Explain how climate change, human activity, invasive species and extinction reduce biodiversity, describe feedback loops between sunlight, ocean, atmosphere and biosphere, and use data to predict and lessen impacts

Learning goal: Explain how heat retention from increasing atmospheric greenhouse gases poses challenges for species; describe the feedback loops between sunlight, the ocean, the atmosphere and the biosphere; compare historical and recent greenhouse gas levels and relate them to climate change and its impact on biodiversity; use data and models to predict how changes reshape the ranges and distributions of species; draw and label a biogeochemical cycle and identify the parts of it influenced by climate change; identify Anthropocene effects and the causes of accelerated extinction; describe the characteristics and impacts of invasive species; and list local impacts and adaptation strategies in Ohio.

Equilibrium, disturbance and the loss of diversity. An ecosystem maintains equilibrium through small fluctuations in its living and nonliving components. Significant fluctuations, natural or human-caused, can produce long-term alterations and ultimately a loss of biodiversity. Humans are a biotic factor in ecosystems and can change the critical variables of many systems at once; several changes happening simultaneously stress ecosystems more than any one alone. Extreme events, such as prolonged drought, floods or the introduction or removal of species, can alter an ecosystem's functions for the long term. Ohio's standard cites estimates that the current rate of extinction is at least 100 to 1,000 times the background rate seen in the fossil record (other assessments give tens to hundreds of times, depending on the method and the groups of organisms counted), a rate that signals severe and widespread disequilibrium. This lesson examines the causes.

Greenhouse gases and heat retention. Sunlight reaches Earth mostly as visible light, warms the surface, and the surface radiates the energy back as infrared. Certain gases in the atmosphere, chiefly water vapor, carbon dioxide, methane and nitrous oxide, absorb infrared and re-radiate part of it downward, so the surface is warmer than it would be without them. This is the greenhouse effect, and it is why Earth is habitable. The change of the last two centuries is in the amount. Air trapped in ice cores shows carbon dioxide near 280 parts per million for thousands of years before industrialization; direct measurements at Mauna Loa Observatory in Hawaii have averaged more than 420 parts per million in every year since 2023 (the global average passed 420 in 2024), higher than at any time in the ice-core record, and the rise tracks the burning of coal, oil and gas and the clearing of forests. Averaged over the decade 2011 to 2020, global surface temperature was about 1.1 degrees Celsius above the late 1800s, and several recent single years have been warmer still. Ohio's standard describes rising mean temperature as increasing the variance of weather; more precisely, a warmer mean makes hot extremes more frequent even if variability stays the same, and a warmer atmosphere holds more water vapor, so heat waves and heavy rains in particular, and droughts in some regions, become more frequent and severe, affecting biotic and abiotic factors together.

Feedback loops among sunlight, ocean, atmosphere and biosphere. Climate depends on loops in which a change feeds back on itself. Ice and snow reflect sunlight; warming melts them, exposing darker water and ground that absorb more sunlight, causing more warming: a positive feedback. Warmer air holds more water vapor, itself a greenhouse gas: positive. The ocean absorbs both heat and carbon dioxide, slowing atmospheric change: a negative feedback for the atmosphere, but the absorbed carbon dioxide forms carbonic acid and lowers ocean pH, which harms organisms that build shells and skeletons of calcium carbonate. Plants take up more carbon dioxide when it is more abundant, a negative feedback, but drought, fire and thawing permafrost release stored carbon, positive feedbacks. Clouds both reflect sunlight and trap infrared, and their net effect is one of the harder questions in climate science. The biosphere is inside all of these loops: forests, soils, plankton and coral reefs move carbon, water and energy, and their changes change the climate that changes them.

The carbon cycle and where climate change touches it. Carbon moves from the atmosphere into plants and algae by photosynthesis, through food webs as organisms eat, back to the atmosphere by respiration and decomposition, into the ocean by dissolving and into rock and fossil fuels by burial over long times. Burning fossil fuels and clearing forests move carbon from long-term stores into the atmosphere far faster than natural processes remove it. Climate change influences several parts of the cycle: warmer soils and waters speed respiration and decomposition, thawing permafrost releases carbon dioxide and methane, warmer oceans hold less dissolved gas, and more frequent fires return forest carbon to the air. A labeled diagram of this cycle, marking each of these influences, is a model students should be able to draw for the water and nitrogen cycles as well.

