Select Committee on Economic Affairs Second Report

CHAPTER 3: The Future Impacts of the enhanced Greenhouse Effect

The nature of temperature change

25.  Much of the global warming literature suggests that warming will be associated with many detrimental, and some positive, effects on human wellbeing and natural environments[23]. By and large, the greater the temperature rise, the larger the effects are likely to be. The IPCC's 2001 Report suggests a range of mean temperature changes of 1.4oC to 5.8oC by 2100[24]. We consider shortly how realistic this range is. These are mean global temperatures. Temperature changes in different continents will vary around this mean, some will be markedly higher, some lower. There will therefore be a spatial variation in temperature change. The lower end of the IPCC global temperature range appears modest. The problem arises because not only is there a problem arising from the trend increase in global temperature, but that trend rate masks substantial increased variability in temperature and probably in precipitation and weather events generally.

26.  Measuring the impacts of global warming is obviously fraught with difficulty. Indeed, one of the Committee's witnesses went as far as to question whether predicting impacts 100 years and more hence has any value at all[25]. There are certainly profound problems involved in peering so far into the future. Nonetheless, it is hard to see the alternative. The problem lies in the time-lags that are endemic in the climate system. Present emissions of greenhouse gases do not have immediate impacts. Warming now is caused by greenhouse gases, emitted decades ago. This is because the emissions cumulate in the atmosphere and what damage is done arises from this concentration of gases, not from the current emissions themselves. Each greenhouse gas resides in the atmosphere before decaying naturally: CO2 persists for 2 to 200 years, methane for 12 years, nitrous oxide for 114 years, and in the case of perfluoromethane upwards of 50,000 years[26]. It follows that action now to reduce emissions will have no immediate short-run effects. Any beneficial results will not accrue for decades to come[27]. By implication, climate policy is about reducing impacts in the decades and centuries to come; therefore, if impacts in 2100 are to be mitigated, action has to be taken sooner rather than later.

Impacts: a thumbnail sketch

27.  Whatever the validity of the temperature projections, the science of measuring impacts remains speculative. Arguably, the most certain effect is sea level rise (SLR) due, in the main, to the thermal expansion of the oceans. The IPCC projects a mean global SLR of 20 to 88 cms by 2100. There will be local variations around this range. SLR clearly threatens low lying islands and deltaic regions in countries such as Bangladesh and Egypt. Some of these regions have additional problems of sinking due to rapid extraction of freshwater or diverted sediments (which offset erosion). Many of the adverse effects can be offset by adaptation and we believe that the economic and social returns from investing in adaptation should be properly weighed against the cost of mitigation. A notable example of such adaptation is the discussion already taking place on plans to extend and enhance the flood defences for London. But we acknowledge that foresight of this kind is a luxury that many poor countries cannot today afford from their own resources. International assistance will be required to help finance the adaptation that is needed. However, in the timescale before major adjustment needs to occur, projected economic growth in the developing countries should enable them to finance greater shares of the measures needed.

28.  Rapid warming, which is what the IPCC's central projections suggest is the case, may be associated with increased weather variability and hence with the incidence or severity of weather events such as storms and monsoons. Despite a popular literature suggesting that cyclones and hurricanes will also increase, the climate models appear to be undecided on these effects. Similarly, often-repeated graphs of rising money costs of extreme weather events can be misleading since money value of damage is partly a function of the intensity of property development (and hence financial value of the assets) in addition to the severity of the weather event. Put another way, weather events could be constant in their severity but damage costs would still rise. Nonetheless, the facts are that more property and more lives are now at risk from major weather events. The IPCC provides evidence that global insured and uninsured property losses currently amount to over $40 billion per annum compared to just $4 billion per annum (all in real terms) some 50 years ago[28].

