Global Systems, Canadian Effects: Winds, Jet Streams, Oceans and Ice

Canadian weather, made far away

In the summer of 2021, a huge dome of hot air parked over British Columbia. On June 29, the village of Lytton, B.C. recorded 49.6 °C, the highest temperature ever measured in Canada. Scientists linked the heat dome to a sharp, slow-moving wave in the jet stream. In other winters, a wobble in the polar vortex sends Arctic air deep into southern Canada, and a warm ocean patch in the tropical Pacific can change how much snow falls on the Prairies.

Canada's weather and climate are tied to global physical systems: the circulation of the atmosphere, the oceans, and the ice at the poles. Expectation B1.4 asks you to analyse these systems and assess their impact on Canada.

System 1: global wind belts

The sun heats the equator much more than the poles. The atmosphere constantly tries to even out that difference by moving heat toward the poles. Because the Earth spins, moving air is deflected (to the right in the Northern Hemisphere), so instead of blowing straight north or south, winds form belts:

• Trade winds (about 0° to 30°): blow from the east toward the equator.
• Westerlies (about 30° to 60°): blow from the west. Most of southern Canada lies here, so weather systems usually travel from west to east. A storm over Alberta today may reach Ontario in a day or two.
• Polar easterlies (about 60° to 90°): cold air flowing out from the Arctic.

Where cold polar air meets warmer air from the south, around the middle latitudes, there is a polar front. Many of the storms that cross Canada form along it.

System 2: the jet stream and the polar vortex

High above the polar front, about 9 to 12 km up, the polar jet stream races from west to east, sometimes faster than 200 km/h. It is the boundary between cold Arctic air to the north and warmer air to the south, and it steers storms.

The jet stream does not flow in a straight line. It waves north and south:

• Where it bulges north (a ridge), warm air moves in and high pressure brings sunny, often hot weather. A stuck ridge can become a heat dome, like the one in 2021.
• Where it dips south (a trough), cold Arctic air plunges south, bringing cold snaps and storms.

When the waves are big and move slowly, the same weather can stay in place for days: long heat waves, long cold spells or repeated rain over the same area.

The polar vortex is a large swirl of very cold air over the Arctic. When it is strong, it stays tight around the pole. When it weakens or is stretched, lobes of frigid air can spill far south into Canada and the United States.

System 3: the oceans

The oceans store enormous amounts of heat and move it around the planet.

• Surface currents are driven mainly by wind. In the North Atlantic, the warm Gulf Stream flows northeast; the cold Labrador Current flows south along Labrador and Newfoundland. In the North Pacific, a warm current flows toward the B.C. coast.
• A slower, deeper thermohaline circulation (a global "conveyor belt") is driven by differences in temperature and saltiness. Cold, salty water sinks in the North Atlantic, including the Labrador Sea, and flows south along the ocean floor. This helps carry heat toward the North Atlantic region.

El Niño and La Niña. Every few years, surface waters in the central and eastern tropical Pacific become unusually warm (El Niño) or cool (La Niña). These changes shift the jet stream. Typical effects (not guaranteed every time):

• El Niño: milder winters across much of western and central Canada.
• La Niña: colder winters in western Canada and the Prairies.

Hurricanes. Hurricanes form over warm tropical Atlantic waters (the season runs from June 1 to November 30). Some travel north and reach Atlantic Canada, usually weakening or changing into post-tropical storms over cooler water, but they can still be very destructive: Hurricane Juan (2003) struck Halifax, and post-tropical storm Fiona (2022) caused severe damage in Atlantic Canada and eastern Quebec.

System 4: ice, snow and the Arctic

Bright snow and ice reflect most sunlight (high albedo); dark ocean water absorbs most of it (low albedo). As the Arctic warms, sea ice and snow melt earlier, exposing dark water and land, which absorb more heat, which melts more ice. This ice-albedo feedback is one reason for Arctic amplification: Canada's North has warmed about three times faster than the global average, and Canada as a whole about twice as fast (Canada's Changing Climate Report, 2019). Arctic sea ice in late summer has shrunk sharply since satellite records began in 1979.

Other global connections

• Volcanic eruptions far away can cool the whole planet briefly: the 1991 eruption of Mount Pinatubo in the Philippines put so much fine material into the high atmosphere that global average temperatures dropped for a year or two.
• Smoke and dust cross borders: smoke from Canadian wildfires has drifted over the United States and as far as Europe.
• The global carbon cycle links fossil fuel burning everywhere to warming in Canada. You will look at the consequences in the climate change lesson.