Energy Flow and Nutrient Cycling in Ecosystems

Transcription

1 BIOLOGY Life on Earth WITH PHYSIOLOGY Tenth Edition Audesirk Audesirk Byers 28 Energy Flow and Nutrient Cycling in Ecosystems Lecture Presentations by Carol R. Anderson Westwood College, River Oaks Campus

2 Chapter 28 At a Glance 28.1 How Do Nutrients and Energy Move Through Ecosystems? 28.2 How Does Energy Flow Through Ecosystems? 28.3 How Do Nutrients Cycle Within and Among Ecosystems? 28.4 What Happens When Humans Disrupt Nutrient Cycles?

3 28.1 How Do Nutrients and Energy Move Through Ecosystems? All ecosystems consist of two components The biotic component of an ecosystem is the community of living organisms bacteria, fungi, protists, plants, and animals in a given area The abiotic component of an ecosystem consists of all nonliving physical or chemical aspects of the environment, such as the climate, light, temperature, availability of water, and minerals in the soil

4 28.1 How Do Nutrients and Energy Move Through Ecosystems? Nutrients are atoms and molecules that organisms obtain from their environment The same nutrients have been sustaining life on Earth for about 3.5 billion years Your body includes oxygen, carbon, hydrogen, and nitrogen atoms that were once part of a dinosaur or a wooly mammoth Nutrients are transported around the Earth, but they never leave Earth

5 28.1 How Do Nutrients and Energy Move Through Ecosystems? Energy, in contrast, takes a one-way journey through ecosystems Solar energy is captured by photosynthetic bacteria, algae, and plants, and then flows from organism to organism Eventually, all of life s energy is converted to heat that is given off to the environment and cannot be used to drive the chemical reactions of living organisms Life requires a continuous input of energy

6 Figure 28-1 Energy flow, nutrient cycling, and feeding relationships in ecosystems energy from sunlight producers nutrients primary consumers detritivores and decomposers higher-level consumers solar energy heat energy energy stored in chemical bonds nutrients

7 28.2 How Does Energy Flow Through Ecosystems? The sun converts hydrogen into helium, transforming a relatively small amount of matter into enormous quantities of energy A tiny fraction of this energy reaches Earth in the form of electromagnetic waves, including heat, visible light, and ultraviolet energy Half of the energy that reaches Earth is visible light

8 28.2 How Does Energy Flow Through Ecosystems? Much of the energy reaching Earth is reflected back into space by the atmosphere, clouds, and the Earth s surface Less than 0.03% of the energy reaching Earth from the sun is captured by photosynthetic organisms, and supports life on Earth

9 28.2 How Does Energy Flow Through Ecosystems? Energy enters ecosystems through photosynthesis Plants, algae, and photosynthetic bacteria acquire nutrients such as carbon, nitrogen, oxygen, and phosphorus from the abiotic portions of ecosystems Photosynthetic organisms capture sunlight s energy Nutrients and energy contained in biological molecules move from photosynthetic organisms to nonphotosynthetic organisms Photosynthesizers bring energy and nutrients into ecosystems

10 28.2 How Does Energy Flow Through Ecosystems? Energy is passed from one trophic level to the next Energy flow through ecosystems begins with photosynthetic organisms and passes through several levels of nonphotosynthetic organisms that feed on the photosynthesizers or each other Each category of organisms is called a trophic level Producers (or autotrophs) make their own food using inorganic nutrients and solar energy from the environment

11 28.2 How Does Energy Flow Through Ecosystems? Energy is passed from one trophic level to the next (continued) Organisms that cannot photosynthesize are called consumers (or heterotrophs) They acquire energy and nutrients from molecules in the bodies of other organisms

12 28.2 How Does Energy Flow Through Ecosystems? Energy is passed from one trophic level to the next (continued) There are several levels of consumers Primary consumers feed directly and exclusively on producers These herbivores include animals such as grasshoppers, mice, and zebras, and form the second trophic level

13 28.2 How Does Energy Flow Through Ecosystems? Energy is passed from one trophic level to the next (continued) Carnivores ( meat eaters ), such as spiders, hawks, and salmon, make up the higher-level consumers Carnivores act as secondary consumers when they prey on herbivores Some carnivores eat other carnivores and are called tertiary consumers