29.  Impacts on human health are also open to some debate. Deaths associated with abnormally high summertime temperatures may well rise. By contrast, deaths may be reduced due to warming winters. Several of the Committee's witnesses referred to the European heatwave of summer 2003 and it was suggested that current warming (due to past emissions of greenhouse gases) accounted for the abnormal number of premature deaths at that time. A carefully researched study in Nature concluded that:

"It is an ill-posed question whether the 2003 heatwave was caused, in a simple deterministic sense, by a modification of the external influences on climate—for example, increasing concentrations of greenhouse gases in the atmosphere—because almost any such weather event might have occurred by chance in an unmodified climate"[29].

30.  But the authors do conclude that, relative to a temperature threshold that was exceeded in 2003 but in no other year since records began in the mid-19th century, "it is very likely (confidence level > 90%) that human influence has at least doubled the risk of a heatwave exceeding this threshold magnitude". The experience of 2003 may therefore not augur well for the future, although we are conscious again of the need to be careful about the policy implications. It will be sensible to manage exposure of vulnerable people to such heatwaves—a relatively simple task—rather than focus solely on emissions reductions to reduce the chance that they will occur again with more regularity.

31.  Mortality and morbidity due to changes in the availability of drinking water are more likely with future warming. Higher temperatures, coupled with rising population growth, and hence growing demand for water, will decrease water availability in some parts of the world. Saline intrusion will affect freshwater supplies in some coastal areas, and water pollution can be expected to increase. The same issues of adaptation versus mitigation arise: much water is wasted, even in poor countries, and better water management policies may be better investments than attempts to reduce warming. This will be especially true if policies to reduce emissions have a limited chance of success, an issue we return to later.

32.  It is also widely argued that vector-borne diseases will increase as regions warm, especially malaria. However, we noted evidence from Professor Paul Reiter of the Institut Pasteur in Paris, which strongly disputed the IPCC's arguments on the likely spread of malaria[30]. Professor Reiter argues that malaria is not a "tropical" disease and that it was widespread during the "little ice age" from mid-15th century to mid-18th century when temperatures were lower than today. Warmth is a factor in the transmission of the disease, but a number of location-specific factors are more important. Professor Reiter's cautions underline the fact that even the IPCC conclusions, based on a scientific process with many hundreds of experts, still need to be treated with care. We return to Professor Reiter's evidence later when we consider the reliability of some of the IPCC evidence.

33.  Global warming will bring about ecosystem change and hence changes in the populations of species. The IPCC cites particular ecosystems at risk: glaciers, coral reefs and atolls, mangroves, boreal and tropical forests, polar and alpine ecosystems, prairie wetlands and remnant native grasslands[31]. A case in point is the coral reefs where the evidence suggests that coral bleaching will increase as oceans become warmer, an effect already identified with El Niño events. Since the reefs embody a great deal of marine biodiversity, the diversity of species is itself under threat. The threats from warming need to be placed in context. There are many other threats to coral reefs: over-fishing, destructive fishing techniques, pollution run-off, oil spills, even tourism. Nonetheless, the impacts of warming cannot be controlled as readily as these other man-made threats. For example, in contrast to some other impacts, it is difficult to see what adaptive measures could be taken to protect reefs from ocean surface warming. There are some offsetting factors. Some species will "relocate": a warmer North Sea, for example, has already experienced increases in a number of species, including large shoals of squid, followed by their predators—species of dolphins and whales that would normally be expected to inhabit more southerly waters[32]. But the available evidence suggests that any benefits to ecosystems are likely to be confined to the lower end of the projected temperature changes. Impacts on other vulnerable ecosystems will also be difficult, or impossible, to reverse, although, again, it has to be recognised that human influence over land use change, brought on by population growth and the extension of agriculture, is the major determinant of ecosystem and species loss.

34.  Impacts of warming on agriculture are debated. The evidence suggests that some regions could gain from a warmer climate and the fact that higher levels of CO2 enhance crop growth. But some regions, notably the poorer ones, will lose because of changes in precipitation and higher temperatures. Many other factors affect agricultural yields and IPCC concludes that it will be difficult to distinguish the impacts of modest climate change from the "noise" in these other factors. Moreover, at the lower end of the projected temperature increases there will be scope for adaptation. Provided the resources are available, farmers will not stand by and watch crops being ruined if there are alternatives available. But, to the extent that it is needed in the short term, adaptation in the poor regions of the world is clearly limited without outside help. At the higher end of the temperature increase spectrum the scope for adaptation is further reduced. Food security issues appear particularly problematic in Africa[33]. Dr Martin Parry has suggested that the positive effects of warming on crop yields would disappear at +1oC for India and perhaps 1.5oC for Southern Europe[34].

