You can’t have your glacier and melt it too

Global Warming is real; there is no controversy. Dr. Bruno Tremblay, from McGill’s Department of Atmospheric and Oceanic Sciences, tells us why.

How is climate change different from global warming?

Global warming is one form of climate change. It means there is a change towards a warmer climate. But climate change could be one way or another; it could be colder or warmer, it could be drier or wetter, or it could just be regional climate change. In the mean, we tend to see a warming of the climate but certain places will see different trends in temperatures. Talking about climate change is recent: global warming has a bad reputation because it implies you have to do something about it.

When it snowed a lot last winter, many asked “where is the warming?”

Global warming does not mean it will not snow anymore; it doesn’t mean it won’t be cold anymore. It just means that, on average, there will be more warm years and less cold years.

Some people have a fundamental distrust in models. The models aren’t perfect but they predict the global mean very well. But when you look at what’s going to happen in Montreal or Albany or Boston, the models might be off. So another argument is “how can we trust the models if they have defects?”. And it’s true, they have defects, but for predicting the global mean, they’re doing very well and we keep improving those models. But we don’t think that the fact that they’re not perfect should prevent us from making a statement and attribution of CO2 to the warming.

What about the natural variability in the sun’s output?

We can’t explain the warming of the past years using solar variability: it’s not strong enough. Even if you multiply it by 2, 3 or 10, its effect is not big enough. The only way we can see similar warming in our models is to add CO2 in the atmosphere.

Is the general public convinced that human activity is at fault?

CO2 is increasing in the atmosphere and no one denies this is due to human activity, skeptic or not. We can look at the ratios of Carbon’s isotopes and find how much comes from fossil fuel burning and how much comes naturally (they have different signatures). We can then measure these ratios’ increase over time. It‘s very clear that human activity is the cause.

What about those who disagree?

Those who do often present an argument that I don’t find particularly convincing but I will present. They question the fact that the global mean temperature is increasing. Since scientists have stations in airports to measure these temperatures, some say that airports are close to cities, and as cities become larger, you expect temperatures to be higher than outside cities due to cars, air-conditioning, heating, etc. So they claim we’re seeing warming because we’re measuring preferentially in cities.

But of course, in our calculations, we correct for these biases. If we remove all data from cities and keep only data from non-populated areas, we see the same warming. And the warming is not in the cities, it’s up in the Arctic, just as you would expect a global warming signal to be. We see melting of ice in the arctic and most warming in the high latitude where ice or snow is less present.

Others might argue that the ocean is a huge reservoir and can take a lot of heat and will buffer those changes. And it’s true that the ocean is a big reservoir, but we already include those factors in our models. We take temperatures of water in the ocean and they warm up as well.

Some quote temperatures from 1998 and say it’s been warming since then?

Well, when you look at the record, 1998 was an extremely warm year because of El Niño. So if you look further back in time, you see the temperatures increasing until 1998, at which point there is a big rise and after that, the temperatures are still rising, but not as much as 1998. So people cut the graph at 1998 and show it as going down.

And then people will ask us why our climate models don’t show this decline. But climate models simulates climate, not year-to-year variability. It does simulate that to a certain point, but we can run 100 simulations with slightly different initial conditions and will give you slightly different things. But the mean of 30 years of your climate will be very similar between a simulation and the next.

How much of the population agrees with global warming?

It changes. When there was a series of hurricanes, people were more receptive to the global warming issue, but 2-3 years later, people don’t really believe it to be an issue. You can see that the opinion of scientists always becomes firmer as time goes on because there’s always more evidence, but in the population, it’s all over the place.

Is the acceptance of global warming similar to that of evolution?

In a sense, science sometimes bothers people because it changes their views on how special humans are. In Galileo’s time, the Earth was thought to be the center of the universe. In evolution, people often reject it because they can’t believe that such a clever species could have monkeys as its cousin. It’s similar in climate change. Many only look at the evidence that matches what they currently think is true, instead of looking at all the evidence and then making an opinion.

In the scientific community, is there unanimous agreement on global warming?

Yes, the vast majority of scientists agree, although there are a few who don’t. For example, there is Richard Lindzen, but he uses estimates of sensitivity of CO2 change that are not in line with what the best models say. But at least he speaks scientifically about a scientific issue. But most others bring arguments just like the general public, arguments that are 10 years old that have already been answered a million times. Some people still don’t have an opinion, but remain on the sidelines.