14 28.2 How Does Energy Flow Through Ecosystems? Net primary production is a measure of the energy stored in producers The amount of life that a particular ecosystem can support is determined by the energy captured by the producers in that ecosystem The energy that photosynthetic organisms store and make available to other members of the community over a given period is called net primary production Biomass, or dry biological material, is usually a good measure of the energy stored in organisms bodies

15 Figure 28-2 Net primary production in ecosystems open ocean (125) continental shelf (140) tundra (140) coniferous forest (800) estuary (1,500) tropical rain forest (2,200) temperate deciduous forest (1,200) grassland (600) desert (90)

16 28.2 How Does Energy Flow Through Ecosystems? Net primary production is a measure of the energy stored in producers (continued) The net primary production of an ecosystem is influenced by many factors The amount of sunlight The availability of water and nutrients The temperature In the desert, lack of water limits production In the open ocean, light is a limiting factor in deep waters

17 28.2 How Does Energy Flow Through Ecosystems? Net primary production is a measure of the energy stored in producers (continued) An ecosystem s contribution to Earth s total production is determined by the ecosystem s productivity and by the portion of Earth that the ecosystem covers The oceans have low net primary production, but they cover about 70% of Earth s surface, so they contribute about 25% of Earth s total production

18 28.2 How Does Energy Flow Through Ecosystems? Food chains and food webs describe the feeding relationships within communities A food chain is a linear feeding relationship with just one representative at each trophic level Plants are the dominant producers in land-based (terrestrial) ecosystems Plants support plant-eating insects, reptiles, birds, and mammals, each of which can be preyed on by the other animals

19 Figure 28-3a A simple terrestrial food chain tertiary consumer (fourth trophic level) secondary consumer (third trophic level) primary consumer (second trophic level) producer (first trophic level) A simple terrestrial food chain

20 28.2 How Does Energy Flow Through Ecosystems? Food chains and food webs describe the feeding relationships within communities (continued) In contrast, microscopic photosynthetic protists and bacteria collectively called phytoplankton are the dominant producers in most aquatic food chains, such as those found in lakes and oceans Phytoplankton are consumed by zooplankton, which consist of protists and small, shrimp-like crustaceans

21 Figure 28-3b A simple marine food chain phytoplankton zooplankton secondary consumer (third trophic level) producer (first trophic level) primary consumer (second trophic level) quaternary consumer (fifth trophic level) tertiary consumer (fourth trophic level) A simple marine food chain

22 28.2 How Does Energy Flow Through Ecosystems? Food chains and food webs describe the feeding relationships within communities (continued) Animals in natural communities often do not fit neatly into the categories of primary, secondary, and tertiary consumers depicted in simple food chains A food web shows many interconnected food chains, and actual feeding relationships in a community Some animals, such as raccoons, bears, rats, and humans, are omnivores ( everything eaters ) and act as primary, secondary, and tertiary consumers

23 Figure 28-4 A simplified grassland food web

24 28.2 How Does Energy Flow Through Ecosystems? Detritivores and decomposers release nutrients for reuse Among the most important strands in a food web are the detritivores and decomposers Detritivores ( debris eaters ) are an army of mostly small and often unnoticed organisms Nematode worms Earthworms Millipedes Dung beetles

25 28.2 How Does Energy Flow Through Ecosystems? Detritivores and decomposers release nutrients for reuse (continued) Decomposers are primarily fungi and bacteria They feed on the same material as detritivores They do not ingest chunks of organic matter They secrete digestive enzymes outside their bodies, where the enzymes break down nearby organic material Decomposers absorb some of the resulting nutrient molecules

26 28.2 How Does Energy Flow Through Ecosystems? Detritivores and decomposers release nutrients for reuse (continued) Detritivores and decomposers are absolutely essential to life on Earth They reduce the bodies and wastes of other organisms to simple molecules Without detritivores and decomposers, ecosystems would gradually be buried by accumulated wastes and dead bodies, whose nutrients would be unavailable to enrich the soil and water

27 28.2 How Does Energy Flow Through Ecosystems? Energy transfer through trophic levels is inefficient A fundamental principle of the branch of physics called thermodynamics is that energy is never completely efficient For example, as a car burns gasoline, only 20% of the resulting energy is used to move the car; the other 80% is lost as heat Inefficiency is a rule in living systems Waste is heat produced by all biochemical reactions that keep cells alive

