Readings:

Journal question: From the two readings make a list of the different types of geologic records in which geoscientists have found a record of past climate changes. An obvious one, discussed in lecture, is in the layers of snow and ice in ice caps. Describe in your own words the picture of regional climate stability of instability that is painted by the authors and this data.


Some introductory thought: This has been and is a very contentious and significant issue. Many, many opinion pieces and news stories on TV, in magazines, and in newspapers have addressed it. Why is it so contentious? Two contributing factors, one scientific the other psychological, may be: 1) the related science is very complex, and 2) many people find many of the implications of our present understanding discomforting. In order to sort some of this out it is very useful to be clear about what question is being addressed. It seems common that public conversations on this issue get confused because the parties involved are actually interested in or addressing different questions. Below is a list of different, but linked, questions.

We can only touch on the tip of this proverbial global warming iceberg here. I encourage you read and find out more, so that you can respond accordingly and with confidence.


Has global warming been occurring?

Just like the Russian dolls, one nested in another, hidden inside are many other questions. How do we measure the 'average' temperature of the earth, or how do we measure whether it has warmed or not? There are both what might be considered direct and indirect approaches in trying to answer this question.

Some direct approaches to answering this question:

Indirect methods or proxy records of global temperature change: These involve measuring changes that can be casually related to temperature changes. Some examples include:

Evidence converges to indicate that global warming has been significant over the last century! The data is extensive, and available to you.


What are the causes of global climate change?

"There must be fifty ways to ...."

Often people are more interested in the question - are humans causing the present warming trend. However, in order to answer this very pertinent question, one needs to understand how the earth system operates, so as to be able to distinguish between 'natural' and "humanity-induced" contributions.

Model for the energy flow of the earth.

Important greenhouse gases:

Some of the myriad of ways to change global climate:

"There must be fifty ways to ...."


How much have humans contributed to global warming?

This is a more difficult question to answer.

History of carbon dioxide levels in the atmosphere. Graph of Mauna Loa observatory readings.

Balancing the carbon budget cycle. Just in terms of shear volume human activity makes significant changes.

GCM and other computer models:

My opinion from reading the literature: The exact percentage of the contribution to global warming by humans is debatable, but I can see no reason to think it is not significant, and plenty of evidence that it is significant.

On interesting debate here is the contribution of carbon dioxide versus water vapor.

From another perspective one can ask the question - is this really the most important question? It is one that is often focused on. Part of it may be the human tendency to play the blame game, but even if humans have not contributed, do we still not need to know what is happening naturally and wouldn't it be wise to anticipate the associated changes?


How fast can changes occur?

The cooling signal associated with the Mt. Pinatubo eruption. The clear lesson is that perturbations can happen on a short time frame.

The best predictor of past behavior is future behavior -> this way to the geologic record.

Tremendous record in Iceland and Greenland ice cores: Chinese dust and Greenland snow.

El Nino and shifting oceanic currents. The basic character of a threshold model. The ocean basins as a reservoir. The geologic record indicates significant climate shift can occur on a scale of decades or less.


What will be the changes associated with global warming?

Changes in oceanic circulation and stratification patterns:

Changes in the distribution of biologic activity:

Changes in sea level:

Changes in weather behavior:

Changes may be a mix of harmful and beneficial from a human perspective, but will involve disruption, require adaptation, and will add uncertainty.


There is one very interesting possibility when it comes to engineering a sea level fall. There are several locations on earth where large basins are below sea level. These could be connected to the sea and flooded! The Afar triangle is one.

In many ways I feel a greater urgency that you understand this issue, more than many others we have discussed this semester.