35.  The impact literature also refers to "socially contingent impacts" which in turn relate mainly to the prospects of wholesale forced migrations of populations in seriously affected regions. The IPCC acknowledges that these effects, if they occur, must be uncertain.

Extreme events

36.  The term extreme events tends to be reserved for weather events such as cyclones, hurricanes, tornadoes, ice storms, blizzards, rain storms, and heatwaves. The IPCC believes that many of these events will increase with warming. Sir John Houghton has declared that "these probably constitute the most important element in climate change impacts"[35]. For obvious reasons, the insurance industry tracks extreme events. Data from Munich Re indicate a more than five-fold increase in the number of weather-related extreme events in the 1990s compared to the 1950s. The economic losses from these events need to be distinguished from the number of events because economic damages will also be influenced by the scale of property at risk. These losses are estimated to have risen by a factor of 10 in the same period (at constant prices)[36]. Dr Madhav Khandekar, a Canadian consulting meteorologist, has challenged the IPCC findings in work he submitted to us[37]. Dr Khandekar cites studies which find no increasing trends for thunderstorms, intense tornadoes, hurricanes or tropical cyclones in the USA, although extreme precipitation events have increased. He finds no evidence for increasing trends of extreme events elsewhere that could be associated with warming rather than natural events like the El Niño Southern Oscillation, which remain, in themselves, unpredictable.

37.  We are in no position to evaluate these contrasting views. We do draw attention to the fact that, if extreme events are indeed to be considered the most important impacts from climate change, there is uncertainty and controversy about the underlying data required to substantiate this claim.

Large scale one-off changes

38.  Some of our witnesses placed considerable emphasis on the role of global warming in generating "surprises", or what IPCC refers to as "large-scale singular events". The GCMs generate results which suggest that, as radiative forcing increases, so climatic change increases in a fairly orderly manner. This result is fairly reassuring in the context of policy since it implies that, while climate change continues unabated during the policy-making period, there is time to adjust and introduce the required changes in policy and practice. But if change is non-linear and abrupt, then that reassurance largely disappears, and there are many examples of non-linear behaviour and thresholds in Earth's climate system[38]. Several GCMs suggest that some of these major events could arise at high levels of warming. One reason for being concerned about surprises, apart from their potential for large scale impacts, is that evidence suggests that some past climate change has occurred within very short periods of time[39]. The kinds of surprises that are prominent in the discussion are:

  • reversal (or "shut down") of the ocean thermohaline circulation (THC). The THC refers to deep-ocean currents that move heat and freshwater between the world's oceans. A major influence on these currents in the past has been the freshwater released from ice melts in the North Atlantic. The Gulf Stream brings warm surface water from the Gulf of Mexico to the North East Atlantic and returns cold deep water to the South Atlantic. The Gulf Stream maintains Europe's temperatures at about 8oC higher than they would otherwise be. It relies on salty and cooling surface water sinking downwards, and the fear is that additions of substantial amounts of fresh surface water will reverse or "switch off" this vertical change in the ocean's waters. Such fresh water additions could come from melting ice in the Arctic and Greenland. European summers would heat up and winters would become very much colder[40];
  • disintegration of the West Antarctic ice caps which would alter the South Atlantic ocean circulation and produce sea level rise on a more dramatic scale than the increase due solely to thermal expansion, with increases of several metres;
  • melting of the permafrost. Methane gas mixed with water, in solidified form, exists in very large quantities in soils beneath the permafrost[41]. High levels of temperature change could release the methane, a powerful greenhouse gas, producing a "runaway" acceleration of warming, in addition to considerable destruction of property that is built on top of these soils;
  • acidification of the oceans, changing ocean life dramatically; and
  • major regional effects that are likely to have global consequences. These include: a lengthening of the dry season in Amazonia, destroying the balance of wet (long) and dry (short) seasons that maintain the Amazon rainforest as we know it today; desertification of large parts of Africa; and major changes to the Indian monsoon.

