US Global Change Seminar on the Earth's Temperature Records and Trends May 20th and 21st

Tony Socci tsocci at
Wed May 15 16:17:11 EDT 1996

    U.S. Global Change Research Program Second Monday Seminar Series 

    A Close Look at Global Satellite and Surface Temperature Records and Tre= 

                                                         (Parts I and II) 

How is the Earth's temperature measured? What are the historical trends in 
the Earth's temperature as observed from surface measurements and from 
satellites? Are these records different? What are the reasons for the 
differences? Can satellite and surface temperature records be reconciled? 
Where do the uncertainties lie and how can they be addressed? To what 
extent do the records indicate that climate is changing due to human 
influences? What is the evidence that humans are having a discernible 
influence on the global climate? 

                                                                 Public Invi= 

Special Two-Part Seminar: Monday and Tuesday, May 20 and 21, 1996, 3:15-4:45= 
                        Rayburn House Office Bldg., Room B369, Washington, D= 

                                                         Reception Following 


Dr. Michael C. MacCracken, Director, Office of the US Global Change 
Research Program, Washington, DC 


Monday, May 20: The Satellite Temperature Record 

Dr. John R. Christy, Earth System Science Lab, University of Alabama, 
Huntsville, Alabama, on  "The Tropospheric Temperature Record from the 
Microwave Sounding Units" 

Dr. Kevin E. Trenberth, Climate Analysis Section, National Center for 
Atmospheric Research, Boulder, Colorado, on "Relating the Satellite and 
Surface Temperature Records" 

Tuesday, May 21: The Surface Temperature Record 

Dr. Tom M. L. Wigley, Senior Climate Scientist, National Center for 
Atmospheric Research, Boulder, Colorado, on "Interpreting the Global 
Warming Record" 

Dr. Benjamin D. Santer, Program for Climate Model Diagnosis and 
Intercomparison, Lawrence Livermore National Laboratory, Livermore, 
California, on "The Search for a "Fingerprint" of Human Activities in 
Observed Climate Records" 


        Temperature is perhaps the most common measure of the climate of a 
region, whether it is the cold temperatures of winter in Minnesota or the 
hot temperatures of summer in Arizona. Temperature, along with 
precipitation, also controls many aspects of ecosystems, helping determine 
spring blooming and the extent of mosquitoes and other vectors for 
diseases. For these reasons and more, the longest records of climate in 
many areas are of temperature. Similarly for the globe, records of 
temperature are the most abundant, provide the longest quantitative record, 
and can be most readily compiled and compared. Analysis of the temperature 
record, on scales from regional to global, has thus been a critical part of 
studies of the patterns and extent of climatic change. 

        While temperature is the most complete record, the measurements and 
available data sets, nonetheless, have many shortcomings. For surface 
measurements, these include changes in measurement techniques, limits to 
the coverage of measurements, changes in the surroundings around a 
stations, and many more. Efforts are therefore being made to measure the 
Earth's temperature from space, but again there are many limitations, 
including, among others, the inability to measure surface temperature, the 
changing sequence of instruments, and the limited length of the record. 

        This seminar will provide the opportunity to look closely at the 
records of both satellites and surface stations, to consider their relative 
strengths and weaknesses, and to consider what these records show and do 
not show. 

The Satellite Temperature Record 

Since 1979, Microwave Sounding Units (MSUs) on NOAA polar orbiting 
satellites have measured the intensity of upwelling microwave radiation 
from atmospheric oxygen. The intensity is shown to be proportional to the 
temperature of broad vertical layers of the atmosphere, as demonstrated by 
theory and direct comparisons with atmospheric temperatures from radiosonde 
(balloon) profiles. A record that is now more than 17 years long has been 
created by merging data from nine different MSUs, each with peculiarities 
(e.g., time drift of the spacecraft relative to the local solar time) that 
must be calculated and removed because they can have substantial impacts on 
the resulting trend. 

A natural step with such a record is to look for trends over this period, 
even though it is quite short compared to the surface temperature record. 
Between 20=9AN-20=9AS, independent view-angle trends in channel 2 and 4 show= 
warming trend in the upper troposphere with cooling in the lower 
troposphere, implying a non-linear vertical temperature adjustment. The 
greatest differences between the satellite and surface records occur 
between 30=9AS-30=9AN and 52=9AN-82=9AN. An important aspect of deriving= 
 trends and 
looking for any human influence, especially over short periods, is 
accounting for what might be irregular and extraneous natural events. For 
the MSU record, these include the century's largest El Nino warming in the 
early 1980s and the century's largest volcanically induced cooling in the 
early 1990s.  The tilt in the trend caused by these two events suggests a 
cooling trend over the period of record. When the MSU records are adjusted 
for El Nino events and volcanoes so that the greenhouse/aerosol effect will 
likely be the dominant influence, the resulting temperature trend is 
positive, rising at a rate of +0.055 to 0.0110 =9AC per decade. 

