EXTREME
WEATHER TRENDS VS. DANGEROUS CLIMATE CHANGE: A NEED FOR CRITICAL REASSESSMENT
Madhav
L Khandekar
Consulting
Meteorologist, Unionville, Ontario, CANADA, L3R 7Z5
Correspondence:
52 Montrose Crescent, Unionville, Ontario, Canada, L3R 7Z5
e-mail: mkhandekar@rogers.com. Phone: 1-905-940-0105
The
ongoing debate on global warming and increasing concentration of atmospheric
greenhouse gases (CO2 in particular) highlights the possibility of increased
incidences of extreme weather events world-wide, as the earthÕs mean
temperature is expected to rise steadily in future. Several recent technical
and scientific conferences have focused on the general theme of Òdangerous
climate changeÓ and on avoiding or reducing this danger. However, a careful
analysis of observed data on world-wide extreme weather events does not reveal
any increasing trend in these events, thus suggesting a mismatch between
reality and the hypothesis of dangerous climate change. There is a definite
need to critically re-examine the hypothesis of dangerous climate change in the
context of observed trend (or lack of it) in the extreme weather events
worldwide.
One of
the main objectives of the UNFCC (United Nations Framework Convention on
Climate change) is the stabilization of greenhouse gas concentration in the
atmosphere at a level that would prevent dangerous anthropogenic
interference with
the climate system. The theme of a recent conference (1-3 February 2005) in
Exeter, UK was on Avoiding Dangerous Climate Change and on Stabilization of
Greenhouse gases.
The
phrase Ôdangerous interferenceÕ is meant to highlight the possibility of
increased incidences of extreme weather events and their catastrophic impacts
on human societies and infrastructure of various nations in the world. The IPCC
(Intergovernmental Panel on Climate change) document Climate Change 2001 [1]
identifies several extreme weather and climate events which are expected to be
observed with increased frequency during the 21st century. Some of
the extreme events (e.g. heavy precipitation, hot spells in summer,
thunderstorm/tornado activity, summer continental drying and associated risk of
drought) are projected to have been observed and detected with increasing
frequency during the latter half of the 20th century. The present
debate on climate change has fostered an intimate link between global warming
and extreme weather. However, a careful analysis of observed extreme weather
events as discussed below does not appear to support such a link.
In a
report on Trends and Changes in Extreme Weather Events published by the
Government of Alberta [2], some of the commonly observed events in Canada like
heat waves, thunderstorms/tornadoes, rainstorms, Prairie droughts, winter
blizzards and ice storms are carefully analyzed using available data of last 25
to 50 years. It is found that none of the events mentioned above show any
increasing trend at this time. In fact, some of the events like winter
blizzards on the Canadian Prairies are definitely on the decline while events
like ice storms in central Canada and winter storms in the Canadian Atlantic do
not show any increasing trend at this time. A careful analysis of mean
temperature over various regions of Canada reveals that it is the winter mean
temperature that has increased in last 50 years, while summer mean temperature
which was highest during the 1930s (the Dust Bowl years on the Canadian
Prairies) showed a decline in the 1990s, these years being adjudged by IPCC as
the warmest years. According to Bonsal et al [3], Canada as a whole is not
getting warmer, but less cold. The total precipitation over Canada as a whole
has increased in last 50 years, but this increase is mainly due to increased
number of low- to moderate-intensity precipitation events. The report concludes
that the likelihood of increased incidences of extreme weather events in the
next 10 to 25 years remains very small at this time.
A
recent study by Balling and Cerveny [4] surveys extreme weather events over
conterminous USA and concludes that there is no increasing trend for
thunderstorms, intense tornadoes or hurricanes and tropical cyclones. Another
study by Changnon [5] documents that shifting economic impacts from weather
extremes in the conterminous USA is a result of societal change and not global
warming. A comprehensive study [6] on extreme precipitation reveals that
extreme precipitation events have increased in the latter part of the 20th
century over conterminous USA. The study also shows a similar increase in
extreme precipitation at the turn of the 20th century (i.e.1890s),
thus suggesting that recent increase in extreme precipitation events could be
due to natural variability and not necessarily due to global warming.
Elsewhere,
available studies do not show an increasing trend in any of the extreme weather
events identified by IPCC. Large-scale climate events like ENSO (El Nino-
Southern Oscillation) do not show any increasing/decreasing trend at this point
in time. The IPCC Climate Change document states that warming associated with
increasing greenhouse gas concentration will cause an increase in Asian summer
monsoon variability. A recent study on Indian/south Asian Monsoon rainfall
variability [7] shows the summer Monsoon over India and south Asia to be
primarily governed by large-scale atmospheric features like ENSO and Eurasian
winter snow cover while showing no increased inter-annual variability in the
Asian Monsoon as a whole. Another recent study on rainfall variability and
changes in Southern Africa [8] shows that the South African rainfall is
primarily governed by ENSO events while showing significant modification in its
variability in recent decades; the South African rainfall does not show any
increasing/decreasing trend at this point in time. For Australia as a whole,
there is no increase in Òheavy rainfallÓ events in recent years [9]. An
analysis of extreme rainfall events for China [10] suggests no increasing trend
for 1 to 3 day extreme rainfall events.
