The Heat is On, Or Why A Few Degrees is a Big Deal

Posted on Posted in Climate Science, Outreach

Sometimes it’s hot. Sometimes it’s not. But, wait: if we’re emitting more and more greenhouse gases into the atmosphere and heating up the planet, why doesn’t the temperature always increase too?

ryan-1-3The answer comes partly because there’s an important difference between “heat” and “temperature.” For example, when you put a pot of water on the stove, it can take a long time before it starts to feel warm. You’re using a red-hot element to add lots of heat, but its effect on the temperature of the water is (sometimes frustratingly) slow. This same effect happens all the time in nature, even at the very large scale of the oceans and the atmosphere.

If you’ve ever visited or lived in a coastal community, you’ll know that temperatures tend to remain pretty moderate throughout the year. Compared to inland communities, the winters are not as cold and the summers are not as hot. Mild coastal temperatures and the slow heating of a pot of water both happen because water can absorb very large amounts of heat without experiencing large changes in temperature. Water heats up and cools down much more slowly than air: it can actually absorb 1000 times more heat than air can. So, during the summer, the oceans absorb and trap heat, preventing nearby communities from warming. Then, during winter, this heat is slowly released back into the atmosphere, keeping those communities warmer than they would be otherwise.

Amazingly, the temperature of the oceans barely changes throughout the year, even though they are constantly absorbing heat. How can something absorb so much heat without getting hot? The answer is that water has a very high heat capacity, or ability to absorb heat energy without changing temperature. It’s why it feels like it takes forever to get that first cup of coffee in the morning: water warms up very, very reluctantly.

And this effect doesn’t just explain coastal temperatures and morning caffeine rage—it also explains some important climate change facts and figures.

The Earth has warmed about 1°C since the year 1900. That may not sound like a lot, but remember: this value combines measurements from the atmosphere and the oceans, and most of the Earth’s surface is covered with water. To change the temperature of so much water, even just by 1°C, requires adding a tremendous amount of heat. So much heat that it’s actually hard to imagine: scientists have calculated that the amount of extra heat energy being added to the climate system due to human activities is equal to detonating four Hiroshima-sized atomic bombs per second!

It turns out that up until now the oceans have absorbed 80-90% of the heat added to the atmosphere by human greenhouse gas pollution. In a sense, the oceans have been protecting us from the effects of climate change, much as they protect coastal communities from extremes of temperature. If our planet had less water on it, then the increase in air temperature would have been much, much larger.

Sometimes people think that climate change isn’t a big deal because it sounds like the average temperature is only going up a little bit. It’s helpful to know that water’s remarkable heat capacity means that it takes unimaginably colossal amount of extra heat to change the temperature at all, let alone by a constantly growing and obvious amount. This why climate scientists are anxious about changes like two and three degrees: in the context of the climate and the oceans, these are amazing, alarming numbers.

And the oceans won’t hold onto that heat forever. Water eventually releases trapped heat back into the atmosphere. In fact, even if we were to stop all greenhouse gas emissions today and somehow magically vacuum up all the extra carbon pollution from the atmosphere, the climate would still warm for years to come because the oceans would gradually release all the extra heat they’ve already stored, continuing to warm the planet. This mechanism means that—as much as we have to push for lower emissions to slow our warming impact on the planet—we also need to work hard to get ready for a much warmer, less predictable climate future.

Fortunately, more and more public and private sector players are getting serious about both preventing things from getting worse and adapting to a world that’s being reshaped by climate change. There’s a lot Canada can do, and there’s a lot you can do.

Steve McCullough & Ryan Smith

Prairie Climate Centre

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