Critique of IPCCs Summary for Policymakers
by Bob Foster
The latest version of the Intergovernmental Panel on Climate Changes scientific consensus is given in Climate change 2001: the scientific basis, the Working Group 1 volume of its Third Assessment Report. Comments on this substantial document are here confined to its Summary for Policymakers, because people at policymaker level whether politicians or public servant would not have the time to venture into the detailed technical chapters. In any case, the SPM of the TAR already encapsulates the key points of difference between the IPCC consensus of 2,500 of the worlds top climate scientists and contrarians like me.
2. Figure 1 (b) the Hockeystick
There is much good scientific literature, going back to 1973 at least, regarding cyclic climate in the Northern Hemisphere in general, and its last warmer/cooler manifestations (Mediaeval Warm Period and subsequent Little Ice Age) in particular. But IPCC has discovered a paper showing little evidence of the prominent twin-troughed LIA widely reported elsewhere and this atypical paper is the one it has chosen. The infamous Hockeystick from this Mann et al study is the basis for Figure 1 (a) in the SPM.
* IPCC prefers to think there was no Little Ice Age.
3. Figure 4 (a) - natural forcing
Sun and climate have marched in lockstep right through the Holocene, but IPCCs climate modellers unilaterally cut the nexus when their models took over at 1860. Implausibly, and ignoring much evidence for increased solar activity during the past 140 years, the Figure purports to show that without human intervention the world would have been cooler in 1950-2000 than back in 1860-80.
* IPCC says that if there really was a Little Ice Age, we are still in it.
4. Figures 4 (b) and (c) -
The failure of its over-predicting models to reconcile with an under-warming world, is an albatross around IPCCs neck. Figure 4 (a) goes part way to solving the problem, by claiming reduced natural forcing since the availability of instrumental records from 1860. This enables a much-less-demanding comparison of calculated and actual warming. But it still isnt enough. Enter IPCCs magic bullet aerosols.
In Figure 4 (b), the warming effect of long-lived greenhouse gases and the cooling effect of short-lived (sulphate) aerosols are combined in calculating a profile of human-caused climate change since 1860. A feature of the modelled output is global cooling from the 1940s to the 70s, despite rapidly increasing consumption of fossil fuels over that period. Global warming resumes thereafter, at a much-increased rate to that in the first half of the 20th Century.
A feature of the modelled output is cooling from the 1940s to the 70s. This serendipitous result is despite rapidly increasing use of fossil fuels, and the consequent emissions of the crucial (and long-lived) anthropogenic GHG - carbon dioxide (CO2). Warming resumes thereafter, and at a much-increased rate compared to that in the first half of the century.
The calculated cooling from the 40s is claimed by IPCC to be
the result of growing sulphur dioxide emissions. They have
a longer life in the atmosphere, and hence greater cooling
effect, from the 60s because of the mandated increase in
smoke-stack heights introduced at that time.
The warming from the 70s is said to be because of increasing fuel use, plus introduction of stack-gas desulphurisation to reduce these (cooling) aerosol emissions.
Figure 4 (c) combines both natural and anthropogenic forcings; and the modelled temperature outcome over the 1860-2000 period becomes an almost-perfect match for the instrumental record on a globally-averaged basis. Models and observations have been reconciled. But, not so fast! Did you not notice the sleight-of-hand? About 90% of the cooling aerosols are emitted in the Northern Hemisphere, and yet it is the Southern Hemisphere which exhibits the cooling. The warming is mostly in the extra-tropical north where the aerosols are. This spurious reconciliation will only work because it uses global averages.
* When in doubt, average!
5. Figure 5 (d) - storylines
5.1 The SRES Projections
IPCC tells us that the future temperatures shown in the Figure are not predictions at all, but projections. No probability can be ascribed to projections, and there is no reason to consider any one more likely than another. Although IPCC says of these projections all should be considered equally sound, we hear media emphasis on warming by 2100 of up to 5.8 0 C - rather than of as little as 1.4 degrees C.
