Critique of IPCC's Report on Climate Change

[This is a direct copy-paste from

http://www.geocities.com/carbonomics/MCtfirm/10tf06/10tf06d.html#00

In the next couple of days, I intend to edit this into a post that is more easily understandable.]

AN ECOLOGICAL CRITIQUE OF THE SCIENTIFIC WORKING PARTY OF THE INTER-GOVERNMENTAL PANEL ON CLIMATE CHANGE
Quatermass: What would we do if we found the Earth was doomed by climate change?
Scientist: Nothing but go on squabbling.
(Quote from the film; 'Quatermass and the Pit' 1957).
ONE: THE IPCC REPORT - A WORLD HISTORICAL TURNING POINT?
i) The Establishment of the Inter-governmental Panel on Climate Change (IPCC).
The ipcc was set up by the united nations environment programme and the world meteorological organization in november 1988 to explore the threats posed by the greenhouse effect. The panel was divided into three working groups; the first researched the science of the greenhouse effect; the second explored the impact of climate change on society; and the third examined the need for political measures to minimize the economic costs of the damage which might be caused by the greenhouse effect. Each group produced a report which was debated at the second world climate conference held in november 1990.
ii) The Earth's Current Carbon Status.
The ipcc scientific working group, the ultimate scientific authority on the greenhouse effect,[1] published the final draft of its first report in may 1990. The report pointed out that the rise in the concentration of atmospheric Carbon over the last couple of centuries, but especially since the second world war, had been dramatic. There is approximately 25% more CO2 in the atmosphere today than there was before the industrial revolution[2] but, if all greenhouse gases are taken into consideration, there is the equivalent of 50% more CO2.[3] The ipcc believes this could lead to a correspondingly dramatic increase in global temperatures, “Under the Business-as-Usual scenario emissions of greenhouse gases, a rate of increase of global mean temperature during the next century of 0.3C per decade (with an uncertainty range of 0.2C to 0.5C per decade. This will result in a likely increase in global mean temperature of about 1C above the present value by 2025 and 3C before the end of the next century.”[4]
iii) The IPCC's Draconian Recommendation for Cuts in CO2 Emissions.
The ipcc scientific working party issued a grim warning that the predicted rise in global temperatures could lead to ecological calamities and therefore recommended an immediate reduction in CO2 emissions of 60-80% in order to stabilize the concentration of atmospheric Carbon at the 1990 level, “The long lived (greenhouse) gases would require immediate reductions in emissions from human activities of over 60% to stabilize their concentration at today’s levels.”[5]
This recommendation was far more extreme than anything previously suggested even by supposedly radical environmental groups such as greenpeace, let alone sober, and supposedly scientific, groups such as friends of the Earth. If the world’s leading climatologists had demanded a cut in Carbon emissions of 40% then the global community may have been able to achieve this target through the implementation of dramatic, but nevertheless reformist, measures on the biggest contributors to the greenhouse effect. However, the ipcc’s demand for a cut of 60% implied that the global community would have to implement radical policies which would affect virtually all human activities generating Carbon emissions. It meant, ceteris paribus, that 60% of all cars would have to be taken off the world’s roads; 60% of the world’s power stations would have to be closed down; and 60% of the world’s factories spewing out Carbon emissions would also have to be dismantled, etc., etc.. But recommending that 80% cuts might also be needed was to raise the spectre of a need for a revolutionary transformation of the relationship between humans and the only Planet in the universe on which they can live.
iv) A Scientific Revolution?.
The ipcc scientists’ recommendation seems like a momentous announcement. Never before in the history of science have so many of the world’s leading scientists issued a joint statement demanding that the global community take action to avert a global ecological disaster. It was the severest advice scientists have ever delivered to world political leaders. However, whether it will be regarded in the years to come as a symbol of the fight against the destruction of the Planet is open to question. It is already highly questionable that it will become a world historical turning point.
The political failures of the second world climate conference and, a few years later, the rio Earth summit, were not due solely to ignorant, corrupt politicians; greedy, evil capitalists; nor servile, careerist environmentalists - although of course having these shits decide on the fate of the Earth wasn’t too helpful. One of the major reasons for the failures was scientific - a petty demarcation dispute within the scientific establishment which led to some of the most important features of global warming being left out of the calculations about the scale of the threat posed by climate change.