28 28.2 How Does Energy Flow Through Ecosystems? Energy transfer through trophic levels is inefficient (continued) Energy transfer from one trophic level to the next is quite inefficient When a grasshopper (a primary consumer) eats grass (a producer), only some of the solar energy trapped by the grass is available to the insect Some was converted into the chemical bonds of cellulose, which a grasshopper cannot digest

29 28.2 How Does Energy Flow Through Ecosystems? Energy transfer through trophic levels is inefficient (continued) Energy transfer from one trophic level to the next is quite inefficient (continued) Only a fraction of the energy captured by producers of the first trophic level can be used by organisms in the second trophic level If the grasshopper is eaten by a robin (the third trophic level), the bird will not obtain all the energy that the insect acquired from the plants

30 28.2 How Does Energy Flow Through Ecosystems? Energy transfer through trophic levels is inefficient (continued) Energy transfer from one trophic level to the next is quite inefficient (continued) Some of the energy will have been used up to power hopping, flying, and eating Some energy will be found in the grasshopper s indigestible exoskeleton Much of the energy will have been lost as heat

31 28.2 How Does Energy Flow Through Ecosystems? Energy transfer through trophic levels is inefficient (continued) The average net energy transfer between trophic levels is roughly 10% efficient and is known as the 10% law An energy pyramid illustrates the energy relationships between trophic levels widest at the base, and progressively narrowing in higher trophic levels

32 Author Animation: Energy Flow and Food Webs Animation: Energy Flow and Food Webs

33 Figure 28-5 An energy pyramid for a grassland ecosystem tertiary consumer (1 calorie) secondary consumer (10 calories) primary consumer (100 calories) producers (1,000 calories)

34 28.2 How Does Energy Flow Through Ecosystems? Energy transfer through trophic levels is inefficient (continued) The most abundant animals are herbivores Carnivores are relatively scarce because there is far less energy available to support them Energy losses within and between trophic levels mean that long-lived animals at higher trophic levels eat many times their body weight in food

35 28.2 How Does Energy Flow Through Ecosystems? Energy transfer through trophic levels is inefficient (continued) If the food contains certain types of toxic substances, they may be stored and become more concentrated This biological magnification can lead to harmful and even fatal effects

36 28.3 How Do Nutrients Cycle Within and Among Ecosystems? Some of the chemical building blocks of life, called macronutrients, are required by organisms in large quantities Water Carbon Hydrogen Oxygen Nitrogen Phosphorous Sulfur Calcium

37 28.3 How Do Nutrients Cycle Within and Among Ecosystems? Macronutrients are required only in trace quantities Zinc Molybdenum Iron Selenium Iodine Nutrient cycles, also called biogeochemical cycles, describe the pathways that macronutrients and micronutrients follow as they move from their major sources in the abiotic parts of ecosystems, called reservoirs, through living communities and back again

38 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The hydrologic cycle has its major reservoir in the oceans The water cycle, or hydrologic cycle, is the pathway that water takes as it travels from its major reservoir the oceans through the atmosphere, to reservoirs in freshwater lakes, rivers, and groundwater, and then back again to the oceans

39 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The hydrologic cycle has its major reservoir in the oceans (continued) The hydrologic cycle would continue even if life on Earth disappeared because the biotic portion of ecosystems plays a small role in the hydrologic cycle The oceans cover 70% of the Earth s surface and contain more than 97% of Earth s water Solar energy evaporates water, and it comes back to Earth as precipitation

40 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The hydrologic cycle has its major reservoir in the oceans (continued) Of the water that falls on land Some is absorbed by the roots of plants Most evaporates from the soil, lakes, and streams A portion runs back to the oceans An extremely miniscule fraction is stored in the bodies of living organisms Some enters natural underground reservoirs called aquifers

41 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The hydrologic cycle has its major reservoir in the oceans (continued) The hydrologic cycle is crucial for terrestrial communities because it continually restores the fresh water needed for land-based life Plant leaves can only take up carbon dioxide gas after it has dissolved in a thin layer of water coating the cells inside the leaf The hydrologic cycle does not depend on terrestrial organisms, but they would disappear without it

