An absolutely huge topic!

Ecology: "the study of interrelationships between organisms and their environment."

What makes us distinctly 'human', differentiates us from other organisms?

Earth system science: attempt to understand the mechanics and history of the earth as a complex system. Renewed focus on because of the question whether humanity through its collective action is changing the system.

Major components of the earth:

• atmosphere: of renewed interest because of global climate change.
• hydrosphere: surface waters, critical component less is known about.
• cryosphere: glaciers, represent a significant fraction of earth's system, critical linkages with other components.
• biosphere.
  • biomes: (very large terrestrial ecosystems) tropical rain forest, confierous forest, grasslands, savanna, desert, tundra, estuaries, reefs, kelp forest, hydrothermal vents
  • Gaia hypothesis
• lithosphere: from the surface on down plate tectonics as a major framework.
• the hydrosphere and biosphere extend well down into the lithosphere.

How can we attempt to understand complex and open systems such as these?

• devising framework conceptual models of linkages often known as cycles:
  • hydrologic cycle.
  • rock cycle: closed vs. open system models
  • carbon cycle.
  • food chain.
  • components: reservoirs, transfer processes, volumes, residence times,
• importance of feedback loops, and non-linear dynamics.
• computer modeling.
  • remote sensing and Geographic Information Science.
  • parallel processing.
  • technology makes new science possible.
• collaborative science.
• mathematics of chaos, fractals and fuzzy logic (new conceptual perspectives):
  • initial conditions sensitivity: small change leads to big long-term impact due to positive feedback loops.
  • simple equations can generate very complex behavior.
  • how do we deal with uncertainty? Partial set identity.

What is the significance of the human population history and future from an ecologic and environmental perspective?

• determines resources use/depletion history.
• major factor in pollutant volume.
• determinant in disease vectors and spread.
• strong influence on ecosystem disruption.
• determines magnitude of fatalities and property loss in natural disasters as influences population density.

What other populations are we interested in, affected by?

• insect populations (locust swarms).
• algal populations (toxic blooms, ecosystem disruption).
• fish (important food resource).
• most populations if understand the importance of ecosystems and biodiversity.
• biodiversity: tool kit, the range of possibleof responses to change.

Malthus (1766-1834)

A specific case of doubling every generation. Take the case where every couple has 4 children which survive to parenthood and repeat their parents history, a doubling of population every generation. this would result in a sequence like: 2 -> 4 -> 8 -> 16 -> 32 -> 64 -> 128 -> 256 -> 516 -> 1032 -> 2064 -> 4128 ...... The general formula is y=2**t , where t is the number of generations (in years the= average age of parent). This produces a J shape curve, and the number 2 can be considered as a growth constant.

The general continuous case: We can describe an increment of growth with the following sentence: population growth (N) = # of reproducing units (N(i)) * growth constant (k) * time increment (t). The shorthand for this is below

If you integrate then this changes into:

where e=2.71 , where ln is the natural log (base e), N(0)=initial population at time 0, N(t) = population after time t. k' is a different growth rate. You can use this equation in plug and chug mode to predict unrestrained constant growth rate population histories (yet consider how likely is such a history to occur?).

Extrapolating present growth rate - how long before there is 1 person for every square meter of long on the the earth?

Reiterative or incremental description. For successive generations imagine a series of numbers: N(0) - N(1) - N(2) - N(3) - N(4) - N(5) - N(6) ...- N(n). If N(n) is the population at present somewhere throughout this history, then the population in the next cycle (generation), N(n+1), is given by: N(n+1)=B*N(n) , where B is the equivalent of k, a growth constant. Notice by the way that there is no reason why B can't change with time.

What will happen as the population begins to reach a maximum population possible (N(max)) as determined by the carrying capacity of the system? The growth constant must decline in value. Verhulst in 1845 came up with this equation for this situation:

B is a inherent growth factor (reproduction rate when restraining factors are not significant). How does the last term behave as you approach or move away from N(max)? Simple rearrangement of the forumula may better show this behavior.

In this formula the growth 'constant' actually varies with time depending on how close or far away it is from some maximum carrying capacity populations.

Summary of equation behavior:

• at low values you reach a steady equilibrium.
• at intermediate values the population regularly fluctuates between two, then four, then eight levels.
• at high values (>3.5) the population fluctuates chaotically.
• above 5 and the population can go extinct.
• exploring the equation using Excel.

Can you think of some species whose populations show chaotic and/or large fluctations, and whether their inherent growth rate is high or low? Remember that this is a model, and if it has a sound theoretical basis it informs of possibilities, not eventualities.

