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
Cryptosporidiumin 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!