Because the MSU observations are measuring the temperature of the 
atmosphere and not of the surface, an important question is how the two are 
related. While the traditional notion has been that they are closely 
coupled at all times and throughout the world, this has turned out not to 
be the case. Recent research is starting to provide explanations for the 
apparent differences and to explain when and where decoupling of the two 
temperatures occurs, and how this is likely to affect comparison of the two 

At the May 20 seminar, Dr. Christy will describe the MSU record and point 
out the different indications that it provides of climate change. Dr. 
Trenberth will describe how the satellite record compares to the surface 
temperature record and what this means with respect to conclusions that can 
be drawn. 

The Surface Temperature Record 

According to a recently released report from the World Meteorological 
Organization, the estimated global mean surface air temperature for 1995 
was the highest since reliable temperature records began in 1861. The 
previous warmest year was 1990, which was just before the Mt. Pinatubo 
volcanic eruption that has suppressed temperatures for the past several 
years. The warmth in 1995, unlike that for 1990, could not be attributed to 
an El Nino because the average Equatorial Pacific Ocean temperature 
anomalies were near the 1961-90 average for 1995. Instead, the warmth was 
evident over other regions, including the North Atlantic Ocean, where sea 
surface temperatures were more than 1=9A C warmer in an area centered around 
the Azores. In addition, parts of Siberia were more that 3=9A C warmer than 
the 1961-1990 period. However, as would be expected because of year-to-year 
variations, the warmth was not uniform; Greenland, the northwest Atlantic 
Ocean, and the mid-latitudes of the North Pacific Ocean were actually 
cooler than average in 1995. 

Temperature records for a representative fraction of the Earth go back to 
1861. The temperature record since that time suggests an overall warming of 
0.3 to 0.6 =9AC from the 1860s to the 1990s, with the early decades of this 
century being slightly cooler temperatures than in the mid-19th century and 
with a secondary maximum of temperatures (compared to the 1990s) in the 
decades around 1940. Proxy records derived from tree rings, ice cores, 
boreholes, and other indirect measures, combined with the thermometer 
record, suggest that the most recent decades are the warmest period since 
at least 1400 AD, and perhaps as far back as the last interglacial (period 
of warmth) about 80,000 years ago. The IPCC concluded that this combination 
of factors suggested that climate change is occurring. 

The fact that there have been natural fluctuations of the climate over the 
past millennium of about 0.5 =9AC (about a cooler mean temperature) 
introduces the possibility that the recent warming might be due to natural 
processes rather than to human activities. To try to distinguish the human 
influence, model simulations have been used to generate the patterns of 
climate change to be expected from changes in a range of different factors, 
both natural and human-induced. Analyses of these characteristic patterns 
(or "fingerprints") indicate that the patterns of climate change are much 
more likely to be due to human activities than to natural factors, leading 
the IPCC to conclude that "the balance of evidence suggests that there is a 
discernible human influence on global climate." 

At the May 21 seminar, Dr. Wigley will describe the records of surface 
temperatures and the climate trends that emerge, and compare these to the 
model projections of climate change since the 1861s.  Dr. Santer will then 
describe the recent studies to attribute the observed changes to specific 
causes of change, especially to human activities. 


Dr. John R. Christy is Associate Professor of Atmospheric Science at the 
University of Alabama in Huntsville, and has studied global climate issues 
since 1987. In 1989 Dr. Roy W. Spencer, a NASA/Marshall scientist, and Dr. 
Christy developed a global temperature data set from microwave data that 
had been recorded by the MSU instrument on NOAA satellites, beginning in 
1979. For this achievement, the Spencer-Christy team was awarded NASA's 
Medal for Exceptional Scientific Achievement in 1991. In 1995 Dr. Christy 
and Dr. Spencer received a Special Award from the American Meteorological 
Society "for developing a global, precise record of Earth's temperature 
from operational polar-orbiting satellites, fundamentally advancing our 
ability to monitor climate." 

        Dr. Christy obtained his B. A. degree from the CA State Univ., 
=46resno (Mathematics) in  1973, and later taught science as a missionary 
teacher in Nyeri, Kenya. After earning a seminary degree in 1978, he served 
four years as a bivocational mission-pastor in South Dakota where he also 
taught college math.  He subsequently received M.S. and Ph.D. degrees in 
Atmospheric Sciences from the University of Illinois (1984, 1987) under Dr. 
Kevin Trenberth. Dr. Christy has served as a contributing lead author on 
climate assessment reports by the Intergovernmental Panel on Climate Change 
(1992, 1994 and 1995), and has also published numerous scientific articles 
including studies appearing in Science, Nature, the Journal of Climate and 
the Journal of Geophysical Research. 