The ipcc recommendation rested on three, fundamentally flawed, assumptions. These flaws will be highlighted in the next three sections and their solutions outlined in the three sections thereafter.
TWO: THE FLAWS IN THE IPCC’S RECOMMENDATION FOR CUTS IN CARBON EMISSIONS.
i) The Concentration on Carbon Emissions.
The ipcc scientists focussed solely on Carbon emissions even though the level of atmospheric Carbon is determined not merely by the amount of Carbon dumped into the atmosphere but by the Planet’s ability to absorb Carbon through Photosynthesis.
ii) Climate Changes Are Inevitable.
Even if the required cuts in Carbon emissions were achieved immediately, ipcc scientists claimed there would still be a rise in global temperatures because of the huge quantities of Carbon dumped into the atmosphere since the beginning of the industrial revolution, “Even if we were able to stablize emissions of each of the greenhouse gases at present day levels from now on, the temperature is predicted to rise by about 0.2C per decade for the first few decades.”[6] Half the Carbon released during the industrial age is still in the atmosphere and this will produce climatic changes in the decades to come which could have calamitous effects on the Planet’s life-support systems.[7] It will be a century and a half before the Carbon dumped into the atmosphere since the second world war is removed and thus no longer contributing to the greenhouse effect, “Even if all human-made emissions of carbon dioxide were halted in the year 1990, about half the increase in CO2 concentration caused by human activities would still be evident by the year 2100.”[8]
iii) The 1990 Concentration of Atmospheric Carbon Too High.
Finally, even assuming that the concentration of greenhouse gases could be stabilized at the 1990 level, it is simply not known whether human civilization could survive over the long term with this level of atmospheric Carbon.
THREE: RECTIFYING THE MISTAKES.
i) The IPCC Scientific Working Group's Fixation on Carbon Emissions.
One of the peculiarities of the scientific working group’s analysis was that whilst it recommended cuts in Carbon emissions it made no parallel recommendations for an increase in the Planet’s Forest cover[9] even though a number of commentators have postulated that the Earth is one continent short of the Forests needed to maintain climatic stability, “Dysen and Marland have calculated that .. to absorb the 20,000 million tons of CO2 currently emitted every year into the atmosphere, an area of 7 million square kilometres (roughly the size of Australia) would have to be planted.”[10] There seems to have been a convergence of political and scientific interests which led to this bizarre, and dangerous, neglect of the Planet’s Photosynthetic capacity.
Government representatives involved in the ipcc political working parties did not want ipcc scientists to make recommendations for extending/preserving the Earth’s Forest cover because of the huge economic costs. As far as the over-industrialized nations were concerned, Reforesting large tracts of their own land to soak up atmospheric Carbon would not only be expensive but a gross misuse of scarce resources which could be used much more profitably for the construction of new car factories, new office blocks, new roads, etc.. On the other side of the Planet, the disintegrating/industrializing nations didn’t want their Forests commandeered as sinks for the Carbon pollution created by rich countries. There seems, then, to have been a tacit agreement between rich and the poor governments to avoid any agreement over the issue of Forest cover.
The ipcc scientists’, however, had their own reasons for focussing on Carbon emissions. These had little to do with the politics of the global political community but everything to do with the politics of the global scientific community. In the scientific world each discipline acts, very unscientifically, like an intellectual closed shop rigorously defending its area of specialized knowledge and discouraging scientists from straying beyond the confines of their own discipline.[11] The scientists involved in the ipcc scientific working party were meteorologists and climatologists - they were not biologists, life scientists, nor ecologists. As a result they concentrated upon their field of expertise, the atmosphere, and ignored the role played by Plants and Wildlife in determining the atmosphere’s chemical composition. During the final discussions for the ipcc’s second report, published in may 1992 in preparation for the rio Earth summit, one commentator complained about this state of affairs, “At this year’s (ipcc) meeting in China, when the 1992 report was finalized, not a single ecologist took the microphone to put their case among the atmospheric scientists who dominated the meeting.”[12] It seems the ipcc scientists were far from disturbed by the political failure to agree policies for Reforestation.
