A Summer of Extremes

Because of our emissions of greenhouse gases like carbon dioxide, a little extra energy gets trapped in our atmosphere every day. Over time, this energy builds up. It manifests itself in the form of higher temperatures, stronger storms, larger droughts, and melting ice. Global warming, then, isn’t about temperatures as much as it is about energy.

The extra energy, and its consequences, don’t get distributed evenly around the world. Weather systems, which move heat and moisture around the planet, aren’t very fair: they tend to bully some places more than others. These days, it’s almost as if the weather picks geographical targets each season to bombard with extremes, then moves on to somewhere else. This season, the main target seems to be North America.

The warmest 12 months on record for the United States recently wrapped up with a continent-wide heat wave and drought. Thousands of temperature records were broken, placing millions of citizens in danger. By the end of June, 56% of the country was experiencing at least “moderate” drought levels – the largest drought since 1956. Wildfires took over Colorado, and extreme wind storms on the East Coast knocked out power lines and communication systems for a week. Conditions have been similar throughout much of Canada, although its climate and weather reporting systems are less accessible.

“This is what global warming looks like,”, said Professor Jonathan Overpeck from the University of Arizona, a sentiment that was echoed across the scientific community in the following weeks. By the end of the century, these conditions will be the new normal.

Does that mean that these particular events were caused by climate change? There’s no way of knowing. It could have just been a coincidence, but the extra energy global warming adds to our planet certainly made them more likely. Even without climate change, temperature records get broken all the time.

However, in an unchanging climate, there would be roughly the same amount of record highs as record lows. In a country like the United States, where temperature records are well catalogued and publicly available, it’s easy to see that this isn’t the case. From 2000-2009, there were twice as many record highs as record lows, and so far this year, there have been ten times as many:

The signal of climate change on extreme weather is slowly, but surely, emerging. For those who found this summer uncomfortable, the message from the skies is clear: Get used to it. This is only the beginning.

Uncertainty

Part 5 in a series of 5 for NextGen Journal
Read Part 1, Part 2, Part 3, and Part 4

Scientists can never say that something is 100% certain, but they can come pretty close. After a while, a theory becomes so strong that the academic community accepts it and moves on to more interesting problems. Replicating an experiment for the thousandth time just isn’t a good use of scientific resources. For example, conducting a medical trial to confirm that smoking increases one’s risk of cancer is no longer very useful; we covered that decades ago. Instead, a medical trial to test the effectiveness of different strategies to help people quit smoking will lead to much greater scientific and societal benefit.

In the same manner, scientists have known since the 1970s that human emissions of greenhouse gases are exerting a warming force on the climate. More recently, the warming started to show up, in certain patterns that confirm it is caused by our activities. These facts are no longer controversial in the scientific community (the opinion pages of newspapers are another story, though). While they will always have a tiny bit of uncertainty, it’s time to move on to more interesting problems. So where are the real uncertainties? What are the new frontiers of climate science?

First of all, projections of climate change depend on what the world decides to do about climate change – a metric that is more uncertain than any of the physics underlying our understanding of the problem. If we collectively step up and reduce our emissions, both quickly and significantly, the world won’t warm too much. If we ignore the problem and do nothing, it will warm a great deal. At this point, our actions could go either way.

Additionally, even though we know the world is going to warm, we don’t know exactly how much, even given a particular emission scenario. We don’t know exactly how sensitive the climate system is, because it’s quite a complex beast. However, using climate models and historical data, we can get an idea. Here is a probability density function for climate sensitivity: the greater the area under the curve at a specific point on the x-axis, the greater the probability that the climate sensitivity is equal to that value of x (IPCC, 2007):

This curve shows us that climate sensitivity is most likely around 3 degrees Celsius for every doubling of atmospheric carbon dixoide, since that’s where the area peaks. There’s a small chance that it’s less than that, so the world might warm a little less. But there’s a greater chance that climate sensitivity is greater than 3 degrees so the world will warm more. So this graph tells us something kind of scary: if we’re wrong about climate sensitivity being about 3 degrees, we’re probably wrong in the direction we don’t want – that is, the problem being worse than we expect. This metric has a lot to do with positive feedbacks (“vicious cycles” of warming) in the climate system.

Another area of uncertainty is precipitation. Temperature is a lot easier to forecast than precipitation, both regionally and globally. With global warming, the extra thermal energy in the climate system will lead to more water in the air, so there will be more precipitation overall – but the extra energy also drives evaporation of surface water to increase. Some areas will experience flooding, and some will experience drought; many areas will experience some of each, depending on the time of year. In summary, we will have more of each extreme when it comes to precipitation, but the when and where is highly uncertain.

