1. The Temperature Puzzle.

Show “Temperature Puzzle” video. Instruct students to watch for:

• Examples of evidence of change (Global sea level is rising; arctic summer sea ice is declining)

• Where we get data (NASA satellites measuring sun’s energy)

• Three pieces of climate puzzle (how much energy from the sun hit the earth; how much of the sun’s energy is reflected back to space; how much of the sun’s energy is trapped, heating our planet)

• Impact of brightness of our planet (brightness is more reflective; when ice cover shrinks, making the surface of the earth darker, the planet becomes warmer; more water evaporates, forming more clouds which potentially can reflect more sunlight, as well as forming a blanket of the most prevalent greenhouse gas – water vapor)

• Potential Human Actions (Humans cannot control the amount of water vapor, but do have the potential to control the second most prevalent greenhouse gas – CO2)

2. Is the world getting warmer?

Just figuring out the average global temperature is difficult, and data is always messy. So different organizations, using different method compile different data sets.

Evidence of Change Data transparency master (slide 1) shows compilation of different data sets measuring different aspects of climate change, compiled by different groups of people or organizations over different time spans.

What are the indicators which provide direct information about global warming? (Land Surface Temperature, Sea Surface Temperature, Marine Air Temperature)

What are the indicators which provide indirect information about global warming? (sea level would increase, Northern hemisphere snow cover would decrease, ocean heat would increase, and glaciers and ice caps would decrease)

More than 50 different data sets are represented. What is the primary trend they show? (The earth is heating up)

Global Temperature and Carbon Dioxide transparency master (slide 2) shows the summary chart developed from these data sets.

What does the horizontal line indicate? (Average global temperature from 1880 until 2010)

What do each of the bars represent? (deviations from the average, for each year)

What are the trends in three time periods: 1880-1936, 1937-1976, and 1977-2008? (1880-1936 all years below the average, 1937-1976, about equally above and below, 1977-2008, all above and increasingly well above)

3. Is there a relationship between temperature and CO2?

The most recent atmospheric carbon dioxide data set measured on Mauna Loa in Hawaii. This record constitutes the longest record of direct measurements of CO2 in the atmosphere, but it is available only since 1959. Data is collected there because it is one of the sites most remote from local and regional sources of CO2 emissions, so it is better able to monitor global atmospheric changes.

CO2 emissions (CO2 produced by fossil fuel burning) and average world temperature can both be estimated, and at least partially by direct measurement, back through 1900.

Student Activity 1: Graphing Temperature and Carbon Dioxide in the 20th century provides three kinds of relatively recent data which can be plotted on the same graph. (Slide 3)

What do the solid circles represent? (degrees different from the average temperature, for 1950-1979)

What two scales are represented on the vertical axis on the right, and in what units of measurement? (millions of tons/decade, and CO2 concentrations in the atmosphere in parts per million)

The graph is incomplete. Complete the graph using circles to represent emissions per decade beginning in the 1960s, and use X’s to represent the concentration of CO2 and answer the questions.

What is a generalization about the relationship between temperature and CO2? (They both increase over the last century, slowly at first, and then more rapidly)

What is the relationship between emissions and CO2 in the atmosphere? (They both increase)

What is the most accurate causal statement about the trends? (The two trends are similar, and we know from experiments that CO2 and temperature are related, but cause cannot be identified) (Slide 4 shows completed graph)

4. How do we know what has happened in the distant past?

In this investigation, we will look at the record shown by a long ice core from Antarctica. Graphing Temperature and Carbon Dioxide over the last 450,000 years (student activity) shows the record of temperatures for the last 450,000 years. (Slide 5)

Over that amount of time, how many temperature peaks do you see? (five)

About how far apart are the peaks? (about 100,000 years)

These peaks correspond with Milankovitch Cycles, which are small variations in the orbit of the earth and the tilt of the earth’s axis that change the amount of solar energy entering the atmosphere.

During the low temperature valleys between the peaks, glaciers expanded in Europe and North America during those times of low temperature. Humans began migrating out of Africa in the most recent ice Age, 90,000 to 100,000 years ago.

The table shows the measurements of carbon dioxide at intervals of 20,000 years during that same time period, up to the year 2,000 CE. Using the scale on the right of the graph put a small dot to indicate each date/ppm observation.

Do temperature cycles and CO2 trends seem correlated? (Yes - All of the times of high temperature were also times of high carbon dioxide concentration, and the cold times were associated with below-average concentrations of carbon dioxide)

Does change in temperature precede changes in CO2, or the reverse? (There are examples of both)

Measurements of gas bubbles in an ice core are accurate and reliable, but they are not precise. It is hard to determine the exact date of a measurement, because each layer of new snow may be only a few millimeters thick after it has been squeezed to ice. Moreover, ice is not completely rigid, and bubbles or sand particles can move a little. As a result, the estimated dates may be off by a few hundred years.

This fact makes it difficult to decide for sure what came first.

Looking at the graph, did the temperature start to rise and the carbon dioxide concentration follow, which would be the case if the carbon dioxide were the results of accelerated decomposition of organic matter? Or did the CO2 rise and the temperature follow, which would be the expected result of a stronger greenhouse effect? (The graph shows evidence of both)

5. Tying it all together.

In the past, temperature changes were consequence of solar energy changes, but the modern rise in temperature is different, because solar energy has not changed much. What has changed is the level of carbon dioxide, which in 2010 was 390 ppm, much higher than even the highest peaks in the last 20 or so cycles.