Ecology Textbook Notes: Climate Change
Ecology Textbook Notes: Climate Change BIOL 3060
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This 18 page Class Notes was uploaded by Naomi Hampton on Wednesday August 24, 2016. The Class Notes belongs to BIOL 3060 at Auburn University taught by Dr. John Feminella in Fall 2016. Since its upload, it has received 41 views. For similar materials see Principles of Ecology in Ecology at Auburn University.
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Date Created: 08/24/16
BIOL 3060 Climate Change Section 1: Why Does Climate Change Matter? Fourth Assessment Report of International Panel on Climate Change (IPCC) distilled huge amounts of info from scientific journals and made it accessible to the public IPCC won Nobel Peace Prize in 2007 What’s the Big Deal about Temperature? o Temperature: A Critical Environmental Variable Life can be described as series of well-regulated biochemical reaction, most being controlled by enzymes Enzymes: catalysts, speed up chemical reactions by lowering the activation energy needed for the reaction Allow cells to grow, move, replicate Temperature determines the effectiveness of enzymes controlling reactions If temp is too low or too high, enzyme activity is reduced Goldilocks Principle: when temperature is just right, enzyme activity is maximized o Enzyme to Organism Goldilocks-like relationship between temperature and performance seen in ectotherms Ectotherms: organism whose body temperature is primarily determined by heat from its environment External temperatures affect growth rate, movement, behavior, etc. Temp can also determine gender in turtles, crocodiles, and some other reptiles o Enzyme to Organism to Population Population growth rates may also follow Goldilocks Principle Temperature can limit locations where species can survive o Enzyme to Organism to Population to Species Species richness: number of species in given area Generally highest in tropics and lowest near poles Section 2: Detecting Climate Change The Earth’s Climate is Dynamic o During ice age 21,000 years ago temps were 4-7 ° C cooler, massive ice sheets locked up water and sea levels were 120-130 m lower than today Lower temps and altered rain patterns Northern forests were large expanses of tundra and steppe because cool, dry air from ice sheets pushed tree habitats southward Tundra: coldest and simplest biome, few species, simple food chains Steppe: similar to tundra but has warmer summers and vegetation is dominated by grasses Climate vs. Weather o Climatologists: scientists who study the climate, can detect and attribute changes in climate o Meteorologists: someone who studies weather and provides short-term weather forecasts o Weather: current atmospheric conditions at a particular location, short-term o Climate: average weather conditions of a given region, long time periods Detecting a Trend: A signal to Noise Problem o Noise: unwanted random information that degrades the desired information o Signal: meaningful information in a data set o Temperature anomalies: values that represent the difference between the observed temperature and a long-term mean or reference value o most commonly used statistics are known collectively as regression analyses determine whether or not a line drawn through a set of data has a slope statistically different from zero o p-value: describes the probability that an error has been made o as signal strength increases, trends become easier to detect o when signal is small and noise high, trend is hard to detect o increasing series length makes it easier to consistently detect underlying data trend Where to Seek Evidence of Climate Change? o Earth’s climate system can be divided into 5 components: Atmosphere (air): the envelope of gas, clouds, and aerosols encompassing Earth Hydrosphere (liquid water): all liquid surface and subsurface water Cryosphere (frozen water): ice sheets, continental glaciers, snow fields, sea ice, permafrost Lithosphere (land): land areas, including crust and uppermost mantle Biosphere (life): all of world’s ecosystem, all living organisms o Predicted Changes What have climatologists predicted should be happening if Earth is growing warmer? Higher air and sea temperatures near surface of earth, along with increasing temp of land itself Alteration of cryosphere by causing snow and ice to melt, glaciers/ice sheets should retreat, permafrost thaw, sea ice should decline Alteration of hydrosphere in two ways: 1) precipitation patterns should change and 2) sea levels should rise as ice melts and oceans expand Biosphere should be affected in predictable but complex ways o The Temperature Instrumental Record Instrumental record: relatively recent and comparatively short record of temperature observations directly or indirectly measure using thermometer, satellite, or other instrument Annual global mean temperature: describes average temp of entire surface of Earth over course of a year Land-air surface temperatures have increased more than sea surface temperatures IPCC climatologists found Earth’s mean annual temperature increased about 0.74 ° C in past 100 years Earth has warmed in two distinct phases with brief cooling period, 1910-1940 and 1980-2005 o 1,300 Years of Temperatures Population dynamics: changes in size of ecological population over time o Other Indicators of Climate Change The Cryosphere Much of cryosphere is seasonal The total amount of ice has declined Some