Angry Weather

Heat Waves, Floods, Storms, and the New Science of Climate Change

Friederike Otto, Sarah Pybus

• Publisher: Greystone Books
• Year: 2020
• Print ISBN: 9781771646147
• eBook ISBN: 9781771646154
• Topic: Biological Sciences
• Subtopic: Environmental Science
• Index: Biological Sciences

From leading climate scientist Dr. Friederike Otto, this gripping book reveals the revolutionary science that definitively links extreme weather events—including deadly heat waves, forest fires, floods, and hurricanes—to climate change.

"Meet the forensic scientists of climate change; if you like CSI, you'll be equally enthralled with the skill and speed these folks exhibit. But the stakes are infinitely higher!" —Bill McKibben, author of Falter and The End of Nature

Tied with Hurricane Katrina as the costliest cyclone on record, Hurricane Harvey caused catastrophic flooding and over a hundred deaths in 2017. Angry Weather tells the compelling, day-by-day story of the World Weather Attribution unit—a team of scientists that studies extreme weather events while they're happening—and their race to track the connection between the hurricane and climate change. As the hurricane unfolds, Otto reveals how attribution science works in real time, and determines that Harvey's terrifying floods were three times more likely to occur due to human-induced climate change.

At the forefront of cutting-edge climate science, Friederike Otto uncovers how the new ability to determine climate change's role in extreme weather events can dramatically transform how we view the climate crisis: from how it will affect those of us who are most vulnerable, to the corporations and governments that may find themselves held accountable in the courts. The research laid out in Angry Weather will have profound impacts, both today and for the future of humankind.

Published in Partnership with the David Suzuki Institute.

1

A NEW BRANCH OF RESEARCH

The Role of the Climate in Our Weather

CHAPTER 1

CAUSE AND EFFECT

How We Created Our Weather

PEOPLE LIVING TODAY are among the first to clearly feel the consequences of a process that began 250 years ago in a Glasgow laboratory. James Watt, a Scottish mechanical engineer and inventor, concocted a new way of reducing steam and fuel consumption in fire-powered engines. When he and his steam engine paved the way for mechanical power and locomotives, they awakened humanity’s voracious hunger for coal, oil, and natural gas. Since then, billions and billions of tons have been extracted and pumped from the ground to be burned in power plants and vehicles, all the while heating up the Earth like a greenhouse.

Why We Need Greenhouse Gases

The Earth draws its energy from sunlight. However, only some of the sun’s rays reach the Earth’s surface. Some of them—the UV (ultraviolet) rays—are absorbed by the ozone layer. A round 30 percent a re reflected straight back into space from within the Earth’s atmosphere or by the ice and other light surfaces on Earth itself. The rest of the sunlight is absorbed by the Earth, which then heats up and emits its own radiation. We cannot see this radiation, but we can feel it in the form of heat; this is mainly infrared radiation. Again, this is absorbed by the “greenhouse gases” in the air and reemitted in all directions with less energy. The most important greenhouse gases are water vapor, carbon dioxide (CO₂), and methane. Some of the radiation is thrown back to Earth, like a game of table tennis between the Earth’s surface and greenhouse gases in which the energy decreases with every point of contact. The molecules absorb some of the radiation energy and convert it into kinetic energy. And that can mean only one thing: the atmosphere grows warmer.

Greenhouse gases make the Earth’s atmosphere over 30°C (54°F) warmer than it would be without water vapor, carbon dioxide, and methane. Without greenhouse gases, most of the radiation emitted by the Earth would return to space unhindered, and our planet would be a pretty cold and uncomfortable place to live. We need greenhouse gases.

As long as the proportion of greenhouse gases and solar radiation remains constant, everything will be fine. The problem starts when we burn huge quantities of fossil fuels, releasing more and more greenhouse gases into the air that are able to absorb more radiation—greenhouse gases like carbon dioxide. Unlike water vapor, which leaves the atmosphere a few days after entering it in the form of rain, carbon dioxide sticks around for hundreds of years. To maintain the energy balance, the Earth has to warm up. We have known that this is happening since 1896, when Svante Arrhenius discovered the connection between global warming and greenhouse gases.