The new top end of the range is a big jump indeed from up to 3.5 0 C in IPCCs Second Assessment Report entitled Climate change 1995: The science of climate change. But the jump from 3.5 0C in SAR to 5.8 0C in TAR has a history. The draft of November 1999 still had a high of only 4.0 0C; it was not until the final draft released in October 2000, that the SRES projection of 5.8 0C appeared. It had been added during government review. No rigorous process of peer review here!
This astonishing increase does not arise from any technical
change to the climate models. Referring to IPCCs
Special Report on Emission Scenarios, the TAR SPM
The globally averaged surface temperature is projected to increase by 1.4 to 5.8 0C over the period 1990 to 2100. These results are for the full range of 35 SRES scenarios, based on a number of climate models.
Temperature increases are projected to be greater than those in the SAR, which were about 1.0 to 3.5 0C based on the six IS92 scenarios. The higher projected temperatures and the wider range are due primarily to the lower projected sulphur dioxide emissions in the SRES scenarios relative to the IS92 scenarios.
IPCCs assertion above, attributing the difference between 3.5 and 5.8 0C primarily to the lower sulphur dioxide emissions, is almost certainly untrue. The SRES scenarios are based on six storylines containing demographic and economic projections, which lead on to the assumptions for human-caused greenhouse gas emissions growth, and hence to a series of equally sound model-based projections for future global warming. Here lies the problem.
5.2 Parity errors: exchange rate vs purchasing power
Ian Castles (visiting fellow, National Centre for Development
Studies at ANU, pers comm) has analysed these storylines
and finds them all unsound, but not equally so. For
instance, storyline A2 postulates extreme population growth, with
a global population of over 15 billion by 2100; most demographers
favour only 7-10 billion. But it is IPCCs economic
analysis on which he has concentrated his attention, and he finds
it to be seriously flawed.
As Castles explains it, IPCCs modellers have not understood that it is the real production of goods and services which is relevant to the projection and measurement of future greenhouse gas emissions from economic activity. Instead, they have used the nominal value of that production measured in national prices, and converted it to a common currency on the basis of the exchange rates prevailing in a particular year (in this case, 1990).
But data in national currencies must be converted into the common currency by means of purchasing power parity, and not (as done by IPCC) via quoted exchange rates. The A1 storyline imposes very rapid economic growth to the century ahead. The projections assume that in the 1990 base year, per-capita output in the OECD was 40 times that of Asia. But using purchasing power parity, IPCC would have found it to be only 9.3 times higher. Asia should have been given a 4 times higher weighting than it was. This is a crucial error, because the A1 storyline has Asian per-capita GDP growing at 5.5% per year during 1990-2050, compared to only 1.6% for the OECD.
IPCC's error makes a big difference to global averages. IPCC tells us that it assumes a growth rate of 2.8%, when in fact its outcome at 2050 has a (correctly calculated) implicit rate of 3.7%. This is much higher than the real per-capita GDP growth rate of 1.4% experienced between 1850 and 1990. Indeed, IPCCs mistake is compounded. Between 1990 and 2000, GDP grew only at the 1.4% rate. This means IPCCs 2050 output demands an implausible 4.2% average annual growth from 2000. For the full period, IPCCs A1 storyline implies an unimaginable 35-times increase in global per-capita real wealth between 1990 and 2100.
IPCC's A1 storyline posits much higher growth rates in
developing than developed countries for 1990-2100. But by using
monetary exchange rates rather than purchasing power parity, it
computes an unrealistically low economic base in 1990 for the
developing countries. IPCC assumes a whole-world average annual
per-capita GDP growth rate of 2.8%, when in fact its outcome at
2050 has a (correctly calculated) implicit rate of 3.7%. This is
much higher than the real growth rate of 1.4% experienced between
1850 and 1990.
Indeed, IPCC's mistake is compounded. Between 1990 and 2000, GDP grew only at the 1.4% rate. This means A1's 2050 target output demands an implausible 4.2% average annual growth from 2000.
