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Originally appears in the Spring 2021 issue.

By Theo Nicitopoulos

It is now common knowledge that since the pre-industrial era, the Earth’s average temperature has increased by about 1°C due to the profound impact that humans have had on the climate system. To many people, this may not sound like much of an increase, but the melting of glaciers and sea ice along with the increase in the frequency and severity of storms, floods, and droughts — to mention but a few examples — signal otherwise. Why does a small increase in the average temperature lead to all of this?

This is an important question to answer when it comes to environmental education, and over the years I have used a variety of teaching strategies to help students discover it. One way that I recently found to be particularly effective was having high school students work with real-life temperature data to explore the effect that a small increase in the average temperature would have on Arctic sea ice.

Working with real-life data

In this activity, students download temperature data for an Arctic climate station of their choice into Excel and count the number of days during the year when the daily maximum temperature is above -1.8°C, the temperature at which sea ice begins to melt. (On account of its salt content, the melting point of sea ice is lower than that of fresh water: 0°C.) The data is available from the Government of Canada Historical Climate Data website at https://climate.weather.gc.ca.

Figure 1: Sea ice-breakup and melting in the Arctic Ocean (courtesy: NSIDC)

For example, data for the Alert climate station on Ellesmere Island shows that there were 102 days when the daily maximum temperature was above -1.8°C during the year 2020. These were days when the sea ice in the surrounding ocean would have been melting for at least a portion of the day.

To explore the effect of a 1°C increase on the average daily maximum temperature on sea ice melting, students add 1°C to each day’s maximum temperature using a formula in Excel.

Figure 2: Use a formula in Excel to add 1°C to the daily maximum temperature. To copy the data, place the mouse at the bottom right corner of Cell H137 and drag down. (Image courtesy of author)

By adding 1°C to each day’s maximum temperature, the average maximum temperature for the entire year increases by 1°C and this adds an extra seven days of sea ice melting. This extra week of sea ice melting would result in a significant decrease in the thickness of sea ice — just imagine how much snow melts during a few hours on a warm spring day. These extra seven days would be in the spring and fall seasons, the transitional times of year when temperatures have a tendency to hover around the sea ice melting point of -1.8°C. Increasing the temperature by 1°C turns days when sea ice would not have melted into days when it does. Additionally, a 1°C increase also accelerates the rate of melting during the rest of the days when sea ice melting occurs, leading to even more sea ice loss.

Data shows that since the 1970s, the average Arctic sea ice extent for the month of September has decreased by about half. Looking at September sea ice is an effective way to gauge the extent of sea ice loss over time, as that is the time of year by which the previous winter’s sea ice has melted. On September 15th, 2020, there were 3.74 million km2 of Arctic sea ice, the second lowest extent on record.

Figure 3: Arctic sea ice extent on September 15th, 2020 (courtesy: NSIDC)

An extra week of sea ice melting would further reduce the sea ice thickness that has already thinned out over the years, potentially causing it to break up the ice into smaller pieces, thus accelerating melting.

Arctic amplification

To make matters worse, the Arctic has warmed by about twice as much as the global average. One of the reasons for this is that the retreat of seasonal sea ice initiates what are known as positive feedback cycles. Specifically, as the bright, reflective sea ice retreats, less of the Sun’s incoming radiation is reflected back into space, causing temperatures to increase even more. This in turn leads to further sea ice retreat and then warmer temperatures… and the cycle continues.

This amplifying effect from positive feedback cycles involving sea ice loss means that a 1°C increase in the global average temperature translates into a 2°C increase in the Arctic’s average temperature. If 2°C is added to each day’s maximum temperature at the Alert climate station, this results in an extra two weeks of sea ice melting.

To explore these concepts further, students can experiment by adding different temperature increases using Excel to see how many extra days of sea ice melting would result. They will initially notice that every 1°C increase in the average daily maximum temperature adds an extra week of sea ice melting. Yet, once they account for Arctic amplification, they will see that every 1°C increase in the global average temperature actually results in an extra two weeks of sea ice melting.

Different scenarios

Countries around the world have pledged to keep the average global temperature from increasing by more than 1.5 °C by the end of the century. In effect, they have pledged to add no more than three extra weeks of Arctic sea ice melting. Students can comment on whether they feel this is good enough.

One of the worst-case scenarios predicted by the Intergovernmental Panel on Climate Change is a 4°C increase in the average global temperature by the end of the century.  If this were to happen, there would be an extra 56 days of sea ice melting. This would result in a substantial decline in sea ice volume, if not widespread sea ice retreat. It is not difficult to imagine even larger areas of the Arctic Ocean being largely ice-free in the summer if sea ice were to melt for almost an extra two months.

Figure 4: Sea ice melting during summer in the Chukchi Sea (courtesy: Yuri Smityuk/TASS via Getty Images)

Using average temperature increases to communicate climate change news has become popular. Hidden behind small increases in this measure of central tendency are severe environmental changes. In the case of sea ice, this is many extra days of sea ice melting, including accelerated melting due to higher temperatures. Understanding this link is an important part of environmental education that allows students to enhance their ecological literacy while leaving a lasting impression that promotes environmental stewardship.

Theo Nicitopoulos is a high school teacher with the Peel District School Board in Ontario, Canada. He enjoys designing a variety of hands-on learning activities that combine mathematics and environmental education to help students think critically about world issues like climate change.