Documenting the Climate Crisis: Ellen Prager’s ‘Dangerous Earth’

In Dangerous Earth, marine scientist Ellen Prager explores the science of investigating volcanoes, earthquakes, tsunamis, hurricanes, landslides, rip currents, and–maybe the most perilous hazard of all–climate change. Each chapter considers a specific hazard, begins with a game-changing historical event, and highlights what remains unknown about these dynamic phenomena. Along the way, we hear from scientists trying to read Earth’s warning signs, pass its messages along to the rest of us, and prevent catastrophic loss.

A sweeping tour of some of the most awesome forces on our planet–many tragic, yet nonetheless awe-inspiring–Dangerous Earth is an illuminating journey through the ‘wish-we-knews’ that continue to frustrate and fascinate the world’s leading scientists.

Read an eye-opening excerpt from the book.

The Atmosphere and Carbon Dioxide

The atmosphere extends from the planet’s surface to the edge of space and is only about 100 kilometers thick. Compared to the Earth, whose radius is nearly 6,400 kilometers, the atmosphere is wafer thin. Yet it is this thin layer of nitrogen, oxygen, and trace gases that provides for our every breath and prevents the planet from plunging into a frigid Mars-like cold. But the atmosphere is not an immobile source of life—it changes over time and space. Its never-ending fluctuations give rise to the day-to-day changes that form our weather and the longer-term variations that constitute climate. And variations in the makeup of the atmosphere influence and can drive change in the Earth’s climate. This is not a big unknown, like the nature of dark matter, whether life exists on other planets, or what Batman wears under his tight-fitting rubber suit. For hundreds of years, scientists have been studying the Earth’s atmosphere and how it affects our planet.

In the early 1800s, mathematician and physicist Joseph Fourier recognized that as the sun’s energy or radiation passes through the atmosphere and strikes the Earth’s surface, it heats up the planet. Without the atmosphere, though, the planet would regularly turn frigid. Fourier was the first to recognize that the atmosphere insulates Earth from heat loss—like a blanket. Then in 1859, scientist John Tyndall discovered something astonishing about one of the trace gases in our atmosphere—carbon dioxide. While the other major components of the atmosphere, nitrogen and oxygen, are essentially transparent to long-wave radiation, carbon dioxide is not. Carbon dioxide, along with water vapor, even in small quantities, absorbs long- wave energy, which is stored as heat. Several decades later, Swedish chemist Svante Arrhenius went further, suggesting that increased levels of carbon dioxide in the atmosphere could alter Earth’s surface temperatures. Since that time, observations and experimental evidence have repeatedly confirmed these early discoveries.

Here’s how it works. Incoming solar radiation (short-wave) passes through the atmosphere and strikes the Earth. Some of this energy is reflected back, especially from light- colored surfaces like ice or snow. But much is absorbed as heat and then re-emitted as longer-wave infrared radiation (we don’t see such energy, much like ultraviolet light). Somewhat like the glass in a greenhouse, carbon dioxide, water vapor, methane, and other gases trap (absorb and re- emit) this long- wave energy as heat in the atmosphere. Again, some is lost to space, but much of the absorbed heat is directed back toward the planet—warming the air, ocean, and land.

The result of heat-absorbing greenhouse gases in our atmosphere: a fertile, warm Earth versus desolate, frigid Mars. But there’s a catch. Humans are at times too smart for their own good. We discovered the power (pun intended) that comes from burning fossil fuels. And when fossil fuels are burned, they release additional carbon dioxide into the atmosphere, and more carbon dioxide captures more heat.

The burning of fossil fuels is not the only way humans add carbon dioxide to the atmosphere. But it is by far the largest anthropogenic source of carbon dioxide, followed by deforestation. Natural sources include the decomposition of organic material, volcanic emissions, weathering of rocks, respiration, and processes within the oceans.

Concurrently, the Earth’s average temperature has risen more than 1°C since 1880. More important, the pace of warming has accelerated since 1950, with the last several years being the warmest ever recorded. Today, whether you look at the atmosphere or the ocean, at direct measurement or satellite data, the same tale is being told: carbon dioxide in the atmosphere is increasing and the climate is warming at a rate unprecedented in modern times.