Correctly calculated to include the true 1990 economic base for the developing world, IPCC's A1 storyline implies an "unimaginable" 35-times increase in real-terms global per-capita wealth between 1990 and 2100. (For the 'Asia' region, but not here including Iran, the Former Soviet Union and Japan, IPCC uses a 140 times increase in per-capita wealth.) In fact, the whole-world increase for 1900-2000 was only 5 times.
* In the climate-change debate, both natural science and social science are crucial.
5.3 The low-end projection
On 7 August 2002, I received a copy of Ian Castles' letter to Dr Rajendra Pachauri (who succeeded Robert Watson as IPCC chairman), analysing the SRES low-case storyline (B1) - which leads on to a human-caused warming of 1.4-2.5 0C by 2100. Castles writes:
As there was no statement of the assumptions underlying the projections of the likely magnitude of climate change in the IPCC's Third Assessment Report, I consider it vital that governments be advised that the lowest of the SRES projections assumed that GDP per capita would increase to more than 70 times its 1990 level in Asia (excluding Japan) and to nearly 30 times its 1990 level in Africa, Latin America and the Middle East by the end of the century. Contrary to statements made in the SRES, these projections imply that real incomes in the whole of the developing world will be many times greater than those in the richest countries of the world today.
In Japan, the Land of the Economic Miracle, real per-capita wealth increased by less then 20 times in the 20th Century. How realistic is 70 (or indeed, 140) times for the rest of Asia?
In Africa, Latin America, and the Middle East (ALM), the greatest driver of GDP, surely, is oil production; but reserves will be largely depleted by 2100, and production must by then be in decline. Where will the per-capita GDP growth of "nearly 30 times its 1990 level" for the ALM region by 2100 come from? The auguries are poor indeed. IPCC's projection contains an implicit assumption that ALM per-capita GDP will grow by about 50% in the decade to 2010. But in 2001 its GDP fell, and another fall is the expectation for 2002.
* Even the economics underpinning the low end of IPCC's projected range are unsound.
6. Figure 5 (a) and (b) - CO2 emissions and concentrations
6.1 IPCC's high-end projection
The introduction of an extreme storyline (A1) for
global economic growth, combined with the most
fossil-fuel-intensive means (F1) of satisfying the projected
energy needs of that extreme growth rate, yields the A1F1
storyline. As explained in the SPM text:
Emissions of CO2 due to fossil-fuel burning are virtually certain to be the dominant influence on the trends in atmospheric CO2 concentration during the 21st century.
By 2100, carbon cycle models project atmospheric CO2 concentrations of 540 to 970 ppm for the illustrative SRES scenarios (90 to 250% above the concentration of 280 ppm in the year 1750).
These projections can be seen in the Figures. But there is more which is not figured:
Uncertainties, especially about the magnitude of the climate feedback from the terrestrial biosphere, cause a variation of about -10 to +30% around each scenario. The total range is 490 to 1260 ppm (75 to 350% above the 1750 concentration).
IPCC's projections start with CO2 emissions of 5.99 billion tonnes (contained-carbon basis) in the 1990 base year, rising in all scenarios to 6.9 BT in 2000. By 1999, actuals had attained 6.459 BT - only a modest 0.358 BT above the 1990 actual of 6.101 BT. The biggest source of CO2 emissions is coal; and the A1F1 scenario is based on the extreme estimate of growth in coal use. This scenario projects carbon emissions increasing to an astonishing 8.6 and 24 BT by 2010 and 2050 respectively, and rising more slowly thereafter to 30 BT in 2100.
On a per-capita basis, global carbon emissions peaked at 1.23 tonnes in 1979, falling to 1.11 tonnes by 1999. But A1F1 has them climbing to an implausible 4 tonnes by 2100.
WORLD CONSUMPTION OF TRADEABLE PRIMARY ENERGY
(Million tonnes oil equivalent)
* Converted on the basis of thermal equivalence, assuming 38%
conversion efficiency in a modern thermal power station. Source:
BP statistical review of world energy.
The A1F1 scenario has consumption of coal growing by 31% in the decade from 1990 -with continued rapid growth thereafter. But reality has already intervened. In the decade 1990-2000, world coal consumption grew hardly at all - as shown in Table 1. Even B1 at the low end, has coal consumption growing by 4% over the 90s. IPCC has already fallen out the bottom of its range! It makes you wonder about its numbers for 2100.