39.  How such catastrophic threats should influence decision-making depends on the scale of the effects, their probability of occurrence, and when they might occur. The scale of these events is clearly very large. The probability of their occurrence appears not to be known. Changes in the THC are not at all likely to occur, as we understand it, in the next 100 years, but might thereafter. Sir David King suggested to us that the important time benchmark is the point at which the Greenland ice sheet begins to melt. He told us that some of the GCMs suggest this could happen with +2oC, well below his own personal belief that, without serious action, the world would be heading for +3oC.

40.  How seriously these risks should be taken clearly depends on many factors, at the very least on the commitment of the current generation to future generations, the degree of credibility in forecasts and projections hundreds of years ahead, and the speed at which technology will change. We recognise that the ways in which these risks can be integrated into decision-making procedures are only now being advanced. If cataclysmic events which threaten the viability of existing societies are even remote possibilities, it is important that policy makers construct frameworks for analysing and debating probability and risks, since the threats associated with such "doomsday" scenarios are fundamental elements in driving the international discourse. We acknowledge that the evidence on all these risks is continually being monitored and it is clearly important to reappraise the risks at regular intervals. There is a balance to be struck.

Summary indicators of warming damage

41.  The detrimental impacts of climate change are likely to manifest many different types of effect. Moreover, the size of the global temperature change matters: low levels of temperature increase may be associated with some beneficial effects on agricultural yields and even ecosystem productivity. For this reason, the Committee sought firmer guidance on the likelihood of the different temperature projections made by IPCC, since IPCC does not currently attach any probabilities to the temperatures within the range they suggest. Of course, even if low temperature increases are benign, doing nothing about climate change may still not be an option: warming does not stop automatically once a given temperature increase has been experienced. But if the lower projections are more likely, there could be more time to devise better strategies for mitigating and adapting to climate change. We think it is a matter of some importance that IPCC moves towards clearer judgements on the probabilities of the projected temperature increases. We return to this issue in Chapter 4.

42.  Getting a concise picture of warming impacts is difficult, not least because the science of impact assessment is uncertain, probably more uncertain than the science of climate change itself. It is for this reason that the Committee sought evidence on summary indicators of climate change damage. Two presented themselves: (a) some indication of global and regional populations at risk now and in the future, and (b) monetary measures of damage which can be benchmarked on world and regional Gross Domestic Product (GDP). Dr Martin Parry has produced estimates of the former[42]. These are summarised in Box 7. (We defer consideration of the measures of economic damage to Chapter 6.) We acknowledge, however, that neither measure accounts adequately for large scale singular events.


Populations at risk from global warming
We note and agree with the view that, while listing the many potential impacts of climate change is important, the end result is a confusing mix of effects, some of which may be very important and others far less so. There is a need for a "reductionist" measure of impact that can be readily understood. In Chapter 6 we look at the available monetary measures of impact. Dr Martin Parry and his colleagues have suggested a measure of climate change impact based on the numbers of people at risk. The measures are located in time in the 2050s and the 2080s. The results are summarised in broad terms below. They vary according to the level of temperature increase which, in turn, corresponds to atmospheric concentrations. Here we show how the impacts vary with temperature increase. The study estimates those at risk from hunger, malaria, coastal flooding and water shortage. We illustrate the malaria and water impacts only, for ease of presentation. (Since the source shows charts only, some error may also be involved in inferring absolute magnitude.)
Temperature increase Additional people (millions) at risk from Malaria (M) and water shortage (W)
+1oC160-230 1250-2250- -
+2 oC200-260 2100-3000225-280 2750-3250
+3 oC- -270-340 3000-3500
The more alarming numbers relate to water shortages, the suggestion being that an additional three billion people would face water problems, or perhaps 40%of the world's population at the time. These are "business as usual" estimates, i.e. there is no climate mitigation and no adaptation. The latter is obviously very questionable, as we argue in this report. We also draw attention in the main body of this report to some serious questions about the estimates for malaria.

