Topic Guide: Paleoclimate

 

In this activity you will form groups, conduct research into paleoclimate, and report back to your lab section in the form of a presentation. At the end of this activity you will find suggestions for the format of the presentation. You will use the data you investigate as evidence for your statements. Please use these suggestions and the “How to make a class presentation” (Resource 1) as guidelines for your presentation.

 

Overview:

To predict the future climate with confidence, we need to understand the historical climate. We know that there have been large natural fluctuations in the climate and we need to keep this in mind when interpreting present day fluctuations.There have been ice ages and even periods where the Earth has been completely covered with snow and ice (called the “Snowball Earth Hypothesis”). Scientists also find correlation between ice ages and variations in the Earth’s orbit (Milankovitch Theory).

 

Data reliability and coverage is of prime importance in paleoclimate studies. So, when doing this study, be sure to understand where the climate data came from, what region it covers, and how the climatic variable (e.g. rainfall, temperature, CO2, etc) was derived from it. In some cases it is possible to directly sample the variable (e.g. CO2 trapped in bubbles in ice cores). In other cases, the variable must be inferred from a “proxy” (e.g. temperature from oxygen isotope ratios).

 

Key processes and concepts to review before beginning:

Resources:

 

After completing this investigation you should be able to:

  1. Understand the significance and possible causes of climate change as recorded in ice cores and sediment cores.
  2. Be able to identify which atmospheric or land properties (or constituents) vary along with the temperature variations.
  3. Use ice core and sediment core data to discuss how the Earth’s temperature and major greenhouse gases have changed during the last hundred thousand years.
  4. Use paleotemperature data to explain how past climate variations compare to currently observed variations . 

 

You can immediately begin exploring the data, but if you need more background information about paleoclimate, please review the websites that provide background information (found after the data section).

 

Data and Background:

http://www.ngdc.noaa.gov/paleo/ei/ei_cover.html

At this site you can access the data necessary to answer some important questions concerning paleoclimate. In order to understand recent (last 150 years or so) climate changes, it is important to understand earlier climate change patterns.

 

Go to the “Temperature Reconstructions” link. This site contains data reconstructions for paleotemperatures for the past 1000 years and other more recent datasets. Because the time period represented varies, the detail of the graphic varies. Be aware of this when you are interpreting the graphs. It is important to examine several graphs. Notice if the data is from a specific hemisphere or if it is global data. Look at Figure 8. How would you interpret this graph?

 

http://www.ngdc.noaa.gov/paleo/ei/ei_millenm.html

This site shows a paleotemperature reconstruction since 1000 AD.

After examining several different graphs, answer the following questions.

What is the trend? Use the data as evidence for your observations. Around 1900 there was a change in the trend of the data. What is it? Again use data from the various temperature reconstructions as evidence.

 

 http://www.ngdc.noaa.gov/paleo/pubs/crowley.html

Figure 1 is a comparison of decadally smoothed (i.e. ten year average) Northern Hemisphere mean and annual temperature records for the past millennium (1000-1993), based on paleotemperature reconstructions from two different groups of scientists. The red and the blue lines represent the data. The gray lines are standard deviation calculations and can be ignored.

Do the two datasets agree? What could be the source of some of the variations (minor or major) between the datasets?

 

http://www.sprl.umich.edu/GCL/Notes-1998-Fall/climate_rec.html

Oceanographers use ice cores to determine global mean sea-surface paleotemperatures. Ice cores can be taken from either the Northern or Southern hemispheres. Specifically, Oceanographers look at differences in the amount of the Oxygen 18 isotope to determine the mean surface temperature of the Earth’s oceans. Figure 1 shows ice core data that provides scientists with estimates of sea-level air temperatures over the past 160,000 years. One axis of the graph is thousands of years, and the other is the change in the oxygen 18 isotope. Use what you have learned so far to interpret the graph. How would you interpret this graph (in terms of global sea surface temperatures) for the past 80,000 years? Be sure to site the evidence in the graphic. 

 

Hint: The change in the oxygen 18 isotope can be interpreted as change in global mean sea-surface paleotemperatures, more negative is colder, less negative is warmer.

 

One side of the graph shows data from ice cores from Antarctica (Southern Hemisphere) while the other side shows data from Greenland (Northern Hemisphere). Does the ice core data for Antarctica and Greenland agree? If there are differences, what could cause those differences? Think of the geographical layout of continents on the Earth.

           

The ice cores also contain other gases such as methane. Figure 2 shows the data for the concentration of methane (parts per billion) versus time. What is the trend? Make sure you note the scales. Can you suggest a reason for this trend?

           

What is the relationship between the concentration of carbon dioxide and methane and paleotemperature. Make a prediction and then use Figure 3 to determine if your prediction was correct.  Please note that the time scale in Figure 3 is reversed. What is the relationship? Cite the data.

           

Figure 5 shows other data sources that help to reconstruct paleotemperatures. Again, note the time scale and that it is reversed from the first few examples you examined. What are these data sources? What is the time frame they cover? Fill in the following chart.

 

Data type            Time frame         Trend (>150 yrs)   Trend (</=150 yrs)      Data

Instrument

~1890-present

N/A

General warming trend since 1900

0.5 degree C increase in temp.

Historical

 

 

 

 

Pollen and glaciers

 

 

 

 

Marine shells and sea level terraces

 

 

 

 

Deep sea sediment cores

 

 

 

 

 

 

http://www.ngdc.noaa.gov/paleo/vostok-dd.html

Use what you have learned to interpret this graph of data from the Vostok ice core. Cite the data and compare this to your findings in other sections of this ministudy.

 

More background information:

Please take some time to learn more about the background information available for the topic of paleoclimate. If you learn something new and interesting, please share it with the lab in your presentation.

 

Information about paleoclimate:

http://www.ngdc.noaa.gov/paleo/globalwarming/paleo.html

Ice ages, glaciations, and sea level change

http://www.ngdc.noaa.gov/paleo/glaciation.html

http://www.museum.state.il.us/exhibits/ice_ages/index.html

http://www.pbs.org/wgbh/nova/ice/chill.html

http://pubs.usgs.gov/factsheet/fs2-00/

The Milankovitch Theory: http://www.ngdc.noaa.gov/paleo/milankovitch.html

Fossil Pollen: http://geology.er.usgs.gov/paleo/sporepollen.shtml

Tree rings: http://tree.ltrr.arizona.edu/skeletonplot/introcrossdate.htm

Presentation Framework

Your presentation should include a brief overview explaining the significance of paleoclimate and how studies of paleoclimate relate to issues of today. You should then choose as many of the following topics as is necessary to explain the concept. Choose topics that you think might be relevant to understanding climate change. Your presentation should include interesting findings from your investigations, backed up with data. You must use the paleoclimate data in your presentation.

 

You may choose from the following list of topics, or investigate a topic of your own. The topics in the list are examples of investigations that could be made using the data available at the URL’s listed above.

 

Data Driven Topics:

 

Overview type topics:


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