Another Ice Age?
The Little Ice Age came to an end around 1860, and since then Earth has been experiencing a general warming trend. This does not mean that temperatures have been steadily increasing. As we have seen in the previous chapter, there was a significant dip in temperature during the middle of the 20th century. There have always been variations in Earth's climate, and history has shown that turning short-term observations into long-term predictions is not a sound idea. Knowing this, however, has not stopped people from doing just that.
Illustration 12 The cover of Science News, March 1 1975.
In the 1970s, Earth was entering a fourth decade of decreasing temperatures. Scientists were concerned what this might imply for the future and warned that the climate might be returning to the chilly temperatures of the Little Ice Age, or worse. The popular press ran articles filled with dire warnings of an impending ice age. When the first Earth Day was celebrated on April 22, 1970, a major concern was the coming new ice age. Science News pictured rampaging glacial ice knocking over skyscrapers on its March 1, 1975, cover.
While the media frenzy in the '70s didn't quite reach the levels of today's global warming “crisis,” the story of an impending ice age, covering major northern cities with glacial ice and forcing mankind to retreat to the tropics, was widely reported at the time. The peril of the coming ice age was wide spread in the popular media. In an article, dated November 13, 1972, Time magazine reported on the looming crisis:
“The arrival of another ice age has long been a chilling theme of science fiction. If the earth's recent history is any clue, says Marine Geologist Cesare Emiliani of the University of Miami, a new ice age could become a reality.”87
Quite a different story from the one presented in the press today. It is hard to fathom, in this time of global warming anxiety, that scientists 30 years ago were worried about global cooling. Like today, the scientific evidence was not conclusive, even if the news media chose to interpret it that way. Dr. Emiliani expressed his uncertainty as the article continued:
Writing in Science, Emiliani reports that the earth has undergone at least eight periods of extreme cold and seven of torrid heat in the past 400,000 years.
In what direction will the earth's climate then turn? Emiliani refuses to speculate. But if man continues his “interference with climate through deforestation, urban development and pollution,” says Emiliani in typical scientific jargon, “we may soon be confronted with either a runaway glaciation or a runaway deglaciation, both of which would generate unacceptable environmental stresses.”88
Illustration 13 Temperature trend in 1972, source Time Magazine.
The reporter disparages Emiliani's “typical scientific jargon” while at the same time sensationalizing his rather equivocal predictions. Similar circumstances exist today, with scientific possibilities restated in headlines as certainties. This tendency on the part of the press has not diminished, as we will see in Chapter 15.
This cooling crisis produced charts and graphs, much like the ones we are bombarded with today. Illustration 13 shows the alarming downward temperature trend in 1972. Then, as now, concerned climatologists were “pessimistic that political leaders will take any positive action to compensate for the climatic change, or even to allay its effects.” They gloomily opined, “the longer the planners delay, the more difficult will they find it to cope with climatic change once the results become grim reality.”89
Newsweek, in April of 1975, reported, “there are ominous signs that the earth's weather patterns have begun to change dramatically and that these changes may portend a drastic decline in food production—with serious political implications for just about every nation on earth.”90
The Newsweek article went on to report delayed growing seasons, disease, drought and devastation. Echoing contemporary warnings about increased severe weather activity, the 1974 tornado season was called, “the most devastating outbreak of tornadoes ever recorded.” The increase in tornado activity was blamed on the cooling climate.
Scientists went so far as to suggest melting the arctic ice caps by covering them with soot. Others suggested diverting the flow of northern rivers or building mirrors in space to capture extra sunlight, all in an effort to warm the planet. “As for the present cooling trend a number of leading climatologists have concluded that it is very bad news indeed,” Fortune announced in February 1974.
This type of environmental alarmism has a long and colorful history. On at least three prior occasions the New York Times has reported impending climate disaster. Here are some headlines from the past:
“America in Longest Warming Spell Since 1776,” March 27, 1933.
“Scientists Ponder Why World's Climate is Changing; A Major Cooling Widely Considered to be Inevitable,” May 21, 1975.
“Geologists Think the World May Be Frozen Up Again.” February 24, 1895.
Take your choice, fire or ice.
Illustration 14: New Scientist, 28 July 2007.
Today, of course, the Times headlines proclaim “Science Panel Calls Global Warming ‘Unequivocal.’” The article describes the IPCC report as “a grim and powerful assessment of the future of the planet.”91 Time, Newsweek and others show similar historical patterns of sensationalist climate reporting. No thinking person confuses the news with the truth.
The drum beat of conjecture continues today with wild speculation in journals that report on scientific matters. The British weekly, New Scientist, is onboard the impending disaster bandwagon, reporting elevated storm frequency in the North Atlantic92 and warning of worldwide flooding, “the most deadly of all natural disasters.”93 On the cover of its July 28, 2007, issue, the state of Florida suffers the calamitous effects of rising sea levels, accompanied by a headline in red reading “Goodbye Miami.”