6.2. Sceptical view of growth in atmospheric CO2 concentration
In 1990, atmospheric CO2 concentration was 354.0 ppm; and it had grown to 369.4 ppm in 2000, an average increase of about 1.5 ppm per year - just as for the previous decade and more. Furthermore, the respective 1999-2000 and 2000-01 increases were only 1.1 and 1.5 ppm. No acceleration is yet in evidence; and in order to reach 1260 ppm by 2100, an implausible annual increase of almost 9 ppm through the century ahead is required.
There is more to the impending shortfall of the AD2100 atmospheric CO2 concentration beneath the top projection of 1260 ppm, than can be explained by IPCC's wrong economic analysis. We now have 23 years of satellite records, and land areas of the Northern Hemisphere from 40 to 70 0N display increased greening during that time. This welcome observation may be explained by both a lengthening growing-season and increasing CO2 fertilisation. Whatever the reason, an increasing proportion of recent CO2 emissions appear not to be ending up in the atmosphere.
(Not discussed further herein is methane, the second most influential of the anthropogenic greenhouse gases. Its atmospheric concentration rose about 1% per year in the 80s; but the rate has declined steadily since - and the concentration fell slightly in 2000. It was 1693 ppb in 1990, and 1753 in 2000; but IPCC's AIFI scenario has it an incredible 3400 ppb in 2100.)
There is a natural process of continual CO2 emission and sequestration involving principally (at least when considering the human time-scale) oceanic waters and land and marine plants; and in the absence of human intervention, the equilibrium concentration of atmospheric CO2 fluctuates naturally in response to variations in oceanic solubility driven by temperature changes. When calculating the impact of human-caused emissions on CO2 concentrations, mean residence time in the atmosphere is a crucial input; and IPCC appears to have taken an extreme position in relation to residence time. For this reason, IPCC's Figure 5 (b) shows CO2 concentration for the A1F1 scenario still rising in a straight line at 2100.
Also, proven reserves (at end 2001) of oil, gas and coal include about 1000 billion tonnes of contained carbon. At the rate of carbon emissions A1F1 assumes for 2050 (24 BT), these reserves represent only about 50 years' consumption. Doubtless there is more, but scarcity of readily-recoverable carbon-based fuels becomes a limiting factor well before 2100.
A more plausible residence-time for CO2, and an assumption that all the coal, twice the oil, and thrice the gas currently proven is burned by 2100, yields a peak in atmospheric CO2 concentration of 470 ppm in about 2075, falling slowly thereafter. By contrast, IPCC's projections have 490 ppm at their low end in 2100 - after deducting 10% for 'uncertainties'. IPCC's high end in 2100 is, remember, 1260 ppm.
6.3 Sensitivity of IPCC's models
The sensitivity of numerical climate models is characterised by the warming they compute for a doubling of atmospheric CO2 concentration. Although the SPM does not specify the range of (doubling) sensitivities inherent in the 7 models used to derive the 1.4 to 5.8 0C projected warming range for 1990-2100, other sources suggests it was 1.5 to 4.5 0C.
A best-estimate doubling sensitivity of about 2.5 0C, and an atmospheric CO2 concentration of 630 ppm by 2100, yields an IPCC-projected 'middle-of-the-road' temperature rise from now until 2100 of 2.1 0C - or 3.2 0C from the beginning of industrialisation. In Peter Dietze's opinion, this outcome is a 6 times exaggeration for the warming impact of human-caused GHG emissions. Applying both his preferred CO2 doubling sensitivity of 0.7 0C and his calculated peak CO2 concentration of 470 ppm, gives a 'realistic' temperature increment from now until 2100 of only 0.24 0C - or 0.52 0C from the beginning of industrialisation.
In summary, IPCC offers an implausibly-high projection of economic growth, leading to implausibly high CO2 emissions, and ultimately to an implausible top estimate for CO2 concentration by 2100. When computed by a particularly-sensitive numerical model of climate, an anthropogenic warming of 5.8 0C is the extremely implausible outcome.