Effects on species and biodiversity. Every species tolerates a range of temperature and moisture. As climates warm, suitable conditions shift toward the poles and up mountainsides, and species that can move follow them; those that cannot move, or that run out of mountain, decline. Data-driven models combine a species' tolerances with climate projections to predict its future range. Timing also shifts: plants flower and insects emerge earlier, and if a bird's migration does not shift with them, chicks hatch after the food peak. In the ocean, buoy and satellite temperature records show warming that has driven cold-water fish and shellfish northward and has bleached coral reefs, which expel the algae that feed them when water is too warm for too long. Ocean acidification weakens shells and reef skeletons. In dry regions, desertification spreads as rainfall falls and soils degrade. A worked prediction in the prose: a hypothetical salamander lives on Ohio hillsides at elevations where summer highs stay below 30 degrees Celsius. If summers warm by 2 degrees, the lowest band of its range becomes too hot, and because Ohio's hills are low, there is little higher ground to retreat to; the model predicts a contraction of range and a fall in population, and the response is to protect cool, shaded ravines where the microclimate lags the regional warming.

Ohio's climate and local impacts. Weather records for Ohio show rising average temperatures, wetter years and more of the rain falling in heavy downpours. Local environmental impacts include increased flooding, shoreline erosion along Lake Erie during high-water years, a northward shift in plant hardiness zones, so that gardeners' planting dates and the trees that thrive have changed, and periods of drought in some summers. Farmers, planners and the Ohio Department of Natural Resources are adapting with strategies such as changed pest control as insect ranges expand, water-supply planning, crop rotations and cover crops that hold soil and water, and stormwater management that slows runoff. Projects using real-time data from these sources can evaluate which strategies work.

Anthropocene effects, extinction and invasive species. Human activity now reshapes the planet enough that some scientists propose a new geological epoch named for it. Beyond climate, Anthropocene effects include urbanization and habitat loss, dams, acid rain, ozone depletion, leaching from landfills, thermal and light pollution, and the global growth of the human population, which passed 8 billion in November 2022 (United Nations) after hovering below a billion for most of the last 10,000 years. Domestication and selective breeding have narrowed the genetic diversity of crops and livestock: commercial apples are grafted clones of a few varieties, and many dog breeds descend from small founding groups. Recent extinctions are categorized by cause: habitat loss, overharvesting, invasive species, pollution and climate change, often several at once. Losing a keystone species, one whose effect on the community is large relative to its numbers, can unravel a food web. Zoos, seed banks and botanical gardens conserve species and support reintroductions, but they hold small populations prone to inbreeding and cannot replace functioning ecosystems; de-extinction proposals raise questions of ecological role, ethics and cost. Invasive species, treated in the ecosystem lesson, are among the leading causes of extinction on islands and in lakes, and warming extends the ranges of disease vectors such as mosquitoes and ticks, increasing human disease. Herbicide-resistant weeds in fields planted with herbicide-tolerant crops and antibiotic-resistant microbes are two faces of the same natural selection.

Misconceptions. "The greenhouse effect is bad" confuses a natural process with its recent strengthening. "A cold winter disproves warming" confuses weather with climate; year-to-year variability continues, so cold extremes still occur, just less often. "Species can just move" ignores barriers, speed limits and species that need specific partners. "Extinction is natural, so current rates are normal" ignores the 100-fold to 1,000-fold acceleration. "A population can grow without limit if individuals keep immigrating" misreads carrying capacity: population change is births minus deaths plus immigration minus emigration, so a steady stream of immigrants can hold a population above the level its own births and deaths would settle at, even though deaths exceed births there; if immigration stops, numbers fall back toward K. Emigration can likewise hold a population below that level. "Competition is only between species" misses that competition within a species (intraspecific) is usually the stronger limit, because members of one species need exactly the same resources.

Investigation you can do. Build two identical enclosed environments from clear 2-liter bottles with the tops cut off, each with a layer of moist soil, a few sprigs of a plant such as moss or clover, and a thermometer, covered with clear plastic wrap. Place both 40 cm from one lamp and record temperature every five minutes for 30 minutes, then vary one factor at a time: move one bottle to 20 cm (light intensity), add extra water to one (humidity), or add a small cup of vinegar and baking soda to one just before sealing (carbon dioxide). A result in which the closer bottle warms faster supports the claim that energy input sets temperature; humidity results show how water vapor affects heating and cooling. What the model cannot show: a bottle traps warm air by blocking convection, not by absorbing infrared, so it does not reproduce the atmosphere's greenhouse mechanism, and the carbon dioxide comparison in bottles is notoriously unreliable because the added gas also changes density, humidity and mixing; a difference of a degree between bottles is not evidence about the atmosphere. The bottle shows what an enclosed system does with energy input; the atmosphere's case rests on the absorption spectra of gases and on global measurements. Pair the bottle work with a data task: download recent carbon dioxide and temperature records from a public agency and plot them on the same time axis.

