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B. Biology: Sustainable Ecosystems and Climate Change · Sustainable Ecosystems and Climate Change

Reading the Signs: Indicators of Climate Change

B2.6 A1.1 A1.4About 70 minutes
Learning goals
  • I can identify physical and biological indicators of climate change.
  • I can use indicator data to describe a trend and separate it from year-to-year variability.
  • I can calculate averages, changes and rates from climate data, including with a short program.
  • I can describe what indicators show about impacts on local and global ecosystems.

Words to know

climate indicator
A measurable feature of the environment that shows how the climate is changing, such as temperature, sea ice extent or the date lake ice melts.
trend
The general direction of change in data over a long period.
variability
Natural ups and downs in data from year to year.
baseline
A reference period (often 30 years) used for comparison.
anomaly
The difference between a measured value and the baseline average; for example, +0.8 °C warmer than the baseline.
phenology
The timing of seasonal events in nature, such as leaf-out, flowering, insect emergence and bird migration.
ocean acidification
The drop in seawater pH caused by the ocean absorbing extra carbon dioxide.
range shift
A change in where a species lives, often moving north or uphill as the climate warms.

Remember from earlier lessons

In Lesson 10 you learned why Earth is warming. Now you will look at the evidence: the measurements, from thermometers to fishing logbooks to maple sap buckets, that show the climate is changing and how ecosystems are responding. In Grade 8 you studied melting glaciers, sea ice and sea-level rise; here you will use these and other indicators together.

Let's start with a lake diary

For generations, people living on Ontario lakes have written down the day the ice went out each spring. Cottagers, lodge owners, First Nations communities and park staff all keep these records. When scientists put many records together, a pattern appears: in many lakes, ice is forming later in the fall and melting earlier in the spring than it did a century ago.

A single lake diary can be bumpy (one cold spring can delay ice-out by weeks), but many decades of data reveal the trend. That is the key skill of this lesson.

Types of indicators

Physical indicators

  • Temperature: global average surface temperature has risen by more than 1 °C since the late 1800s. Canada has warmed about twice as fast as the global average, and northern Canada about three times as fast.
  • Ocean: the ocean has absorbed most of the extra heat. Warmer water expands, and melting land ice adds water, so sea level is rising. The ocean has also absorbed a large share of the extra CO₂, which has lowered the pH of surface seawater from about 8.2 to about 8.1, roughly a 30% increase in acidity.
  • Ice and snow: Arctic sea ice in September (its yearly low) is much smaller than in the 1980s; glaciers are shrinking; snow cover is decreasing in spring; lake ice seasons are shorter; permafrost is warming and thawing.
  • Extreme events: more frequent and intense heat waves, heavy rainfall events in some regions, and longer, more severe wildfire seasons.

Biological indicators

  • Phenology: many plants leaf out and flower earlier; some birds arrive earlier in spring; maple sap runs earlier in some years.
  • Range shifts: many species are moving north or uphill. In Ontario, blacklegged ticks (which can carry Lyme disease) have spread to new areas as winters warm.
  • Ecosystem stress: coral bleaching in warm oceans; insect outbreaks in forests where winters no longer get cold enough to kill overwintering insects.
Air temperaturerisingOcean heat and sea levelrisingOcean acidityrising (pH falling)Sea ice, glaciers, snowshrinkingLake ice seasonshorterSpring events (buds, migration)earlier
Six groups of climate change indicators and the direction each has been moving over recent decades. When many independent indicators point the same way, scientists can be confident the climate is changing.

Trend versus variability

Climate data always bounce around. One year is warm, the next is cool; one spring the ice leaves early, the next it stays late. To find a trend, scientists:

  1. Use long records (decades, not a few years).
  2. Compare to a baseline (for example, the average from 1961 to 1990). The difference is an anomaly.
  3. Average over several years, or draw a line of best fit (trend line).
  4. Check whether many independent indicators agree. Temperature, ice, sea level, ocean heat and phenology are measured in totally different ways, and they all point to a warming world.
100105110115120125130197019801990200020102020ice-off day of yearyeardashed line = trend
Practice data (made up for this lesson) for the day each spring when the ice leaves a lake (day 121 is May 1). The points bounce up and down from year to year, but the trend line slopes down: the ice is leaving earlier.
years = [1975, 1980, 1985, 1990, 1995, 2000, 2005, 2010, 2015, 2020]
ice_off = [121, 124, 117, 119, 114, 118, 112, 110, 113, 106]
first = sum(ice_off[:5]) / 5 # average of the first five values
last = sum(ice_off[5:]) / 5 # average of the last five values
print("1975-1995 average:", first)
print("2000-2020 average:", last)
print("Change:", round(last - first, 1), "days")
# Output:
# 1975-1995 average: 119.0
# 2000-2020 average: 111.8
# Change: -7.2 days

Comparing the averages of two time periods smooths out year-to-year ups and downs. ice_off[:5] means the first five items; ice_off[5:] means item 5 to the end.

Worked example

Let's calculate a rate of change

Using the practice data, the 1975–1995 average ice-off day was 119.0 and the 2000–2020 average was 111.8. The middle years of these periods are 1985 and 2010. (a) How many days earlier is ice-off? (b) What is the rate of change per decade? (c) Predict the average ice-off day around 2035 if the trend continued.

  1. (a) 119.0 − 111.8 = 7.2 days earlier.
  2. (b) Time between the middle years: 2010 − 1985 = 25 years = 2.5 decades. Rate = 7.2 days ÷ 2.5 decades ≈ 2.9 days per decade earlier.
  3. (c) 2035 is 2.5 decades after 2010: 111.8 − 7.2 = about day 104.6, around April 14 or 15.
  4. Caution: a prediction assumes the trend stays the same; it could speed up or slow down.