* IPCC's 5.8 0C projection is a stunt - just like Greenpeace climbing a chimney-stack.
7. Figure 5 (e) sea level rise
IPCC says that "global mean sea level is projected to rise by 0.09 to 0.88 metres between 1990 and 2100". It attributes this rise primarily to thermal expansion of the oceans, although some allowance is made for loss of mass from glaciers and ice caps. The National Tidal Facility (at Flinders University, Adelaide) keeps score in our region; and it finds long-run sea-level rise in the Pacific to be a modest 0.8 mm/yr (0.08 metres/century) although, around the Australian circumference, the rise is only 0.3 mm/yr. An NTF paper (W. Mitchell et al 2000, "Sea level rise in Australia and the Pacific", delivered at James Cook University, Townsville) concludes:
it is difficult to find evidence of any change in the sea level trend in the whole region, as might have been expected, based on the output of climate models. And over recorded history, sea level rise has occurred, but at a rate which falls significantly short of the IPCC world assessment [1-2 mm/yr over the 20th Century]. Is it possible that the indications of real sea level trends, which are derived from observations, may set tighter bounds on the prognoses of the numerical models?
Below is a similar, but much more forthright, statement from the website www.pog.su.se/sea of the INQUA Commission on Sea Level Changes and Coastal Evolution, whose President is Professor Nils-Axel Mörner of Sweden. Under the title "Research Topics 5: The expected sea level changes in the next century", the Commission says:
This is a topic of much controversy. As it is now, the scenarios are primarily presented by people with little or no specialization in sea level research. This is especially true for the IPCC p roject where "sea level changes" are treated in ways far away from proper observational records.
Island nations, such as the Maldives in the Indian Ocean and Tuvalu in the Pacific, have an elevation only a little above sea-level; and their national leaders are assiduous in blaming the developed world for the supposed threat posed by our fossil-fuel profligacy. But we know that at the Last Glacial Maximum, 20 thousand years ago, sea level was 130 metres lower than today - because so much ice was piled then on northern continents (a kilometre of ice at the site of Detroit, for instance). And yet those (then uninhabited) coral atolls appear to have mostly kept pace with its subsequent remarkable rise. Needlessly, IPCC is scaring the Small Island Developing States. They have a serious problem of course, but it isn't because of greenhouse gas emissions accelerating the previous rate of sea-level rise. It is population pressure and over-development which are inhibiting the growth of stony organisms including coral - and hence inhibiting the continuation of natural island-building.
* IPCC's projection of sharply accelerating sea level rise is inconsistent with observations.
8. Figure 1 (a) - surface temperature
But the fundamental graph in the SPM is Figure 1 (a) headed
"Variations of the Earth's surface temperature for the past
140 years". This figure shows 20th Century warming of about
0.6 0C in two roughly-equal tranches to the mid 40s,
and from the late 70s to the present, with slight cooling between
the 40s and the 70s.
8.1 The human-caused 'greenhouse effect'
Is the warming since 1860, greenhouse warming? First, let's define what we mean:
* The 'greenhouse effect' is a phenomenon of the atmosphere. Naturally-occurring water vapour is the gas most responsible for greenhouse warming; and it is largely water which keeps Earth at a habitable temperature. The other naturally-occurring greenhouse gases (GHGs) - eg carbon dioxide and methane - are subordinate to water. They are well-mixed in the atmosphere; but crucially, water vapour is not.
* Human-caused emissions result in an increased atmospheric concentration of lesser GHGs, particularly CO2; and the principal source of anthropogenic CO2 is the burning of fossil fuels. Coal-fired electricity is the largest contributor.
* Extra GHGs, while transparent to incoming solar radiation (in the short-wavelength visible spectrum), trap more of the heat outgoing from Earth toward Space (in the longer-wavelength infrared); and the lower troposphere warms as a consequence.
* This extra warmth is redistributed in its turn. Less is then radiated upward to Space than before, and some is now returned instead to the Earth's surface.
