The Year Without Summer (11 page)

While the amateur meteorologists of the early nineteenth century understood the links
between their own atmospheric measurements and immediate changes in their weather,
they were unable to forecast the weather more than an hour or two in advance. Having
developed reliable, if elementary instruments and a rudimentary understanding of atmospheric
physics, there remained three key challenges that would make accurate weather predictions
impossible for another 150 years. The first was the speed at which meteorological
data could be transferred and collected at a central location. Forecasting the weather
requires accurate information about the current state of the atmosphere. A crude,
but often effective prediction technique is to simply use the weather from a nearby
location upwind of the location for which one is forecasting. If the wind moves at
a greater speed than the information, however, even this technique is useless. Not
until the development of a widespread telegraph network in the mid nineteenth century
could scientists collect meteorological data quickly enough to make these basic forecasts
for a few hours ahead, or warn of the approach of severe weather.

To move beyond the simple, upwind forecasting method, meteorologists must understand
the circulations of and interactions between air masses around the globe. As scientists
continued to develop meteorological instruments through the seventeenth, eighteenth,
and nineteenth centuries, they also developed hypotheses to explain the changes in
the readings they obtained. Aided by the instruments aboard ships, many mathematicians
and “natural philosophers” turned their attentions to the causes of the direction
and strength of the transoceanic winds. These projects carried significant potential
benefits to them and their government sponsors, since knowledge of the seasonal variations
in the paths of the strongest winds would allow merchant vessels and warships to cross
the ocean more quickly than their competitors and enemies.

As the British Empire and the Royal Navy expanded during this period, British scientists
engaged in a fierce debate over the origin of the east-to-west trade winds (named
for their importance in conveying goods-laden ships to the Americas) that blow steadily
across the Atlantic and Pacific in both the Northern and Southern Hemispheres. Some
supported Galileo’s earlier hypothesis that the winds were caused by Earth rotating
more quickly in the tropics than at the poles; the tropical atmosphere could not “keep
up” with the spinning Earth below, they argued. To one standing on the ground, rotating
to the east with Earth, the wind would indeed appear to blow from east to west. Others,
such as the late-seventeenth-century astronomer Edmund Halley, believed that the winds
blew from the east because the sun’s energy flowed from east to west during each day.
Halley argued that the sun’s energy heated the air, which rose to form a wind; the
sun’s movement caused this wind to appear to blow from the east. Halley’s explanation
became canon and was widely accepted in the early nineteenth century.

It would be another twenty years after the eruption of Tambora before scientists acknowledged
the true explanation for the trade winds. First advanced—with some inaccuracies—by
the British lawyer and amateur meteorologist George Hadley in 1735, the theory stated
that the trade winds are caused by air trying to flow from each hemisphere towards
the equator. When viewed from the perspective of someone standing on the rotating
Earth, however, the winds—which are not rotating—appear to curve to the right in the
Northern Hemisphere and to the left in the Southern, giving east-to-west winds in
both hemispheres. For his contributions, climatologists still refer to the circuit
of winds between the equator and the middle latitudes as the Hadley Cell.

Hadley’s theory was often discussed, but the idea of Earth as a rotating frame of
reference was difficult for scientists to grasp. Hadley’s principle did not gain meaningful
traction until Gaspard-Gustave Coriolis conclusively demonstrated in 1835 the actions
of the various forces acting in a rotating reference frame. (Coriolis, incidentally,
thought his work would be most useful for those who built waterwheels, or played billiards.)

Many other fundamental principles of atmospheric science relevant to weather forecasting
were developed in the decades following the eruption of Tambora, but remained unknown
or as working hypotheses to those attempting to explain the cooling climate and extreme
weather after 1815. The Navier-Stokes equations, which describe the three-dimensional
flow of viscous fluids, including the atmosphere, were derived in 1845, when George
Gabriel Stokes updated Claude-Louis Navier’s 1822 formulation. These equations are
crucial to describing the ever-evolving state of the atmosphere; today they form the
basis for the computer simulations of Earth’s climate that make it possible to predict
the weather days and sometimes weeks in advance. Similarly, the Clausius-Clapeyron
relationship, which explains that a greater quantity of water vapor can exist in warmer
air, was advanced by its namesakes in the mid-1830s. Without the understanding of
the global circulation of the atmosphere that these theories provide, the gentleman
scientists of the early nineteenth century lacked the knowledge to understand that
volcanic eruptions would affect the world’s weather patterns; certainly they could
not have forecast the disruption that the eruption of Tambora would create.