The consequence of the ipcc scientists’ intellectual closed shoppism was a half baked ecological analysis whose focus on Carbon emissions has led to a global repetition of this nonsense.[13] Far worse is that it has allowed governments around the world to continue ransacking their Forests in the absurd belief that as long as they reduce their Carbon emissions they can continue to deforest their country, and thus the Planet, with climatic impunity. But, even if the required reductions in Carbon emissions are eventually achieved, the level of atmospheric Carbon could go on rising if the Planet’s Photosynthetic capacity continues to be decimated. One commentator blames scientists for allowing governments to go on ransacking Forests and for failing to come to an agreement about the need to increase the Earth’s Forest cover .. “the halting progress of the continuing discussions on forests in the Prepatory Committee of the UNCED. The critical observation .. was that in no case has there been political progress in addressing environmental issues internationally without consensus from the scientific community as to the definition of the problem and an equally clear definition of potential solutions.”[14]
ii) Climate Change Not Inevitable.
Perhaps the ipcc scientists’ most disturbing error was their view that climate change is inevitable because of the current levels of atmospheric Carbon. This error stems directly from their failure to take into account the role of Forests in regulating the climate.
For the sake of simplicity, it can be argued that deforestation boosts global warming in three ways;
firstly, by releasing Carbon emissions which boost the greenhouse effect;
secondly, by reducing the Planet’s ability to absorb atmospheric Carbon and,
thirdly, by changing the Planet’s albedo so that the Earth absorbs more sunlight, “The evaporation of water from forests is part of Gaia's cooling system.”[15]
Conversely, Reforestation could be used to combat global warming in two ways; firstly, by absorbing atmospheric Carbon (thereby decreasing the greenhouse effect) and, secondly, by generating clouds which reflect sunlight back into space (thereby decreasing the heat effect). The point which needs to be emphasized is that whilst the former reduces the greenhouse effect only slowly over the decades and centuries, the latter reduces global warming within years by increasing the Planet's albedo. Reforestation thus has a critical, short term, role in reducing global temperatures. Although it cannot combat global warming in the short term via a reduction in Carbon emissions, it can do so via a reduction in the heat effect, “Changes in the terrestrial biota will also effect the overall albedo of the planet. Lashof believes this to be 'probably the most significant feedback produced by the terrestrial biota'.”[16] There is, therefore, no inevitability about a latent rise in global warming since it could be prevented by Reforestation. Even though the build-up of Carbon emissions will exert a considerable upward pressure on global temperatures this does not mean there will inevitably be a rise in temperatures because Reforestation could create a refrigeration effect which, if extensive enough, could more than offset such pressures.
It is imperative to reduce Carbon emissions and prevent further boosts to the greenhouse effect. However, this does not mean that cutting Carbon emissions is the most important policy for combatting global warming. The most urgent priority is Reforestation.
The consequence of the IPCC climatologists’ closed shop mentality was that it led them, and thereby many politicians and green organizations, to dismiss the priority of Reforestation.[17] The irony is that although the IPCC scientists measured the effect of sea-ice albedo on the climate, they did not measure the role of biomass albedo, “biogeochemical feedbacks such as .. vegetation albedo are generally neglected.”[18] If they had done so it is doubtful whether they would have made such a dangerous mistake.
iii) The Need to Return to Pre-industrial Levels of Atmospheric Carbon.
Politically, the ipcc scientists played safe by recommending that the concentration of atmospheric Carbon should be stabilized at the 1990 level. Given that the current level of greenhouse gases is 50% higher than in pre-industrial times and could have serious climatic consequences, the ipcc scientists should have been courageous enough to risk the ire of the global community by insisting that the concentration of atmospheric Carbon should be reduced to pre-industrial levels to avoid any potential environmental disaster - even if this meant even more draconian action than that entailed by the demand for 60-80% reductions in CO2 emissions.