The
mean temperature variation over earthÕs land areas reveals several interesting
features of temperature variation. The early 1990s show a gradual warming of
the earthÕs surface, reinforcing the global warming argument. According to
IPCC, the 1990s have been identified as the warmest decade with 1998 as the
warmest year in 1000 years. Since January/February 1998, the two consecutive
warmest months in Figure 1, the mean temperature over the earthÕs land areas
appears to be slowly declining despite increasing concentration of CO2 in the
atmosphere. According to the most recent WMO statement of 27 December 2004 (http://www.wmo.ch), the year 2004 has been
identified as the fourth warmest year, following 1998, 2002 and 2003. In a
recent study, Kumar et al. [11] show that the sustained North American warming
of 1998 was primarily due to the 1997 El Nino which produced and maintained
high SST (Sea Surface Temperature) values over the Pacific basin as well as
over other ocean basins through the middle of 1998. The North American warming
of 1998 contributed significantly to make 1998 as the globally warmest year of
the 1990s. Since mid-1998, the SST values are slowly declining suggesting that
the earthÕs land area mean temperature may be governed more by worldwide SST
distribution and less by enhanced greenhouse gas warming. Further, increased
urbanization and land-use change over various regions of the earth are now
considered to be significant contributors to the earthÕs surface warming in
recent years.
An
analysis of available data on extreme weather suggests no discernible link
between global warming and extreme weather at this point in time. The link
appears to be more perception than reality (Khandekar et al [14]). The earthÕs
land area mean temperature appears to be declining following the intense El
Nino event of 1997/98. These and many other observational studies strongly
point out a need for critical assessment of the UNFCC and the hypothesis of a
dangerous climate change. The greenhouse gas emission control strategy must be
commensurate with the present state of our knowledge on climate change.
This
paper was prepared for a possible presentation at the Exeter (UK) conference on
Avoiding Dangerous Climate Change. I am grateful to Ms Sonja
Boehmer-Christiansen for encouraging me to revise the paper for publication in
Energy & Environment.
[1]
IPCC, Climate Change, 2001: The Scientific Basis. Cambridge University Press,
881 p. [2] Khandekar, M.L. 2002: Trends and changes in extreme weather events:
An assessment with focus on Alberta and Canadian Prairies. Report No:ISBN;0-7785-2428-0,
Alberta 330 Energy & Environment á Vol. 16, No. 1, 2005 Figure 1. Monthly
global (Top), Northern Hemisphere (Middle) and Southern Hemisphere (Bottom)
temperature anomalies (land-areas, ¡C), from January 1990-present. The
anomalies are computed relative to 1971-2000 base mean period (Climate
Diagnostics Bulletin, October 2004: NOAA, USA). EE 16/2_final 14/04/05 12:38 pm
Page 330 Environment, Edmonton, Alberta, 56 p. (Available on
website:www.gov.ab.ca/env/
info/infocentre/publist.cfm)
[3]
Bonsal, B.R., Zhang X., Vincent L.A. and W.D. Hogg, 2001: Characteristics of
daily and extreme temperatures over Canada. J. of Climate, 14, 1959-1976. [4]
Balling, Jr. R.C. and R.S. Cerveny 2003: Compilation and discussion of trends
in severe storms in the United Staes: Popular perception v. climate reality.
Natural Hazards, 29, 2, pp. 103-112. [5] Changnon, S.A. 2003: Shifting economic
impacts from weather extremes in the United
States:
a result of societal change, not global warming. Natural Hazards, 29, 2, pp. 273-290.
[6] Kunkel, K.E. 2003: North American trends in extreme precipitation. Natural
Hazards, 29, 2, pp. 291-305. [7] Kripalani, R.H, Kulkarni, A., Sabde, S.S. and
M.L. Khandekar 2003: Indian Monsoon variability in a global warming scenario.
Natural Hazards, 29, 2, pp. 189-206. [8] Fauchereau N., Trzaska, S, Roulault,
M. and Y. Richard 2003: Rainfall variability and changes in Southern Africa
during the 20th century in the global warming context. Natural
Hazards, 29, 2, pp. 139-154. [9] Hennessy, K.J., R. Suppiah and C.M. Page,
1999: Australian rainfall changes, 1910-1995. Australian Met. Magazine, 48,
pp.1-13. [10] Zhai, P., Sun, Ren, Liu, Gao and Zhang 1999: Changes of climate
extremes in China, Climatic Change, 42, 203-218 [11] Kumar, A., W. Wang, M.P. Hoerling,
A. Leetmaa and M. Ji 2001: The sustained North American warming of 1997 and
1998. J. of Climate, 14, pp. 345-353. [12] Pielke, Sr, R A et al., 2002: The
influence of land-use change and landscape dynamics on the climate system:
relevance to climate-change policy beyond the radiative effect of greenhouse
gases. Phil. Trans. R. Soc. London, A, 360, 1705-1719 [13] de Laat, A.T., J.
and A.N. Maurellis, 2004: Industrial CO2 emissions as a proxy for anthropogenic
influence on lower tropospheric temperature trends. Geophy. Res. Letters, 31,
L05204, doi:10.1029/2003GL019024 [14] Khandekar, M.L., T.S. Murty and P.
Chittibabu 2005: The global warming debate: A review of the state of science.
Pure & Applied Geophysics (PAGEOPH), Sp Issue, in press
Copyright
2005, Energy & Environment