What can we expect in the future?
While scientists can't be 100% positive, most think that we are still in an active ice age. This means that Earth will probably return to glacial conditions, with much colder temperatures, lower sea levels, and advancing ice sheets. The return to glacial conditions assumes global warming hasn't disrupted the natural rhythms of Earth's climatic system.
Some think that humanity's greenhouse gas emissions are sufficient to derail the current ice age and drive the planet into catastrophic hot house conditions. Is humanity really so powerful that our profligate burning of fossil fuels will irreversibly alter the course of climatic development—or is this just hubris?
Another point to consider is this: scientists defining an ice age as a period of time when there are permanent ice sheets in both the Northern and Southern Hemispheres, implies that there have been times when Earth was not in the grip of an ice age. During those times there was no permanent glacial ice—no Greenland ice sheet and no Antarctic ice cap. In the public debate, the disappearance of the world's glaciers is touted as one of the catastrophic effects of global warming. If Earth has been ice free for long periods in the past, how catastrophic can the disappearance of the ice sheets be?
As Winston Churchill said, “The farther backward you can look, the farther forward you are likely to see.” To understand the true story of Earth's changing climate, and the magnitude of the forces that shape it, we must dig deeper. We need to understand more of Earth's history: Where our planet came from, how life developed, the interaction of life and the environment, the effect of the Sun, the planets and even the stars.
Unprecedented Climate Change?
“What has been is what will be, and what has been done is what will be done; there is nothing new under the sun.”
— Ecclesiastes 1:9
To read about global warming in newspapers or listen to pundits' sound bites on TV, you can't avoid the impression that the current rate of global warming has no historical precedent, that the increase in temperature is something new and unparalleled in the history of life on Earth. Indeed, part of the justification for taking urgent, drastic action is predicated on the unprecedented nature
of this change in Earth's climate. But is this really true? Has Earth's average temperature never reached current or higher levels before? Because if it has, then a number of other questions arise. Questions such as: If the temperature has been higher than it is today, why is this a crisis? What caused the climate to change before? What happened to bring the temperature back down the last time?
To answer these questions we must look at the history of Earth and of life on Earth because Earth's climate is intimately tied to the life it hosts. We will see that Earth's climate has changed life, but that life has also changed Earth's climate. This chapter will trace the history of our planet from its first formation along with the Sun and the other planets of the solar system. We will examine the development of life on Earth from its first appearance, when Earth more closely resembled Hell than a natural paradise. We'll see how Earth's atmosphere was transformed by the smallest of life-forms. Special attention will be given to the time since complex life arose, the geologic time period called the Phanerozoic Eon.
From the Cambrian Explosion, 545 million years ago (mya), through five major extinction events—including the Permian-Triassic extinction that nearly destroyed all life on our planet—to the asteroid that ended the reign of the dinosaurs, and down to the present, life's struggle will be examined. Along the way, despite wide variation in climate and any number of natural cataclysms, an increasing trend toward greater species diversity will be uncovered. In fact, without climate shifts and mass extinctions in the past, mankind would not exist today.
In The Beginning
Scientists believe that our planet was formed about 4.5 billion years ago when our sun and the other planets of the solar system coalesced out of interstellar gases and debris left over from the explosions of other, older stars. At some point, the Sun collected enough hydrogen from space and deep in its heart nuclear fires ignited—our star was born. There was a period called the “Great Bombardment,” some 4 billion years ago, when the last rubble left over from the formation of the solar system was swept up by the larger planetary bodies.94
Illustration 15 The Earth during the Great Bombardment.
During that time, Earth's crust solidified and was remelted over and over. If we could peer back in time to view our planet, we would not recognize it and we certainly wouldn't want to live there. A collision with a planetesimal (or small planet) the size of Mars nearly destroyed Earth, ejecting large volumes of matter. A disk of orbiting material was formed and this matter eventually condensed to form the Moon in orbit around the planet. This off-center impact also gave Earth its spin leading to today's 24 hour day-night cycle.
First proposed in the 1970s, this giant impact theory95 ,96 was not believed by most scientists for nearly a decade. However, in 1984, a conference devoted to the origin of the Moon prompted a critical comparison of existing theories. The giant impact theory emerged from this conference as the best explanation of how the Moon formed. Scientists adopted this model of planet formation in which large impacts were common events in the late stages of terrestrial planet formation. This explanation remains the dominant theory of the Moon's origin today.
Illustration 16 The Moon's surface as seen from Apollo 11. Source NASA.
How long the bombardment lasted is not known, but it must have affected every planet in the solar system. On Earth, the signs of this terrific pounding have long since been erased by weather and Earth's active geology, but the effects of the bombardment can still be seen today in the cratered, pockmarked face of the Moon.
