THE BREAKDOWN OF CLIMATE

HUMAN CHOICES OR GLOBAL DISASTER?

PETER BUNYARD

FLORIS BOOKS            1999

PART II

Chapter 1: The Nature and History of Climate (continued)

Climate and misery

• The change to a less hospitable climate appears to have come abruptly. The late medieval period was marked by colder weather which was most severe during the 17^th and 18^th centuries.
• The decade 1310-20 was disastrous, especially in Northern Europe. Wet, miserable summers meant that crops failed to ripen and millions of people starved.
• By the beginning of the 15^th century, the seas around Greenland had frozen, and the old Viking population died out. The Thames at London regularly froze over and winters were marked by fairs and people congregating on the ice.
• In Scotland in the 1430s, as in Sweden, successive crop failures led to desperate measures such as baking a type of bread from the bark of trees.
• During the 17^th century, northern Europe was gripped by severe winters, and glaciers again advanced in Iceland, Norway and the Alps, engulfing farmland and forcing entire families off the land.

Stormy weather

• Sea floods in the 13^th and 14^th centuries took a terrible toll, with 330,000 people drowning in one that struck the Dutch and German coasts. The island of Heligoland was so eroded by storms that from being 60km across in 800, it now measures no more than 1.5 km at its widest point.
• The storms and deaths continued through the 17^th century and entire communities and towns disappeared overnight. On the east coast of Scotland, in Aberdeenshire, all that can be seen of the medieval town of Forvie is a 30m high sand dune that covered it during a southerly storm in August 1413.
• The changes from one general climatic regime to another, from the Medieval Optimum climate to the Little Ice Age several centuries later, indicate the sensitivity of the system to small changes in the mean surface temperature; changes that globally may amount to little more than one degree centigrade.

Weather Forecasting

• The need for daily, professional weather forecasting followed the sinking of the pride of the French Navy in a hurricane-force storm on November 14, 1854.
• The unpredictability of weather makes weather forecasting a treacherous business; on 15 October 1987 UK weathermen failed to warn of the approach of one of the most severe wind storms to hit southern England in a century, ripping 15million trees from the ground.
• Putting the study of climate on a scientific footing has been a major undertaking that has shown the extent to, and rapidity with, which climate does change, and how vulnerable living creatures such as ourselves are to such variation.
• Two hundred years ago the world population was one sixth of its present size and its overall impact in terms of agricultural and industrial activities was considerably less. During the Medieval Optimum, the population and its impact was smaller again, yet the climate still changed dramatically.

Desertification

• ‘Man of the Trees,’ Richard St Barbe-Baker spent his life dedicated to the restoration of forests, believing that the desert could be held back if trees were planted and carefully nurtured during their first years of growth, and he put his ideas into practice in Tunisia.
• Robert Mann is convinced that the drying out of West Africa is a consequence of the massive deforestation that has occurred with increasing speed over the past century.
• In 1975, Jules Charney suggested that deforestation in arid areas of the Tropics would bring subtle changes in the absorption of energy and in wind currents that could lead to a substantial reduction of rainfall.
• Robert Mann cites how, because of the air becoming drier, midday temperatures that used to peak at 35ºC are now rising to as much as 65ºC, resulting in even more rapid drying out of the soil and of the lower atmosphere, thus instigating desertification.
• The greater contrast between the temperatures of day and night brings about stronger wind currents and the barren, arid soil is swept upwards into the atmosphere as dust. The quantities of Sahelian dust in the atmosphere have increased significantly over the past few decades.
• According to United Nations figures, desertification is advancing at a rate of 60,000 km² per year out of a total dry land area of 60 million km², of which one third is Africa.

Historical records

• Historians are in general agreement that temperature data up to 1720 is accurate to within 1ºC. Today, reliable measurements are taken on a daily basis at thousands of sites.
• Michael Hume of the University of East Anglia has reviewed data collected from 8,300 different sites across the globe and has found evidence in recent years of significant increased rainfall in northern latitudes above 50º with corresponding drops over the Tropics.
• The 1980s proved to be both the warmest and the wettest in high northern latitudes, at least from records going back over the past century.

Climate models

• Currently the most advanced computer system is at the European Centre for Meteorology at Reading, which every day can number crunch a million observations at the rate of 250 billion calculations a second. The Centre claims it can forecast the world’s weather up to ten days ahead with 80% accuracy for five days.

Chapter 2: Sun, Earth and Moon

Driving forces

• The sun is the driving force behind the Earth’s climate, bathing our planet in highly energetic electromagnetic radiation, including visible light, ultraviolet light and heat.
• Terrestrial life is fortunate that ozone, during its generation from oxygen, reduces the effects of the most energetic and damaging ultraviolet rays.

