Some major uncertainties in climate science
I suspect that claims about the certainty of climate science matter
more for the perception of future risk, and for political reasons,
than as a realistic statement of the state of the science. I believe
that most scientists and engineers must understand something of the
problems and uncertainties in our understanding of such a complex and
dynamic system. Some of this is spelled out by the IPCC. LOSU – the
“level of scientific understanding.” The LOSU for some critical
elements of the system is low to medium.
Even such a seemingly simple question as to the rate of recent warming
is subject to wide interpretation. Climate fluctuates strongly –
principally in line with ENSO. Large interannual and decadal changes
in surface temperature makes the interpretation of trend sensitive to
both the end points and to the length of the record.
Period Trend (degrees C/decade)
1900 - 2008 0.07
1945 – 2008 0.11
1958 – 2008 0.13
1979 – 1997 0.11
1976 – 2008 0.17
Table 1: A quick comparison of periods and temperature trends
The evaluation of a warming trend depends on a reasonable scientific
justification for the period over which trends are assessed. The
1900-2008 period is certainly the longer term but misses much of the
period of high carbon emissions. 1945-2008 is justifiable – it is the
period of strongly increasingly carbon emissions. 1958 to 2008 is the
last 50 years in accordance with the period adopted by the IPCC. It
has been argued that the trend between 1979 and 1997 is the rate of
forced warming when nonlinear climate behaviour (discussed below) is
accounted for. The rate of warming between 1976 and 2008 is the usual
trend claimed – but arguably the trend is evaluated over too short a
period because of multidecadal variation of ENSO and other
factors.
Thompson et al (2009) filter out ENSO, the effects of aerosols emitted
by explosive volcanic eruptions, and “variations in the advection of
marine air masses over the high latitude continents during winter,”
which they term “dynamically induced variability.” The temperature
bottom line of this study was a trend of 0.12 degrees centigrade per
decade from 1950.
There is a satellite based temperature record of the lower
atmosphere. This has global coverage and a trend that is less than
the surface station methodologies.
“Using NOAA satellite readings of temperatures in the lower
atmosphere, scientists at The University of Alabama in Huntsville
(UAH) produced a dataset that shows global atmospheric warming at the
rate of about 0.07 degrees C (about 0.13 degrees Fahrenheit) per
decade since November 1978,” said Dr. John Christy, who compiled the
comparison data. “That works out to a global warming trend of about
0.7 degrees centigrade over 100 years. That's a definite warming
trend, which is probably due in part to human influences. But it's
substantially less than the warming forecast by most climate models,
and it isn't entirely out of the range of climate change we might
expect from natural causes.”
The rate of recent warming is of critical importance in evaluating the
social and environmental risk of global warming – and it is probably
the easiest aspect of climate science to spin in the required
direction.
Temperature increased in the last decades of the 20th Century to a
peak in the large (~ 50 year frequency) 1998 El Niño and has been a
little cooler since. Temperature has not increased by 0.2 degrees
centigrade over the past decade as predicted by the IPCC. That is the
simplest part of climate science. The more pertinent factors in our
limited knowledge of climate include solar, cloud and complex system
uncertainties.
Solar
Scafetta and West (2007) find a large solar influence on global
temperature in the 20th Century.
“A phenomenological thermodynamic model is adopted to estimate the
relative contribution of the solar-induced versus anthropogenic-added
climate forcing during the industrial era. We compare different
preindustrial temperature and solar data reconstruction scenarios
since 1610. We argue that a realistic climate scenario is the one
described by a large preindustrial secular variability (as the one
shown by the paleoclimate temperature reconstruction by Moberg et al.
(2005)) with the total solar irradiance experiencing low secular
variability (as the one shown by Wang et al. (2005)).
Under this scenario the Sun might have contributed up to approximately
50% (or more if ACRIM total solar irradiance satellite composite
(Willson and Mordvinov, 2003) is implemented) of the observed global
warming since 1900.”
Satellite monitoring of solar irradiance commenced in the late
1970's. The record is marred by having three instruments with
intercalibration and drift problems as well as a 2 year gap following
the Challenger disaster. The records have been “stitched” together
but with conflicting results. NASA’s SORCE project since 2003 will
provide more reliable data on future total solar irradiance (TSI)
changes.
Climate model TSI inputs favour constant solar irradiance for the 21st
Century - or irradiance varying about a constant mean in 11 year
cycles. Solar activity has 11 year (approximately) sunspot cycles, 22
year magnetic reversal cycles and changes in activity over the mid to
very long term. Solar activity peaked in last centuries “Modern Grand
Maxima.” It is much the safest bet in climate science that solar
activity is declining steeply from the recent high point.
Clouds
“The new method is a conceptual breakthrough in how we analyze data,”
said Anthony Del Genio, a scientist at the Goddard Institute for Space
Studies.
“What it shows is remarkable," said Dr. Bruce Wielicki of NASA’s
Langley Research Center. "The rising and descending motions of air
that cover the entire tropics, known as the Hadley and Walker
circulation cells, appear to increase in strength from the 1980s to
the 1990s. This suggests that the tropical heat engine increased its
speed. The faster circulation dried out the water vapor that is
needed for cloud formation in the upper regions of the lower
atmosphere over the most northern and southern tropical areas. Less
cloudiness formed allowing more sunlight to enter and more heat to
leave the tropics. It's as if the heat engine in the tropics has
become less efficient using more fuel in the 90s than in the 80s. We
tracked the changes to a decrease in tropical cloudiness that allowed
more sunlight to reach the Earth's surface. But what we want to know
is why the clouds would change.”
