Last week we talked about glaciers and their impact on climate change. This week, we’ll be going into more depth while also discussing other topics such as vegetation and corals. We’ll continue where we left off showing some pictures of different glaciers throughout the world.
Fig. 3-18: Image Credit: National Snow and Ice Data Center, W. O. Field, B. F. Molnia
On the left is a photograph of Muir Glacier in Alaska taken on August 13, 1941 by glaciologist William O. Field. On the right is a photograph taken from the same vantage point on August 31, 2004 by geologist Bruce F. Molnia of the United States Geological Survey (USGS).
According to Molnia, between 1941 and 2004, the glacier retreated more than twelve kilometers (seven miles) and thinned by more than 800 meters (almost half a mile). Ocean water has filled the valley, replacing the ice of Muir Glacier and the end of the glacier has retreated out of the field of view.
The glacier’s absence reveals scars where glacier ice once scraped high up against the hillside. In 2004, trees and shrubs grew thickly in the foreground. In 1941, there was only bare rock. This plant growth is a good example of the first stage of succession we discussed earlier in the series.
New habitat with niches for colonizer species is now available after rock covered with ice for thousands, in some cases, millions of years is exposed.
Grinnell Glacier, Glacier National Park, Montana
Fig. 3-19: Left: Summer 1938. Right: Summer 2005. (Photo: U.S. Geological Survey)
Pedersen Glacier, Kenai Fjords National Park, Alaska
Fig. 3-20 Left: Summer 1917. Right: Summer 2005. (Photo: The Glacier Photograph Collection, National Snow and Ice Data Center/World Data Center for Glaciology.)
Qori Kalis Glacier, Peru
Fig. 3-21: Left: July 1978. Right: July 2004. (Photo: Glacier Photograph Collection of the National Snow and Ice Data Center/World Data Center for Glaciology.)
Professor Lonnie Thompson, Senior Research Scientist, Byrd Polar and Climate Research Center at The Ohio State University, has been mapping the retreat of Qori Kalis Glacier since 1978. In fact, he took the photo on the right. “In our first 15 years of observation it was retreating at a rate of 6 meters per year and in the last 15 years it’s been averaging 60 meters per year,” says Thompson. “It is the world’s largest tropical ice cap and it has lost about 25 percent of its area since we started observing it.”
What’s involved in the Interaction of Land and Sea Ice?
When white sea ice melts, the ocean surface becomes dark, and solar heat that was previously reflected is now absorbed. The reflectivity of a surface is called its albedo. The earth’s average albedo is about .31 which means that about ⅓ of the sunlight which hits the earth is reflected. According to the National Snow and Ice Center, sea ice reflects 50 to 70 percent of the incoming solar radiation while the ocean only reflects around 6%. (Remember water has a high ability to absorb heat.)
Sea ice is melting and the earth is absorbing more of the sun’s heat. In this way, the existence of ice in a region tends to keep it cooler. The loss of ice over this time period and the increased absorption of heat which accompanies open oceans are two more pieces of evidence of a warming climate.
I’d like you to do an experiment.
Fill a glass full of ice. Now fill it as close to the top as you can with water. Let the glass sit at room temperature until all of the ice melted. Does the glass overflow? Now, place the full glass of water in the sink, and slowly drip water into it. Does the glass overflow?
I suspect your answer to the first question will be no, the glass did not overflow when the ice melted, and to the second question, yes, the glass overflowed when water was dripped into it.
Melting ice, floating in water like the ice in the glass, will not cause the sea level to rise. However, ice which has melted over land and flows into the ocean will raise the sea level.
Greenland and the Antarctic are the two places with the most ice over land. Data from NASA’s Grace satellites show that the continent of Antarctica has been losing about 134 billion metric tons of ice per year since 2002, while the Greenland ice sheet has been losing an estimated 287 billion metric tons per year. (Source: Grace satellite data). This data further confirms the earth’s warming.
The question we asked at the beginning of this section was: “How do we know the earth is warming?” The answer is: by temperature measurements from satellites, airplanes, land, ships, buoys and submarines. With that warming, we see melting of snow and ice all over the planet, and since matter cannot be created or destroyed and must go someplace, we see increases in ocean levels and changes in ecosystems.
Please remember the difference between weather (short term) and climate (long term) factors. The fact, for example, that the winter of 2013-2014 was colder than average does not mean that climate change is not happening. Weather is the daily or seasonal variation in conditions such as temperature, precipitation and wind. Climate is a long-term phenomenon and the sum of short-term weather conditions. You will recall that the graph of record highs and lows contained some record lows. The graph showed a trend, though, that there were fewer record lows and increased number of record high temperatures – a pattern indicating a long-term warming trend.
