A Matter of Degrees | Gino Segré


Published in: 2003

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In this book Gino Segré, professor of physics and astronomy at the University of Pennsylvania, observes humans and the world from a temperature perspective. Measurement of temperature is only a few hundred years old and scientific understanding of the temperature of the gas is even newer. The Fahrenheit scale, named after Daniel G. Fahrenheit, was discovered in England / Holland in the 1730s, but most countries adopted the Celsius scale, after its proponent Anders Celsius.

SUN, EARTH. SEA AND OZONE. The four main contributors to earth’s temperature: (1) the sun – our main source of heat, (2) heat generated directly in the earth, i.e. volcanic eruptions – small amount of heat compared to what sunlight supplies the earth, (3) the oceans and (4) the atmosphere – its coverage both protects the earth from harmful radiation and keeps much of the ground heat from entering space. All these climate changes are linked. There are also other contributors, such as collisions with asteroids (main source of climate change is the dust that is injected into the atmosphere).

TEMPERATURE AND LIFE. Life originated on Earth about 3.8 billion years ago, with slow development over the first 3 billion years. 565 million years ago, new organisms suddenly arose in abundance. Within 50 million years, members of all basic forms of wildlife emerged. The development depends on a series of rise and fall in the earth’s temperature, all caused by factors such as Agassiz’s glacier movements, Croll’s feedback loops, a leap in the greenhouse effect, Wegener’s continental drift and temophilic bacteria. Each of them was crucial at some point in the development. Changes in temperature have shaped and reshaped the earth’s surface, destroyed life, and stimulated rebirth.

CONTINENTAL DRIFTS. At the beginning of the 20th century, Alfred Wegener suggested that the east coast of South America and the west coast of Africa were once together (now called continental drift). Fifty miles below the surface the temperature is 2000 degrees Fahrenheit; enough to create volcanoes and movements of continents and the seabed. Despite the visual manifestation of thermal activity of volcanoes, they are insignificant compared to plate-tectonic movements. A valley or gorge can symmetrically spread away from the central gorge by about an inch per year.

ICE AGE CYCLES. In 1941, Serbian mathematician Milutin Milankovitch was able to give a thermal history of the earth for more than half a million years (ice is as the rings in tree, showing past climates). Milankovitch showed warmer temperatures about 103,000, 82,000, 60,000, 35,000 and 11,000 years ago. His graphs showed a long interglacial epoch between 200,000 and 400,000 years ago and nine sharp minima during the last 650,000 years – nine significant ice ages. During these ice periods, the summers were about 12 degrees Fahrenheit colder than today (enough to cover the earth with large layers of ice). The ice age follows what all geological textbooks call Milankovitch cycles.

ANOMALIES AND SURPRISES. The two coldest summers of the last 500 years, 1601 and 1816, were followed by major volcanic upheavals that threw huge amounts of dust into the stratosphere. This connection is easy to understand. However, we do not know why the period between 1100-1250 was so hot in Europe and America that the Vikings could grow crops in Greenland. We also know little about the events behind the period 1400 to 1800, “Little Ice Age”, when the Dutch canals froze over, and the Swedish army invaded Denmark by marching over an icy North Sea. Also, we know that El Nino (rain) comes every 3-7 years and lasts for 12-18 months, but we do not know how big the next one will be. From a little more than 5,000 years ago, El Nino appeared only a few times per century, and then only in a weakened form. Because the Earth’s position relative to the Sun varies very slowly, these global events cannot be explained by Milankovitch cycles.

METAN-RUN. For billions of years, methanogens have produced 15 trillion tons of methane buried on the seabed. 55 million years ago, groundwater warming, probably due to displacement of ocean currents, triggered methane emissions into the atmosphere. Methane has a heating capacity of 30x carbon dioxide. The temperature was not adjusted fast enough which caused the release of more methane. This created a rampant greenhouse effect. Over the next 10,000 years, one trillion tons of methane made their way to the atmosphere. Then the earth finally managed to reach equilibrium. The sea temperature had then risen 10 degrees. Half of the foraminifera species disappeared.

KNOWLEDGE OF AIR IS ”NEW”. Before 1750, air was assumed to be “subtle matter” or “ether”. The greenhouse effect was not mentioned until 1822. The next big step was taken in the 1890s, by the Swedish chemist Svante Arrhenius, who with the feedback effects of water vapor predicted that a doubling of the amount of carbon dioxide in our atmosphere would lead to an average global temperature increase of 10 degrees Fahrenheit. In the 1950s, Roger Revell observed that 80% of the carbon dioxide added to the atmosphere remained there for a long time.