scientists hypothesize that tice-free summers may be seen in Artic ocean within 25 years The Hydrosphere Hydrologic cycle should be altered due to changing amount of liquid water that evaporates o Ex: as winters warm, more precipitation in Northern Hemisphere is being seen as rain instead of snow o El Nino and La Nina Warmer air can hold more water The atmosphere’s water-holding capacity increases by 7% per 1 degree C increase in temp o Can expect more intense storms Sea Level Rise o As ocean warms, same amount of water will expand to fill more space through thermal expansion o Sea levels rose by 1.7 +/- 0.5mm/yr. during 20 century Climatologists have documented strong trend of increasing annual global mean temp, shrinking cryosphere, increasing sea levels Also documented changes in hydrologic cycle Section Summary o Temperature is critical biologic variable, affecting processes at a wide range of scales o Climatologists are interested in detection and attribution o Climatologists rely on statistics to detect changes, easier when signal-to-noise ratio high and data sets long o Scientists have found clear & consistent evidence of change, specifically: Mean surface temp warmed significantly over past 150 years Dramatic changes in cryosphere Global precipitation patterns changed Sea levels risen due to thermal expansion and addition of water from melting snow and ice Section 3: Earth’s Climate and Climate Models A Simple Climate Model o Earth has an average surface temperature of roughly 15 ° C o Mathematically-based simulation models can be used to describe current understanding of planet’s climate o Spatial variation: differences that result from observations made in different locations, but at the same time o Temporal variation: differences in observations made at the same location, but at different points in time o Planet X (hypothetical planet used to create simple climate model that predicts mean surface temperature) Solar radiation: energy emitted in form of electromagnetic radiation Sun has surface temp around 5505 ° C Black body: an object that emits heat in direct proportion to its temperature First, simplest model Some of sun’s energy will hit planet X Planet is black body-planet absorbs all energy then re-radiates it back into space Planet X is warm enough to emit same amount of energy it absorbs from sun o Modeling Earth’s Temperature: Solar Irradiance Solar irradiance: total amount of solar radiation striking a surface perpendicular to the sun per unit time per unit area most important variable is planet’s distance from sun energy reaching planet X depends on inverse-square of distance to sun 2 energy is proportional to 1/d o Modeling Earth’s Temperature: Solar Output early in earth’s history, sun was 30% cooler than today o Modeling Earth’s Temperature: Albedo All planetary bodies absorb a fraction of solar energy they intercept, reflecting the rest back into space Albedo: the degree to which a planet reflects radiation o What If Snow Were Black? Average albedo of planet is result of albedo of its various surfaces Earth reflects about 30% of solar radiation it intercepts Venus shrouded in thick layer of clouds and reflects most solar radiation Mars comparatively dark and absorbs most solar radiation Albedo also affected by wavelength of solar radiation Plants reflect green light, water reflects blue light Angle of sun affects albedo More light reflected when sun low on horizon Soot released during burning of biomass and fossil fuels have reduced snow and sea-ice albedo from 1%-3%, enough to increase surface temperatures o Modeling Earth’s Temperature: Atmosphere Venus, Earth, Mars often considered sister planets All have atmospheres and rocky, weathered surfaces Earth’s atmosphere: primarily N, O, water vapor, CO 2 methane, other gases Mars’s and Venus’s atmospheres are primarily CO and exceptionally dry 2 o Greenhouse Gases Earth’s atmosphere acts like blanket trapping heat and raising surface temperatures, the greenhouse effect Key to greenhouse effect if the difference in wavelength between incoming and outgoing radiation Sun is hot and radiates mostly short wavelengths, Earth is cooler and radiates at longer wavelengths Nitrogen and oxygen are transparent to long and short wavelengths Greenhouse gases absorb longwave radiation from Earth’s surface Feedbacks to the Climate System o Modeling Feedbacks Requires Time Feedbacks require temporal component As surface temperatures increase, albedo decreases until climate reaches new equilibrium Ice-albedo feedback is an example of positive feedback where effect of initial change is amplified by feedback loop o Other Feedbacks to the Climate System Positive feedback: a feedback that amplifies or accelerates a change in the climate Negative feedback: dampen changes and stabilize climate Carbon cycle acts a negative feedback mechanism over very long periods of time Clouds act as both positive and negative feedbacks to temperature Trap more outgoing longwave radiation and leads to warming Have high albedo, as cloud cover increases, more solar radiation reflected back into space, cooling planet More Complex Physical Models o Parameterize: calibration of models with parameters o complex models divide land, atmosphere, and other components into pieces called cells o Layered Atmosphere In physical climate models, atmosphere presented as layered column of air Each layer has slightly different composition and height Layering helps