* It is the resultant surface warming which is called the 'greenhouse effect'. If the lower troposphere isn't warming, the surface can't warm up because of it. Human-caused GHG emissions don't warm the surface directly.
However, a comprehensive coverage of temperatures in the atmosphere is available back to 1979, derived from polar-orbiting weather satellites. Amazingly, for this 23-year period at least, the lower troposphere has warmed only a quarter as fast as the surface on a globally-averaged basis. Furthermore, at least for the tropics, satellites reveal increasing long-wave radiation from the top of the atmosphere to Space. The simplest explanation is that most of the observed surface warming since 1979 is not 'greenhouse effect' warming!
The satellite-derived record shows that tropical regions are little changed over the past 23 years; and warming in the lower troposphere is largely confined to the extra-tropical Northern Hemisphere - north of about 30 0N latitude. Indeed, in the Southern temperate and polar regions south of 45 0S, the lower troposphere has cooled.
Greenhouse warming appears largely confined to on-land regions beneath the very cold and bone dry high-pressure cells of winter in Siberia, particularly, but also Alaska/Yukon - where the (dominant) overlapping impact of water vapour is absent, and tropospheric warming is also evident. In these harsh regions, winter temperatures still remain far below freezing; and the main impact of warming is an extended growing-season.
8.2 Non-anthropogenic causes of warming
Setting aside imperfections of the instrumental record (urban heat island effect, land-clearing and over-grazing, and bureaucratic breakdown in the Former Soviet Union and Africa), what caused the majority of the observed surface warming, as shown in Figure 1 (a)? Sadly, 'imagination block' rules IPCC's thinking. As a result, the SPM findings are dominated by atmospheric science and numerical modelling; while observational/deductive geoscience - chronically under-funded by comparison, including in Australia - is virtually ignored.
There is a persistent warmer/cooler climate cycle of variable period around an average of 1500 years; and it runs right through the dominant 100,000-year Glacial/Interglacial cycle. During the 10,000 years of the present Holocene interglacial, at least, this cycle has been convincingly linked to solar activity - particularly to variations in magnetic flux, as recorded in the cosmogenic 14C and 10Be concentrations preserved in trees, ice-cores, and stalactites. (New work finds that, at the 100,000-year Glacial/Interglacial time-scale, solar influences supplement previously-recognised orbital factors.) The cycle ends with the historical Roman Empire Warm Period, Dark Ages, Mediaeval Warm Period and Little Ice Age.
In the Northern Hemisphere, where this cyclicity is best recognised, the prominently-twin-troughed LIA is clearly solar-related. Overprinted on the 1500-year cycle are shorter cycles, and these too influence the record of surface temperatures shown in Figure 1 (a). There is some evidence for cyclicity at a period of about 200 years (including a trend of decreasing windiness - and hence reduced evaporative cooling - in the Pacific from at least 1860, reversing in the 1940s). On a sub-decadal scale, is the apparently-a-periodic ENSO regime, including El Niño warm events which develop in the eastern Pacific. Both also might be solar-driven, although in ways not yet understood.
The current warming trend, whose latter part appears in the
Figure, includes solar-driven rebound from the last cold snap of
the LIA (the Dalton Minimum) of 1800-20. It in turn is
overprinted by warming peaks at around the 1820s, 1870s, 1930s
and 1990s. Here following Leonid Klyashtorin, the 50/60-year
cycle is present, not only in global temperature, but in
length-of-day and in the movement of atmospheric mass. This cycle
was particularly prominent in the 20th Century, with warming from
the 1920s, cooling from 1946, and renewed warming from 1977.
8.3 The Great Pacific Climate Shift of 1976/77
The Great Pacific Climate Shift of 1976/77, coinciding with a sharp reduction in the upwelling of cold water in the eastern Pacific, was the most prominent physical/biological event of the 20th Century.
This concurrent step-change in sea-surface and tropospheric temperatures, and in the pattern of atmospheric pressure fields, was inertia-related - as evidenced by the coincident change in rate of change of length-of-day. The Shift had an impact far beyond the Pacific - and yet the SPM fails to mention this remarkable and highly-relevant climatic event. 'Imagination block' is a terrible thing.
