Climate vs. Weather

Canadians pay a lot of attention to weather, and for good reason: we have some of the most interesting weather on the planet. For example, over the course of the year most of us see remarkable extremes of heat and cold compared to most places on Earth—from -30°C in the winter to +30°C in the summer. What it’s like outside seriously affects our daily lives. So we’re used to predicting, preparing for, and (of course) complaining about the weather. We’re much less used to talking about climate, and the differences between “climate” and “weather” can be a real barrier to understanding climate change.

We’re all familiar with how the weather can be hot or cold, wet or dry, windy or calm—sometimes all in the same day. You’ll run into versions of the saying “If you don’t like the weather, just wait 15 minutes” almost everywhere in Canada. So one of the things we know to expect about weather is that it changes. A lot.

But while weather varies often and sometimes very rapidly, climate stays relatively stable. We might not know exactly what the high temperature will be next Tuesday, but we can be sure that next February will be colder than next June, or that a February in Iqaluit will be colder than a February in Charlottetown. So one important difference between weather and climate is that “climate” refers to long-term overall patterns and averages, which are different from place to place, and are—compared to weather—relatively stable and predictable.

The climate of a region determines what kind of weather is expected there, even if the details vary from day to day. The climate of Florida, for example, includes the possibility of a hurricane whereas the climate of Winnipeg does not. A key mistake we often make is thinking that climate is variable in the same way as weather. For instance, Canadians are used to temperatures going up or down by several or even dozens of degrees over the course of a day or week, so reports that Earth has warmed by 1°C or warnings that we might see an overall increase of 4°C can sound trivial. But climate changes so slowly and so slightly under normal circumstances that these are actually remarkable and alarming numbers.

For example, about 20,000 years ago Earth was experiencing an ice age, and what is now Canada was almost entirely buried in glaciers and ice sheets up to thousands of metres thick. That’s a drastically different world than we live in today, but the average global temperature was only about 4°C colder than it is now. Amazingly, our current level of greenhouse gas emissions is expected to cause an average global temperature increase of about that same amount again by the end of this century.

This is one reason why global warming is so alarming: we’re seeing changes in the world’s climate over a few decades that would otherwise happen over thousands of years. This also means that numbers that sound small when we think in terms of weather are actually a huge deal for climate.

And that’s the main reason why it’s important to recognize the difference between weather and climate. When it comes to understanding climate, our experience with weather can actually get in the way. We deal with and react to the weather every day, but we don’t have the same direct connection with the climate. Weather is vivid, immediate, and sometimes remarkably changeable. Climate is abstract, historical, and relatively stable. We have to look at average values over many decades to understand climate, which means it’s less readily understood and harder to relate to than weather.

This makes some climate change predictions all the more dramatic: the summer climate of southern Manitoba may resemble the climate of northern Texas in about 80 years unless humanity drastically reduces its greenhouse gas emissions. One of the shocking effects of climate change is that changes in climate, which are normally so gradual and so long term that they’re hard to detect, are likely to become obvious within our lifetimes.