THE HUMAN IMPACT. Carbon dioxide increases from population growth and lifestyle. The Stefan-Boltzmann radiation law predicts how much radiation comes out of each square meter of a surface at a given temperature. Thermal equilibrium means that the same amount of heat comes in and goes out (changed marginally over time). By doing the calculation of heat in versus heat out, the average temperature of the earth should be 0 degrees Fahrenheit. But it is 60 degrees Fahrenheit. Greenhouse gases are the main cause of the temperature difference (though not so simple because the volume in air is about 78% nitrogen, 21% oxygen and 1% argon).

UN-ESTIMATION 1990. In 1990, carbon dioxide in the atmosphere was 360 ppm (parts per million) compared to 277 ppm in 1750 (the beginning of both the industrial revolution and the first large-scale deforestations). Based on population growth, economic development and technological development, the UN panel in 1997 concluded three estimates of carbon dioxide in the atmosphere over the next 100 years: the most optimistic forecast for 2100 was 450 ppm, the intermediate scenario was 700 ppm and the worst case was 954 ppm. Based on this, the average world temperature would rise by 2-6 degrees Fahrenheit and sea levels would rise from six inches to three feet. In 2000, the “worst case” was revised to predict a temperature increase of 6.3–11 degrees from the 1990 level.

RISING SEA LEVELS. When liquid Arctic ice melts, no more water is displaced. But when “land-ice” melts and slides into the oceans, water levels rise around the world. An increase in temperature in one place can trigger an environmental disaster in another. If Antarctic Ice Sheets (WAIS), estimated to contain one million cubic miles of ice, were to melt, it would lead to global flooding and the disappearance of most ports around the world. Bangladesh would be under water; the Netherlands would be endangered and much of Florida and Louisiana would disappear.

Humans and degrees

98.6 DEGREES FAHRENHEIT. The human temperature under the tongue is 98.6 degrees Fahrenheit (37.1 degrees Celsius). If the temperature varies 2% in any direction you will feel sick and if it varies 5% in any direction it is time to go to the hospital. However, internal temperature varies depending on the organ, metabolism, and blood flow. No single gene has been confirmed to control temperature.

98.6 DEGREES IS CHEMISTRY. The first evidence of man is traced to two million years ago and in Africa. There, the daily temperature was low 70s (F). A body temperature in the high 90s optimized the dissipation of heat generated by metabolic processes. Man’s move to cooler areas has been handled with bonfires and clothing. There is no significant effect on body temperature. The main reason for thermoregulation is the optimization of complicated sets of chemical reactions that allow humans to perform difficult activities.

A DELICATE BALANCE. Chemical reactions usually occur faster when the temperature rises, so a fluctuating brain temperature would lead to unpredictable reactions. When the surplus cannot be emptied and information arrives too quickly, the system breaks down. Humans, other mammals, and birds are most effectively around 100 degrees (F) and most comfortable with an external temperature of about 20-30 degrees below our own temperature (provides a comfortable heat loss). If it is colder, we lose heat too quickly and if it is warmer, we retain too much. We regulate this with clothes, blankets and muscular activity such as shaking or sweating.

FEVER BOILS THE DEFENSE. Heat shock proteins are often called stress proteins and are thought to play an important role in diseases. The immune system works by recognizing intruders, attacking back, and destroying them. But there may be an intermediate stage where the intruder triggers stress proteins that alert the immune system. These proteins play an important role in the human fever response where the rise in temperature in case of disease is simply a way to stimulate our body to increase hsp production (everything from fruit flies to humans has hsp production).

HIGHER TEMPERATURES ARE CREATED. The ability to create fire allowed people to move towards harsher climates (especially if they had hunting tools and clothes). Man has since created ever higher temperatures, a development that includes the combustion of coal, the production of bronze and irons, the steam engine, the 19th century large Bessemer furnaces (manufactured steel) and finally nuclear power. The story can be read 0 degrees, 500, 1000, 2000, 2500 and finally millions of degrees Fahrenheit. In the last 200 years, lower temperatures have also been achieved in laboratories as all known gas species have been liquefied.

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