Transcript Climate During the Past Millennium

Large-Scale Temperature
Changes During the Past
Millennium
Michael E. Mann,
Department of Environmental Sciences
University of Virginia
Smithsonian Environmental Research Center
Edgewater Maryland
March 15, 2000
OVERVIEW
•Climate Change
OVERVIEW
•Climate Change
•Reconstructing the climate in
previous centuries with “proxy”
climate records
OVERVIEW
•Climate Change
•Reconstructing the climate in
previous centuries with “proxy”
climate records
•Diagnosing the factors influencing
climate variations
OVERVIEW
•Climate Change
•Reconstructing the climate in
previous centuries with “proxy”
climate records
•Diagnosing the factors influencing
climate variations
•Conclusions
GREENHOUSE EFFECT?
GLOBAL RADIATION BALANCE
GREENHOUSE
EFFECT
ENHANCED GREENHOUSE EFFECT?
CO2 Concentration
Measurements of CO2 in parts per million (ppm) at Mauna Loa Observatory.
GLOBAL TEMPERATURE TREND SINCE MID 19th CENTURY
Greenhouse Gases and
Warming
CO2
Related?
MANTRA OF PALEOCLIMATOLOGY
ASTRONOMICAL CLIMATE FORCING
Eccentricity
Obliquity
Precession
ASTRONOMICAL
CLIMATEAND
FORCING
ASTRONOMICAL
CYCLES
ICE AGES
ICE CORES
CORALS
TREE RINGS
HISTORICAL DOCUMENTS
VARVED LAKE SEDIMENTS
Map showing global proxy climate network. All of the
records date back to at least 1820, most to the early 18th
century, and many back to 1600. Before 1400, the network
is too sparse to constrain large-scale patterns of variability
without greatly expanded uncertainties.
INSTRUMENTAL
TEMPERATURE
RECORD
GLOBAL PROXY
CLIMATE
RECORDS
Five leading
patterns of
global
temperature
variation
during the
20th century.
Calibration (1902-1980)
Verification (1854-1901)
Figure 3. Map showing spatial pattern of resolved variance in calibration (top) and verifica
Reconstructions of time histories of 5 leading temperature
patterns. Note that fewer eigenvectors are reconstructed further
back in time.
1791
RECONSTRUCTED
GLOBAL
TEMPERATURE
PATTERNS
RECONSTRUCTED
GLOBAL
TEMPERATURE
PATTERNS
NORTHERN HEMISPHERE MEAN ANNUAL DURING THE
PAST MILLENNIUM
El Niño and La Niña
1791
El Niño
“Niño3”
CLIMATE FORCINGS
CLIMATE FORCINGS
Temperature
Solar Irradiance
Greenhouse Gases
Volcanism
Relationship of
variations in Northern
Hemisphere mean
temperature
reconstruction to
estimates of three
candidate forcings
CONCLUSIONS
•1990s likely the warmest decade in past 1000 years
CONCLUSIONS
•1990s likely the warmest decade in past 1000 years
•Recent El Ninos among the largest of the past
few centuries
CONCLUSIONS
•1990s likely the warmest decade in past 1000 years
•Recent El Ninos among the largest of the past
few centuries
•Natural (volcanic and solar) forcings have
detectable influence during past several centuries
CONCLUSIONS
•1990s likely the warmest decade in past 1000 years
•Recent El Ninos among the largest of the past
few centuries
•Natural (volcanic and solar) forcings have
detectable influence during past several centuries
•Anthropogenic likely the dominant forcing during
the late 20th century