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12 The Context of Global Climate Change: Climate-Driven Demography
Climate, Present, Past and Future [1] is unequalled both in its comprehensive detail
and scope. Lamb defines the two global climate periods of most relevance to our
study. The Medieval Climatic Optimum [2], which lasted 200–300 years, brought
the warmest conditions the planet had known for about 8,000 years. The timings for
this period were not entirely synchronous: they varied between northern and southern hemispheres and with latitude. For example, Lamb tells us, “In the heartland of
North America, as in European Russia and Greenland. . . the warmest times may be
placed between about A.D. 950 and 1200. In most of Europe the warmest period
seems to have been between 1150 and about 1300, though with notable warmth
also in the late 900 s. In New Zealand the peak may have been as late as 1200 to
1400” [3].
The remarkable warmth of this period ended abruptly with the onset of the Little
Ice Age which lasted in many places until the beginning of the 20th century, the
harshness of conditions varying with time and location. This period brought with it
the coldest conditions in 1,800 years. In areas with cooler climates, the favourable
warm conditions of the Medieval Climatic Optimum led to extensions of horticulture, both in the varieties of crops and in the locations in which they could be
grown. It led, too, to a dramatic increase in fish stocks – rich harvests on sea and
land. Such bounty led to significant population increases and general prosperity. In
Europe, for example, this prosperity is reflected in the undertaking of major building
projects, such as the construction of cathedrals. The demographic consequences of
the Little Ice Age were the opposite: widespread crop failures, the abandonment of
horticultural land, migration, starvation and population collapse.
How extreme the demographic consequences were, varied in different parts of
the world. The population of Britain, for example, tripled in the Medieval Climatic
Optimum, then plummeted by 10% in the 1290s alone, though this was only the
first decade of cold conditions that were to last for at least 400 years. Studying pabuilding in New Zealand during the Little Ice Age, in this climate context, and in
terms of the associated global demographic patterns for cooler climates, enables us
to make sense of the extraordinary number of pa.
The demographic assumption of late settlement theorists is of a population
rapidly increasing over 200 years from AD 1200 to AD 1400, during the Medieval
Climatic Optimum, and then, in contradiction to global patterns, continuing to
increase at the same rate during the Little Ice Age. A continuing population increase
would be reasonable if New Zealand lacked the evidence, common elsewhere in the
world during the Little Ice Age, of food scarcity and associated conflict over land
and resources. Evidence for environmental deterioration from midden analysis and
from the 7,000 pa built during this period challenge the assumption of population
increase.
Evidence for severe food shortages in New Zealand during the Little Ice Age
and associated conflict over land and resources supports the conclusion that population levels in New Zealand were high enough when adverse conditions affected the
biota for ceilings of sustainability to be breached. Given the large landmass of New
Zealand, population levels would have to have been very considerable for this to
12 The Context of Global Climate Change: Climate-Driven Demography
Climate, Present, Past and Future [1] is unequalled both in its comprehensive detail
and scope. Lamb defines the two global climate periods of most relevance to our
study. The Medieval Climatic Optimum [2], which lasted 200–300 years, brought
the warmest conditions the planet had known for about 8,000 years. The timings for
this period were not entirely synchronous: they varied between northern and southern hemispheres and with latitude. For example, Lamb tells us, “In the heartland of
North America, as in European Russia and Greenland. . . the warmest times may be
placed between about A.D. 950 and 1200. In most of Europe the warmest period
seems to have been between 1150 and about 1300, though with notable warmth
also in the late 900 s. In New Zealand the peak may have been as late as 1200 to
1400” [3].
The remarkable warmth of this period ended abruptly with the onset of the Little
Ice Age which lasted in many places until the beginning of the 20th century, the
harshness of conditions varying with time and location. This period brought with it
the coldest conditions in 1,800 years. In areas with cooler climates, the favourable
warm conditions of the Medieval Climatic Optimum led to extensions of horticulture, both in the varieties of crops and in the locations in which they could be
grown. It led, too, to a dramatic increase in fish stocks – rich harvests on sea and
land. Such bounty led to significant population increases and general prosperity. In
Europe, for example, this prosperity is reflected in the undertaking of major building
projects, such as the construction of cathedrals. The demographic consequences of
the Little Ice Age were the opposite: widespread crop failures, the abandonment of
horticultural land, migration, starvation and population collapse.
How extreme the demographic consequences were, varied in different parts of
the world. The population of Britain, for example, tripled in the Medieval Climatic
Optimum, then plummeted by 10% in the 1290s alone, though this was only the
first decade of cold conditions that were to last for at least 400 years. Studying pabuilding in New Zealand during the Little Ice Age, in this climate context, and in
terms of the associated global demographic patterns for cooler climates, enables us
to make sense of the extraordinary number of pa.
The demographic assumption of late settlement theorists is of a population
rapidly increasing over 200 years from AD 1200 to AD 1400, during the Medieval
Climatic Optimum, and then, in contradiction to global patterns, continuing to
increase at the same rate during the Little Ice Age. A continuing population increase
would be reasonable if New Zealand lacked the evidence, common elsewhere in the
world during the Little Ice Age, of food scarcity and associated conflict over land
and resources. Evidence for environmental deterioration from midden analysis and
from the 7,000 pa built during this period challenge the assumption of population
increase.
Evidence for severe food shortages in New Zealand during the Little Ice Age
and associated conflict over land and resources supports the conclusion that population levels in New Zealand were high enough when adverse conditions affected the
biota for ceilings of sustainability to be breached. Given the large landmass of New
Zealand, population levels would have to have been very considerable for this to