42 Figure 28-6 The hydrologic cycle reservoirs processes water vapor in the atmosphere precipitation over land precipitation over the ocean evaporation from the land and from the leaves of plants evaporation from the ocean evaporation from lakes and rivers lakes and rivers seepage through soil into groundwater runoff from rivers and land extraction for agriculture water in the ocean groundwater, including aquifers

43 Author Animation: The Hydrologic Cycle Animation: The Hydrologic Cycle

44 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The carbon cycle has major reservoirs in the atmosphere and oceans Carbon atoms form the framework of all organic molecules The carbon cycle is the pathway that carbon takes from its major short-term reservoirs in the atmosphere and oceans, through producers and into the bodies of consumers, detritivores, and decomposers, and then back again to its reservoirs

45 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The carbon cycle has major reservoirs in the atmosphere and oceans (continued) Carbon enters communities through capture of carbon dioxide (CO 2 ) during photosynthesis Producers on land get CO 2 from the atmosphere Aquatic producers get CO 2 dissolved in the water

46 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The carbon cycle has major reservoirs in the atmosphere and oceans (continued) Primary consumers eat producers and acquire carbon stored in their tissues These herbivores release some of the carbon through respiration as CO 2, excrete carbon compounds in their feces, and store the rest in their bodies, which may be consumed by higher trophic levels

47 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The carbon cycle has major reservoirs in the atmosphere and oceans (continued) All living things eventually die, and their bodies are broken down by detritivores and decomposers, whose cellular respiration returns CO 2 to the atmosphere and oceans The complementary processes of uptake by photosynthesis and release by cellular respiration continually recycle carbon from the abiotic to the biotic portions of an ecosystem and back again

48 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The carbon cycle has major reservoirs in the atmosphere and oceans (continued) Much of Earth s carbon is bound up in limestone rock, formed from calcium carbonate (CaCO 3 ) deposited on the ocean floor in the shells of prehistoric phytoplankton Fossil fuels, which include coal, oil, and natural gas, are additional long-term reservoirs for carbon

49 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The carbon cycle has major reservoirs in the atmosphere and oceans (continued) These substances were produced from the remains of prehistoric organisms buried deep underground and subjected to high temperature and pressure In addition to carbon, the energy of prehistoric sunlight is trapped in these deposits When human beings burn fossil fuels to tap this stored energy, CO 2 is released into the atmosphere, with potentially serious consequences

50 Author Animation: The Carbon Cycle Animation: The Carbon Cycle

51 Figure 28-7 The carbon cycle reservoirs processes trophic levels CO 2 in the atmosphere CO 2 dissolved in the ocean burning fossil fuels respiration fire photosynthesis consumers producers decomposition detritivores and decomposers fossil fuels (coal, oil, natural gas)

52 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The nitrogen cycle has its major reservoir in the atmosphere Nitrogen is a crucial component of proteins, many vitamins, nucleotides (such as ATP), and nucleic acids (such as DNA) The nitrogen cycle is the pathway taken by nitrogen from its primary reservoir nitrogen gas (N 2 ) in the atmosphere to much smaller reservoirs of ammonia and nitrate in soil and water, through producers, consumers, detritivores and decomposers, and back to its reservoirs

53 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The nitrogen cycle has its major reservoir in the atmosphere (continued) While nitrogen gas (N 2 ) makes up 78% of the atmosphere, this form of nitrogen cannot be utilized by plants Plants utilize nitrate (NO 3- ) or ammonia (NH 3 ) as their nitrogen source

54 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The nitrogen cycle has its major reservoir in the atmosphere (continued) N 2 is converted to ammonia by specific bacteria during a process called nitrogen fixation Some of these bacteria live in water and soil and convert the ammonia into nitrate that plants can directly use Others live in symbiotic associations with plants called legumes, which include alfalfa, soybeans, clover, and peas

55 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The nitrogen cycle has its major reservoir in the atmosphere (continued) Some nitrogen is released in wastes and dead bodies Decomposer bacteria convert this back to nitrate and ammonia in the soil or water, which is then available to plants Denitrifying bacteria break down nitrate, releasing N 2 back to the atmosphere

