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Sustainability Matters 19: Ice Cores

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Ice Cores – Global Temperature, Carbon Dioxide, and other Natural Phenomena

Antarctica has been cold for a long time. Each year a new layer of snow and ice builds up, as surely as a tree adds a ring each year it lives. By analyzing the relative number of atoms of isotopes of hydrogen and oxygen, the temperature over time can be indirectly measured. This blog will focus on natural phenomena concerning global temperatures.

Using this information, researchers have come up with the following Antarctic temperature record over the past 400,000 years.  The present time is to the left.

Fig. 3-33:   Temperature Graph Sources: 2000-1979: Satellite stratospheric data: 1979-1871: S. Hemisphere ground temp. data,1871- 422k B.P.: Vostok Ice Core Data, http://www.geocraft.com/WVFossils/last_400k_yrs.html

Five interglacial periods are represented by the shown here (five major peaks), and we have had a spell of relatively warm climate for the past 12,000 or so years. 

Ice cores give us more information than just past temperatures. Air bubbles are frozen into the ice. Inside each air bubble is a sample of the atmosphere, as it was at the time the bubble was frozen into the ice. By measuring the concentration of CO2 in the air bubbles over the course of time, researchers have developed a record of the CO2 in the atmosphere dating back almost half a million years. These measurements are in parts per million by volume (ppm/v).


Fig. 3-34: CO2 Graph Sources: 2001-1958: South Pole Air Flask Data 1958-1220 B.P.: Law Dome, Antarctica 1220 B.P.- 2302 B.P.: Taylor Dome, Antarctica2302 B.P.- 414k B.P.: Vostok Ice Core Data http://www.geocraft.com/WVFossils/last_400k_yrs.html

You can see from the above graph that there is a range in the ppm/v of CO2 as well as a pattern of increases and decreases over time.  The range has consistently been between around 180-280 ppm/v for almost the last half million years. http://www.geocraft.com/WVFossils/last_400k_yrs.html The concentration of CO2 in the Antarctic atmosphere prior to the Industrial Revolution was about 280 ppm/v.  

Of particular interest is the pattern shown when both temperature and CO2 concentrations are plotted on the same graph over the course of time.  In the following graph, carbon dioxide concentrations are plotted in red, and temperatures are in blue. The present time is to the right.

Fig. 3-35:http://www.daviesand.com/Choices/Precautionary_Planning/New_Data

The figure above shows the temperature and CO2 data plotted together on one graph published in 1999. The temperature scale (degrees C) is on the right and the CO2 scale (parts per million by volume – ppm/v) is on the left.  By combining these two scales onto one graph, we can see that there is an intimate relationship between CO2 and temperature.  

This graph indicates that the total variation in temperature at the Antarctic has remained within a 14 degree C range for the 425,000 years, and the CO2 concentration has ranged between 180 and 380 ppm/v.  

If you look at the upper right side of this graph, you will see that in 1999, where the graph ends, the CO2 levels were in the 380-ppm range. “In 2014, the average global atmospheric carbon dioxide level rose to 397.7 parts per million, substantially higher than the 278 parts per million floating in the atmosphere during preindustrial time…or before 1750” 

Fig 3-36 Ice core data (1999) with updated CO2 data for 2015

CO2 levels go up and down seasonally, and according to NASA, in February of 2015 they reached 400.26 ppm for the first time. I took Figure 3-31 which reflected data from 1999 and added another row of yellow boxes on the top line of the figure (3-36) above to show today’s numbers. Compare today’s CO2 reading at the far right of the graph to previous levels.  We are at the highest level, by far, in the last 425,000 years.

“For the past ten years, the average annual rate of increase is 2.07 parts per million (ppm) This rate of increase is more than double the increase in the 1960’s. 

We’ve discussed several proxies for climate data from, tree rings, corals, ice cores, bogs, boreholes, and we’ve only scratched the surface.  Through numerous creative research projects, scientists we have generated lots of data on past temperatures and atmospheric composition and seen a correlation between CO2 and temperature.  We’ve found climate proxies representing all latitudes of the world. 

What are Bore Holes?

Bore holes come from humans drilling for resources in the ground.

This, in turn, gives us access and ability to measure temperatures at different depths. Such measurements reveal a pattern where the temperature rises with depth. Using these measurements, as well as known information about the sun’s input of energy, it is possible to work out the expected temperatures at various depths below the surface.  

When the temperature of the earth is warmer, it stands to reason that more heat will be absorbed.  This heat moves into the earth via conduction, warming the material it encounters. Thus, if higher temperatures than expected are found, they are an indication that heat energy from warmer surface temperatures has diffused down to that layer of the earth.

As a side note: The University of Michigan maintains a Global Database of Borehole Temperatures and Climate reconstructions which can be found at https://www.ncdc.noaa.gov/data-access/paleoclimatology-data/datasets/borehole

Using information from bore holes shown on the map below, we get a good idea of current and past temperatures as shown in Figure 3-30.