Even with speedily transmitted data by telegraph and comprehension of physical laws
that govern the atmosphere, meteorologists failed to produce reliable, useful weather
forecasts until after the Second World War due to the third and final hurdle: computational
speed. The Navier-Stokes equations and the other key atmospheric formulae require
computers in order to generate timely forecasts. The human brain simply is not sufficiently
powerful, as the early-twentieth-century British mathematician Lewis Fry Richardson
discovered when he tried to apply the equations developed in the nineteenth century
to real weather observations. It took Richardson nearly three years—working part-time
while serving as an ambulance driver during the First World War—to make a six-hour
weather forecast for France, a forecast that turned out to be spectacularly inaccurate.

In the absence of data, theories, and computers, amateur meteorologists of the early
nineteenth century fell back upon the centuries-old method of pattern recognition
when attempting to forecast the weather and climate. They looked for signs from nature—larger
than normal berries on trees, an early appearance of acorns, even the thickness of
onion skins—as forewarnings of the coming seasons. (Thin onion skins supposedly meant
a mild winter.) Links between these signals and the subsequent climate, whether real
or imagined, became established in “weather lore” and provided the basis for many
almanacs. Such sayings often thrived due to their adherents’ selective memories, attaching
greater importance to the instances in which the lore proved accurate than to those
(often more frequent) times when it failed. Some meteorologists of the era also proposed
associations between the seasons themselves, such as a cold winter following a warm
autumn. In some cases modern science has proven these relationships to be correct,
but only because the abnormal conditions in both seasons are caused by the same variation
in the atmospheric circulation.

4.

THE HANDWRITING OF GOD

“The atmosphere still seems as cold as in March or November…”

O
N
J
UNE 5,
President Madison (annual salary: $25,000) left his temporary dwelling in Washington,
D.C. (annual rent: $1,814), and headed for Montpelier, his home in Orange, Virginia,
about 50 miles south of the nation’s capital. (No one voluntarily spent the summer
in the hot, muggy, mosquito-infested District of Columbia.) Since Congress adjourned
on April 30, the president had spent much of his time negotiating with Britain a reduction
in armaments on the Great Lakes. Through the United States ambassador at the Court
of St. James’s, John Quincy Adams, Madison also informed Foreign Secretary Lord Castlereagh
that the U.S. intended to obtain equal commercial access to export markets—primarily
for American grain—in the British West Indies.

Before he left Washington, Madison sailed down to Annapolis to inspect a new U.S.
warship; since the president decided the trip was not, strictly speaking, official
business, he insisted on paying out of his own pocket the twenty-five-dollar fee due
to the sailors who took him down the Potomac. Then a messenger arrived with a letter
from the Dey of Algiers, whom the American public regarded as one of the widely despised
“Barbary Pirates.” The Dey’s letter was written in Turkish and translated into Arabic,
but since no one in the president’s immediate circle could decipher either language,
the letter sat, unread, for two months until a translator could be found.

Madison reached Montpelier just in time for the arrival of the cold wave that was
devastating New England’s crops. Freezing temperatures had settled over New Jersey
and Pennsylvania on June 6 and 7; then frost struck the fields of central Virginia,
damaging corn, wheat, and vegetables. “This is an extraordinary spring,” declared
a Richmond newspaper. “On Thursday morning last we had a
frost
in this city.” To make matters worse, the effects of the springtime drought were
felt even more strongly in the south than in New England; Charleston, South Carolina,
suffered through eight weeks without rain in March and April. “We do not recollect
to have witnessed a more distressing drought, than that which at this time visits
every portion of our country,” lamented the
American Beacon
, published in Norfolk. “The temperature of the weather with us is very fluctuating—the
evenings and mornings generally so cool as to render a fire quite agreeable. The Earth
is so parched…”