56 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The nitrogen cycle has its major reservoir in the atmosphere (continued) People significantly manipulate the nitrogen cycle, both deliberately and unintentionally About 150 million tons of nitrogen-based fertilizer are applied to farms each year The heat produced by burning fossil fuels combines atmospheric N 2 and O 2, generating nitrogen oxides that form nitrates Human activities now dominate the nitrogen cycle

57 Author Animation: The Nitrogen Cycle Animation: The Nitrogen Cycle

58 Figure 28-8 The nitrogen cycle reservoirs processes trophic levels N 2 in the atmosphere burning fossil fuels lightning application of manufactured fertilizer consumers producers ammonia and nitrates in water detritivores and decomposers uptake by producers nitrogen-fixing bacteria in soil and legume roots decomposition denitrifying bacteria ammonia and nitrates in soil

59 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The phosphorus cycle has its major reservoir in rock, bound to oxygen as phosphate Phosphorus is found in biological molecules such as nucleic acids and the phospholipids of cell membranes It also forms a major component of vertebrate teeth and bones The phosphorus cycle is the pathway taken by phosphorus from its primary reservoir in rocks to much smaller reservoirs and back

60 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The phosphorus cycle has its major reservoir in rock, bound to oxygen as phosphate (continued) Throughout its cycle, almost all phosphorus is bound to oxygen, forming phosphate (PO 4 3- ) There are no gaseous forms of phosphate, so there is no atmospheric reservoir in the phosphorus cycle As phosphate-rich rocks are exposed by geological processes, some of the phosphate is dissolved by rain and flowing water

61 28.3 How Do Nutrients Cycle Within and Among Ecosystems? The phosphorus cycle has its major reservoir in rock, bound to oxygen as phosphate (continued) Throughout its cycle, almost all phosphorus is bound to oxygen, forming phosphate (PO 4 3- ) (continued) Dissolved phosphate is absorbed by producers, which incorporate it into biological molecules From producers, phosphate is passed through food webs At each level, excess phosphate is excreted Detritivores and decomposers return the phosphate to the soil and water

62 Figure 28-9 The phosphorus cycle reservoirs processes trophic levels phosphate in rock geological uplift application of manufactured fertilizer consumers producers runoff from fertilized fields runoff from rivers detritivores and decomposers uptake by producers phosphate in water decomposition phosphate in soil phosphate in sediment formation of phosphate-containing rock

63 28.4 What Happens When Humans Disrupt Nutrient Cycles? Ancient peoples, with small populations and limited technology, had relatively little impact on nutrient cycles As the human population grew and technology increased, people began to act more independently of natural ecosystem processes The Industrial Revolution resulted in a tremendous increase in our reliance on energy stored in fossil fuels for heat, light, transportation, industry, and agriculture

64 28.4 What Happens When Humans Disrupt Nutrient Cycles? Fertilizer use on commercial farms grew exponentially Human use of fossil fuels and chemical fertilizers has significantly disrupted the global nutrient cycles of nitrogen, phosphorus, sulfur, and carbon

65 Figure An algal bloom in the Gulf of Mexico

66 28.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the nitrogen and phosphorus cycles damages aquatic ecosystems Fertilizers are applied to farm fields to help satisfy the agricultural demands of a growing human population Water dissolves and carries away some of the phosphate and nitrogen-based fertilizer As water drains into lakes, rivers, and ultimately the oceans, these fertilizers can disrupt the delicate balance of food webs by overstimulating the growth of phytoplankton

67 28.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the nitrogen and phosphorus cycles damages aquatic ecosystems (continued) The phytoplankton die, and their bodies sink into deeper water and provide food for decomposer bacteria The decomposers use up most of the available oxygen, and other aquatic organisms, such as invertebrates and fish, die, creating dead zones in many waters

68 28.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the sulfur and nitrogen cycles causes acid deposition Burning of sulfur-containing fossil fuels, primarily coal, accounts for about 75% of all sulfur dioxide emissions worldwide These two substances combine with atmospheric water and form nitric and sulfuric acids Days later and often hundreds of miles from the source, these acids fall to Earth in rain or snow

69 28.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the sulfur and nitrogen cycles causes acid deposition (continued) This acid rain more accurately called acid deposition was first recognized in New Hampshire, where a sample of rain collected in 1963 had a ph of 3.7, about the same as that of orange juice Acid deposition damages forests, can render lakes lifeless, and even eats away at buildings and statues