James lovelock, however, doubts whether even a return to pre-industrial levels will be sufficient to prevent a climatic disaster, “In the last few tens of millions of years the solar output has reached a level where it is becoming increasingly difficult for the CO2 pumping system to operate. To keep cool when the solar output is as high as now requires efficient pumping by the system so that a carbon dioxide level below 200 parts per million (ppm) is sustained.”[19]
Lovelock’s target for the concentration of atmospheric Carbon needs to be put into context. There are currently about 700,000,000,000 tonnes of Carbon in the atmosphere - approximately 350 ppm. Carbon is being dumped into the atmosphere at the rate of about 5-6 billion tonnes a year and, as a consequence, “It is estimated that by the year 2040 it (the concentration of Carbon) will have increased to 560 ppm.”[20] Prior to the industrial revolution there were approximately 270 ppm of atmospheric Carbon. Further back in history, “At the height of the ice age, 18,000 years ago... the content in the atmosphere of CO2 was 210 parts per million.”[21]
In other words, for the sake of the Planet’s health, lovelock recommends a concentration of atmospheric Carbon which is lower than that found at the height of the last ice age. He believes the Earth’s natural state is an ice age, warm periods seem to be geophysiological abnormalities, “The present interglacial warm period could be regarded as a fever for Gaia and that left to herself she would be relaxing into her normal, comfortable for her, ice age.”[22] Given the rapid accumulation of atmospheric Carbon over the last couple of centuries and the rate at which Carbon is currently being dumped into the atmosphere, it should be obvious that attempting to decrease current levels of Carbon to that which existed not merely before the industrial revolution but during the height of the last ice age would require nothing less than a total revolution in humans’ attitude toward the Earth. But, if it is imperative to make a dramatic reversal of current trends in which humans are turning large portions of the Planet into a lifeless deserts, is it necessary to go all the way to the other extreme and actively regulate the climate to encourage the return of ice sheets to the north american and euroasian continents?
FOUR: THE IPCC’S INTELLECTUAL APARTHEID.
i) The Inadequacies of the IPCC's General Circulation Model.
I: The Inadequacies of Computing Power.
The ipcc scientists’ recommendation for draconian cuts in Carbon emissions was derived from forecasts about the Planet’s long term climate produced by computer models, known as general circulation models, (gcms).[23] They simulate the Earth’s past, present and future, climates. At the moment, however, even the most powerful supercomputers and the most sophisticated computer software can measure the Planet’s climate only by aggregating climatic conditions across huge areas of the Earth’s atmosphere, covering tens of thousands of cubic miles - which means they can’t even resolve the climate of the brutish isles. In addition, at present gcms can handle only a limited number of climatic variables. Not surprisingly, a number of factors influencing the Planet’s climate had to be left out of the ipcc's computer model - many of which could boost global warming, “Unfortunately, even though this is crucial for climate change prediction, only a few models linking all the main components of the climate system in a comprehensive way have been developed.”[24]
II: The Failure to Incorporate Phyotomass.
The first major deficiency of the ipcc’s computer model was, as has been pointed out above, the failure to incorporate the role played by terrestrial Phytomass. “Today's (climate) models do not account fully for the removal of CO2 from the atmosphere by land plants, but may overstate the oceans' ability to absorb it.”;[25] “The role of forests in affecting climate has been grossly underestimated by climatologists, largely as a result of too heavy a focus on the role of the oceans. The distortion persists in the recent report of the scientific sessions of the second World Climate Conference held in Geneva (WMO, 1990). The role of forests is acknowledged as potentially contributing to solution of the problem by storing additional carbon through reforestation, but the need to stop deforestation is not emphasized.”;[26] “The weaknesses of current climate models in respect of clouds and oceans arise even before other pieces of the Earth system, like icecaps, vegetation and volcanoes, are incorporated properly.”[27] One of the leading ipcc scientists pointed out that none of the world’s seven major computer models incorporated the biosphere, “Very little has been said in this chapter about the biosphere. The large three-dimensional gcm described in this chapter contain a lot of dynamics and physics but no interactive chemistry or biology.”[28]
The role played by Phytoplankton was also ignored, “The damage done to certain species of plankton by increased ultra-violet radiation .. was highlighted recently by the ozone trends panel of the UNEP but ignored by the IPCC.”[29] “One group of plankton, the Coccolithophorids, are apparently a major source of DMS and their bloom processes would most likely respond, although in uncertain ways, to changes in ocean-atmosphere exchanges resulting from climate change.”[30]
III: The Failure to Take into Account Biotic Feedback Processes.