us understand importance of changes in greenhouse gas concentrations or aerosols and dust occurring at different altitudes o Curved Earth Accounting for curve of Earth’s surface can be added to physical models sunlight striking Equator is direct, concentrated, from directly overhead sunlight striking poles is at oblique angle hot air lighter than cold air, so hot air rises and cold air sinks differential heating creates temperature gradient, causing heat to tend to flow from Equator to poles o General Circulation models (GCMs) Topography: configuration of planet’s surface GCMs contain multi-layered atmosphere and divide Earth’s surface into grid of cells divided by elevation and surface characteristics Model resolution: ability of models to accurately represent smaller-scale phenomena o Air Movement on a Spinning Sphere Differential heating sets up series of circulation cells that run parallel to the Equator Curvature of Earth creates north-south air currents Winds moving toward the Equator are deflected to the west, while winds moving toward poles deflected to the east This deflection is called the Coriolis effect Easterlies: strong east-to west winds Westerlies: west-to-east winds Northern storms spin counterclockwise while southern storms spin clockwise o Oceans Water can hold much more heat than an equivalent volume of air Global ocean conveyor system: large-scale circulation pattern where cold salty water sinking largely drive turnover of surface and subsurface water because water warms and cools slowly, oceans dampen changes in atmospheric temperature oceans important regulators of atmosphere’s chemical composition Putting It All Together o GCM cells interact with each other based on rules describing chemistry, physics, and biology of the climate system Model Verification o Climatologists continuously check their model outputs against real-world observations as models grow more complex o Current models reproduce large-scale spatial patterns in atmospheric temp, precipitation, solar radiation, wind, ocean temps, currents, and sea ice o Current models also succeed at recreating historic climate patterns Section Summary o Models reflect current understanding of climate, allow scientists to test hypotheses about factors affecting it o Planet’s equilibrium surface temp can be predicted from simple climate model that accounts for: Solar output-energy warming a planet Distance from sun-determines amount of solar radiation intercepted Albedo Greenhouse gases o More complex models describe non-equilibrium systems, incorporate clime feedbacks o GCMs even more complex, incorporate layered atmosphere, 3-D spinning sphere structure, complex topography, layered oceans o Current GCMs accurately reproduce recent large-scale patterns in average temp Section 4: Humans and Climate Change Attribution of Recent Climate Change o Attribution: process of determining probable cause(s) of observed phenomenon o Attribution poses more challenges than detection o Paleoclimatic data: Earth’s climate at times in the distant past o Natural vs. Anthropogenic Climate Forcings Climatologists distinguish between two classes of climate forcings: Natural climate forcings: include aerosols from volcanic eruptions, changes in solar irradiation due to variation in Earth’s orbit or in solar output Anthropogenic climate forcings: result from human actions, include greenhouse gases, man-made aerosol emissions, land use changes, exhaust from jet airplanes o Modeling Recent Climate Change Direct radiative forcings: changes in climate forcings directly that affect the radiative budget of Earth’s climate system Use this idea to create attribution model estimating how Earth’s temperature will change when direct radiative forcings change Sum up changes Multiplied by a climate sensitivity parameter (λ) that attempts to account for various feedbacks in the climate system ΔT =(λ)(Σ)(ΔRF) s i o ΔT =csange in surface temps o (Σ)(ΔRF)=sui of changes in each direct radiative forcing Can Solar Variation Explain Recent Warming? o Solar output increases and decreases on 11-year solar cycle corresponding to variation in number of sunspots Judith Lean used historic records of sunspot activity to reconstruct solar activity over past 4 centuries o two recent studies concluded changes in solar output over last century could not explain global warming, supported by recent satellite-based observations o If solar output was driving temp increases, we would expect all layers of atmosphere to grow warmer, instead, the lower atmosphere is warming while the upper atmosphere is cooling Can Greenhouse Gases Explain Recent Warming? o Atmospheric CO conc2ntration has increased dramatically since Industrial Revolution o CO re2eased from changes in land use is 3x higher now than in the 1850s o Charles Keeling reasoned release of so much carbon might alter concentration of CO 2 in the atmosphere o Scientists have used data from ice cores drilled to extend this data set further back in time o Estimating Effect of CO Inc2eases, 1900-2000 Climatologists have developed variety of techniques to estimate how an increase in CO 2oncentration affect radiative forcing Temperatures modeled using both solar variation and carbon dioxide show a cyclic increase/decrease superimposed on a general trend of steady increase throughout the century o Climate Forcing IPCC has also examined methane, nitrous oxide, halocarbons and other factors that may have caused warming