Climate Change and Ecosystems

Earth stays warm enough for life because of the greenhouse effect: gases in the atmosphere such as carbon dioxide, methane, nitrous oxide and water vapour absorb heat given off by Earth's surface and send some of it back down, like a blanket. This natural effect is essential; without it, Earth's average temperature would be well below freezing. The problem is that human activities have added extra greenhouse gases, thickening the blanket. This enhanced greenhouse effect is the main cause of the warming observed since the mid-1900s.

• Rising temperatures: Earth's average surface temperature is now more than 1 °C warmer than in the late 1800s. Canada is warming faster than the world as a whole: Canada's Changing Climate Report 2026 found that Canada warmed about 2.0 °C from 1948 to 2023, roughly 1.7 times the global rate over that period (and almost twice the global rate since 1970). Northern Canada warmed about 2.6 °C, more than twice the global rate. The Arctic as a whole has warmed nearly four times as fast as the global average since 1979.
• Rising greenhouse gas levels: atmospheric carbon dioxide has climbed from about 280 ppm before industrialization to over 420 ppm.
• Shrinking ice: Arctic sea ice in late summer covers much less area than it did in the 1980s, and glaciers in the Rockies and the Arctic are shrinking.
• Thawing permafrost: ground that stayed frozen for thousands of years is thawing, damaging buildings and roads and releasing stored carbon as carbon dioxide and methane.
• Rising sea level: melting land ice adds water to the ocean, and warmer water expands.
• Shifting seasons and extremes: earlier spring, later freeze-up of lakes, and more frequent heat waves, droughts, heavy rainstorms and severe wildfire seasons. In 2021, Lytton, British Columbia, set Canada's all-time temperature record of 49.6 °C, and a wildfire destroyed most of the village the next day. In 2023, wildfires in Canada burned roughly 15 million hectares, more than twice the area of the previous record year (1989).

• Range shifts: as temperatures rise, many species are moving north or to higher elevations. Blacklegged ticks, which can carry Lyme disease, have spread into much more of Ontario. Species that cannot move fast enough, or that are already at the edge of their range, can decline.
• Timing mismatches: warmer springs make some plants flower or insects hatch earlier, but migrating birds or pollinators may still arrive on their usual schedule and miss the food they need.
• Warmer water: lake trout and brook trout need cold, oxygen-rich water. Warmer lakes hold less dissolved oxygen and shrink their habitat, while warm-water species and algal blooms increase.
• Loss of sea ice: polar bears hunt seals from the sea ice. In Hudson Bay, the ice now melts earlier and freezes later, so bears spend longer on land with little food.
• Pests and fire: milder winters let pests such as the mountain pine beetle survive cold snaps that used to kill them, and hot, dry conditions make forests more likely to burn. Dead and burned forests release carbon, adding to warming in a feedback loop.

First Nations, Métis and Inuit peoples have lived sustainably in the ecosystems of what is now Canada for thousands of years. Many of their practices are built on close, long-term observation of how ecosystems balance themselves, the same idea scientists call dynamic equilibrium. Practices differ from nation to nation, so it is important to name which community a practice comes from.

• The Three Sisters (Haudenosaunee and other nations): corn, beans and squash are planted together. The tall corn gives the beans a pole to climb; bacteria in the bean roots fix nitrogen that enriches the soil; and the broad squash leaves shade the ground, keeping moisture in and weeds down. Each plant supports the others, and the field stays productive for many years without synthetic fertilizer: a small ecosystem in balance.
• Cultural (controlled) burning: many First Nations used carefully timed, low-intensity fires to renew grasslands, oak savannas and berry patches, encourage new growth for animals they hunted, and clear built-up fuel so later wildfires would be less severe. Fire agencies now work with some nations to bring cultural burning back.
• Seasonal and respectful harvesting: harvesting at the right time of year and taking only what is needed leaves enough for populations to replace what was taken. For example, the Anishinaabe harvest manoomin (wild rice) by canoe, gently knocking ripe grains loose; many grains fall into the water and seed the next year's crop.
• Thinking across generations: the Haudenosaunee principle of considering how decisions will affect people seven generations into the future is a long-term view of sustainability.
• Two-Eyed Seeing (Etuaptmumk): an approach brought forward by Mi'kmaw Elders Albert and Murdena Marshall, which means seeing with the strengths of Indigenous knowledges through one eye and Western science through the other, and using both eyes together. Programs such as SmartICE, a northern social enterprise that trains and employs Inuit to combine sea-ice sensors with Inuit knowledge of ice so people can travel more safely, and Indigenous Guardians programs that monitor lands and waters, put this idea into practice.