: The slow cycling of phosphorus mainly through rocks, soil, water and organisms; unlike carbon and nitrogen it has no significant gas phase.Example: Weathering of phosphate rock releases phosphorus that plants absorb from soil.
Water cycle: Continuous movement of water by evaporation, transpiration, condensation, precipitation, infiltration and runoff, driven by solar energy and gravity.Example: Evapotranspiration from crops returns water vapour to the atmosphere.
Residence time: The average time a substance spends in a reservoir, equal to the amount in the reservoir divided by the flow in or out.Example: A lake holding 1000 units of water with an outflow of 50 units per year: 1000/50 = 20 years.
Eutrophication: Over-enrichment of water with nutrients, especially nitrogen and phosphorus, causing algal blooms that can lead to oxygen depletion when they decay.Example: Fertilizer runoff has contributed to recurring algal blooms in Lake Erie.

Climate system

Weather versus climate: The first is the state of the atmosphere over hours to days; the second is the long-term statistics of those conditions, usually averaged over 30 years or more.Example: One cold week in Edmonton is weather; the average January temperature from 1991 to 2020 describes climate.
Greenhouse effect: Warming of a planet's surface because gases in the atmosphere absorb outgoing infrared radiation and re-emit part of it back downward.Example: Without it, Earth's average surface temperature would be well below freezing.
Greenhouse gases: Atmospheric gases that absorb and emit infrared radiation, mainly water vapour, carbon dioxide, methane, nitrous oxide and fluorinated gases.Example: N2 and O2, which make up most of the air, absorb very little infrared.
Global warming potential: A factor comparing the warming caused by a mass of a gas with the same mass of CO2 over a set period, often 100 years; used to compute CO2-equivalent.Example: Methane's 100-year value is roughly 27 to 30 in AR6; using 28, 10 t of methane is about 280 t CO2e.
Albedo: The fraction of incoming sunlight a surface reflects, from 0 (absorbs all) to 1 (reflects all).Example: Fresh snow reflects most sunlight (often 0.8 or more); open ocean reflects under 0.1.
Radiative forcing: A change in the balance between incoming and outgoing energy at the top of the atmosphere caused by a driver such as greenhouse gases or aerosols, in W/m^2; positive values warm.Example: Added CO2 gives a positive value; reflective sulphate aerosols give a negative one.
Climate feedback: A process that amplifies (positive) or dampens (negative) an initial change in climate.Example: Ice-albedo: warming melts ice, exposing darker surfaces that absorb more sunlight and warm further.
Ocean acidification: The decrease in seawater pH as the ocean absorbs CO2, which forms carbonic acid and reduces carbonate ions that shell-building organisms need.Example: Oyster hatcheries on the Pacific coast have been affected by more acidic upwelled water.
Observed global warming (IPCC AR6): The IPCC AR6 Synthesis Report states global surface temperature was about 1.09 C higher in 2011 to 2020 than in 1850 to 1900, and attributes the warming unequivocally to human activities.Example: The assessed range for that figure is 0.95 to 1.20 C.
Atmospheric CO2 level (IPCC AR6): The AR6 Synthesis Report gives an atmospheric CO2 concentration of about 410 parts per million in 2019, higher than at any time in at least 2 million years.Example: Pre-industrial levels are commonly given as about 280 ppm, so 410 is roughly 46% higher.
Observed sea level rise (IPCC AR6): Global mean sea level rose by about 0.20 m between 1901 and 2018, according to the AR6 Synthesis Report, from melting land ice and thermal expansion of warming water.Example: The assessed range is 0.15 to 0.25 m.
Remaining carbon budget: The total net CO2 that can still be emitted while keeping warming below a given level with a stated likelihood.Example: AR6 estimates about 500 Gt CO2 from the start of 2020 for a 50% chance of limiting warming to 1.5 C.
Climate change mitigation: Actions that reduce greenhouse gas emissions or increase their removal from the atmosphere.Example: Switching to low-carbon electricity, improving building efficiency, protecting carbon-rich peatlands.
Climate change adaptation: Adjustments that reduce harm from current or expected climate effects or take advantage of new conditions.Example: Raising flood defences, changing crop varieties, updating building codes for heat.

Energy

Renewable and non-renewable energy: The first group is replenished naturally on human timescales (solar, wind, hydro, geothermal, biomass); the second is finite stocks (coal, oil, gas, uranium).Example: Hydroelectricity supplies most of the electricity in Quebec, Manitoba and British Columbia.
Fossil fuels: Coal, oil and natural gas, formed over millions of years from buried organic matter; burning them releases CO2.Example: Burning methane: CH4 + 2 O2 gives CO2 + 2 H2O.
Kilowatt-hour: A unit of energy equal to 1 kW of power used for 1 hour, which is 3.6 MJ.Example: 5 kWh = 5 x 3.6 = 18 MJ.
Capacity factor: Actual energy produced over a period divided by what the plant would produce running at full power the whole time.Example: 100 MW wind farm at 30%: 100 x 8760 h x 0.30 = 262,800 MWh per year.
Energy conversion efficiency: Useful energy output divided by energy input, as a percentage; the rest is mostly lost as heat.Example: A plant converting 1000 MJ of fuel energy into 350 MJ of electricity is 35% efficient.
Life cycle assessment: An analysis of a product's environmental impacts from raw material extraction through manufacture, use and disposal.Example: Comparing the total emissions of an electric and a gasoline car including battery production.

Sustainability

Sustainable development: Development that meets the needs of the present without compromising the ability of future generations to meet their own needs (the 1987 Brundtland Report definition).Example: Managing a forest so harvests do not exceed regrowth.
Ecological footprint: An estimate of the biologically productive land and water area needed to supply what a person or population consumes and absorb its wastes.Example: Usually expressed in global hectares per person.
Tragedy of the commons: The tendency for a shared, open-access resource to be overused because each user gains the full benefit of extra use but bears only part of the cost.Example: Overgrazing a shared pasture.
Circular economy: An economic model that keeps materials in use through reuse, repair, remanufacturing and recycling, reducing waste and new extraction.Example: Refurbishing returned phones for resale.
Environmental impact assessment: A formal process for identifying and evaluating the likely environmental effects of a proposed project before a decision is made.Example: Canada's federal Impact Assessment Act sets out such a process for designated projects.
Precautionary principle: Where there are threats of serious or irreversible damage, lack of full scientific certainty should not be used as a reason to postpone cost-effective preventive measures.Example: Limiting use of a new chemical while studies of its effects continue.