The tilt of the earth

• The Earth was once spinning much faster, but has now settled into a motion that takes it close to 24 hours to make one complete turn.
• The Earth is tilted from the perpendicular by 23.44, resulting in the seasons. Without the seasons we would probably be locked into a permanent ice age.
• Over a period of 90,000 to 100,000 years, the Earth shifts its course from one that is circular to one that is more elliptical. When the path is elliptical the solar energy received by the earth may vary by 30%.
• Such variations have a strong impact on climate. The Earth is now experiencing a slightly elliptical orbit; as a result, those in the northern hemisphere receive 3.5% more energy in the winter compared to what we would receive if the orbit were circular, and 3.5% less in the summer.

Axial precession

• 12,000 years ago, when we were coming out of the last ice age, the northern hemisphere enjoyed its summer when it was closest to the sun and its winters when furthest away – the antithesis of today.
• This process of axial precession results from the North Pole wobbling around the axis of a line drawn between the North and South Poles.
• This has considerable consequences for climate, since the northern hemisphere has far more continents and a greater land mass compared to the southern hemisphere. Land masses tend to respond more quickly to heat input than the ocean.
• Ice ages seem to be associated with circular rather than elliptical orbits and with less tilt in the Earth’s axis.

Milankovich’s Wobble

• Confirmation that ice ages are caused by the Milankovich Wobble has been hard to come by, despite the conviction of some climatologists that they see correlations between the 100,000 year shift in the orbit around the sun and the coming and going of ice ages.

The moon

• Without the moon, the Earth would have no tides, its rotation would be unstable and a Moon-less Earth would probably tumble chaotically around the sun, leaving little possibility for seasons and no semblance of a stable climate.
• The amount and intensity of sunlight that strikes the earth’s surface is also affected by the movement of the Moon around the Earth

Reflection

• On average about one-quarter of the earth’s outer surface is exposed to the Sun at any one moment, yet not all the 342 Wm² of energy gets down to sea level.
• Clouds reflect roughly 30% of incoming radiation back into space. The shininess of the Earth’s surface and atmosphere makes a difference, since the whiter, or more glassy the surface the more sunlight is reflected back into space.
• If clouds tend to cool the Earth, dark oceans under a clear sky absorb light and get warm. The Earth’s climate therefore results from a combination of the earth’s motion around the sun and features of the Earth’s atmosphere and surface which either reflect or absorb light and heat.
• Since the sun shines down on a spinning, off-centre sphere – our planet – its rays are perpendicular to the surface only in one spot during one moment in time, That constant disparity helps generate climate by generating gigantic convection cells.
• Cooler air from one region is drawn to a warmer region, while warmer air compensates by moving to a cooler region. Consequently, energy is transferred from one part of the planet to the other, giving us the south-westerlies and the Gulf Stream in the northern hemisphere, and the corresponding north-easterlies and ocean currents in the southern hemisphere.

Ice ages

• Scourings of the rock face and movement, even uphill, of massive boulders in the Jura mountains must be evidence that massive glaciers had once covered much of northern Europe. Similar features elsewhere confirmed that glaciers had once stretched for 2,300 kilometres between the 50^th and 72^nd parallel.

Carbon dating

• Accurate dating had to wait until the American chemist Willard Frank Willy dated fossilized remains, including vegetation and animals, using radioactive substances which decay at set rates.
• Carbon loses one half of carbon-14 in 5,730 years. After 100,000 years very little of the original carbon-14 is left, thus giving a natural limit to the use of carbon-14 for telling us how old a fossil is.