Much more importantly than the ipcc’s biotic blinkeredness was that no account was taken of biotic feedback processes whereby increases in anthropogenic global warming cause changes to the Earth’s Phytomass which stimulates further increases in global temperatures, “Current gcms contain the key geophysical climate feedbacks, such as changes in water vapour, clouds and sea ice albedo, but biogeochemical feedbacks such as changes in methane emissions, ocean CO2 uptake and vegetation albedo are generally neglected.”;[31] “Several atmospheric feedback processes are well defined in GCM but those relating to ocean productivity are not yet sufficiently well understood to be included.”[32]
The ipcc’s second report failed to remedy this inadequacy, “Biological feedback processes were left out of the IPCC’s climate models.”[33] Two examples of the scale of such omissions can be given. Firstly, the Arctic Tundra contains vast quantities of methane, “About 27% of the world's carbon store is locked up in the peat bogs of the tundra and the boreal forests.”[34] Although the Arctic Tundra is melting and releasing methane, “The IPCC report says this effect has probably been underestimated.”[35]. Since then it has been learnt that the Arctic Tundra is now a net source of methane, “Meanwhile, in February (1993) we learned that the demonstrably-warming Arctic tundra has transformed from a CO2 sink into a significant source of CO2. Biogeochemical feedbacks like this, however, are omitted from most climate models. The dreadful rates of warming the IPCC forecasts may in fact be underestimates.”[36] Secondly, and more worrying, is the failure to take into account the release of trillions of tons of methane currently locked up in polar waters, “Potentially the most important biogeochemical feedback is the release of methane from near-shore ocean sediments.”[37] The escape of such huge quantities of methane could generate a runaway greenhouse effect.
If, as a result of such feedback mechanisms, a quantum leap in the climate took place the likelihood of a global ecological breakdown would increase dramatically. The longer it takes to implement effective policies to combat global warming, the greater the accumulation of atmospheric Carbon, the greater the chance of a quantum change in the Planet’s climate, the greater the difficulties of reversing such a change.
IV: The Vulnerability of Ecosystems.
Another factor not considered by ipcc scientists is a danger highlighted by james lovelock - that an ecological system is likely to collapse if it surpasses a threshold level of damage, “To a planetary physician, by far the most dangerous malady afflicting the Earth is that of exfoliation - destruction of its living skin. In human medicine the loss of skin from whatever cause is a serious threat to life: the loss of more than 70% of the skin by burning is usually fatal. To denude the Earth of its forests and other natural ecosystems and of its soils is like burning the skin of a human. And we shall soon have destroyed or replaced with inefficient farmlands 70% of the earth's natural land surface cover.”[38] If this is the case then the safety margin before an ecological collapse may be much smaller than the ipcc assumed.
V: Research Failures.
It should also be noted that a number of atmospheric pollutants could not be included because their contribution to the greenhouse effect had not been quantified, e.g. “Ground level (tropospheric) ozone (from vehicles) makes a significant contribution to global warming, but is very difficult to quantify. For this reason the IPCC did not include it in its estimates of the contribution that various greenhouse gases make to global climate change.”[39]
ii) Conclusions.
The ipcc’s gcm is not merely inadequate and fundamentally flawed, it is also dangerous because by concentrating solely upon the greenhouse effect they have ignored the contribution which deforestation makes to gobal warming and this has allowed countries all over the world to continue ransacking their Forests. Even worse is that it underestimates the threat posed by global warming. The ipcc have admitted that, “although many of the feedback processes are poorly understood, it seems likely that, overall, they will act to increase, rather than decrease, greenhouse gas concentrations in a warmer world.”[40] The inadequacies of the ipcc’s model meant, “Uncertainty led to 7 of the potentially most alarming factors being left out of the UN's final report.”[41] This led one commentator to criticize the ipcc for failing to warn political leaders about the possibility of a runaway global warming, “The scientists of the IPCC have undersold the worst possibilities outlined in their analysis of global warming.”[42]
The ipcc scientists’ failure to explore biotic factors critical to global warming is partly technological due to inadequate computers and computer software, but mainly a result of the scientific establishment’s creation of intellectual demarcation zones and the disputes between Earth scientists and life scientists; climatologists and biologists; as well as battles between those inside the scientific establishment and those outside, primarily Gaians, who do not subject themselves to the same constraints as the ipcc scientists. Whilst ipcc scientists like john houghton admit that they do not take the biosphere into account when assessing global warming, james lovelock has shown that the climate is regulated by the biosphere. Although it is argued that, “There have been no long term studies of the responses of most of the world’s ecostsyems to elevated CO2 or climate change.”[43] the fact is that huge masses of information about the state of the Earth’s Vegetation cover have been collected from satellites over the last decade or so, “When Tucker and Townsend mapped the vegetation index, season by season, they were able to distinguish broad areas of rainforest, grassland and so on, by the density of vegetation and its seasonal behaviour.”[44]The vegetation index .. “turned out to be a prime measure of the influence of plants in the Earth system.”[45] Only one team of scientists have created a computer model to use this information to determine what is happening to the Earth’s Vegetation. Piers Sellars and his colleagues in Maryland designed a computer model of the climate to interpret the satellite’s data. By 1986 they were feeding the model with vast quantities of information and helping to evaluate a huge segment of the Earth’s Carbon spiral, “Their Simple Biosphere Model takes in conventional weather data and computes changes in leaf temperatures, the rain, and dew wetting the leaves, and the wetness of various layers of soil.”[46] It might have been thought that it should be the highest priority for the ipcc, and the other major climate modellers, to incorporate this simple biosphere model and the vast quantities of information it contains.