Scientists are also unsure about the rate and extent of future sea level rise. Warming causes the sea to rise for two different reasons:

  1. Water expands as it warms, which is easy to model;
  2. Glaciers and ice sheets melt and fall into the ocean, which is very difficult to model.

If we cause the Earth to warm indefinitely, all the ice in the world will turn into water, but we won’t get that far (hopefully). So how much ice will melt, and how fast will it go? This depends on feedbacks in the climate system, glacial dynamics, and many other phenomena that are quantitatively poorly understood.

These examples of uncertainty in climate science, just a few of many, don’t give us an excuse to do nothing about the problem. As Brian, a Master’s student from Canada, wrote, “You don’t have to have the seventh decimal place filled in to see that the number isn’t looking good.”. We know that there is a problem, and it might be somewhat better or somewhat worse than scientists are currently predicting, but it won’t go away. As we noted above, in many cases it’s more likely to be worse than it is to be better. Even a shallow understanding of the implications of “worse” should be enough for anyone to see the necessity of action.

The Applause Continues

The New York Times deserves a clap too. Thanks to toby and Eli for the hat tip.

An article just as good as the Associated Press piece made the front page of the New York Times. Justin Gillis wrote In Weather Chaos, a Case for Global Warming, and, as Eli pointed out, there wasn’t even a question mark in the title.

Gillis does a great job explaining how, for example, there will still be record cold days with climate change – just fewer of them. Here’s one of my favourite passages from the article:

The warming has moved in fits and starts, and the cumulative increase may sound modest. But it is an average over the entire planet, representing an immense amount of added heat, and is only the beginning of a trend that most experts believe will worsen substantially.

If the earth were not warming, random variations in the weather should cause about the same number of record-breaking high temperatures and record-breaking low temperatures over a given period. But climatologists have long theorized that in a warming world, the added heat would cause more record highs and fewer record lows.

The statistics suggest that is exactly what is happening. In the United States these days, about two record highs are being set for every record low, telltale evidence that amid all the random variation of weather, the trend is toward a warmer climate.

Read the full article here.

The Associated Press Gets it Right

It’s been quite the summer. Moscow has experienced several months of weather more akin to Texas, and is literally burning up. Floods in China have killed more than a thousand and left countless others displaced. Pakistan has experienced similar floods due to a massive monsoon season, and now they have to deal with cholera, too. The Arctic sea ice extent is not much larger than 2007, and, so far, it’s been the warmest year on record globally.

We can’t tie a single extreme event to climate change. We can tie long-term trends, like 30 years of declining Arctic sea ice, to a warming world, but we don’t yet have the technology to attribute a single anomalous season to a particular cause. In 2007, for example, factors other than high temperatures contributed to the lowest Arctic sea ice extent on record.

However, these events are exactly what we expect from anthropogenic climate change. We shouldn’t look at them as evidence for global warming, but as examples of what is to come. This is an important warning that most newspapers have been shying away from. After nearly a year of terrible climate change journalism across the board, they didn’t even mention the connection between extreme events and climate change, or the fact that this summer is a very real glimpse into our future.

I gave up on my local newspaper months ago, and I don’t regret that decision. On the handful of mornings that I’ve flipped through the paper instead of reading the Globe and Mail on the Internet (journalism of much higher quality, and it saves money and paper), I’ve seen far too many op-eds and letters to the editor saying very strange things about climate science.

However, a headline yesterday caught my eye. A fantastic article by Charles J. Hanley, a Pulitzer Prize winning journalist, was distributed by the Associated Press and, consequently, picked up by dozens of newspapers across the continent – including my local paper.

I became more and more pleasantly surprised as I began to read through the article:

Floods, fires, melting ice and feverish heat: From smoke-choked Moscow to water-soaked Iowa and the High Arctic, the planet seems to be having a midsummer breakdown. It’s not just a portent of things to come, scientists say, but a sign of troubling climate change already under way.
The weather-related cataclysms of July and August fit patterns predicted by climate scientists, the Geneva-based World Meteorological Organization says – although those scientists always shy from tying individual disasters directly to global warming.

Read the whole article here.

Hanley does a fantastic job of distinguishing between weather and climate, and stressing that we can’t yet attribute extreme events to specific causes while acknowledging that this summer’s wild weather fits with IPCC predictions and will become a lot more common in the future. He interviews our good friend Gavin Schmidt, and explains how rising greenhouse gases are “loading the climate dice” – changing the relative odds of different extremes, rather than eliminating all cold days entirely.

I stood there and clapped. I was so proud of the Associated Press, and of my local paper, that I clapped for them. I feel like there is a smidgen of hope for climate change journalism and public understanding of this issue again. Or perhaps it just comes in waves, and we’re riding our way to the top again.