People often argue that Earth has, throughout its history, gone through cycles of cold and warmth. Why then is today different from the past?

Our record of instrument-measured temperatures goes back only about 100 to 150 years. To compare today’s rate of warming or current concentrations of carbon dioxide with those of the more distant past, scientists must find indicators or proxies that record previous atmospheric conditions. These include plants or other organisms that are sensitive to temperature or other climate variables and preserve records of their growth over time, such as corals, trees, and foraminifera (small shelled marine organisms). Bubbles of air trapped within layers of ice, undisturbed layers of sediment in lakebeds or oceans, and accumulations of ice, dust, pollen, and volcanic ash may also been used to establish prehistoric temperatures, dates, and carbon dioxide concentrations.

By combining the data from such indicators and from modern observations, scientists are able to reconstruct a record of global temperatures and carbon dioxide concentrations going back hundreds of millions of years. The detail or resolution diminishes as you go further back in time, but even so the data reveal a great deal about Earth’s distant past. For instance, based on data from Antarctic ice cores, over the last eight hundred thousand years and up until about the 1950s, carbon dioxide concentrations in the Earth’s atmosphere has varied between about 170 and 300 parts per million.

But going way back, some fifty million years ago, data indicate the concentration of carbon dioxide in the atmosphere was about 1,000 parts per million. Back then, there were no ice sheets, temperatures were 8 to 12°C warmer than today, and sea level was some 75 meters higher—the Earth was definitely less hospitable

than it is today. Some three million years ago, carbon dioxide concentrations were similar to what we see today (350 to 400 parts per million). Temperatures were 1 to 3°C warmer than now and sea level was up to 20 meters higher. Again, it was not a very hospitable world for modern society as we know it. During the last peak interglacial (warm) period, 125,000 years ago, carbon dioxide concentrations were about 300 parts per million, temperatures were slightly warmer (1 to 2°C), and sea level was some 5 meters higher than today. The takeaway: in Earth’s past, when carbon dioxide levels in the atmosphere were higher than or at levels similar to today, the planet was warmer, more sea-covered, and certainly a less roomy, hospitable home for its residents.

So what drove climate change millions or even thousands of years ago? It wasn’t anthropogenic releases of carbon dioxide. Data suggest that back then the climate system was driven by other factors, including changes in solar output, massive volcanic emissions, the distribution of land and sea, ocean circulation, and tectonic upheavals followed by weathering. On time scales of about ten thousand to a hundred thousand years, orbital variations play an important role, particularly in forcing glacial and interglacial periods; these include the varying shape of Earth’s elliptical orbit about the sun, the tilt of the Earth’s rotational axis, and the wobble of the Earth’s spin. Carbon dioxide played a role as well, but rather than driving change it appears to have either enhanced or reduced the effects of the other variables through feedback mechanisms. Today, these same forcing factors are present, but they are being overshadowed by the influence of carbon dioxide in the atmosphere.

Since 1950 the concentration of carbon dioxide in the atmosphere has risen to greater than 400 parts per million—a level far higher than it has been in hundreds of thousands of years. In the Northern Hemisphere, a long-term gradual decline in temperature continued until about a hundred years ago. Then something happened. The temperature began to increase and at an accelerated pace. There have been similar periods of warming in Earth’s past, following ice ages, but the amount of warming that has occurred over the last century, back then took ten times longer, on average a thousand years. So here’s the point: It is not the actual temperature that is the issue. Rather it is the rapid pace at which the global thermometer is rising that is unusual and problematic.

Data on the amount of emissions and deforestation support the conclusion that most of the carbon in the atmosphere comes from the burning of ancient plants, a.k.a. fossil fuels. Data clearly indicate that carbon dioxide in the atmosphere is increasing, mainly due to human influences, and that Earth’s surface temperatures are rising unnaturally fast.

Here then is where the big unknowns come in: at what rate will the climate continue to change, and just how extreme will the consequences be.