The Little Ice Age: How Climate Made History 1300-1850 (39 page)

Solar activity is currently at a high level relative to the record of the past
8,000 years, which suggests that future impacts of solar radiation on global
climate will be much smaller than those stemming from greenhouse gases.
Even during sunspot minima, reduced solar luminosity probably accounted for no more than half a degree Centigrade of cooling. Solar radiation is large enough to shape global warming, but not to dominate it.

Even if the sun does significantly influence climate change on earth,
humanly generated greenhouse gases, virtually absent during the Little
Ice Age, are almost certainly the major agents of the current sustained
warming. Prudence suggests that we plan for an entirely new era of climate change.17

What form will this change take? One school of thought, popular with
energy companies, is serenely unfazed by global warming. Gradual climate change will bring more benign temperatures. Sea levels will rise
slightly, there may be some extreme weather events, but within a few centuries we will emerge into a more uniform, warmer regimen of shrunken
ice sheets, milder winters, and more predictable weather-much like
earth in the time of the dinosaurs. Humanity will adjust effortlessly to its
new circumstances, just as it has adjusted to more extreme changes in ancient times.

The record of history shows us that this is an illusion. Climate change
is almost always abrupt, shifting rapidly within decades, even years, and
entirely capricious. The Little Ice Age climate was remarkable for its rapid
changes. Decades of relatively stable conditions were followed by a sudden shift to much colder weather, as in the late seventeenth century,
1740/41, or even the 1960s. The same pattern of sudden change extends
back as far as the Great Ice Age of 15,000 years ago, and probably to the
very beginnings of geological time. Given this history, we would be rash to assume that sudden climate change will miraculously give way to a
more uniform warming trend. The exact opposite seems more likely. In
all probability the dinosaurs lived through short-term climatic shifts that
were just as unpredictable as those of the past 10,000 years, if for no
other reason than that large-scale volcanic activity was just as prevalent
then as it is today. The Little Ice Age reminds us that climate change is inevitable, unpredictable, and sometimes vicious. The future promises exactly the same kinds of violent change on a local and global scale. If the
present, unusually prolonged high mode of the North Atlantic Oscillation is indeed due to anthropogenic forcing, then we must also assume
that global warming will accentuate the natural cycles of global climate
on the largest and smallest scales. Some of these potential cycles of change
are frightening to contemplate in an overpopulated and heavily industrialized world.

This concern has ample historical precedent. Eleven thousand years ago,
long before the Industrial Revolution, humanity experienced a fast climate
change that came as a complete shock. After some three millennia of global
warming, rising sea levels, and shrinking ice sheets at the end of the Great
Ice Age, a massive influx of fresh glacial meltwater into Arctic waters shut
down the downwelling that carried salt water into the deep ocean. The
warm conveyor belt that had nourished natural global warming in the
north abruptly stopped. The warming itself ceased perhaps within a few
generations, plunging Europe into near-glacial cold for a thousand years.
Glaciers advanced, pack ice spread far south for much of the year, and
forests retreated southward. Rainfall zones shifted, and intense drought settled over southwestern Asia, causing many Stone Age bands to turn from
foraging to farming. The millennium-long "Younger Dryas" event, named
after a polar flower, ended as rapidly as it began, when the downwelling
switch abruptly turned on again and warming resumed.

Younger Dryas Europe was sparsely populated by hunter-gatherer
groups that were mobile enough to adapt to rapidly changing environmental conditions. What would happen today if northern downwelling
were to slow down or cease and plunge Europe into near-glacial cold? Anthropogenic global warming could easily flip the switch. Models of ocean
circulation patterns hint that even a modest increase in fresh meltwater
inflow into arctic seas could choke off downwelling in the North At lantic. The pulse of fresh water would float atop the dense, salty Gulf
Stream, just as it did 11,000 years ago, forming a temporary "lid" that
would effectively prevent the Gulf Stream water from cooling and sinking. A sea ice cap could form in short order, preventing the Gulf Stream
from starting up again, and trigger an intensely cold regimen in Europe
within perhaps a few years. No one can predict how long such a cold snap
would last. A few unusually warm summers might melt the ice and expose the Gulf Stream, allowing downwelling to resume and milder climate to return. Or evaporation of water vapor in the tropical Atlantic far
from the ice sheets could cause such a buildup of salt water that downwelling would begin at the edges of the ice zone, far from the traditional
spots, again causing a rapid warmup of European climate.

The consequences of a Younger Dryas-like event to industrial agriculture alone, though truly frightening to contemplate, are not beyond the
grounds of possibility. The chance is remote, but Europe's planners factor
it into their scenarios for the climatic long-term future.

The short-term climatic future is relatively easy to predict. If warming
continues on its present trajectory, growing seasons in Europe will
lengthen, vineyards will again be established in central England, and
farms will be cleared closer to the Arctic Circle. Northern Europe and
much of North America may prosper from the warmth, but southern Europe, much of tropical Africa, and Central and South America will suffer
more frequent water shortages and greater heat, as well as diminished
agricultural capacity. Confrontations over water rights will flare in countries like Egypt, which depend on river flow from across national borders.
People will adapt as they always have, but drier tropical regions with at
least 400 million people subsisting in overpopulated marginal environments will make that adaptation difficult.