There was no shortage of explanations put forth by self-appointed experts to account
for the recent extraordinary weather. News of the eruption of Mount Tambora had reached
the United States by June 1816, but no one had yet published a theory to link Tambora’s
ash cloud to the frigid temperatures in North America. Instead, numerous newspaper
stories attempted to connect the cold wave with the previously sighted sunspots. “The
sun is no doubt the great fountain of caloric, or heat, as well as of light,” mused
a typical report, “and it is very rational to suppose that the objects which exhibit
to us the appearance of spots on the sun, by intercepting the
calorific rays
, may have deprived the earth of some part of the quantity which it usually receives.”
Although sunspots visible to the naked eye had largely faded from view by the end
of May, they suddenly reappeared during the first week of June. One enterprising amateur
astronomer tried to revive the hypothesis by suggesting that even weakened sunspots
might have combined with a total lunar eclipse on the evening of June 9—which left
New Englanders in darkness for sixty-seven minutes—to somehow enable the moon’s gravitational
pull to disrupt the normal flow of winds around Earth.

Skeptics remained unimpressed. “The alarm from spots on the Sun proves the small progress
of science and of the advantages nominal science has over superstition and prejudice
and ignorance,” sniffed Reverend William Bentley of Salem. “We think the alteration
took place before the spots were observed,” scoffed
Niles’ Weekly Register
, “but it is foolish to be positive about any opinion in a question of this kind.”

Perhaps. But the proponents of the sunspot theory were correct in presuming a connection
between sunspots and temperatures and weather patterns on Earth, albeit not in the
manner they suggested. The spots on the sun’s surface appear darker than the rest
of the sun because less heat from the sun’s fusion reactions reaches the surface there.
While this would suggest a reduction in the energy emitted by the sun, the opposite
is in fact the case: An increase in sunspot activity is associated with an
increase
in the energy leaving the sun.

Although the sunspots are cooler than the remainder of the sun, they are surrounded
by warmer, brighter areas that are often more difficult to notice against the background
of the sun itself. The net effect of the cool sunspots and the warmer regions around
them is to slightly increase the total amount of energy that the sun produces. These
changes in solar energy may affect temperature and precipitation patterns on Earth,
but temperature variations associated with sunspot activity are considerably less
than those caused by volcanic eruptions. The aerosol cloud produced by Tambora likely
reduced the amount of solar energy reaching Earth’s surface by 0.5 percent, an effect
ten times stronger than that caused by a normal minimum in the eleven-year sunspot
cycle, and more than three times stronger than the Maunder Minimum, the period of
lowest sunspot activity on record. While the coincidence of Tambora and the Dalton
Minimum probably increased the cooling effect of the aerosol cloud on Earth’s climate,
the volcanic ash was the primary and proximate cause for the exceptionally cold and
wet summer of 1816.

An understanding of the relationship between sunspot activity and solar energy lay
more than thirty years in the future, however. Not until 1848 did Joseph Henry, the
first director of the Smithsonian Institution, demonstrate that sunspots were cooler
than the surrounding sun. It is not surprising, therefore, that a number of incorrect
and conflicting theories over the origins and effects of sunspots circulated as North
America’s weather began to change in 1816.

Other Americans attributed the snow and frigid temperatures to the unusually large
concentrations of ice still floating in the Great Lakes and—according to British merchant
sailors—in the North Atlantic, off the coast of Newfoundland. These immense fields
of ice purportedly absorbed substantial quantities of heat from the atmosphere, and
thereby reduced its temperature. Critics noted, however, that if this hypothesis were
true, coastal areas in New England (specifically, Maine, eastern New Hampshire) would
have endured deeper snows and lower temperatures than inland regions such as Vermont,
more than one hundred miles from the ocean. But they had not. Perhaps the afflicted
inland regions were cooled by the ice on the Great Lakes; yet this argument seemed
to go only round in circles. “Very cold weather produced great quantities of ice,”
concluded one skeptic quite properly, “and great quantities of ice, at their dissolution,
were the cause of uncommon cold weather.”