(a) 7.2 days earlier; (b) about 2.9 days per decade; (c) about day 105 (mid-April) by 2035 if the trend continued.

Worked example

Let's interpret indicators for an ecosystem

Lake trout need cold, well-oxygenated deep water in summer. Indicators for an Ontario lake show: ice-off 10 days earlier than 50 years ago, summer surface water 2 °C warmer, and a longer period each summer when the lake is layered (warm water on top of cold). Describe the likely impact on lake trout.

  1. Earlier ice-off and warmer summers mean the lake warms up and layers (stratifies) earlier and for longer.
  2. While the lake is layered, the cold deep water is cut off from the air and doesn't get new oxygen. Decomposers keep using up oxygen there.
  3. A longer layered season means deep water may run low on oxygen by late summer.
  4. Lake trout get squeezed: the warm surface is too warm, and the cold bottom may be too low in oxygen.

The indicators suggest less suitable summer habitat for lake trout, which could reduce growth and survival: a local ecosystem impact of climate change.

Hands-on activity

Become a climate indicator observer (A1.1)

You need: a notebook or phone, access to the internet (with a grown-up's OK), and a nearby tree, garden or bird feeder.

Part 1: Research a local indicator. Choose one: lake ice dates for an Ontario lake, first frost date in your town, the number of days above 30 °C, or snow-cover days. Find long-term data from a reliable source (for example, Environment and Climate Change Canada's historical climate data, a conservation authority, a provincial park, or a local naturalist club). Record at least 20 years if you can.

  1. Make a table and a scatter plot by hand or in a spreadsheet.
  2. Draw a line of best fit by eye (equal numbers of points above and below).
  3. Calculate the average of the first 10 years and the last 10 years, and the change.
  4. Write 3 to 4 sentences: is there a trend? How confident are you, and why?

Part 2: Observe phenology. Pick one tree or plant near home. Each week this season, record the date and stage (buds, leaves, flowers, colour change, leaf drop). Canadian citizen science programs such as PlantWatch collect observations like these from across the country.

What to look for: a good answer separates trend from variability, uses numbers, and names the source of the data. Not every place shows a strong trend in 20 years; saying so honestly is good science.

Just for fun

Some of the longest records of spring in North America come from people who simply wrote down, every single year, the day the ice went out on their lake. Proof that never missing a day of note-taking can make you a climate scientist.

Your turn

1

Name three physical and two biological indicators of climate change.

2

What is the difference between a trend and variability?

3

Why do scientists use many different indicators instead of just one?

4

How fast has Canada warmed compared with the global average?

5

What is ocean acidification, and what causes it?

6

A temperature anomaly is +1.4 °C. What does that mean?

7

In the Python program, what does ice_off[:5] select?

More practice: warm-up

1

What is phenology?

2

What is a baseline?

3

Which direction are many species' ranges shifting as the climate warms?

4

Name an Ontario species that has spread north as winters have warmed.

5

Is one very early spring enough to show a climate trend?

More practice: on your own

1

Temperatures for five years were 0.2, 0.6, 0.3, 0.8 and 0.6 °C above the baseline. Find the average anomaly.

2

Why might warmer winters lead to more forest damage from insects like the mountain pine beetle?

3

Explain why a shorter lake-ice season can matter to an ecosystem, not just to people who go ice fishing.

4

Change the program so it prints the average of ALL ten values. Write the new line and the output.

5

A student finds that their town's last-frost date shows no clear trend over 15 years. Does this disprove climate change? Explain.

Challenge

1

Phenology mismatch: some insects now emerge earlier in spring because of warming, but some migrating birds still arrive at the same time, guided by day length. Explain why this could harm the birds.

2

The trend line for the practice data has a slope of about −0.32 days per year. Estimate how much earlier the ice leaves in 2020 than in 1975 according to the trend line, then compare the trend line's change from 1985 to 2010 with the 7.2-day answer from the averages method.

3

Describe one global and one local (Ontario) ecosystem impact shown by indicators, and the indicator that reveals each.

Check your understanding

Quiz

1.

Which is a BIOLOGICAL indicator of climate change?

2.

Ice-off averaged day 120 in the 1980s and day 114 in the 2010s. What is the change per decade?

3.

Why do scientists look at long records instead of a few years?

4.

About how fast has Canada warmed compared with the global average?

5.

What happens to ocean pH as the ocean absorbs more CO₂?

6.

What does this program print? x = [4, 6, 8] then print(sum(x) / 3)

7.

A temperature anomaly of −0.3 °C means...

For parents and teachers

Big idea (B2.6, identify and use indicators): many independent physical and biological indicators (temperature, ocean heat and pH, sea level, ice and snow, phenology, range shifts) show the climate is changing and reveal impacts on local and global ecosystems. The key skill is separating trend from variability. Researching real data builds A1.1; the Python averages program builds A1.4.

How to help: Help find a long-term data set (Environment and Climate Change Canada historical climate data works well) and plot it together in a spreadsheet. Start a family phenology log for one tree or the first robin of spring.

Common difficulties:

  • Reading one unusual year as a trend. Look at decades.
  • Calculating rate per decade. Divide the change by the number of decades between the middle years.
  • Python division. / gives a decimal (6.0); // gives a whole number.

Note: the lake ice data in the graph and program are practice data made up for this lesson, not measurements from a real lake.

Sources: Canada's warming rates (Canada's Changing Climate Report, 2019); global warming of more than 1 °C (IPCC Sixth Assessment Report); ocean pH change from about 8.2 to 8.1 (NOAA); PlantWatch citizen science (NatureWatch Canada).