Since 1776, the year in which King George III granted James Watt patent number 913 for his steam engine, the Earth’s temperature has increased by around 1°C (1.8°F). Carbon dioxide emissions increased slowly at first and were then accelerated by industrialization. Accordingly, the average global temperature rose gently at first by just 0.2°C (0.4°F) to 1960. Today, it is 1°C hotter worldwide. The hottest year on record was 2016, the second hottest was 2017, and the third hottest was 2015, followed by 2018, 2014, 2010, and 2013. The seven hottest years have all taken place within the last decade.

However, this additional 1°C on the global average is an abstract measure. We don’t notice it directly, only its effects. To put it bluntly, the change in the average global temperature isn’t killing anyone. At least not directly. But its influence on the weather is.

The Face of Climate Change

This 1°C has major consequences for our weather. Because the Earth’s atmosphere is connected via global circulation, temperatures rise in almost every region on the planet. In the simplest case, the temperature rises everywhere, the probability of heat waves increases, while cold spells become less likely.

When the air becomes warmer, it can absorb more water vapor before the water begins to condense and form clouds. The water remains in the air and clouds for a few days. But if the relative humidity exceeds 100 percent, it will fall as rain or snow. It’s a simple formula: the more water the air absorbs, the more it rains. It’s like a sponge; the larger it is, the more water it can soak up—and when you squeeze it, it releases all this water. Our atmosphere is like a constantly growing sponge.

The tropics demonstrate this well, as it generally rains much more intensely there than at temperate latitudes. But we can see the difference in Great Britain, for example, too; we simply have to compare the seasons—summer rain is often much heavier (though shorter and less frequent) than winter rain.

However, the Earth’s growing hotter does not mean that we will all experience nothing but tropical downpours no matter where we are. The quantity and intensity of rain is only increasing as a global average; some places will get more rain, others less.

Rising temperatures and increased water vapor in the atmosphere follow simple physical laws. We climate scientists refer to the changes in weather that follow these laws as the “thermodynamic effect.”

Climate change also influences the weather in another way.* Greenhouse gases don’t just make the atmosphere warmer; altering its composition by adding more carbon dioxide, methane, and water vapor (as we have done) also changes the atmospheric circulation.

Essentially, circulation is the movement of air that we experience as wind. It is created by the constant balancing of differences in pressure and temperature. If you’ve ever blown up a balloon and let it go without tying a knot in it, then you’ll know that higher and lower pressure compensate for one another unless prevented by something like the shell of a balloon. Differences in temperature result from the fact that the Earth is more or less round and, therefore, the equator gets more sun than the poles because the sunlight hits the equator vertically and the poles at a sharp angle. This temperature imbalance creates wind systems—“jet streams”—that cover an entire hemisphere. They blow where cold and warm air masses meet and are diverted and accelerated by the rotation of the Earth. They blow all the time at high speeds and high altitudes.

And yet pressure and temperature also differ on a smaller scale: air heats up faster over land than it does over water, and faster over flat terrain than over mountains. Then we have clouds, which also influence temperature and pressure. If we change all these factors—the temperature, composition of the atmosphere, and cloud formation (and we are changing them)—then we also alter the circulation. We are therefore changing when and where areas of high and low pressure develop and where they go, when and where it rains, the strength of the wind, the season in which the wind blows, and the direction from which it comes.

Other factors also play a role, such as how the land surface is used and how it interacts with the atmosphere.

These changes have consequences. Today, hurricanes can develop in regions where this was not previously possible. The oceans are heating up, and in some regions the temperature threshold at which the water becomes so warm that it provides enough energy for a tropical cyclone to form has now been exceeded for the first time. For centuries, we have experienced weather in a stable climate—but with global warming, some of the familiar patterns of rainfall, drought, and storms are being disrupted.

Among climate researchers, this effect of changing circulation is known as the “dynamic effect.” While it also follows physical laws, it is much more complicated to reliably simulate in climate models than the thermodynamic effect.