Can Human Actions Explain Recent Warming? o Different models from different research groups use different assumptions o Best estimate comes from averaging these models to create multi-model ensemble mean In one run, used only natural forcings Next run, used both natural and anthropogenic forcings Only simulations that include anthropogenic forcings able to reproduce warming that has occurred since 1960 Both simulations indicate temperature decreases associated w/four major volcanic eruptions of the last century o Modern Climate Change in Context IPCC concluded greenhouse gases “very likely” to have caused more global warming than changes in solar output in past 50 years Observed warming unprecedented in past 1300 years Climatologists combined model results w/data from ice cores and other proxies to reconstruct 800,000 year record of changes Two key pieces of info to take from long-term record: Concentration of greenhouse gases much higher today than any time in past 600,000 years Changes in greenhouse gases cannot explain all variation in climate Milankovitch cycles: orbital eccentricity, tilt of Earth’s axis relative to orbital plane, the cycles of earth moving and tilting One of the best supported theories about causes of glacial and interglacial periods o Climate Change in the 21 Century If CO 2oncentrations increase by 40% by the year 2100, the expected temp increase of Earth is 0.866 ° C If CO 2oncentrations increase by 100%, expected increase in temp is 1.84 ° C Uncertainty in Climate Models Model predictions are estimates and each has an associated uncertainty At least two important sources cause uncertainty: o Weather-weather influences climate, uncertainty known as internal variability of climate system o Error in way models represent climate system o Future Drivers of Climate Change Changes in atmospheric CO de2end on the proportion of emissions that remain in the atmosphere versus those incorporated into plants or dissolved in oceans IPCC envisioned emission scenarios based on four story lines (3 explained below Increasing World Affluence: future w/globally high economic growth, energy demands met by mix of energy sources, as world becomes more affluent, population growth expected to decline Regionality: future where global economic growth moderate and regional, wide differences b/w countries’’ economies, population growth continuous throughout century Green Growth: future where governments successfully reduce income/social inequities and increase environmental conservation, cleaner technologies, population peaks mid-century then declines o Spatial Distribution of Temperature Changes If we can minimize greenhouse emissions, surface temps will increase less than if we continue at current pace Warming unlikely to be same everywhere on globe Land masses are expected to warm more than oceans and northern latitudes more than other regions Most models predict precipitation changes o Feedbacks and Potential Tipping Points Important source of uncertainty is in understanding of feedbacks in the carbon cycle and cloud formation Feedbacks can cause abrupt climate changes Occur when aspect of climate system crosses tipping point How Will Climate Change Affect People? Precipitation will likely come during fewer, more intense events, causing more flooding Sea level rise will increase coastal flooding Subtle ecosystem-level effects Ocean acidification due to CO 2 Could stimulate primary production through fertilization effect o Size of effect depends on availability of other nutrients/water Could change respiration Section Summary o Models are critical tools for attribution studies Evaluate relative importance of natural and anthropogenic climate forcings o Solar output changes are too small to account for increases in average surface temp on Earth o Since 1850s, greenhouse gas concentrations increased markedly o Models suggest observed warming probably direct result of increased greenhouse gases o Climate models used to forecast how climate will respond to different emission scenarios o High latitudes will warm more than mid-latitudes, land surfaces more than oceans, precipitation patterns will change o Heat waves, droughts, severe storms likely to increase o Ecosystems affected by ocean acidification/altered patterns of primary production and respiration o Further changes may occur abruptly/unexpectedly Section 5: Biological Consequences of Climate Change Species Must Respond to Climate Change o Three possible ways for species to avoid extinction in response to climate change: Species may move Species may acclimate Species may evolve o Most important approaches are experimental, correlational, and theoretical Experimental: studies in which the researcher manipulates one or more real entities to determine how they affect the system Correlational: researchers look to see if two variables are correlated Theoretical: attempt to use current understanding to test questions about what factors could be driving behavior or how it might change o How Does Climate Change Affect Existing Genotypes? Genotypes: combination of alleles the individual carries Some effects large/obvious Coldwater fishes (trout, salmon, etc.) die when water temps get too high Some effect subtle African satyrid butterflies raised at warmer temps lay smaller eggs Ectotherms: organism whose body temp primarily determined by heat form environment How quickly each stage of a butterfly life cycle is affected by temperature