Transcript Global Warming

Global Warming
Michael E. Mann,
Department of Environmental Sciences
University of Virginia
ESO Global Warming Forum
Department of Environmental Sciences, UVA
Feb 20, 2001
OVERVIEW
•Observed Climate Change
OVERVIEW
•Observed Climate Change
•The Greenhouse Effect
OVERVIEW
•Observed Climate Change
•The Greenhouse Effect
•Detecting and Attributing
Climate Change
Observed Climate Change
TEMPERATURE ANOMALY (oC)
1.2
1
20th CENTURY TEMPERATURE
TRENDS
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
1998 Global Temperature Pattern
EL NINO/SOUTHERN OSCILLATION (“ENSO”)
Substantial interannual climate variability associated with ENSO,
but decadal variability is also evident as well. The recent decadal
trend towards El Nino conditions could be natural or anthropogenic.
Multivariate
ENSO Index
(“MEI”)
NORTH ATLANTIC
OSCILLATION
Negative Phase
Positive Phase
NORTH ATLANTIC OSCILLATION
Explains enhanced warming in
certain regions of Northern
Hemisphere in past couple
decades
Pacific
Decadal
“Oscillation”
Atlantic Multidecadal Oscillation
There is
evidence of
multidecadal
natural
variability in
the North
Atlantic
ocean
circulation
The Greenhouse Effect
GREENHOUSE EFFECT?
ENHANCED GREENHOUSE EFFECT?
CO2 Concentration
Measurements of CO2 in parts per million (ppm) at Mauna Loa Observatory.
Greenhouse Gases and
Warming
CO2
Related?
Detecting and Attributing
Climate Change
Intergovernmental Panel on Climate Change (United
Nations), Third Assessment Report, 2001
`There is new and stronger
evidence that most of the
warming observed over
the last 50 years is attributable to
human activity'
MANTRA OF PALEOCLIMATOLOGY
TREE RINGS
CORALS
ICE CORES
VARVED LAKE SEDIMENTS
HISTORICAL DOCUMENTS
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.
1791 El Nino
Warm In Europe 
Warm in Northern
Hemisphere!!
CLIMATE FORCINGS
CLIMATE FORCINGS
Science
CONCLUSIONS
•“Anthropogenic” activity associated with increased
greenhouse gas concentrations during the past two
centuries
•Recent global surface temperatures are unprecedented
this century, and likely at least the past millennium
•It is difficult to explain the recent surface warming in
terms of natural climate variability
•Recent surface warming is consistent with simulations of
the effects of anthropogenic influence on climate
•Given uncertainties, future projected climate changes
vary from the modest to the dramatic