The results show cloud cover in the tropics to be more variable than
previously thought. “It suggests that current climate models may, in
fact, be more uncertain than we had thought,” Wielicki added. “Climate
change might be either larger or smaller than the current range of
predictions.”
“The observations capture changes in the radiation budget-the balance
between Earth's incoming and outgoing energy-that controls the
planet's temperature and climate. The previously unknown changes in
the radiation budget are two to four times larger than scientists had
believed possible. The reason why and the degree to which it changed
are surprising scientists and create a powerful new test for climate
models.”
“The question is, if this fluctuation is due to global climate change
or to natural variability," said Del Genio. "We think this is a
natural fluctuation, but there is no way to tell yet.”
Large changes in cloud cover are being observed in the International
Satellite Cloud Climatology Project (ISCCP) record from 1984. The
radiation effect of Earth albedo changes is estimated by Pallé et al
(2009) at a 4 W/m2 increase of shortwave radiation at the surface from
1984 to 1998 and a decrease of 2.7 W/m2 between 1999 and 2008. The
changes in Earth’s radiation budget are climatologically
significant.
Complexity
Climate shifts occurred 4 times in the last 100 years around 1910, the
mid 1940’s, the mid 1970’s and 1998/2001 (Tsonis et al, 2007, Swanson
et al 2009). Small changes in forcings (solar, gases and aerosols,
albedo) are alternately amplified and damped (nonlinear) by global
climate processes and climate then oscillates for a time around a
different climate mean. Climate shifts can be seen in the inflection
points of the global near surface temperature record. Warming after
1910, a little cooler between the mid 1940’s to the mid 1970’s,
warming to 1998 and a little cooler since.
The direct impact of greenhouse gas increase since the start of
industrialisation is about 0.5 degrees centigrade of global
temperature increase theoretically. It is not insignificant as energy
in the climate system. The total effect is unknown because it feeds
into a dynamic climate system of sun, orbit, ocean, atmosphere, ice,
clouds, gases and aerosols operating interactively. All of these
change all the time. The exponential growth of ice cover is
implicated as a causal factor in ice ages - extreme nonlinear climate
events. Global cloud cover has been known to change from ISCCP data
collected from 1984 and the argument has been about cause and effect.
There is a little more cloud cover since about 1999 - which came first
the clouds or the current cooling? The question is not answerable as
climate is dynamic and complex. Small changes in initial conditions
lead to climate fluctuation which then settles into a different
climate state – until the next unpredictable climate shift.
At the policy level – and here I am speaking as an engineer, an
environmental scientist and as a human being - it is a matter of
social, economic and environmental risk.
Increasing greenhouse gases increases forced complex system
instability - accepted. But I don’t accept that there is a social
trade off to be made. In a sense the accuracy or otherwise of climate
science makes very little difference to sensible policy. Carbon cap
and trade is emphatically not sensible environmental or social
policy. Recent calculations by Bjorn Lomberg point to a business as
usual increase of carbon dioxide in the atmosphere from 1990 to 2012
of 42.7% without Kyoto. The increase with Kyoto will be about 42.2%.
Far more effective to maintain economic growth (as environmental
scientists have long argued) and thereby have the confidence and
resources to drive both technological innovation and environmental
conservation. All of the environmental problems, including
population, are made easier with economic development.
While the lack of a recent (10 year) trend in atmosphere and ocean
temperatures continues there is a less urgent environmental risk.
Given the rate of technological evolution – a matter of decades at
most is all that is required to develop dozens of low cost options for
energy and development.
The global economy is itself a complex and dynamic system. The only
way to maintain high rates of global economic development is to have
honesty and constancy in economic governance, continued economic
growth and good luck. The consequences of the economic risk of carbon
taxes or charges – are more than significant. Thankfully widespread
support for much more of a much to be feared command and control style
economy is limited to noisy “ecosocialists”. The most extreme
economic risk leads to hunger for hundreds of millions of
people.
Pallé, E., P. R. Goode, and P. Montañés-Rodríguez (2009), Interannual
variations in Earth's reflectance 1999–2007, J. Geophys. Res., 114,
D00D03, doi:10.1029/2008JD010734.
Thompson, D.W.J., J.M. Wallace, P.D. Jones, and J.J. Kennedy, 2009:
Identifying Signatures of Natural Climate Variability in Time Series
of Global-Mean Surface Temperature: Methodology and Insights. J.
Climate, 22, 6120–6141.
Tsonis, A. A., K. Swanson, and S. Kravtsov (2007), A new dynamical
mechanism for major climate shifts, Geophys. Res. Lett., 34, L13705,
doi:10.1029/2007GL030288.
Scafetta, N., and B. J. West (2007), Phenomenological reconstructions
of the solar signature in the Northern Hemisphere surface temperature
records since 1600, J. Geophys. Res., 112, D24S03, doi:
10.1029/2007JD008437.
Swanson, K. L., and A. A. Tsonis (2009), Has the climate recently
shifted?, Geophys. Res. Lett., 36, L06711, doi:10.1029/2008GL037022.
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