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Human impacts and climate change Overfishing Deforestation Pollution Any physical, biological, or chemical change in environmental quality that adversely affects living organisms can be considered pollution Point sources Discharge pollution from specific locations – Factories, power plants – Easy to control through regulations Non-point (diffuse) sources Non-point sources - Scattered or diffuse, having no specific location of discharge – Agricultural fields – Very difficult to monitor and regulate – Largest pollution problem currently Water pollution Infectious agents Main source of waterborne pathogens is improperly treated human waste Animal wastes from feedlots and fields is also important source of pathogens Infectious agents Oxygen-demanding wastes Certain organic materials added to water stimulates oxygen consumption by decomposers – Sewage – Paper pulp – Food-processing wastes Oxygen sag Gulf of Mexico hypoxia In 1974, scientists found areas where oxygen had disappeared from bottom sediments and the water column Hypoxic area in 1993 after Mississippi floods doubled in size Stays from May to September Influx of nitrogen from Midwest/Great Plains is cause Hypoxic area continues to grow Harmful algal blooms (HABs) HABs have become increasingly common in slow-moving and shallow waters, usually due to nutrient enrichment Algal blooms produce toxins Red tides are blooms of deadly aquatic algae Cryptosporidium in 1993 entered the Milwaukee public water supply, making 400,000 people sick and killing at least 100 people Sediment Human activities have accelerated erosion rates in many areas Fills lakes, obstructs shipping channels, makes drinking water purification more costly Organic chemicals Thousands of natural and synthetic organic chemicals are used to make pesticides, plastics, pharmaceuticals, pigments, etc. Many are highly toxic and bioaccumulate Biomagnification Cells have special mechanisms for bioaccumulation - selective absorption and storage – Dilute toxins in the environment can build to higher levels inside cells and tissues Biomagnification - toxic contents of a large number of organisms at a lower trophic level is accumulated and concentrated by a predator at a higher trophic level Thermal pollution Raising or lowering water temperatures from normal levels can adversely affect water quality and aquatic life – Oxygen solubility in water decreases as temperatures increase Species requiring high oxygen levels are adversely affected by warming water Air pollution Sulfur compounds Two thirds of total sulfur in the atmosphere is from human activity – Predominant form of anthropogenic sulfur is sulfur-dioxide from fossil-fuel combustion Can react with water to form acid rain or acid deposition Acid deposition pH and atmospheric acidity – pH scale ranges from 0-14 7 = Neutral; <7 = Acidic; >7 = Basic – Unpolluted rain generally has ph of 5.6 Acid deposition Aquatic effects – Many fish unable to reproduce at low pH Forest damage Carbon oxides Predominant form of carbon in the air is carbon dioxide – Increasing levels due to human activities Carbon monoxide is a colorless, odorless, toxic gas produced by incomplete fuel combustion Particulate matter Respirable particles smaller than 2.5 micrometers are among most dangerous Diesel fumes dangerous Reduces visibility and leaves dirty deposits on surfaces Nitrogen compounds Also called NOx 60% of NO emissions are anthropogenic Produced by fuel combustion in transportation and electric power generation Excess nitrogen causing eutrophication in water bodies Encourages growth of weedy plant species Photochemical oxidants Products of secondary atmospheric reactions driven by solar energy – Ozone formed by splitting nitrogen dioxide Metals Many toxic metals occur as trace elements in fuel Since leaded gasoline was banned, children’s average lead levels have dropped 90% and IQs have risen by 3 points Mercury Released from coal burning power plants and waste incinerators Bioaccumulation in aquatic ecosystems Long-range transport Grasshopper effect Contaminants evaporate from warmer areas and condense and precipitate in cooler areas Stratospheric ozone Discovered in 1985 that stratospheric ozone levels were dropping rapidly during September and October – Occurring since at least 1960 At ground-level, ozone is a pollutant, but in the stratosphere it screens UV radiation Stratospheric ozone depletion CFCs were main culprit – Persist for decades – Ban established in 1987 – Models show that stratospheric ozone levels could reach normal levels by 2040 Free Cl is a catalyst Is global climate changing? – Global average surface temperature rose 0.6o C during 20th century – Cold and frost days decreased for nearly all lands in the 20th century – The 1990’s were the warmest decade of the past 1000 years – Average summer and winter temperature in Alaska are 4°C higher than average Keeling curve IPCC In 1988, the Intergovernmental Panel on Climate Change (IPCC) was formed – Released third report in February 2001 700 scientists from 100 countries reviewed results from 3,000 studies Recent changes in world’s climate have had discernable impacts on physical and biological systems Human activities are at least partially responsible IPCC in 2007 IPCC now recognizes that humans are responsible for global climate change and that there is even more evidence of effects on biological and physical systems What effect is climate change already having on physical systems? What effect is climate change already having on biological systems? What are the disagreements among scientists? Potential global climate change What is being done? International Climate Negotiations Kyoto Protocol (1997) - United Nations Pact – 178 nations agreed to roll back carbon dioxide, methane, and nitrous oxide emissions about 5% below 1990 levels by 2012 Controlling greenhouse emissions Reducing carbon dioxide levels – Renewable energy sources may offer the best solution to climate problems Capturing and storing carbon dioxide – Carbon management Other countries are already doing it!