70 Figure Acid deposition is corrosive

71 28.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the sulfur and nitrogen cycles causes acid deposition (continued) Many lakes and ponds in the Adirondack Mountains are too acidic to support fish Acid rain also increases the extent to which organisms are exposed to toxic metals, such as aluminum, mercury, lead, and cadmium, which are far more soluble in acidified water

72 28.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the sulfur and nitrogen cycles causes acid deposition (continued) Acid conditions dissolve aluminum out of the soil into soil water and lakes, where it inhibits plant growth and kills fish Calcium and magnesium, which are essential nutrients for all plants, are leached out of the soil by acid precipitation

73 28.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the sulfur and nitrogen cycles causes acid deposition (continued) Plants in acidified soil become weak and more vulnerable to infection and damage by insects The decline has been shown to be caused by acid conditions, coupled with drought, insect attack, and climate change About half of the red spruce and one-third of the sugar maples in the Green Mountains of Vermont have been killed

74 Figure Acid deposition can destroy forests

75 28.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the sulfur and nitrogen cycles causes acid deposition (continued) Since 1990, government regulations have resulted in substantial reductions in emissions of both sulfur dioxide and nitrogen oxides from U.S. power plants Sulfur dioxide emissions are down about 40% and nitrogen oxide levels have been reduced by more than 50% Air quality has improved, and rain has become less acidic

76 28.4 What Happens When Humans Disrupt Nutrient Cycles? Overloading the sulfur and nitrogen cycles causes acid deposition (continued) Damaged ecosystems recover slowly Adirondack lakes are gradually becoming less acidic If acid deposition is completely eliminated, eventually the lakes will return to their normal ph Most aquatic life should then recover in 3 to 10 years, depending on the species Forests will take much longer to recover

77 28.4 What Happens When Humans Disrupt Nutrient Cycles? Interfering with the carbon cycle is warming Earth s climate Some of the energy from sunlight is reflected back into space by the atmosphere, and by Earth s surface, especially by areas covered with snow or ice Most sunlight strikes relatively dark areas of the surface and is converted into heat that is radiated into the atmosphere Water vapor, CO 2, and several greenhouse gases trap some of the heat in the atmosphere

78 28.4 What Happens When Humans Disrupt Nutrient Cycles? Interfering with the carbon cycle is warming Earth s climate (continued) This is a natural process called the greenhouse effect, which keeps our atmosphere relatively warm and allows life on Earth as we know it For Earth s temperature to remain constant, the total amount of energy entering and leaving Earth s atmosphere must be equal

79 28.4 What Happens When Humans Disrupt Nutrient Cycles? Interfering with the carbon cycle is warming Earth s climate (continued) If atmospheric concentrations of greenhouse gases increase, more heat is retained than is radiated into space, causing Earth to warm Greenhouse gases are increasing because people burn fossil fuels, releasing CO 2 Other important greenhouse gases include methane (CH 4 ), released by agricultural activities and burning fossil fuels

80 Figure The greenhouse effect Sun Sunlight energy enters the atmosphere Most heat is radiated into space Some atmospheric heat is retained by greenhouse gases Some energy is reflected back into space Most sunlight strikes Earth s surface and is converted into heat Heat is radiated back into the atmosphere power plants and factories volcanoes forest fires vehicle emissions agricultural activities homes and other buildings

81 28.4 What Happens When Humans Disrupt Nutrient Cycles? Burning fossil fuels is causing climate change Since the mid-1800s, human societies have increasingly relied on energy from fossil fuels As we burn fossil fuel in our power plants, factories, and cars, we harvest the energy of ancient sunlight and release CO 2 into the atmosphere Burning fossil fuels accounts for about 80% to 85% of the CO 2 human activities release into the atmosphere annually

82 28.4 What Happens When Humans Disrupt Nutrient Cycles? Burning fossil fuels is causing climate change (continued) A second source of added atmospheric CO 2 is deforestation, which destroys tens of millions of forested acres annually and accounts for 15% of CO 2 emissions Deforestation occurs principally in the tropics as rain forests are cut and burned Collectively, human activities release about 35 to 40 billion tons of CO 2 into the atmosphere annually

