Figure 11. Same as Figure 8 but for UKMET early model temperature rises for a doubling of CO2.
3. IMPOSSIBILITY OF SKILLFUL GCM CLIMATE PREDICTION
Skillful initial-value numerical GCM climate prediction will likely never be possible. This is due to
the overly complex nature of the global atmosphere/ocean/land system (Figure 12) and the inability
of numerical models to realistically represent the full range of this physical complexity and to be
able to integrate this overly complex physics forward in time for hundreds of thousands of time
steps. Skillful initial-value numerical forecasts currently cannot be made for more than a few weeks
into the future. This is because any imperfect representations of the highly non-linear parameters
of the atmosphere-ocean system tend to quickly degrade (the so-called butterfly effect) into
unrealistic flow states upon integration of longer than a week or two. Skillful short-range prediction
is possible because there tends to be a conservatism in the initial value momentum-pressure fields
which can be extrapolated or advected for a week or two into the future. But after 1-2 weeks, one
must deal with the far more complex variation of the moisture and energy fields. Model results
soon decay into chaos as indicated in Figure 13.
If skillful GCM climate forecasts were possible for a longer period of a season to a few years, we
would be eager to track their skill. Currently, GCMs do not make official seasonal or yearly
forecasts. They dare not issue these forecasts because they know they are not skillful and would
quickly lose their credibility if they gave real time forecasts that could actually be verified. How can
we trust GCM climate forecasts 50 and 100 years into the future (that cannot be verified in our
lifetime) when these same models are not able to demonstrate shorter range forecast skill of a
season or a year or two?
1
Figure 12. Flow diagram of the climate system illustrating the massive and complicated physical
processes involved and the multiple feedback loops that need to be considered. It is impossible to
write numerical code that would accurately replicate these many physical and non-linear feedback
loops for long periods into the future.
Figure 13. A depiction of initial value numerical forecasting. Skillful forecast out to 10-15 days
have been developed with skill. After 10-15 days the non-linear imperfections of the model grow
into near random turbulence (or butterflies). This chaos prevents skillful climate forecasts.
2
4. GLOBAL WARMING DUE TO NATURAL PROCESSES
The global warming that has been observed since the mid-1970s and over the past century should
not automatically be blamed on human-produced greenhouse gases. There is an alternate
physical mechanism. This alternate mechanism is related to the globe’s deep ocean circulation. A
weaker Atlantic Ocean thermohaline circulation (THC) or Meridional Overturning Circulation (MOC)
for the period of a decade or a decade-and-a-half can bring about a gradual surface global
warming. When this happens the Southern Hemisphere oceans upwell less cold water into their
near surface mixed layer, the cold upwelling in the eastern equatorial Pacific becomes weaker,
there is slightly less global rainfall and a modest globe warming ensues. The opposite occurs
when the THC and/or MOC is stronger than normal. The deep water upwelling into the Southern
Hemisphere near surface mixed layer is enhanced. The eastern equatorial Pacific cold upwelling
becomes stronger, global rainfall becomes slightly greater and with a lag of 10-15 years from the
onset or the strong THC and/or MOC the globe undergoes a gradual cooling (Figure 14 and 15).
I judge the THC and/or MOC to have been generally weaker over the last century and especially
over the period from the late-1960s to the late-1990s. It is this weaker THC and/or MOC and not
the increase in global CO2 that was the primary cause of the recent global warming we have
observed. The globe typically reaches its highest or lowest average temperature in the 10-15
years following the onset of a weak or a strong THC and/or MOC. We have recently been very
close to the maximum global warming period following the onset of a strong THC or MOC
circulation in 1995. Continued global warming should not be expected. We should be entering a
weak global cooling period similar to what occurred between the mid-1940s and mid-1970s.
Observations indicate that we have in fact entered a global cooling period which began in 2001.
We should expect this weak cooling to continue for another couple of decades.
Figure 14. Idealized portrayal of the deep water Global Ocean Conveyor Belt (often referred to as
the Meridional Overturning Circulation – MOC) showing the typical locations in the Southern
Hemisphere where upwelling occurs into the upper ocean thermocline and mixed layer (areas 1, 2,
and 3) that is required to balance the North Atlantic thermohaline circulation (THC) subsidence (H
areas). The MOC = (THC + Antarctica subsidence). Estimates are that the mass of the North
Atlantic deep water subsidence is about twice the mass as the ocean subsidence around
Antarctica. The ocean subsidence surrounding Antarctica is not shown. Figure courtesy of John
Marshall, of MIT.