Scientists who study ancient life (palaeontologists) and those who study the physical structure and processes of our planet (geologists), classify periods of time based on changes in the layers of rock that make up Earth's crust—the rock record. For them, time is broken into Eons, Eras, Periods and Epochs. Eons, of which there are four, are the longest intervals into which Geologic Time is divided. The earliest three, the Hadean, Archean, and Proterozoic Eons, are frequently lumped together and referred to as Pre-Cambrian Time or just the Precambrian.
Table 4 shows the time spans of the major geologic time periods and their names. It is important to realize that, when new information about boundaries in the rock record or new measurements dating geological formations become available, the time scale can change. Revisions to the geologic time scale, also called deep time, have occurred since its inception in the late 1700s. As scientific tools rapidly improved since the 1930s, the dates attached to the various time spans have been continuously refined.97 However, the magnitude of adjustments made with each revision have become smaller over the decades.98
Table 4 Geological Time Periods. Source ICS99
The Hadean and Archean Eons
The Hadean, or pre-geologic, Eon is the time period during which Earth was transformed from a gaseous cloud into a solid body. The name Hadean comes from Hades, the mythological underworld of the Greeks. Hadean time is not a true geologic period because no rock that old has survived intact to the present day. The beginning of the rock record available to scientists dates back to the start of the second oldest eon, the Archean.
The oldest rock, dating from about 3.9 billion years ago, shows that there were volcanoes, continents, oceans, and Life on Earth even in those days. Not that life back then was the same as we see around us today. Life started as simple, single-celled organisms, called prokaryotes by biologists. Karyose comes from a Greek word which means “kernel” or “nucleus,” and pro means “before.” So, prokaryote means “before a nucleus.” Though prokaryotes were single-cell organisms of simple construction, they were the most complicated life on Earth for more than a billion years.
These microscopic organisms were to have a significant impact on Earth's environment. Prokaryotes are responsible for building the atmosphere that surrounds the modern Earth and makes our planet a suitable home for higher life forms. The early atmosphere contained nitrogen (N2), water vapor (H2O), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), ammonia (NH3), hydrogen (H2), helium (He) and trace gases. Hydrogen and helium are very light and tend to escape the atmosphere into space. Oxygen was present, but was bound to other elements. This atmosphere is thought to have been quite similar to the present day atmosphere of Titan, one of the larger moons of Saturn. To humans, and most other life-forms that inhabit Earth today, this atmosphere would have been toxic.
Illustration 17 Chroococcus sp., a type of cyanobacteria. Source NASA.
The tiny one-celled organisms, that were the primitive Earth's only inhabitants, labored for more than a billion years to convert the poisonous atmosphere into a more life-friendly form. Over time, the tiny bacteria—in particular, those called cyanobacteria—developed ways of fixing nitrogen and freeing oxygen. Cyanobacteria, also called blue-green alga, developed a way to use light as an energy source (see Illustration 17). This natural process is called photosynthesis, and it is the same mechanism used by green plants today. Energy from sunlight is used to split CO2 into carbon and oxygen. The carbon is absorbed, becoming part of the growing plant, and the oxygen is released into the atmosphere.
The climate during the Archean Eon was hot and wet with very warm oceans. Worldwide, volcanic eruptions ejected volcanic ash and dust into the atmosphere causing violent lightning storms and continual rain. In the oceans, reefs were built by stromatolites, colonies of photosynthesizing cyanobacteria that formed in shallow waters.100 There were no corals as there are in today's oceans—they would not appear for billions of years.
The Proterozoic Eon
The Proterozoic Eon was from 2,500 mya to 540 mya. In rock deposited during the Proterozoic Eon, the first evidence of multi-celled organisms is seen. Stromatolites remained common in the shallow waters of Proterozoic Eon oceans. Many other life-forms were also present, such as archaea, another type of single-celled organism that have only recently been placed in their own biological domain. Archaea may be the only organisms that can live in extreme habitats, such as thermal vents or extremely acidic, alkaline or salty
water. Many types of archaea produce methane (CH4). Today, archaea can be found in the stomachs of cows and the guts of termites where they manufacture more greenhouse gases than all of man's planes, trains, and automobiles combined.101
The Oxygen Catastrophe was a dramatic environmental change believed to have happened about 2.4 billion years ago, near the beginning of the Paleoproterozoic Era. Measurable amounts of free oxygen appeared in Earth's atmosphere for the first time. Before this significant increase in atmospheric oxygen, caused by the cyanobacteria mentioned previously, almost all life did not require oxygen. In fact, to these types of anaerobic organisms, large amounts of free oxygen (O2) are poisonous. This event is called a catastrophe because for the first time, but by no means the last, most life on Earth went extinct.
This was a positive event for our own species. If the cyanobacteria had not “polluted” the atmosphere with toxic oxygen, the world we live in would not exist. With the advent of an oxygen-rich atmosphere, Earth gained something else that helped Life survive and expand; the ozone layer.
The Resilient Earth: Science, Global Warming and the Fate of Humanity Page 6