I would say that 90% of the population does not choose to believe or deny global warming based on the evidence. That’s because, unfortunately, it takes a lot of time to have an informed opinion of the subject because there’s a lot to know about, much of which requires scientific background.

If we can’t predict tomorrow’s weather, can we predict it 50 years from now?

There’s a good analogy to that. I cannot predict the exact position of Joe Blow on the South Shore crossing the bridge in the morning in his car because he might buy milk on the way. Predicting his exact position is very difficult but I can predict the behaviour of all car drivers because I know that shops in Montreal open at 9 AM and close at 5 PM.

And you’ll have a traffic jam from 7 AM to 9 AM, and from 5 PM to 7 PM. I have a hard time predicting the exact behaviour of one individual but I have amazing skills predicting the behaviour of the average driver, simply because the average behaviour is dictated by opening hours of stores.

It’s the same for climate and weather. Weather is very difficult to predict, it’s a chaotic system. But climate is not dictated by this; it’s dictated by CO2 and water vapour (two greenhouse gases), how much sun comes back from the top of the atmosphere, and the reflectivity of the planet (are clouds or ice reflecting the sunshine?). And these we know very well so we can predict climate, but weather is harder.

Is there an “idiot’s guide to climate change?”

There is realclimate.org. It’s climate science explained by climate scientists to a general public. When something comes out from the literature, there’s a debriefing. It’s really good because you don’t have to read all the papers; the website gives a good opinion on what we know and don’t know.

Besides “raising awareness”, do we have concrete solutions?

People would first like to get everyone to agree it is happening. They would like to put laws in place to limit the emission from cars. Or to make people burn fuels cleanly, or to devise alternative energy sources like wind or solar.

But mainly, from what I’ve seen, what is suggested is a reduction in consumption and a better use of what we have right now. And whether you accept global warming or not, it makes sense. Fuel is not infinite, so let’s use it as best as we can. And why not put laws to force companies to be more competitive and better for the environment. They will sell more if they manage to do that because people are willing to buy things that are more energy efficient. This could very well help your business if you are proactive in taking these measures.

But a lot of people say this is not enough and are looking into carbon sequestration: taking CO2 from the atmosphere and burying it in the ground.

How much has temperature changed over the years?

For the last 700 000 years, we were always in a glacial/inter-glacial cycle. Every 100,000 years, you would have 80 000 years of cold climate with ice migrating all the way south to New York city, for example and here in Montreal, there would be 2 km of ice about Montreal; 20,000 years ago, you could see ice covering whole North America all the way down to New York and all the way down to Switzerland on the European side.

Then, you have 20,000 years of inter-glacial (like today) where all the ice breaks to pieces, and the climate is warm, the ice retreated all the way to Northern Canada on a few mountains, Greenland and Antarctica.
This corresponds to 5oC changes in global mean temperature. A glacial period is 5oC colder; an inter-glacial period is 5oC warmer. And you see that every 100,000 years, like a clockwork, and it’s been like that for the last 3 million years and we know that also from the ocean core records, which goes even further back in time.

What about now?

Now, we see the CO2 increasing and temperature warming (~0.5oC); we would be ready in another several thousand years for another glacial period, but we think that if the CO2 keeps increasing (see graph on next page), we will not go back into a glacial period. The glacial periods are because the Earth’s orbit around the Sun changes, so there are moments every 100,000 years, we receive one or two W/m squared less from the Sun, enough to cool the climate a little bit and there is feedback that amplifies the system a lot. The CO2 is getting us 2W/m2 extra. This shows the climate is very sensitive to very tiny changes. And now we’re putting 2 extra W/m2 in the climate system and we think the climate can respond drastically to small changes like this.

What kind of research do you do?

I study Arctic climate. I look at sea ice in the Arctic Ocean and how it changes through time. I study the effects of the atmosphere and the ocean because this is where the ice is retreated drastically. And the question is: what’s the role of the ocean?

It is getting warmer and melting the ice? Is the atmosphere getting warmer? Is the wind changing and blowing the ice south, where it’s warmer? That’s what I mainly study. We go in the Arctic and deploy beacons, we drill holes in the ice and put sonars to measure the thickness of the ice every hour. The changes in ice thickness are monitored every day and we use that data in our models