What of the longer term, if global warming accelerates? Sufficient reserves of fossil fuel exist to cause a continued growth in atmospheric carbon dioxide levels well into the twenty-second century. If this growth continues unchecked, the climate changes on earth will probably be very large indeed and extremely unpredictable. But many scientific uncertainties remain. Recently, James Hansen and a group of his colleagues have argued
that the rapid warming of recent decades has in fact been driven mainly by
non-CO2 gases such as chlorofluorocarbons. Fossil fuel burning CO2 and
aerosols have both positive and negative climatic forcing effects, which
tend to cancel each other out. Hansen and his team point out that the
growth rate of non-CO2 gases has declined over the past decade and could
be reduced even further. This, combined with a slowing of black carbon
and CO2 emissions, could lead to a decline in the rate of global warming.18 Much more research is needed to confirm this hypothesis.

Optimists assume that we will adapt comfortably. We humans do have
a striking ability to adapt to changing environmental circumstances at the
local level. Witness the agricultural revolution in Flanders, the Low
Countries, then Britain during the climatically unpredictable sixteenth
and eighteenth centuries.

Yet optimism fades in the face of demographic reality. Six billion of us
now inhabit earth, with hundreds of millions still subsisting from harvest
to harvest, from rainy season to rainy season, just as many European peasants once did. For Europe and North America, with their industrial-scale
agriculture and elaborate infrastructures for moving food over long distances, famine is remote. But subsistence farmers on other continents still
live with the constant threat of hunger. As I write this, more than 2 million cattle herders in northeast Africa face starvation because of severe
drought. Such numbers are hard for us to comprehend in the prosperous
West. They will become still harder to comprehend if global temperatures
rise far above present levels, when rising seas inundate densely populated
coastal plains and force millions of people to resettle inland, or far more
severe droughts settle over the Sahel and the less well watered parts of the
world? I have avoided discussing wars in this book-it would be simplistic to say that wars or other complex political events were caused by climatic change-but it's implausible to suppose that famines and massive
dislocations of poor populations will be unaccompanied by civil unrest
and disobedience. We can only imagine the potential death toll in an era
when climatic swings may be faster, more extreme, and completely unpredictable because of human interference with the atmosphere. The
French Revolution or the Irish potato famine pale into insignificance.

Even if the present warming is entirely of natural origin, greenhouse
warming in the future could be accentuated by fossil fuels. We would be
rash to ignore even theoretical scenarios, for we and our descendants are
navigating uncharted climatic waters. In that respect we are no different
from medieval farmers or eighteenth-century peasants, who took the
weather as it came. Today we can forecast the weather and model climatic
change, but globally we are still as vulnerable to climate as were those
who endured the famine of 1315 or the great storms of the Spanish Armada, simply because there are so many of us and we are so closely
linked, environmentally, economically, and politically. Fortunately, we
now have, or will shortly have, the scientific data that document the full
extent of the danger. We also know what has to be done, and have many
of the tools to make significant changes. But to implement countermeasures to reduce greenhouse gasses and minimize the impact of climatic extremes on an increasingly crowded world community will require a new
altruism, and a desire to work for the global rather than the national
good, for the welfare of our grandchildren and great-grandchildren rather
than to satisfy short-term, often petty, goals. Political bickering, selfish
national interests and the intense lobbying of international business have
so far militated against broad agreement as to the path ahead.

Over a century ago, Victorian biologist Thomas Huxley urged us to be
"humble before the facts." The facts stare us in the face, yet we do not
display sufficient humility. As British diplomat Sir Crispin Tickell recently remarked: "Mostly we know what to do but we lack the will to do
it."19 The vicissitudes of the Little Ice Age remind us of our vulnerability
again and again. In a new climatic era, we would be wise to learn from
the climatic lessons of history.

The literature surrounding the Little Ice Age is diffuse, enormous, and profoundly
contradictory, much of it in extremely obscure, specialized journals. To fully reference this book would festoon it with hundreds of footnotes. Instead, I have elected
to provide a guide to further reading among the citations, footnoted at a general
level to the text. The reader will find comprehensive bibliographies in most of the
works cited below, which will provide an entry into the technical literature.

PREFACE

The quote from George Philander is from Is the Temperature Rising? (Princeton:
Princeton University Press, 1998), 3.

PART ONE WARMTH AND ITS AFTERMATH

The Chaucer quote is from the Canterbury Tales, edited by John Coghill (Baltimore: Pelican Books, 1962), 17.

The German chronicler of 1315 is quoted in William Chester Jordan's The Great
Famine (Princeton: Princeton University Press, 1996), 20.

CHAPTER 1

The excerpt from Hafgerdinga Lay ("The Lay of the Breakers") is quoted in Magnus Magnusson and Hermann Palsson, eds., The Vinland Sagas (Harmondsworth,
England: Penguin Books, 1965), 52.

1. H. H. Lamb, Climate, History and the Modern World (London: Methuen,
1982), 165. Lamb's work is an excellent, thorough summary. M. L. Parry, Climatic
Change, Agriculture, and Settlement (Folkstone, England: Dawson, 1978) covers expansion and contraction of agricultural activity, especially in Scotland.