Phenology: seasonal timing of animal and plant life history events o Has Climate Change Affected Phenology? Temperature can affect insect phenology Timothy Sparks & David Roy found historical emergence data on 35 English butterfly species United Kingdom Butterfly Monitoring Scheme Butterflies emerged earlier in years with warmer temperatures Meta-analysis: analysis of many studies Can Changes in Phenology Affect Population Growth? o Population dynamics: changes in size of ecological population over time o Can use population’s average finite rate of increase (λ) to determine if population growing or shrinking over time =1, stable >1, growing <1, declining Can Changes in Phenology Affect Species Interactions? o Increasing temps allowed butterflies to emerge two weeks earlier and fly longer Populations grew faster as climate warmed o Generalist: organism that can exploit several different species or broad set of environmental conditions o Specialist: organism that exploits only one species or narrow set of environmental conditions o Altered Phenology Causes Mismatches Multitrophic species pair: two species from different trophic levels that have some sort of biological link Highly synchronized in phenology Climate change may cause trophic mismatches Eric Post & mads Forchhammer conducted correlational study to see if climate change is creating trophic mismatch between caribou and the plants they eat Climate Change and Fitness o Fitness: organism’s ability to survive and reproduce in its environment o Changes in environmental conditions can produce changes in fitness o Evolutionary ecologists estimate individual fitness as the intrinsic growth rate (maximum rate at which population can grow with unlimited resources) o Temperature performance curves: describes how expression of particular trait varies with temperature o Temperature Performance Curves Usually show optimal temperature at which species does best, minimum and maximum When species is well adapted to environment, optimal temp is a little higher than mean temp, provides thermal cushion Thermal safety margin: difference between average and optimal temperatures Tropical species are more vulnerable than temperate species How Does Climate Change Affect Species Distributions? o Can use temperature performance curves to help see if climate change affects distributions o Species Distributions Have Shifted Poleward Camille Parmesan examined range shifts in 35 non-migratory European butterflies and found 63% had northward range shifts Directional shift if common response to warming climate Temperature-performance relationships can also predict how mountain populations should respond to climate change o Communities Don’t Move; Species Do Not all species will move at same rate Mobile species (birds, insects) able to respond relatively quickly Stationary long-lived trees may shift ranges slowly Climate change likely to alter composition of existing communities, could lead to community dynamic changes that ripple through ecosystem Evolutionary Responses o Movement may occur across continents, can also be localized o Acclimate: adjust to new climate o Phenotypic plasticity: variation in the phenotype associated with a particular genotype produced by changes in environmental conditions o Adapt through evolution by natural selection Genes that allow individuals to perform better and survive will pass on at a higher rate o Populations near warm tropics can withstand higher temps for longer periods than populations at cooler high latitudes, and vice versa Experiments suggest it is due to changes in allele frequencies and not just phenotypic plasticity Evolution of Performance Curves o Populations might evolve as climate warms where they occur o Adaptations arise from genetically-controlled changes in shape or position of population’s avg. temp. performance curve Limit to Evolution o If temp changes faster than population can adapt, thermal safety margin gets smaller and eventually disappear, increasing the probability the population will go extinct o Initial Genetic Variation With higher genetic variation, more chance offspring will have temp-perf curves better adapted to higher temps o Generation Time Ability of population to adapt to changing climate affected by how quickly climate changes and amount of genetic variation Generation time: average amount of time from birth of female until birth of her daughters Species with shorter generation times can evolve more quickly Climate Change Will Affect Life o Evolutionary constraints limit how far ranges can shift, how much species can acclimate, and how quickly evolution occurs o Climate change allowing pest species to expand ranges o Tropical and temperate species may respond differently to climate change Section Summary o Species may respond to climate change by moving, acclimating or evolving o Climate change may affect phenology o Altered phenologies may produce mismatches between predators and prey or flowers and pollinators, reducing population growth of one or both species o Individual’s fitness varies with temperature, summarized using temperature performance curve o Species distributions expected to shift poleward or uphill o Climate change may alter community composition and community dynamics o Adaptation through evolution through natural selection can alter temp-perf curve o Species’ ability to evolve depends on rate of climate change and species’ genetic variation and generation time