Measuring a Changing Planet: Ice, Sea Level, Wind Patterns and the Carbon Budget

Let's start at the Athabasca Glacier

If you drive the Icefields Parkway in Jasper National Park, you can walk toward the toe of the Athabasca Glacier. Along the path are markers with years on them, showing where the ice ended in the past. The early markers are a long walk from the ice today. Parks Canada reports that the glacier has retreated more than 1.5 km since the late 1800s.

One glacier isn't proof of global change. But when glaciers on every continent, the polar ice, the oceans and the atmosphere all show the same direction of change, scientists can be confident. In Grade 9 you met a wide range of indicators. This lesson goes deeper into four that the Grade 10 curriculum highlights: ice, sea level, wind patterns and the global carbon budget.

Indicator 1: Glacial and polar ice

Sea ice in the Arctic grows each winter and shrinks to its yearly minimum each September. Satellites have measured it since 1979. The September extent has declined by roughly 12 to 13% per decade, and the ice that remains is thinner and younger than it used to be: much of the thick ice that survived many summers is gone.

Glaciers and ice sheets are measured by repeated photographs and surveys, by satellites that measure ice height, and by satellites (the GRACE missions) that measure tiny changes in Earth's gravity as ice mass is lost. Both the Greenland and Antarctic ice sheets are losing ice, and mountain glaciers are shrinking on every continent.

In Canada's High Arctic, the ice shelves on the north coast of Ellesmere Island have been breaking up; in 2020, the Milne Ice Shelf, then described as Canada's last fully intact ice shelf, lost about 40% of its area.

Indicator 2: Sea level

Global average sea level has risen about 20 cm since 1900, and the rise is speeding up. Two causes make up most of it:

1. Thermal expansion: as the ocean absorbs heat, the water expands.
2. Melting land ice: water from glaciers and the Greenland and Antarctic ice sheets flows into the ocean.

Sea level is measured by tide gauges (some with records over a century long, including at Halifax) and, since 1993, by satellite altimetry, which bounces radar off the sea surface.

Why sea level changes differently across Canada

The sea level that matters to a community is relative sea level: the sea measured against the local land. And in Canada, the land itself is moving.

During the last ice age, the Laurentide Ice Sheet pressed the land down by hundreds of metres in places. Since the ice melted, the land has been slowly rebounding, a process called glacial isostatic adjustment. Around Hudson Bay, where the ice was thickest, the land is still rising by around a centimetre a year, faster than the sea, so relative sea level there is falling. Around the edges of the old ice sheet, including much of the Atlantic coast (Nova Scotia, New Brunswick, Prince Edward Island), the land is slowly sinking, so relative sea level is rising faster than the global average. University of Toronto physicist W. Richard Peltier's models of this process are used around the world to separate land motion from ocean change.

This matters for planning: coastal communities in the Maritimes face more flooding and erosion, while communities on Hudson Bay see shorelines moving outward.

Indicator 3: Wind patterns

Wind patterns are harder to measure and show more natural variability than temperature, so scientists are more cautious here. Changes that have been detected or are being studied include:

• Widening of the tropics: some evidence that the edges of the Hadley cells (Lesson 3), and the dry zones near 30°, have shifted poleward since about 1980.
• Southern Hemisphere westerlies: the strong westerly winds around Antarctica have strengthened and shifted toward the pole, linked to both the ozone hole and greenhouse gases.
• Storm tracks and the jet stream: models project a poleward shift of mid-latitude storm tracks. Whether Arctic warming is making the Northern Hemisphere jet stream wavier is still actively debated (Lesson 3).

This is a good example of how scientists express confidence: the evidence for warming air and ocean is overwhelming; evidence for some wind changes is moderate; others remain uncertain.

Indicator 4: Global carbon budget assessments

Each year the Global Carbon Project (Lesson 8) publishes the global carbon budget: how much CO₂ humans emitted, how much the ocean and land absorbed, and how much stayed in the air. It is an indicator of the cause of climate change and of whether our actions are working. Recent assessments show:

• Fossil CO₂ emissions reached new record highs in the mid-2020s (about 37 to 38 Gt per year), although emissions have started to fall in some countries, including Canada.
• The ocean and land sinks keep absorbing roughly half of emissions, but the land sink weakens in hot, dry, fire-heavy years.
• The remaining carbon budget for limiting warming to 1.5 °C is only a few years of current emissions, according to recent scientific estimates. That's why 1.5 °C is now considered very hard to avoid exceeding, and why every tenth of a degree avoided matters.