Populations that show dramatic fluctuations: insects, lemmings, algal blooms, rabbits in Australia.

The lesson is simply in how such systems can behave, and that small differences can have big long term results.

• medical and agricultural technology, disease, environmental toxins, warfare, behavior, space availability, change in critical resource base (food, water, energy).
• Now trying ranking them in order of likely importance.
• Bongaarts (1994) - perhaps possible to feed 10 billion people in 2050. But if doubling time 50 years how about in 2100?

Some examples of ongoing global scale changes.

• deforestation (mainly rainforests).
• desertification and salinization.
• ozone depletion.
• dramatic increase in extinction rates.
• fishery collapses.
• changes in sedimentation patterns.
• global climate change.
• local anoxic events in oceans due to nutrient overload.

The best predictor of future behavior is past behavior:

• Vendian Glaciation Snowball earth: new hypothesis that around 600 Ma oceans frozen to equator.
• Cretaceous super greenhouse: at around 100 Ma earth much warmer than today, interior of continents flooded, and much more.

A model for the myriad of ways global climate can change is given below.

Some of the myriad of ways to change global climate:

• increase upper atmosphere backscatter:
  • by injection of volcanic sulfur aerosols and ash high into atmosphere (residence time of several years)
  • nuclear winter, large asteroid impacts.
• change surface albedo (water, bare land, vegetated land and ice as main surface categories):
  • increase in ice/snow cover and positive feedback cycle (Icebox earth around 600 Ma).
  • change in sea level (interesting feedback loops possible).
  • deforestation and change in albedo
• change in greenhouse gas composition in atmosphere:
  • burning of fossil fuels.
  • exchange with oceanic reservoirs.
  • biologic extraction and preservation in geologic reservoirs.
  • volcanic contributions out of the ordinary.
• consistent change in cloud cover extent (difficult to model).
• change in heat exchange between oceans and atmosphere.
• Gaian component - the role of the biosphere. The basic idea is that the biosphere influences conditions on the planet so that stay favorable to life; i.e. it is homeostatic.

Effects of present global warming?

• Possible change in circulation patterns in the oceans and attendant changes in weather patterns. One model suggests that global warming may cause local cooling in Europe.
• Increase in sea level as ice melts and water warms.
• Change in large storm frequency.
• Increase locally in desertification.
• Ecosystem shifts, especially in polar regions.
• Hard to predict because of complexity of the system. Some may be beneficial to humans, some deleterious.
• Important to remember that population densityhighs often along coasts.

Rwanda - one example.

• 1950-1994 pop. went from 2.5 to 8.8 million, 1992 average number of children per woman = 8.
• 1960s->1990s grain production overall increased, but per person decreased by 50%
• freshwater supply, classified as one of the world's 27 water scarce countries.
• information source: Brown, 1995, State of the World
• other factors contributed to intense social chaos and genocide, but these played some role.

Gulf War: I will leave as self explantory.

Akkadian empire: in Tigres-Euphrates area: sudden collapse at 4170+/-150 yr B.P.Coincides with a sudden (with a sudden aridity episode 300 years long). Local climatic shift. Cullen et al., 2000, Climate change and the collapse of the Akkadian empire: Evidence from the deep sea; Geology, vol. 28, p. 379-382.

Many more examples. History courses often doesn't deal with them, but environmental issues have been a major factor in human history.

Present political framework of environmental efforts:

• over 170 environmental treaties (most ineffective).
• Montreal Protocol - controls CFC s and ozone releases. Partially successful. 1.3 billion kg in 1988 to .510 billion kg release in 1993.
• U. N. Conference on Environment and Development - Agenda 21 (also known as Rio Summit). Much discussion on contribution of fossil fuel combustion to global warming. Also Kyoto conference.
• Law of the Sea, 1994, recognizes EEZs. U.S. refuses to sign.

Changing economic perspective on environmental issues:

• short vs. long term perspective.
• material capital, information capital, social capital, aesthetic capital(?): basic recognition of worth of non-material entities. In addition, there is a redefinition of material capital to include things such as the cleansing benefits of wetlands.
• ecotourism a budding discipline.

Closing statement: Humanity has at least two challenges ahead of us. First, to understand the complexity of systems that make up the earth, and how we affect and are affected by them. Second, to act appropriately with this knowledge. We have addressed a small bit of the first challenge. I leave the second challenge up to you. Those who argue that we are destined to survive has little appreciation for the character of history or the ways of nature, and are wearing blinders. We will ultimately have to act with collective wisdom if we are to survive as an advanced civilization.

Lecture 2