Worked comparison of greenhouse gas levels: Ice-core air gives carbon dioxide at about 280 parts per million before industrialization; recent direct measurements exceed 420. The increase is 140 parts per million, a rise of 50 percent. Almost all of it has occurred since about 1850, and more than half since 1980, while ice cores show no comparable rise in the preceding thousands of years. The timing matches fossil fuel use and forest clearing, and the extra carbon carries the isotopic signature of fossil carbon. Relating this to biodiversity: the added gas retains heat, raising mean temperature and the frequency of many extremes, which shifts ranges, timings and ocean chemistry faster than many species can adapt.

Worked range prediction from data: A hypothetical tree species occurs where the average January temperature lies between −8 and −2 degrees Celsius. Take, as rounded illustrative figures and not station records, January averages in Ohio running from about −3 °C near Lake Erie to about 0 °C near the Ohio River (a real analysis would use published climate normals for named weather stations); on those figures the band's warm edge (−2 °C) crosses the northern part of the state and the species grows in Ohio only in the coldest northern counties; the rest of Ohio is already too warm for it. Across that illustrative gradient January averages change by roughly 1 degree per 100 km, so a projection of 2 degrees of winter warming moves the −2 °C edge north by roughly 200 km, past Lake Erie, and the Ohio populations would fall outside their tolerance while the band's cold edge extends farther into Canada. Prediction: over decades, the Ohio stands fail to regenerate while seedlings establish farther north if seed can reach there. Because trees disperse seed only a short distance per generation, the northern edge may lag the climate, and the species' total range shrinks unless people plant it northward.

Worked feedback identification: (a) Melting sea ice exposes dark water that absorbs more sunlight, warming the ocean and melting more ice: positive feedback, amplifying warming. (b) Warmer oceans dissolve more carbon dioxide from the air? No: warmer water holds less gas, so the ocean's uptake slows and more stays in the atmosphere: positive. (c) Higher carbon dioxide lets many plants grow faster and take up more carbon: negative feedback, damping the rise, but limited by water and nutrients. (d) Thawing permafrost releases methane: positive. Adding the signs shows why the system can amplify a modest initial change.

Worked categorization of extinction causes: Passenger pigeon, once the most abundant bird in North America and abundant in Ohio, extinct in 1914: overharvesting combined with loss of forest. Island birds eaten by introduced rats: invasive species. Amphibians lost to a spreading fungal disease carried by trade: pathogen spread by human movement. Coral species declining under bleaching: climate change and ocean acidification. Each case names a cause that can be addressed by a specific policy, which is why categorizing causes matters.

Supported record: Draw and label the carbon cycle with at least six arrows (photosynthesis, respiration, decomposition, ocean exchange, burial, fossil fuel burning and deforestation), then mark with a star every process that climate change speeds up or slows down and write one sentence for each star. Beside it, list four local Ohio impacts of climate change and one adaptation strategy for each.

Independent performance: Using real data from a public source such as NASA or NOAA, produce a short data report on one factor involved in climate change and its impact on biodiversity, for example ocean temperature and coral bleaching, or atmospheric carbon dioxide and a local species profile. Success criteria: (a) at least one graph is constructed from downloaded data with the source, dates and units labeled; (b) historical and recent greenhouse gas levels are compared numerically; (c) the report explains the greenhouse mechanism and one feedback loop involving the ocean or biosphere correctly; (d) it uses the data to predict a change in the range or distribution of a named species and states the assumptions of the prediction; (e) it identifies at least two Anthropocene effects besides climate change and one invasive species characteristic that warming makes more dangerous; (f) it states what the two-bottle model cannot show about the atmosphere.

Extension: three further data tasks. Each uses records you download yourself, with the source, station or region and dates stated. (1) Ocean temperature: plot sea-surface temperature from a buoy or satellite record for one region over at least twenty years and relate the trend to one marine organism that lives there. (2) Local profile: choose one Ohio tree, insect, amphibian or reptile and assemble a profile from historical and current records, such as first-flowering or first-sighting dates or range maps, going back as far as the records allow, up to a century. (3) Local weather: tabulate temperature and precipitation for one Ohio weather station by decade, count the heavy-rain days or heat-wave days in each decade, and state what the pattern suggests for that part of Ohio. For any one of these, plan how a community planner, a farmer or the Ohio Department of Natural Resources could use the same data to choose an adaptation strategy.