Dr. Kevin Trenberth was born in New Zealand, where he remains a citizen. He 
is Head of the Climate Analysis Section at the National Center for 
Atmospheric Research (NCAR) in Boulder, CO. After completing a first class 
honors degree in mathematics at the University of Canterbury, Christchurch, 
New Zealand, he obtained his Sc. D. in meteorology in 1972 from 
Massachusetts Institute of Technology. Following several years in the New 
Zealand Meteorological Service, he joined the Department of Atmospheric 
Sciences at the University of Illinois as an Associate Professor and became 
a full Professor in 1984, before moving to NCAR in 1984. He continued as an 
Adjunct Professor until 1989. From 1991 to 1995 he served as Deputy 
Division Director of the Climate and Global Dynamics Division at NCAR. 

        Dr. Trenberth has served as Editor of the Monthly Weather Review, 
Associate Editor for the Journal of Climate, and presently serves as editor 
of the new electronic scientific journal Earth Interactions. and is the 
author of many research papers.   He serves on the executive committee of 
the National Oceanic and Atmospheric Administration (NOAA) Advisory Panel 
on Climate and Global Change, the National Academy of Sciences Global Ocean 
Atmosphere Land System (GOALS) panel, the Atmospheric Observation Panel for 
Climate of the Global Climate Observing System, and the International 
Scientific Steering Group for the CLIVAR (Climate Variability and 
Predictability) Program. Dr. Trenberth has been a prominent author in the 
Intergovernmental Panel on Climate Change (IPCC) Scientific Assessment 
activities and is a lead author for Chapter 1 of the 1995 Scientific 
Assessment. He is a fellow of the American Meteorological Society, and was 
made an Honorary Fellow of the New Zealand Royal Society in 1995. 

Dr. Tom Wigley was born and educated in Australia. After his undergraduate 
degree he trained as a meteorologist and worked for a year as a research 
meteorologist before returning to university to complete a Ph.D. in 
Mathematical Physics. He then joined the faculty of the Mechanical 
Engineering Department at the University of Waterloo, Ontario, Canada. In 
1975, he moved to the United Kingdom to the Climatic Research Unit of the 
University of East Anglia, becoming Director in 1978. In 1993, he left the 
Unit to join the University Corporation for Atmospheric Research (UCAR) in 
Boulder, CO. In 1994, he received a Senior Scientist appointment with the 
National Center for Atmospheric Research. 

        Dr. Wigley has published widely on diverse aspects of the broad 
field of climatology; from data analysis, to climate impacts on agriculture 
and water resources, to climate, sea level and carbon cycle modeling, to 
paleoclimatology. Dr. Wigley has concentrated recently on facets of the 
greenhouse problem, and has contributed as a lead author to all of the IPCC 
assessments of the climate change issue. Dr. Wigley had a major role in the 
preparation of the 1995 IPCC Working Group I Second Assessment Report, and 
contributed important information to the reports of the other Working 
Groups. He was responsible for producing the future concentration profiles 
for achieving stabilization of CO-2 concentrations used in Working Groups I 
and III; he produced the global-mean projections for temperature and sea 
level change given in Working Group I; and he was a lead author for the 
Working Group I detection chapter. 

Dr. Benjamin D. Santer is a senior member of the Program for Climate Model 
Diagnosis and Intercomparison (PCMDI) at the Lawrence Livermore National 
Laboratory (LLNL), Livermore, CA. His research interests include detection 
of anthropogenic climate change and climate model validation. He received 
his B.Sc. in environmental sciences in 1977, graduating with first class 
honors, and his Ph.D. in climatology in 1987. Both were obtained at the 
University of East Anglia, Norwich, U.K.  Dr. Santer's doctoral work 
focused on the use of Monte Carlo methods (randomization) in the regional 
validation of climate General Circulation Models. 

        Dr. Santer then served as a postdoctoral research scientist (for 
two years), and later as a research scientist (for three years) at the 
Max-Planck Institute for Meteorology (MPI) in Hamburg, Germany, where he 
worked closely with Dr. Klaus Hasselmann on climate-change detection. He is 
the Convening Lead Author for Chapter 8 ("Detection of Climate Change, and 
Attribution of Causes") of the 1995 Second Assessment Report of the 
Intergovernmental Panel on Climate Change. Dr. Santer is also currently a 
member of the Science Advisory Group of NOAA's Climate Change, Data and 
Detection Program, and of the International CLIVAR (Climate Variability and 
Predictability) Numerical Experimentation Group on anthropogenic climate 

                                  NEXT SEMINAR: Monday, June 10, 1996 

      Forest Responses to the Changing Composition of the Atmosphere 

=46or more information please contact: 

Dr. Anthony D. Socci, U.S. Global Change Research Program Office 
300 D St., SW, Suite 840, Washington, DC 20024 
Telephone: (202) 651-8244; Fax: (202) 554-6715 

Additional information on the U.S. Global Change Research Program (USGCRP) 
and this Seminar Series is available on the USGCRP Home Page at: Normally these seminars are held on the second 
Monday of each month. 

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