3
Typical Pattern
mid-1940s to mid-1970s
Typical Pattern
mid-1970s to 1999
Figure 15. Comparison of typical global wind patterns when the Atlantic Thermohaline Circulation
(THC and/or the MOC) has been strong for a long period and cold water upwelling in the Southern
Hemisphere has been greater than the long period average. This leads to global temperatures
becoming gradually cooler than average (top diagram). Bottom diagram shows the typical global
wind patterns when the Atlantic THC and/or MOC have been weaker than average for a long
period and there has been reduced cold water upwelling in the Southern Hemisphere. The globe
becomes gradually warmer during these periods. The top diagram shows characteristics of the
conditions which existed during the modest global cooling period between the mid-1940s and the
mid-1970s. The bottom diagram is characteristic of the conditions during the warming period of the
mid-1970s to 1999.
5. PAST AND FUTURE GLOBAL TEMPERATURE CHANGES
We are seeing glaciers receding and arctic ice melting because we have been in a general
warming period over the last century and particularly over the last 35 years (from the mid-1970s to
1999). The generally increased global temperature we have witnessed over this warming period
should, of course, be expected to bring about a degree of sea ice and glacier melting. The overall
northern hemisphere middle-latitude winter wind patterns of most of this warming period (i.e.,
positive North Atlantic oscillation – positive Pacific North America pattern) caused warming in
Alaska, northwest Canada, reduced snow in the European Alps, and general global glacial retreat.
This is to be expected from such a weak THC or MOC flow regime. Similar warming conditions
occurred from 1910 to the early 1940s (Figure 16). The Arctic ocean and Greenland experienced
a similar melting in the late 1930s and early 1940s as has recently been occurring. These are
natural back-and-forth shifts in multi-decadal climate. But this recent warming pattern has now
begun to reverse itself to a cooler pattern. Historically, cooling and warming trends such as we
have seen since the early 1940s do not maintain themselves for much more than 3-4 decades
(Figures 16 and 17).
4
Figure 16. Land (green) and ocean (blue) global mean temperature during the last 125 years.
Note the two distinctive multi-decadal periods of cooling (1880-1910 and 1945-1975) and the two
distinctive periods of warming (1910-1940 and 1975-1999). Most warming and cooling periods do
not last more than 30-35 years. The onset of these warming and cooling periods can be related,
with a 10-15 year lag, to the strength of the THC and/or MOC.
Figure 17. Same as Figure 16, but showing how much error one would have made by
extrapolating a cooling or warming curve beyond 30-35 years. The recent 1975-1999 warming
trend should not be expected to continue and indeed it has stopped. We have seen weak global
cooling since 2001. I estimate global temperature by 2030 will be somewhat below the value of
today’s global temperature.
5
I judge our recent global ocean circulation conditions from the mid-1970s to the late 1990s to have
been similar to that of the period of 1910-1945 when the globe had shown a large warming. There
was concern in the early 1940s as to whether this 1910-1940 global warming would continue. It
did not. A weak global cooling began from the mid-1940s and lasted until the mid-1970s. I predict
this is what we will see in the next few decades. Since 2001 there has been a weak cooling.
The globe has been gradually coming out of the Little Ice Age since about 1850. The author views
this long period change to be a result of a multi-century slow-down in the Atlantic THC and/or MOC
due to a general lowering of Atlantic salinity. CO2 increases are judged to have played only a very
small role in the temperature rises that have been observed.
6. SUMMARY DISCUSSION
I believe this deep ocean circulation hypothesis offers the best explanation for the global
temperature changes of the last century. I have not been a fan of variations in solar activity,
cosmic rays, dust, ozone, volcanic activity, etc. as being adequate explanations for the global
temperature changes that has been observed.
I have been studying weather and climate for over 50 years and have been making real-time
seasonal hurricane forecasts for a quarter-century. I and many of my colleagues with similar
experience have been dismayed at the untrue and exaggerated media hype about impending
catastrophic global warming that has been so prominently discussed since the hot summer of
1988. We decry this alarmism. We do not believe we are in climate crisis! There are many other
more serious national and global problems that need to be confronted.