The next question we must ask is, “What was the climate like before we could measure the temperature?”
Measuring Temperature Prior to the Invention of the Thermometer
Earth is about 4.6 billion years old, and humans have been measuring temperature for around 150 years. We’ve got a clear picture from the previous section that virtually all measurements made during this period indicate the current climate is warming. How can we also tell what the temperature was prior to human measurements? There are a variety of indirect methods for making these measurements. They include observations of such things as tree rings, coral, boreholes, changes in plant and animal species, precipitation patterns, ice and snow cover, and peat bogs. All leave clues which can be used to estimate past temperatures. These indirect methods or proxies help us model climatic conditions from the past.
How are Tree Rings and Coral affected?
Both trees and coral grow each year, and the record of their growth is left in their rings and layers, respectively. In northern latitudes, where there is distinct and extreme weather variation, annual tree rings are often visible to the eye. One new ring forms each year, which not only tells us the tree’s age, but also provides us with information about past conditions and the history of the tree.
figure 3-24 An increment borer has been inserted into the trunk of the huon pine in Tasmania pictured here. The scientist is holding the extractor with tree-ring core that was removed on it.
There is a correlation between environmental conditions and the size and composition of tree rings. Many factors contribute to the size of each tree ring, including water availability, sunshine, temperature and air quality. A year with good environmental conditions will produce a healthy, wide ring. A year with difficult conditions, such as drought or fire, will produce a thin, restricted ring.
The atmosphere’s composition also affects tree growth. Trees, like all plants, need carbon dioxide for growth. At times when there is more CO2 in the atmosphere, trees grow faster.
When trees grow densely packed together, there is more competition for light and nutrients, and therefore the trees grow more slowly. Growth may also be slowed down by the presence of parasites. While the correlation between tree ring width and temperature is not a simple measure, what is believed to be a reasonable record of temperature can and has been established.
The following graphs plot tree ring data and measured temperature in the Northern Hemisphere, the Southern Hemisphere and the world. The pink line represents the tree ring data and the black line represents the measured temperature. Look at the portions of the next three graphs which show both tree ring and temperature data sets. It is clear from the areas where the two sets of data overlap, that there is a correlation between the information provided by the tree ring data and the measured temperature.
Figure 3-25: Source: http://www.climatedata.info/proxies/tree-rings/
Using these three graphs, what do you think the temperature trend was between 1800 and 1850? Are you confident in your answer? What was the temperature in 1825? Are you as confident in your answer? Why?
Data collected with tree rings won’t tell us what the temperature was at 9 am on April 3, 1860, but in each of the above graphs we can see a correlation between recorded data and tree ring or ‘proxy’ data. Though we certainly cannot know the exact temperatures at a specific time, tree ring data gives us information about trends which we can be fairly confident are accurate.
What’s the story with Coral?
Similar to tree rings, coral adds a layer of calcium carbonate each year. The thickness and composition of the layers give a good indication of the temperature and other environmental factors present when the layer was formed.
Figure 3-28: Credits: Jerry Wellington, Department of Biology, University of Houston and NOAA Paleoclimatology program/Dept. of Commerce (left) Rob Dunbar, Department of Geology and Geophysics, Rice University and NOAA Paleoclimatology program/Dept. of Commerce (right)
The X-ray image (left) of coral samples from the Galapagos Islands clearly shows a banded growth pattern. The coral samples (right), also from the Galapagos, show the appearance of samples before and after they have been X-rayed and the growth bands have been marked. Black lines indicate annual growth bands, while the orange and blue lines indicate seasonal patterns discerned within the annual trends.
Sensitivity to environmental factors makes coral a good gauge of local climate. The layered structures that corals deposit as they grow have annual banding patterns reminiscent of those found in tree rings, ice cores and lake sediments. The texture of the calcite deposits varies seasonally, with lighter-shaded layers appearing during the summer when growth is fast, and dark layers forming in the winter when growth slows. Individual corals can live for decades or centuries. As in the case with tree ring records, we can correlate data from living corals with those from older, dead corals to establish continuous climate records spanning several hundred years.
Figure 3-29: Credit: NOAA Paleoclimatology program/Dept. of Commerce
Yellow dots on the map show locations from which coral samples have been collected. The paleoclimate proxy data gleaned from coral nicely complements tree ring and ice core data. Since coral is found near the equator, tree ring data is frequently collected in mid-latitude temperature forests, and most ice cores come from high-latitude polar regions in order to cover all regions of the globe.
We hope you learned a lot from this week’s blog! Next week we’ll start discussing global temperatures and carbon dioxide!
What did you find most interesting about this week’s blog?
Wes Golomb Photography