Whilst the scientific establishment’s closed shop could have been condoned when the dangers posed by climate change were still in serious dispute, this is no longer the case. It is frightening that climatologists’ self-imposed “intellectual apartheid” has caused scientific misjudgements which have not only ignored the role of the biosphere on the Earth’s climate, but have overlooked the vital priority of Reforestation in combatting climate change, and considerably underestimated the threat posed by global warming.
It seems the ipcc scientists have not so much initiated a full-blown scientific revolution as allowed their own petty rivalries to override a comprehensive analysis of the ecological calamities looming on the horizon. What is certain, however, is that politically they have utterly failed to expose, and then challenge, the frightening ecocidal behaviour of the over-industrialized nations.
In a number of ways the ipcc scientists did take a number of risks in their first report. They could easily have become an object of derision for basing their extreme recommendations for reductions in atmospheric Carbon on such inadequate knowledge of the Earth’s ecological processes. However, by going out of the way to indicate the inadequacies of the evidence, and by admitting the areas of uncertainty, the ipcc not merely followed correct scientific procedures but put pressure on politicians to fund the necessary research for a comprehensive understanding of global warming.
iii) The IPCC’s 1992 Rio Update.
In May 1992 the ipcc scientific working group published an updated scientific report in time for the rio Earth summit. This included new scientific evidence about the greenhouse effect which had emerged in the intervening period. Whilst this led to minor modifications in the understanding of the greenhouse effect it did not require the ipcc scientists to change their views about the threat posed by global warming, and they reiterated their earlier recommendation, “Findings of scientific research since 1990 .. do not justify alteration of the major conclusions of the first IPCC scientific assessment.”[47]
I: The Failure to Incorporate Phyotomass.
In the second edition, the ipcc acknowledged its failure to take Phytomass into account, “Since IPCC (1990) particular attention has focussed on understanding the processes controlling the release and uptake of CO2 from both the terrestrial biosphere and the oceans, and on the quantification of the fluxes. The terrestrial biospheric processes which are suggested as contributing to the (Carbon) sinks are sequestration due to forest regeneration, and fertilization arising from the effects of both CO2 and nitrogen (N) but none of these can be adequately quantified.”[48]
The ipcc has set up a new research programme to develop a common methodology to assist each country around the world in drawing up national ecological inventories. The national inventories of net emissions of greenhouse gases will measure not only Carbon sources but sinks, “In order to support national and international responses to climate change, it is necessary to estimate emissions and sinks at the national level in an agreed and consistent way. The IPCC has established a work programme to:
i) develop an approved detailed methodology for calculating national inventories of greenhouse gas emissions and sinks
ii) assist all participating countries to implement this methodology and provide results by the end of 1993.
An IPCC workshop on National Greenhouse Gas Inventories, held in Geneva from 5 to 6 December 1991, proposed guidance on needed improvements in the draft methodology and priorities for the work programme.”[49]
II: The Failure to Incorporate Biological Feedbacks.
“Biological feedbacks have not yet been taken into account in simulations of climate change.”[50]
III: The New Evidence Concerning Global Warming.
Firstly, as many commentators had suspected, it was confirmed that ozone depletion was counteracting the effects of global warming, “Depletion of ozone in the lower stratosphere in the middle and high latitudes results in a decrease in radiative forcing which is believed to be comparable in magnitude to the radiative forcing contribution of CFCs (globally averaged) over the last decade or so.”[51]
The role of aerosols was elaborated, “In most cases aerosols tend to cool climate. In general, they have a much shorter lifetime than greenhouse gases so their concentrations respond much more quickly to changes in emissions.”[52]This led to a modification of the ipcc’s conclusions, “If sulphur emissions continue to increase, this warming rate is likely to be reduced, significantly in the northern hemisphere, by an amount dependent on the future magnitude and regional distribution of the emissions.”[53]