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

20th CENTURY TEMPERATURE TRENDS TEMPERATURE ANOMALY (oC)

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HISTORICAL DOCUMENTS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 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.

Warm In Europe  Warm in Northern Hemisphere!! 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