Carbon-14, solar flares, sunspots and the Aurora Borealis

• Carbon-14 is created from the atmosphere. Over time the amount generated and the amount vanishing reaches an equilibrium.
• The amount of carbon-14 created varies because of variations in the streaming of high energy particles from the Sun. During a time of solar flares, when the solar wind is stronger, the amount of carbon-14 tends to decline.
• Minze Stuiver determined times of solar flares over the past 1000 years and estimated the proportion of atmospheric carbon-14 from year to year.
• By analysing the carbon-14 in tree rings, he was able to pinpoint which years were abnormal. When the Earth’s surface temperature is matched against such ups and downs an inverse relationship emerges.
• The relatively low levels of carbon-14 in tree rings 900 years ago, during the so-called Medieval Optimum, correlate well with the warmer climate of that time, when average temperatures may have been 1ºC higher than today.
• The link between high relative levels of carbon-14 and a colder climate seems to be borne out.
• There is a connection between sunspot activity and climate. The Chinese recorded 150 sunspots between 26 BC and the 16^th century.
• Enhanced solar activity causes spectacular displays such as the aurora borealis. When we compare the results of radiocarbon in tree rings with observations of the aurora we find a close correlation.
• Observations of sunspot activity over the past 120 years show that the numbers wax and wane over an 11-year cycle. Through the use of satellites we can now measure solar radioactive flux; the Sun’s energy at the top of the Earth’s atmosphere.
• The ultraviolet reaching the Earth nearly tripled in 1960 compared with the end of the last century.
• From 1100-1300, we know that Europe experienced an uncommonly warm climate with incredible consequences for culture. Historians of the Middle Ages called the 13^th century ‘the greatest of all centuries,’ when magnificent cathedrals and works of art flourished. It was also a time of successful agriculture and the doubling of the European population. Solar flares and sunspots may have been double that of today.
• If the Middle Ages were warm, the next couple of centuries were not, and Europe suffered bitter cold and miserable weather that destroyed harvests, particularly in the North. Millions died of starvation, if not of the plague.
• Again we find a correlation between the chill period of the Little Ice Age, from 1650 until 1720, and what appears to be a minimum of sunspots. Wigley and Kelly concluded that the Little Ice Age could have resulted from a quarter to one half per cent decline in solar energy.
• After World War II, when industrial development really took off with a vengeance, any changes in solar constant would have been outweighed by changes to the atmosphere in terms of greenhouse gases and cloud formation.

Chapter 3: Ice Ages and Greenhouse Gases

• Unquestionably, climate has undergone dramatic changes during the history of the Earth. One hundred million years ago the planet was warmer than now, with a tropical climate stretching from the Equator to the poles. Seas were 100 metres higher than today and at high latitudes some 15ºC hotter.
• Four million years ago climate changed dramatically, undergoing periodic cycles between one glacial period and the next, with interglacials lasting little more than 10,000 years.
• Since we are now 10,000 years on from the last ice age, we are definitely due for another, but perhaps we have put paid to that with global warming.
• At the peak of the last ice age 20,000 years ago, giant ice sheets, heaped into domes more than a kilometre thick, stretched across North America from New York State to the Rockies, and across equivalent latitudes in northern Europe.

Albedo and positive feedback

• The degree to which a surface reflects light from the Earth is known as the albedo; a highly reflecting surface, such as fresh snow, has an albedo of 90%, and the oceans of 10%.
• As ice and snow melt, exposing ground, so more heat is absorbed, which in turn leads to more melting and the exposure of more ground. This snowball effect is categorized as positive feedback.
• The higher the overall albedo of the Earth’s surface the greater the chance of the planet entering an ice age, and the lower the albedo the greater the chance of an interglacial.
• The previous interglacial, known as the Eemian, which ended 114,000 years ago, was even warmer than the current interglacial; hippopotamuses lived among the Thames marshes, and elephants and lions roamed in Cornwall and the south-west of England.
• Most of the West Antarctic ice sheet had melted and sea levels were 6-8 metres higher than at present. Temperatures fluctuated between warmer and cooler spells during the early part of the Eemian, with sudden drops of as much as 10ºC putting the planet back in the grip of bitter cold.
• The periodic switch between ice ages and interglacials, over the past two million years, has led some climatologists to believe that the causes of such dramatic climate shifts would completely obscure the climatic consequences of human activities.
• However, the evidence now points to human activities as being largely responsible for climate change and for more extreme climatic events, such as strong and persistent El Niňos.

Greenhouse effect and clouds

• Although rarely mentioned in the same breath as carbon dioxide, the most significant greenhouse gas is water vapour, which accounts for 70% of greenhouse gas warming.
• This is a classic self-generating feedback in which the more warmth in the atmosphere the more water evaporates from the surface, and the more water vapour in the atmosphere the more the atmosphere warms until a point is reached when the dynamics of water evaporation, followed by precipitation, cancel each other out.
• Should global warming occur then the amount of water vapour held in the atmosphere also increases, thus accentuating warming. If a doubling of carbon dioxide from pre-industrial levels were to raise surface temperatures by 1.2ºC, the water vapour drawn into the atmosphere would amplify the temperature increase to 1.9ºC.
• Clouds have a twofold effect: to reflect light away and cool the surface which appears to be the dominant effect; and to hold back heat radiating up from the earth’s surface.
• Warmer clouds tend to rise higher, reducing their ability to emit heat out to space. An increase in greenhouse gases could reduce the overall cooling effect of clouds by as much as one sixth. Just that decline in cloud-cooling would increase by half the global warming effect resulting from a doubling in carbon dioxide concentration.

Greenhouse gases and global warming

• The year 1957 was a moment of profound significance for global climate studies when the United States offered to establish an atmospheric laboratory on Mauna Loa, an extinct volcano in Hawaii.
• Charles Keeling’s pioneering work meant that the origin of recent atmospheric carbon emissions could be identified, from the burning of fossil fuels and wood, and from other non-fossilized organic material.