"Abrupt Climatic Changes and Events in the Cordilleran Holocene

and Possible Cultural Implications"

Reid A. Bryson and Alison Stenger

Climate, People, and Environment ProgramCenter for Climatic Research, University of Wisconsin –

Madison

WHO CARES?

• Time is critical for cultural adaptation to climatic change.

• Adjustment to slow change is easy- to rapid change may be impossible or traumatic.

• The old idea of slow climatic change is no longer tenable.

1. THERE MAY BE SHORT BUT INTENSE EVENTSOF GREAT HUMAN SIGNIFICANCE

AND2. SINCE CLIMATE SERIES ARE NON-STATIONARY, THE AVERAGE CLIMATE MAY CHANGE ABRUPTLY AND REMAIN CHANGED FOR MILLENNIA

1. Tropical cyclones are very abrupt events and change

rapidly in frequency

They produce very heavy precipitation

Landslides and rivers of mud in the Nicaraguan

Highlands

What does this mean inThe Rockies?

MOST “GULLY-WASHER” EVENTS IN THE INTERIOR ARE THE RESULT OF LEFTOVER REMNANTS OF TROPICAL STORMS OR DEPRESSIONS- EVEN IN HIGH LATITUDES AND THE WEST

THE ORIGIN MAY BE OBSCURE SINCE THEY MAY ENTER THE WESTERLIES AND APPEAR AS ORDINARY, BUT VERY WET, WESTERLY STORMS

-14000 -12000 -10000 -8000 -6000 -4000 -2000 0

RADIOCARBON DATE BP

100

200

300

400

500

MEAN TROPICAL STORMS PER 30 YRS

010625

MODELED TROPICAL STORM HISTORYMANILA

EXAMPLE IN PREHISTORY:FOUR TIMES AS MANY MID-HOLOCENE TROPICAL STORMS

IN THE WESTERN PACIFIC. THESE RECURVE AND HEAD TOWARDS NORTH AMERICA

TROPICAL STORM REMNANTS REACHING THE COAST SHOW UP AS HIGH INTENSITY

PRECIPITATION

-11000-10000

-9000-8000

-7000-6000

-5000-4000

-3000-2000

-10000

RADIOCARBON DATE BP

0

5

10

15

20

25

30

35

OCTOBER PREC./ DAY W/ PREC. (mm/day)

0

5

10

15

20

25

30

35

AUGUST PREC./DAY W/ PREC. (mm/day)

OCTOBER INTENSITY AUGUST INTENSITY 030908

MODELED PRECIPITATION INTENSITY HISTORYNEHALEM 9 NE, OR

2. THE DYNAMICS OF THE ATMOSPHEREFORCES RAPID CLIMATIC CHANGES

WHICH PRODUCE WHAT ARE CALLEDNON-STATIONARY CLIMATIC SERIES.

THIS MEANS THAT STANDARD STATISTICSDO NOT APPLY.

CHANGES HAPPEN RAPIDLY, AND VARIABILITY CHANGES, AS DO EXTREMES.

WAVES IN THE WESTERLIES, THE NORTH-SOUTH MEANDERING SO OBVIOUS ALOFT, MUST OCCUR IN WHOLE NUMBERS AROUND THE HEMISPHERE- 3 OR 4 OR 5 ETC., BUT NEVER FRACTONS LIKE 3.27.

THUS AS CONDITIONS CHANGE, THE NUMBER MUST CHANGE ABRUPTLY BY A WHOLE STEP.

THIS CHANGES THE PATTERN OF THE WHOLE HEMISPHERE AT THE SAME TIME.

CHANGE OF WAVE NUMBER

IN THE WESTERLIES MAY MAKE

LITTLE CHANGE OVER CREST, BUT OPPOSITE CHANGE ON

FLANKS

THE CORDILLERA ITSELFFORCES CONTRASTS

DRY WET

WET DRY

RIDGE NORTH OF THE JETSTREAM,TROUGH SOUTH OF THE JETSTREAM.

THE ROUGHNESS OF THEMOUNTAINS FORCES A RAINFALL PATTERN

A SMALL SHIFT IN THE MEAN

LATITUDE OF THE JET MAY CHANGE

THE ROCKIES CLIMATE

DRAMATICALLY AND FAST

THE DIVISIONS OF THE HOLOCENE WERESHARPLY DEFINED- AS WERE THE

CORRESPONDING CULTURAL STAGES

WITH HIGH RESOLUTION SAMPLING THE RAPIDITY OF CHANGE MAY BE OBVIOUS AS COMPARED

HERE AGAINST A MODEL

SMALL CHANGES IN THE AVERAGE MEANSDRAMATIC CHANGES IN THE EXTREMES

SUMMARY1. CLIMATE IS MORE THAN WET/DRY,

WARM/COLD. THERE ARE IMPORTANT SHORT EVENTS LIKE TYPHOONS AND FLASH FLOODS.

2. CLIMATE NORMALLY CHANGES RAPIDLY.

3. THESE CHANGES WILL BE MISSED WITHOUT CLOSE SAMPLING i.e. 100 YEAR RESOLUTION OR LESS.