Figure 3-30: NOAA Borehole Data Sites

The diagram below is a global perspective of surface temperature change over the last five centuries, averaged from 837 individual reconstructions.  The thick red line represents the mean surface temperature since 1500 relative to the present-day. The further back we go, the larger the margin of error as the shading around the line shows.  The blue line represents measured temperature. 

Figure 3-31: Source: https://www.ncdc.noaa.gov/paleo/borehole/core.html

Upon first reading, there is a natural tendency to think this is some crazy scientist’s idea of a fun time. How can it be accurate?   Analysts have a way of testing the accuracy of this and other proxy studies because we can compare the readings, we get using this methodology with actual measured data from 1900 through 2000.  Using these two sets of data, we can calibrate the differences in temperature between model and reality, thereby verifying the validity of this method as a measurement tool.   This research measures the relative temperature dating back 500 years and concludes that the earth has warmed by about 1 degree Celsius or 1.8 degrees F during this period.  

What are Peat Bogs?

These plants die and decay into a material we call peat. Peat bogs accumulate material at a rate of 1 cm in ten years. A bog in Northern Europe, which started accumulating peat after the last Ice Age receded, would today have a depth of 12 meters.  In regions that are fed by rainwater only (including areas of the United Kingdom and Northwest Europe as well as tropical areas in the Southern Hemisphere), a record of both temperature and rainfall can be discerned by taking core samples of this decaying matter.  

Using core samples from peat bogs, past climatic conditions can be determined. The age of a specific part of a core can be determined by radiocarbon dating. Since history has recorded the date of many volcanic eruptions, volcanic ash in peat cores can be used to pinpoint a date more accurately with a set of climatic conditions.

Figure 3-32: Peat bogs around the world: (Top left) The hummocky terrain of Kaipo Bog a remote site accessed by hiking through The Urewera National Park, North Island, New Zealand

(Top right) Deep moss bank on Green Island, Antarctic Peninsula provides a vivid and unexpected splash of color in a landscape dominated by ice 3) The range of colors and intricate mix of landforms on a sunny day at Petite Bog, Nova Scotia, soften the common image of bogs as dull, dour places (Bottom left) Vivid orange bog dominated by Sphagnum magellanicum sits in the shadow of the Southern Andes.

The dated samples are analyzed using one or more proxy methods which can be used to investigate past climate from evidence left in rain-fed peat bogs.

For example, if we know the age of a sample from a peat core, we can analyze that sample for the insects and moss which are preserved in that core.  We have a good knowledge of which species prefer which climates, so by correlating species with time we can make an estimate of the climate in a particular period.

Other climate proxies include measuring the amount of a heavy isotope of oxygen which is typically deposited in a stratum of a bog located in northern latitudes.   Since deposition of heavy oxygen is dependent upon temperature, a temperature record can be established using this data. Similarly, cellulose preserved in bogs can be tested and another set of proxy climate data can be created.

Are there any Multi-proxy studies?

When more than one proxy study exists for the a given period, comparing the results of several studies can help to further verify the results.

Here is an example of how this is done. 

The first graph below uses seven proxy studies, two of which go back 1,800 years. The ‘call-out’ second graph looks at fifteen different studies covering the last 1,000 years of that time. The accuracy of the data can be verified and calibrated to the actual thermometer readings which are shown in bright red.

Each line represents a separate proxy study. There is as much as a degree C variation in the exact temperature predicted by the different studies. Interestingly, there is a clear pattern of warm periods and cool periods, and even with the number of predictions, historical highs and lows within a degree can be established.

Figure 3-37: Spaghetti plot of the new reconstructions over a) 1800 and b) 1000 years along with selected older ones for comparison. – See more at: http://www.realclimate.org/index.php/archives/2008/09/progress-in-millennial-reconstructions/langswitch_lang/en#sthash.bM4d9LQq.dpuf


The value of proxy data is reinforced when measurements taken from different places using different methods are compared and show high correlation.   The following graph represents the work of eleven different proxy studies.  Although there is a relatively wide range of variation, the results are remarkably similar over this time frame.


Figure 3:38: Temperature Anomalies for the Last 2000 Years

[above from global warming art http://en.wikipedia.org/wiki/Image:2000_Year_Temperature_Comparison.png ]

Here is a series of proxy measurements going back 800,000 years which gives us information about a range of factors used which have each been the subject of a separate proxy study.  When we combine them, we find high correlations in their results. The result gives us more confidence in the overall results.  

Figure 3-39: Climate Proxy data for the past 800,00 years.

Taken as a whole, the proxy methods described in this section reveal a consistent correlation between carbon dioxide levels and temperature over the course of geologic time. The correlation is clear and supported by multiple peer-reviewed studies by multiple teams of scientists from all over the world.  As carbon dioxide goes up, so does temperature.

If you are interested in finding out more, a very accessible article can be found in Maurangi Magazine on paleoclimate. 

http://www.mahurangi.org.nz/Climate/Paleoclimate-Implications/Human-Made-Climate-Change-v2.php

Photo: Wes Golomb

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