Source: M. Parry et al. op.cit.

Positive effects of warming

43.  The Committee noted that the scientific literature tended to focus on the negative impacts of climate change. This is understandable given that some of these effects are thought to be catastrophic, and because individuals tend to be more averse to a loss than they are in favour of an equivalent gain[43]. But a rigorous appraisal of climate change does need to include positive effects. The beneficial effects of CO2 "fertilisation" on crops was noted above. But there will also be gains in amenity across large areas. Several studies were presented to us which indicated the nature of some of these amenity gains: increased opportunities for tourism, for example, but also the fact that many people simply prefer to live in mild climates. In his evidence, Professor Mendelsohn of Yale University argued that regions have "optimal" climates: regions that are "too cold" gain from warming, while those that are "too hot" will lose[44]. Dr David Maddison of University College London and Ms Katrin Rehdanz of Hamburg University argue that impacts at the level of the household will be the most profound, yet little is known about how households perceive climate change. Like Professor Mendelsohn, they invoke the notion of an optimal climate but at the household level, with households moving towards or away from that optimum as climate change occurs[45]. The research suggests that people will accept lower wages to work in areas of "better" climate typified by lower rainfall, lower mid-summer temperatures (in countries such as Italy) and lower cloud cover. Similarly, house prices tend to be higher in regions with preferred climates. Household expenditures also change with climate. Finally, individuals' own ratings of their "happiness" have been shown to vary directly with income and climate[46]. Overall, there appear to be distinct amenity gains for the countries of Northern Europe, with generally neutral effects in Southern Europe. Once the focus moves to Asia there are serious household losses, confirming the general picture that it is the poorer parts of the world that suffer most from warming. We are clear that fuller consideration needs to be given to the literature on the positive effects of warming.

44.  We draw attention to this literature for several reasons. First, we heard little about the positive effects of warming from the scientific witnesses. Second, we observe that this category of benefit is mentioned only in passing in the IPCC Working Group II assessment of impacts, where it is noted that economic impact studies "may have overlooked" positive impacts[47]. We conclude that there are weaknesses in the way the scientific community, and the IPCC in particular, treats the impacts of climate change. We call for a more balanced approach and look to the Government to take an active role in securing that balance of research and appraisal.

Adaptation versus mitigation

45.  The IPCC 2001 Reports make explicit reference to adaptation to climate change. Adaptation can take various forms. The IPCC reports distinguish "autonomous" and "planned" adaptation. First, market forces and natural behaviour will lead to some "natural" adaptation to climate change, e.g. by changing crop strains so that crops are more tolerant of dry conditions. Second, conscious and deliberate policies and investments will also be needed to encourage further adaptation. We understand the IPCC cautions on adaptation: it is easy to see that reliance on adaptation alone would be risky since it may not be possible to adapt to major risks. But it also seems to us that nearly all of the public debate on global warming is about mitigation—reducing emissions—rather than about adapting to climate change and, assisting the most vulnerable societies in the world to adapt to the risk they may face.

46.  In evidence to us, Dr Indur Goklany of the US Department of the Interior argued that mitigation can do little to reduce many of the impacts from warming, whereas investment in adaptation now would both reduce the baseline risks that will occur even without any warming, and the warming impacts as well. His estimates suggest that warming could add substantially to the population at risk, notably from hunger, water shortage and coastal flooding. Those at risk from additional water shortage could, however, be offset by those who benefit because of warming-induced water gains[48].

47.  The issue is clearly one of balance. Most adaptation expenditures would be local, while mitigation requires action on a global scale. Few would suggest doing nothing by way of mitigation, and few would suggest no adaptation expenditures at all. But the policy literature seems to us to be overly focussed on mitigation. We therefore urge the Government to ensure that greater efforts are made to understand the relative costs and benefits of adaptation compared to those of mitigation.

