328
19 Correlation of Significant Voyaging Activity with Rare Extreme Climate Events
was vital, not for shorter distances where seasonal westerlies might prove adequate,
but for the longer time required for long-distance exploration, trading and migration.
An El Niño in the Pacific is heralded by westerlies. As these become stronger,
the normal southeast trade winds below the equator are completely suspended,
for reasons that the technical accounts of the oceanic and atmospheric processes
above makes clear. And so strong do these westerlies become that the normal east–
west flowing South Equatorial Current is not only halted but actually reversed,
flowing west to east with the winds. In warm period exploration, return-voyaging
in the lower latitudes of the Pacific is always possible because an El Niño is a
“contained event”, an oscillation. When the cycle underlying the phenomenon is
complete, weather patterns will reverse, the trade winds and the west–east currents they support will return, ensuring a fast homeward as well as a fast outward
voyage.
Optimal conditions for successive stages of exploration and settlement in the
southern Pacific depended on periods of global warmth. By reversing contrary winds
and currents, ENSO events played a secondary role in providing a speedy passage
and safe return for the long-distance voyages undertaken within tropical Polynesia
during global warm periods. During a long-lasting El Niño, cloudless skies would
have made it easier to navigate by the stars, strong winds and the faster voyaging these facilitated would have decreased risks of hypothermia, starvation and
thirst.
In this chapter we focus on the exploits during the Medieval Climatic Optimum
and earlier warm periods of a line of famous Eastern Polynesian navigators. Using
two climatic bounds – global warmth and periodic strong ENSO events – in relation to events recorded in oral traditions, we endeavour to sketch a chronology for
the history of oceanic migration in the periods covered by low Nile ENSO proxy
data.
There are some caveats we should note first. There is difficulty in dating climate
periods with any precision because they vary from hemisphere to hemisphere, continent to continent and latitude to latitude. The Medieval Climatic Optimum had
begun by AD 900 in some parts of Europe and ended by AD 1300. In New Zealand,
by contrast, Lamb claims that it may have peaked between AD 1200 and AD 1400
[4]. We are dealing with worldwide warming and cooling events of considerable
magnitude and, usually, duration, moderated in some cases by local factors, such
as distance from the equator, warm currents, local precipitation factors and glaciation. Long-term factors, such as variation in the earth’s distance from the sun, and
short-term factors such as increase in sun-spot activity also have profound effects
on climate but these effects are unevenly distributed.
The warm and cold periods that Lamb lists and the time scales he proposes
for them give us a broad chronological foundation. For more precise calibration
of “windows of opportunity” for long-distance oceanic migration and significant
voyaging in the Pacific, however, we have chosen another path: we propose to use
ENSO events, occurring within the imprecisely bounded global warm periods, to
give more exact datings for major voyages recorded in oral traditions. Advances in
climatological research in the past 20 years make this feasible.
19 Correlation of Significant Voyaging Activity with Rare Extreme Climate Events
was vital, not for shorter distances where seasonal westerlies might prove adequate,
but for the longer time required for long-distance exploration, trading and migration.
An El Niño in the Pacific is heralded by westerlies. As these become stronger,
the normal southeast trade winds below the equator are completely suspended,
for reasons that the technical accounts of the oceanic and atmospheric processes
above makes clear. And so strong do these westerlies become that the normal east–
west flowing South Equatorial Current is not only halted but actually reversed,
flowing west to east with the winds. In warm period exploration, return-voyaging
in the lower latitudes of the Pacific is always possible because an El Niño is a
“contained event”, an oscillation. When the cycle underlying the phenomenon is
complete, weather patterns will reverse, the trade winds and the west–east currents they support will return, ensuring a fast homeward as well as a fast outward
voyage.
Optimal conditions for successive stages of exploration and settlement in the
southern Pacific depended on periods of global warmth. By reversing contrary winds
and currents, ENSO events played a secondary role in providing a speedy passage
and safe return for the long-distance voyages undertaken within tropical Polynesia
during global warm periods. During a long-lasting El Niño, cloudless skies would
have made it easier to navigate by the stars, strong winds and the faster voyaging these facilitated would have decreased risks of hypothermia, starvation and
thirst.
In this chapter we focus on the exploits during the Medieval Climatic Optimum
and earlier warm periods of a line of famous Eastern Polynesian navigators. Using
two climatic bounds – global warmth and periodic strong ENSO events – in relation to events recorded in oral traditions, we endeavour to sketch a chronology for
the history of oceanic migration in the periods covered by low Nile ENSO proxy
data.
There are some caveats we should note first. There is difficulty in dating climate
periods with any precision because they vary from hemisphere to hemisphere, continent to continent and latitude to latitude. The Medieval Climatic Optimum had
begun by AD 900 in some parts of Europe and ended by AD 1300. In New Zealand,
by contrast, Lamb claims that it may have peaked between AD 1200 and AD 1400
[4]. We are dealing with worldwide warming and cooling events of considerable
magnitude and, usually, duration, moderated in some cases by local factors, such
as distance from the equator, warm currents, local precipitation factors and glaciation. Long-term factors, such as variation in the earth’s distance from the sun, and
short-term factors such as increase in sun-spot activity also have profound effects
on climate but these effects are unevenly distributed.
The warm and cold periods that Lamb lists and the time scales he proposes
for them give us a broad chronological foundation. For more precise calibration
of “windows of opportunity” for long-distance oceanic migration and significant
voyaging in the Pacific, however, we have chosen another path: we propose to use
ENSO events, occurring within the imprecisely bounded global warm periods, to
give more exact datings for major voyages recorded in oral traditions. Advances in
climatological research in the past 20 years make this feasible.