Notes

Outline

Lecture 1: Is Our Planet Fragile or Robust?

What is Climate Change?  Climate change is “a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods.” (from United Nation’s Framework Convention on Climate Change)

Global Warming in the Past 100 Years

Global Warming: Natural or Man Made? Observed warming       0.6°C in the last 100 years. Tectonic Scale       Cooling by 0.00002°C within 100 years Orbital Scale       Cooling by 0.02°C within 100 years Millennial Scale       Uncertain, but probably on the order of 0.02°C (such as the net cooling into the Little Ice Age) Solar Activities       May cause 0.2°C warming

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Human Injection of Carbon

Dilemma for Policy Makers  How do we weight the possible harm of our actions against the advantage of economic growth? è Policy makers want scientists to make precise predictions of the timing and magnitude of the future global warming.

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Can Scientists Predict Future Warming?  YES. Our understandings of the climate system and the recent advancements in computer climate modeling have allowed us to predict the future global warming and its impacts. But with uncertainties. There are still significant uncertainties in predicting the timing and magnitude of the warming.

Why Uncertainties In Climate Prediction? Earth’s climate is determined by enormously complex interactions among the atmosphere, ocean, land surface, vegetation, ice ….. The complexity of the Earth climate system leads to inevitable uncertainties in scientific predictions of the impacts of human activities.

Climate – A Chaotic System  In an effort to study the predictability of weather, Edward Lorenz (a meteorology professor at MIT) started the study of “chaos” systems. The weather/climate system is a nonlinear system. A small change in its initial condition can be amplified to a huge disproportionate effect on the whole system. For example, the small change caused by the flapping of the butterfly's wings in the Far East may causes massive changes in the eventual overall behavior of the storm in the North America.

An Example of Chaos

"It is important to accept..."  It is important to accept that fact that “..although accurate predictions are, in principle, possible on the basis of the laws of physics, such forecasts may be impossible in practice..” because the complexity of our climate system.

How Should Policy Makers Cope with the Uncertainties in Science?  Rather than implement comprehensive programs that decree a rigid course of action  to reach grand and final solution,  We should promote adaptive programs whose evolution is determined by the results of these programs and by the new scientific results that become available.

A Successful Case of the Adaptive Approach  In 1987, the world agreed in the Montreal Protocol that each country would limit its production of the chlorofluorocarbons (CFCs) that contribute to the depletion of the ozone hole.  This decision was made before clear evidence  that CFCs are harmful to the ozone layer.  The regulations were agreed in subject to periodic reviews to accommodate new scientific results.

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Explosive Growth Events  A gardener finds that his pond has one lily pad on a certain day, two the next day, four the subsequent day and so on. After 100 days the pond is completely filled with lily pads. On what day was the pond half full? ANSWER: Day 99

Global Change – An Explosive Growth Event

Consequence of Late Response  Suppose the gardener, once he realizes what is happening, quickly enlarge the pond to twice its size. On what day will the new pond be completely filled? ANSWER: Day 101

Sooner Is Better Than Later  Is our global warming problem close to Day 1 or Day 100?  In stead of waiting for a precise answer to end this debate, it is more important to recognize the explosive-growth nature of the global warming problem.  It is wiser to act sooner than later.

Is Global Warming Really A Catastrophe?

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The Gaia Hypothesis The Gaia hypothesis argues that life itself has been responsible for regulating Earth’s climate. This hypothesis states that the biosphere acts as an organism that maintains conditions that are favor to life.

A White Daisy World When the intensity of sunshine increase     è increase global temperature     è favor the growth of daisy     è increase the number of white daisies     è daisies reflect more sunshine back to space     è global temperatures stop to increase     è daisy acts as a thermostat to control global temperature     è support the Gaia hypothesis.

Controversy About the Gaia Hypothesis  However, if there is threshold temperature beyond which the white daisy would die, then the Gaia hypothesis won’t work. When the intensity of sunshine increase     è increase global temperature TOO MUCH     è decrease the number of white daisies     è daisies reflect less sunshine back to space     è global temperatures continue to increase     è white daisies distinct     è against the Gaia hypothesis.

"There is no doubt that..." There is no doubt that life can affect global climate. But it is controversy whether the biosphere is capable of controlling the global environment to its own benefit.  Our planet may seem robust from the perspective of the entire biosphere, but it can appear fragile from the perspective of individual species, specially for us.

Lessons Learned  Uncertainties in science are inevitable.  We need to familiarize ourselves with the processes that determine the climate of this planet and the sensitivity of these processes to perturbations.  Over tens of thousands of years, we are unlikely to do great harm to our planet as a whole. We can, however, cause inconvenience to ourselves in the next several decades by continually perturbing the global climate.