These two effects always occur together, never in isolation; however, since the dynamic effect in particular may vary wildly in strength and impact, the effect on the weather can differ greatly. If both warming and circulation change in the same direction, the overall effect will be stronger and disaster may be looming. Some regions experience more rain simply because the temperature of the air has increased and it can absorb more water. But when more low-pressure areas move into the region, bringing rain with them, the two can combine to produce an awful lot of rain.

My fellow U.K. residents know what I’m talking about. When I moved from Potsdam to Oxford a few years ago, I braced myself for typically rainy British weather, but it took a while to materialize. Over the last few winters, however, the south of England has experienced precisely this dual effect: More low-pressure areas from the Atlantic have brought more rain than would have been expected in pre-industrial times. In addition, the warmer atmosphere has made the rain heavier. The south of England has always experienced most of its rain in winter, while snow is rare. However, climate change has increased the probability of record rainfall such as that of January 2014, the wettest January since records began.¹ And it often doesn’t stop with the rain: the more that rain falls, the higher the risk of flooding, particularly where houses have been built on floodplains. And there are plenty of these areas in southern Britain. Thanks to an ingenious flood system, Oxford was largely spared from floods that winter—unlike the people living farther south. Large swaths of Devon and Somerset in particular were transformed into lakelands. Railroads broke away and were undermined by the water, isolating these regions from the rest of the country for several weeks.

Equally, these two effects can take the wind out of each other’s sails and have opposing impacts. While it may rain more on average in the warmer atmosphere, the altered circulation may mean that fewer low-pressure systems develop or that they enter a particular region less frequently. Ultimately, everything remains the same and the probability of wet winters or summers does not change, despite the altered climate. For example, the flooding of the River Elbe and the Danube in 2013 was not an extreme event that bore the hallmarks of climate change.²

There is, however, a third possibility: the change in atmospheric circulation is so strongly opposed to the thermodynamic effect that it wins out over the thermodynamic effect. In other words, the dynamics of when and where it rains change so much that certain regions suddenly receive hardly any rain at all. It doesn’t matter that the warmer air could hold much more water vapor and produce a lot more rain; without the right flow of air, no rain clouds will form—and if the land is already dry, no clouds will form locally. This explains why the risk of drought can increase in some parts of the world even though the world as a whole is growing wetter. For example, southwest Australia has seen a dramatic decline in rainfall in the last fifty years; this is partially due to climate change.³

Looking at the world as a whole, it is fairly easy to explain how the climate can influence our weather. But of course, if a hurricane develops and threatens thousands of coastal residents, nobody will be interested in large-scale averages.

To date, nobody has systematically taken stock of the impact of human-caused climate change. To do so, we need to step away from large-scale averages and understand how climate change is reflected in a specific drought, flood, or storm. In other words, we need to make the connection between cause and effect, between where people live and what they are experiencing right now. This is now possible, but it requires laborious detective work.

Like all good detectives, we start not with the cause of an event, but with its impact. By finding out what happened.

Reconstructing the Event

It might sound trivial, but—as we know from every good thriller—it’s not that easy to reconstruct an event. When it comes to floods, it is often not immediately clear where we should look at rainfall data. When floodwater breaches riverbanks, we first need to determine where the rain has actually fallen: Did it fall where the flooding occurred, or farther upstream? Was the rain actually heavy, or has someone simply failed to build a dam correctly? Or has the river been straightened, meaning that floodplains cannot prevent entire settlements from flooding? Was the entire season wet? Or was there an exceptional downpour on a particular day?

Most countries in the world have some sort of weather station network measuring temperature, rainfall, and air pressure every day. Measurements have also been regularly taken from satellites since 1979. Both of these observation methods document weather around the world and provide us with the data we need for our work....

Table of contents

• Cover
• Title Page
• Dedication
• Contents
• Preface
• Prologue: The New Weather
• 1. A New Branch of Research: The Role of the Climate in Our Weather
• 2. Consequences: The Power of Attribution Science
• Epilogue
• Acknowledgments
• Editorial Note
• Notes
• Bibliography
• Index
• Copyright Page