Ecosystem Health: Human Impacts
1. Ecosystem health linked directly with human population
Ecosystems have supported humans 1,000s years
This is changing -scale of human population growth
2. Human population growth currently > exponential
Increasing @ 1.33% per year
HOW MUCH IS A BILLION ANYWAY???? (Box 28.1)
3. Problem: No population can increase without limits
What is happening now in terms of population growth?
Can we estimate long-term carrying capacity?
2 stable configurations population
Movement between 2 states = demographic transition (1st vs 2nd world)
1950s mortality rates declined sharply
Fertility rates declining more erratically
China most populous nation planet declined sharply
Human population growth patterns 1st vs 2nd world countries
4. How many humans can the biosphere support??
What is the carrying capacity of the Earth (K)?
People trying calculate this for humans since 1679.
> Variance & approaches calculations
Logistic equation
Amount food available
Amount land inhabitable & Maximum density level
Current approach integrate multiple constraints survival
Ecological footprint: arable, pasture, forest, ocean etc. /person
Ecological Footprint various countries vs Ecological capacity: 2 ha globally
Identify sustainability countries > using resources
5. Water (water cycle) may limit water >food in near future
Humans world-wide use 26% all ET water
54% all freshwater runoff (Maximum ~64%?)
Significantly influencing below-ground storage reserves (pollution)
Desalination expensive may not be a solution poorer countries
6. Other major concern human population growth-Climate change
Carbon Cycle – significant impacts burning fossil fuels
Global Carbon Cycle (CO2 cycle)
Dominated by inorganic C in oceans (56xs Atm)
Fluxes land-atm & ocean-atm ~equal; 5 year atm residence time
How fast is CO2 in the atmosphere changing?
Antarctic Ice Cores
900-1750 A.D. 270-280 ppm
last ice age 20-50K ya 180-200 ppm
7. Only 56% CO2 from fossil fuels going Atmosphere.
Where is the rest going??
Latest global budget for Carbon (Schlesinger 1997 in 1015 g C/yr)
Missing 1 billion tons C/yr??
8. Perhaps positive feedback between increasing CO2 and uptake biosphere
Some evidence suggest plants take up > CO2 with higher concentrations
Clear in C3 but not C4 plants because C3 plants usually carbon-limited
May be limited by other factors, nutrients, light, competition no CO2 effect
Long-term studies showing some reduction of stimulatory effects
Tropical forests (97 sites) Amazon may account missing C sink
9. Important know pools (keep in place) & fluxes (max. uptake)!
10. Carbon dioxide atmosphere related to changes in climate
Related to greenhouse effect caused by CO2 other trace gases
Venus (dense CO2 very high temp.)
Mars (thin CO2 very cold temp.)
Sun’s radiation dominated short wavelengths absorbed or reflected (long)
Long wavelengths absorbed Changing Heat Balance Earth –slowly warms
11. Ice cores 160,000 years history important investigate past climate
Direct correlation between CO2 & Temperature last 160,000 yrs
Questions: Can we extrapolate into future based past?
Rate change much faster now than historically
Which was affecting which temp vs CO2
Greenhouse trace gases: Nitrous Oxide, Methane, CFCs, Ozone
12. The Big Picture - Major important impact by increasing human population
13. Ecosystem Services: What Ecosystems do for YOU!
What is all this worth$$$$ How can we calculate it???
Field Ecology : Ecological Economics (Constanza et al.)
Calculated US $33 Trillion per year 2xs Gross National Prod. world
Problem is willingness to pay not there & No cost-benefit analysis projects
Under-appreciated services – Only when gone recognize & appreciate value
Example #1 Purification of Water naturally:
New York City water supply – Catskill Mountains
Water naturally purified forests & streams
Sewage, fertilizer, pesticide local agriculture 1990s pollution
EPA drinking standards not met
1996 – NY City either build treatment plant 6-8 billion $
Or restore integrity Catskill ecosystem
Cheaper buy land in & around catchment & better treatment
Example #2 Pollination Honey Bee Crops Agriculture:
20% decline in honey bee population US
Losses crops 1-6 billion $ per year
14. Summary:
Human impacts on Earth’s ecosystems proportional population
6 Billion people inhabit Earth today increasing 214,000 @ day
Less developed nations contribute to most of this increase
Developed nations use most of resources (energy & materials)
Carrying capacity Earth difficult estimate
May be at or approaching K; Over capacity everyone high std living
Rising CO2 in atm. 1 indication impact humans-climate change
Missing sink of C in global budget – growing forests?
Major effects humans summarized:
Climate change
Global loss biological diversity
Modifying global biogeochemical cycles
Land use change
Ecosystems provide us many services most which we take for granted
Future generations will have to understand & protect these services
Planet has some potential resilience to impacts, but not infinate
You can affect positive change in many different ways
Think Globally – Act Locally!