* Climate change in the 20th Century followed natural cycles on several time-scales.
9. Carbon dioxide - hero not villain
If CO2 concentrations are not the main driver of contemporary climate, should its emission be limited for other environmental reasons?
9.1 A long backward look
We live in an Ice Age, where the atmosphere is depleted in CO2. The Permian glaciation, 300 million years ago, was the last time that a concentration as low as the 180-280 parts per million of our Pleistocene Ice Age persisted. During the warm, wet, earthly paradise of the Thermal Maximum at the beginning the Eocene (about 55 million years ago, when there were crocodiles in the Arctic), for instance, it was 2000-4000 ppm. Our trees evolved in a CO2-rich world. This natural atmospheric constituent is not a 'pollutant'.
9.2 How CO2 works
Literally hundreds of laboratory and out-door experiments, including well-controlled, large-scale, and realistic field trials of multi-year duration, demonstrate that plants do better in an atmosphere enriched with CO2 - to, say, double the ambient 370 ppm. I quote from The Faber Book of Science (edited by John Carey, Faber and Faber 1995, pp 492-4):
Owners of commercial greenhouses discovered long ago that seedlings grow faster when the air in the greenhouse is enriched with carbon dioxide. [Experiments on the American poplar in the 1970s show that] the saturation value of growth rate is one and a half times the rate at the outdoor [CO2] level, and is reached at three times the outdoor level. So far, the results are unsurprising.
More surprising and of greater practical importance are the measurements of water transpiration in the poplar experiment. Transpiration means the loss of water by evaporation from the leaves. The rate of transpiration falls steadily as carbon dioxide increases, and is reduced to about half its present value when the carbon dioxide is enriched threefold. How is this decrease of transpiration to be explained?
The essential point is that carbon dioxide molecules are rare in the atmosphere. They are hard for a plant to catch. The only way a plant can catch a carbon dioxide molecule is to keep open the little stomata or pores on the surface of its leaves, and wait for the occasional carbon dioxide molecule to blunder in. But the air inside the stomata is saturated with water vapour. On average, about two hundred water molecules will blunder out of the hole for every one carbon dioxide molecule that stumbles in.
The moral of this story is that for plants growing under dry conditions, enriched carbon dioxide in the atmosphere is a substitute for water. Since the growth of plants, both in agriculture and in the wild, is frequently limited by lack of water, the effect of carbon dioxide in reducing transpiration may be of greater practical importance than the direct effect in increasing photosynthesis.
* CO2 is not 'dirty'; and emission of this vital plant food confers environmental benefits.
The TAR Summary for Policymakers is flawed in several crucial respects:
* Its projected human-caused warming of up to 5.8 0C, and sea level rise of up to 88 cm, by 2100 stem from a rate of global average real per-capita GDP growth which is extremely implausible.
* Even its low-end projection of 1.4 0C warming by 2100 is founded on implausible economic assumptions.
* Any model-based projection of climate a hundred years hence can be no more than quantified arm-waving.
* The SPM ignores natural climate change at a variety of time-scales, and wrongly attributes most observed warming since 1950 to greenhouse gas emissions.
* No amount of 'doing the right thing' about anthropogenic greenhouse gas emissions can stabilise climate, or limit the incidence of extreme weather events.
* Mitigation remains the only practical way forward.
* The vain attempt at climate stabilisation which IPCC misleadingly encourages, already diverts scarce money and zeal from real-life here-and-now environmental needs.
Finally, IPCC says it "presents a comprehensive, objective and balanced view of the subject matter". And yet, when time reveals that it has made a wrong estimation, it seems always to be the one way - towards the apocalypse. Funny that.
But what should sceptics say when believers remind us that IPCC's work represents the consensus of 2,500 of the world's top climate scientists? Tell them that the advancement of science is not a matter of voting. For 1400 years, from Ptolemy to Savanarola, the intellectual elite agreed on a geocentric cosmology - but that didn't make it right.
Posted 20, October, 2002
© 2002 Bob Foster
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