83 28.4 What Happens When Humans Disrupt Nutrient Cycles? Burning fossil fuels is causing climate change (continued) Since 1850, atmospheric CO 2 has increased by 40% This increase is from 280 ppm to 392 ppm, with a current annual increase of 2 ppm A larger and growing body of evidence indicates that human release of carbon dioxide and other greenhouse gases has amplified the natural greenhouse effect, thereby altering the global climate

84 28.4 What Happens When Humans Disrupt Nutrient Cycles? Burning fossil fuels is causing climate change (continued) Surface temperature data, recorded from thousands of weather stations around the world and from satellites that measure temperatures over oceans, show that Earth has warmed by about 1 F (0.6 C) since 1970 The overall impact of increased greenhouse gases is now usually called climate change, which includes both global warming and many other effects on our climate and Earth s ecosystems

85 Figure Global temperature increases parallel atmospheric CO 2 increases CO 2 (ppm) year Atmospheric CO 2 global average temperature F C year Global surface temperature

86 28.4 What Happens When Humans Disrupt Nutrient Cycles? Burning fossil fuels is causing climate change (continued) Spring snow in the Northern Hemisphere is declining Glaciers are retreating worldwide The World Glacier Monitoring Service reports that about 90% of the world s mountain glaciers are shrinking, and that this trend seems to be accelerating Glacier National Park, Montana, now has only 25 glaciers remaining

87 28.4 What Happens When Humans Disrupt Nutrient Cycles? Burning fossil fuels is causing climate change (continued) Climate scientists predict that the warming atmosphere will cause more severe storms, including stronger hurricanes Greater amounts of rain or snow will fall in single storms More frequent and more prolonged droughts will occur Increased CO 2 makes the oceans more acidic

88 Figure Glaciers are melting Muir Glacier, 1941 Muir Glacier, 2004

89 28.4 What Happens When Humans Disrupt Nutrient Cycles? Continued climate change will disrupt ecosystems and endanger many species Predictions of continued climate change are based on sophisticated computer models developed and run independently by climate scientists around the world As models improve, they match past climate with ever-greater accuracy, providing increasing confidence in their predictions for the future

90 28.4 What Happens When Humans Disrupt Nutrient Cycles? Continued climate change will disrupt ecosystems and endanger many species (continued) The models provide evidence that natural causes cannot account for the recent warming The models match the data only when human carbon emissions are included in the calculations The Intergovernmental Panel on Climate Change (IPCC) predicted that even under the best-case scenario, the average global temperature will rise by at least 3.2 F (1.8 C) by the year 2100

91 28.4 What Happens When Humans Disrupt Nutrient Cycles? Continued climate change will disrupt ecosystems and endanger many species (continued) The IPCC s high-level emissions scenario projects an increase of 7.2 F (4.0 C) Thousands of species will change their ranges, moving away from the equator toward the poles or higher up mountainsides Some plants and animals will find it easier to move than others

92 Figure Projected range of temperature increases F C projected global temperature increase year

93 28.4 What Happens When Humans Disrupt Nutrient Cycles? Continued climate change will disrupt ecosystems and endanger many species (continued) It is highly unlikely that entire communities of organisms can just pack and move, intact Some species will have nowhere to go For example, the loss of summer sea ice is bad news for polar bears and other marine mammals that rely on ice floes as nurseries for their young

94 28.4 What Happens When Humans Disrupt Nutrient Cycles? Continued climate change will disrupt ecosystems and endanger many species (continued) Some of the movement of species may have direct impact on human health Many diseases, especially those carried by mosquitoes and ticks, are currently restricted to tropical or subtropical parts of the planet These disease vectors will probably spread poleward as a result of warming temperatures, bringing their diseases, such as malaria

95 28.4 What Happens When Humans Disrupt Nutrient Cycles? Continued climate change will disrupt ecosystems and endanger many species (continued) Some of the movement of species may have direct impact on human health (continued) It may become so hot and dry in parts of the tropics that mosquitoes and some other insects may have shortened life spans, thus reducing vector-borne diseases in these regions

96 28.4 What Happens When Humans Disrupt Nutrient Cycles? Continued climate change will disrupt ecosystems and endanger many species (continued) Although computer models can predict temperature changes, no one can confidently predict the resulting overall effects on human health