23   Detailed assessments of the likely impacts can be found in Inter Governmental Panel on Climate Change, Climate Change 2001: Impacts, Adaptation, and Vulnerability. Cambridge: Cambridge University Press, 2001. Back

24   J. Houghton et al. Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge: Cambridge University Press. 2001. The benchmark for these temperature increases is not always clear, but is usually the "pre-industrial" period, i.e. around 1750. Thus, a projected rise of, say, 2.60C would imply warming of about 20C compared to the present day. Some of the scientific opinion at the conference convened in Exeter early in 2005 considered that the IPCC 2001 Assessment understates likely temperature change.  Back

25   Evidence of Professor Colin Robinson (Vol II, pp 1-14) Back

26   R. Watson et al. op.cit. p.182 Back

27   In many cases, reducing greenhouse gas emissions also reduces other pollutants, such as particulate matter. For example, any reduced road transport would have this effect since particulates and CO2 are emitted from vehicles. The benefits of reducing particulates would, however, be fairly immediate. This joint effect is known as "ancillary benefits" in the literature. However, if the pollutant reduced is sulphur, then reduced sulphur emissions may actually increase warming-see the section on "negative forcing". Back

28   R. Watson et al. op.cit. p.256 Back

29   P. Stott, D. Stone and M. Allen, Human contribution to the European heatwave of 2003. Nature, 432,
2 December 2004, 610-613. 

30   Evidence of P. Reiter: The IPCC and Technical Information. Example: Impacts on Human Health (Vol II pp 284-288) Back

31   See R. Watson et al. op.cit. p.223. In his evidence to us (Vol II, pp 96-106), Sir David King was clear that current evidence suggests glaciers are in retreat for the first time in the current warming period. Back

32   The Guardian, 2 April 2005, reporting evidence from Dove Marine Laboratory, Newcastle University. Back

33   R. Watson et al. op.cit. p.231 Back

34   M. Parry et al. Viewpoint. Millions at risk: defining critical climate change threats and targets. Global Environmental Change. 11, 2001. 181-3 Back

35   Sir John Houghton, Global Warming: The Complete Briefing. Third Edition. 2005. Cambridge: Cambridge University Press. P179. Back

36   R. Watson et al. op.cit. p256. Back

37   M. Khandekar . Are climate model projections reliable enough for climate policy? Energy and Environment, 15 March 2004 Back

38   For an overview of these features see J. Rial et al. Nonlinearities, feedbacks and critical thresholds within the Earth's climate system. Climatic Change. 65. 2004. 11-38. Back

39   See M. Maslin, Global Warming: a Very Short Introduction. Oxford: Oxford University Press. 2004. Back

40   In his evidence to us (Vol II, pp 96-106), Sir David King thought this shut-down process might take only a decade and that the temperature fall might be -200C.  Back

41   These gas hydrates also exist in vast reserves below the world's oceans. There is a scientific debate about the extent to which high warming levels could also begin to release these hydrates, something that does appear to have happened many millions of years ago.  Back

42   M. Parry et al. op.cit. Back

43   This phenomenon of "loss aversion" is well documented in the psychological and economics literature. Back

44   Evidence from R. Mendelsohn (Vol II, pp 266-269). See also R. Mendelsohn and M. Schlesinger, Climate response functions. Ambio, 28, 1999, 362-6 Back

45   Evidence from D. Maddison (Vol II, pp 256-262).  Back

46   K. Rehdanz and D. Maddison. Climate change and happiness. Ecological Economics. 52. 2005. 111-125. Back

47   There is no chapter or sub-section of the IPCC Working Group II 2001 Report dealing with positive impacts. Chapter 19 lists positive effects in the agricultural sector and possible reductions in winter mortality but makes no mention of amenity effects.  Back

48   Evidence from I. Goklany (Vol II, pp 217-225). Back

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