Implementation of proposed international treaties restricting future greenhouse gas emissions by
as much as 20 percent (by 2020) and 80 percent (by 2050) of current emissions would lead to a
large slowdown in the world’s economic development and, at the same time, have little or no
significant impact on the globe’s future temperature. Such policies should be rejected.
A FOLLOW-UP PAPER FURTHER EXPANDING AND FURTHER
DOCUMENTING THE DISCUSSION OF THIS APPENDIX WILL
HOPEFULLY FOLLOW IN ANOTHER COUPLE OF MONTHS.
Acknowledgement. To Abraham Lincoln who was reported to have said “You can’t fool all the
people all of the time.” I have received encouragement from the belief that in the long run Lincoln
may be right – even for the predictions of global warming.
6
VITAE
Professor William M. Gray
Professor Gray has worked in the observational and theoretical aspects of tropical meteorological research for more
than 40 years, much of this effort going to investigations of meso-scale tropical weather phenomena. He has
specialized in the global aspects of tropical cyclones for his entire professional career. He studied under Professor
Herbert Riehl who arranged his early reconnaissance flights into hurricanes in 1958. He has been involved with
studies of broad-scale cumulus interactions and has extensively studied the processes associated with tropical cyclone
structure, development, and movement. Numerous satellite-based studies of tropical weather systems have also been
accomplished. Current areas of research include: 1) tropical cyclone structure, movement and intensity change; 2)
seasonal prediction; 3) meso-scale tropical weather systems, 4) diurnal variability of tropospheric vertical motions and
5) ENSO variability. Professor Gray has made Atlantic basin seasonal hurricane forecasts for the last 25 years. He
was a pioneer in developing these types of forecasts. In recent years he has also been performing research of the
causes of global climate change and the possible role of humans in such changes. He is a skeptic to the hypothesis
that humans are the primary cause of the global warming we have seen in recent years.
EDUCATION:
B.A. George Washington University (1952)
M.S. University of Chicago (1959), in Meteorology
Ph.D. University of Chicago, Dept. of Geophysical Sciences (1964)
METEOROLOGICAL EXPERIENCE:
Weather Forecasting duty as Air Force Officer, 1953-1957
Research Assistant, Dept. of Meteorology, Univ. of Chicago, 1957-1961
Faculty of Dept. of Atmospheric Science, Colorado State University, 1961-present
Professor, 1974 to 2004
Professor Emeritus, 2005 to Present
ABBREVIATED SUMMARY OF PI'S PROFESSIONAL ACTIVITY:
Advisor of 50 successful MS (theses) graduates and 20 successful Ph.D. graduates in Atmospheric Science, eight of
whom have received AMS awards as students. Panel Member - U.S.-Japan Mutual Science Program (Panel 7Tropical Storms) - 1964-1969; Panel Member - American Meteorological Society Committee on Hurricanes and
Tropical Meteorology 1968-1973, 1978-1981. Chairman 1987-1990; Advisor - U.S. GATE Meso-scale and Cumulus
Sub-Programs 1969-1972; Panel Member - USAF Scientific Advisory Board on Tropical Cyclone Aircraft
Reconnaissance (1973-1974); USAF Reserve Officer - 1957-1973; U.S. Representative - WMO Working Group on
Tropical Meteorology (1975-1988); Co-organizer of three-week NCAR GATE Workshop (summer, 1977); Chairman,
Organizing Committee for first WMO International Workshop on Tropical Cyclones, Bangkok, Thailand, 1985.
AWARDS/HONORS:
Fellow, American Meteorological Society; CSU “Jack E. Cermak” Graduate School Award for Outstanding Adviser
(1992); Co-recipient of AMS Banner I. Miller Award (1993); AMS Jule L. Charney Award (1993); Neil Frank Award of
the National Hurricane Conference (April 14, 1995), “for pioneering research into long-range hurricane forecasting and
for developing a better understanding of how global climatological conditions shape the creation and intensity of
tropical cyclones"; Invited lecture for Eighth IMO Lecture to the 12th WMO Congress, Geneva, June, 1995. (This is an
honorary award given to senior scientists in recognition of lifetime research achievements; ABC Television ``Person of
the Week", September, 1995; Man of Science Award by the Colorado Chapter of Achievement Reward College (ARC)
Scientist (1995).
PUBLICATIONS & RESEARCH REPORTS:
Over 80 published papers and 60 more extensive research reports.
Hundreds of Conference talks and conference proceedings.
Papers available on CSU website (http://tropical.atmos.colostate.edu/)
7