Book Review
Below you will find Part 7 of the review of Climate Change: Turning up the Heat by A. Barrie Pittock. These are some snippets: “Studies of past episodes of rapid climate change such as the Younger Dryas event deserve special attention. There is much evidence to suggest that past climatic fluctuations have not been smooth, but rather have often involved rapid changes from one circulation regime to another.” “Human populations at the time of the last deglaciation were relatively small, and people could migrate more or less freely to more suitable regions. That would be very difficult now, with more than six billion people, national borders and immigration restrictions.” “In a paper entitled Abrupt Climate Change: Should We Be Worried? Robert B. Gagosian, President and Director of the illustrious Woods Hole Oceanographic Institute in Massachusetts, USA, states that two scenarios are useful to contemplate.” “Schwart and Randall suggest that such an abrupt climate change scenario would led to food shortages, decreased water supplies in key regions, and disruption to energy supplies, with likely downstream risks for the US national security, including border management, global conflict and economic malaise.” “The message for now is that the projected climate changes are large enough and rapid enough to cause some pretty big problems which we need to take very seriously indeed.”
CLIMATE CHANGE
TURNING UP THE HEAT
BARRIE PITTOCK
EARTHSCA/CSIRO PUBLISHING 2005
PART VII
Chapter 6: Impacts: Why Be Concerned? (Cont)
Aggregate impacts
• A number of studies have attempted to estimate the overall cost of climate change impacts, but these are beset by problems that have only partly been overcome.
• Agricultural and coastal impacts have been fairly well quantified, as has health to some extent (although it is controversial). Estimates of the cost of the loss of species and ecosystems are very uncertain. Different studies get different results.
• Overall, the IPCC 2001 report states that ‘our confidence in numerical results from aggregate studies remains low’, and they ‘may underestimate the true cost of climate change’.
• Results to date suggest that the majority of people may be negatively affected at average global warmings of 1 to 2°C, although the net aggregate monetary impact may be slightly positive due to the dominance of rich countries in monetary terms.
• At higher levels of warming, estimated monetary impacts generally become negative, and studies allowing for disastrous possibilities can reach high negative outcomes, such as about 10% loss of world GDP for 6°C warming.
Waking the sleeping giants
• Gradual but ongoing climatic changes set in train in the next several decades may make some of these large-scale discontinuities inevitable in the following centuries as thresholds for discontinuities are reached, with possibly huge impacts on natural and human systems.
• The risk of such events is at present poorly quantified, both as to their likelihood in this or later centuries and the magnitude of their impacts on natural and human systems.
• Modelling and paleo-analysis must extend not only to the basic physical events but also to their global and regional impacts including changes in rainfall, aridity, flooding, and impacts on ecosystems and cropping potential.
• Studies of past episodes of rapid climate change such as the Younger Dryas event deserve special attention. There is much evidence to suggest that past climatic fluctuations have not been smooth, but rather have often involved rapid changes from one circulation regime to another.
• Some scientists who are familiar with these past large variations in climate, react by saying that if such change happened before due to natural causes and life survived, what is there to worry about now?
• Human populations at the time of the last deglaciation were relatively small, and people could migrate more or less freely to more suitable regions. That would be very difficult now, with more than six billion people, national borders and immigration restrictions.
Effects of a breakdown in the ocean circulation
• Slow-down or cessation of the convective overturning in the North Atlantic (see Chapter 5) and around Antarctica would cause regional cooling, as well as connected changes elsewhere in the world. This overturning powers what has been described as the oceanic ‘conveyor belt’, which redistributes heat around the globe.
• North of 24°N the Gulf Stream presently conveys roughly a million gigawatts of energy northwards from the tropics, warming much of Europe by 5-10°C.
• If complete cessation of overturning were to happen this century, which is unlikely but not completely impossible, it might lead to colder temperatures in the North Atlantic region than at present, with greater warming elsewhere.
• A return to regionally cooler conditions in Europe and North America would have disastrous impacts on food production, health, economics and ecosystems. This could be worse than at the time of the Little Ice Age because of far larger human populations, and the greater inter-connectedness of global economies.
• Modelling suggests that any such shutdown of the ocean circulation may be long-lasting relative to human lifetimes.
• At the time of the younger Dryas, the Earth’s orbital changes favoured a ‘quick’ recovery (which occurred after 1200 years), whereas there is no such force for recovery operating this time.
• We are thus not just talking about a short-term disaster from which the world might recover, but one that might last for millennia.
• In a paper entitled Abrupt Climate Change: Should We Be Worried? Robert B. Gagosian, President and Director of the illustrious Woods Hole Oceanographic Institute in Massachusetts, USA, states that two scenarios are useful to contemplate:
Scenario 1: Conveyor slows down within next two decades. This could quickly and markedly cool the North Atlantic region, causing disruptions in global economic activity. These disruptions may be exacerbated because the climate changes occur in a direction opposite to what is commonly expected, and they occur at a pace that makes adaptation difficult.
Scenario 2: Conveyor slows down a century from now. In this case, cooling in the North Atlantic region may partially or totally offset the major effects of global warming in this region. Thus, the climate of the North Atlantic region may rapidly return to one that more resembles today’s – even as other parts of the world, particularly less-developed regions, experience the unmitigated brunt of global warming. If the Conveyor subsequently turns up again, the ‘deferred’ warming may be delivered in a decade.
• Clearly the consequences of either of Gagosian’s scenarios are serious, although the first is the more alarming because of its rapid onset.
• The report to the US Pentagon by Peter Schwart and Doug Randall, widely reported in the media in 2004, seems to have taken the first scenario as its starting point, ‘as an alternative to the scenarios of gradual climate warming that are so common’.
• While the resulting geo-political scenario has been widely criticised as sensational and even irresponsible, it seems to me that as a worst-case scenario it fulfils a purpose for the Pentagon, whose business is to plan for unlikely but not impossible scenarios.
• Schwart and Randall suggest that such an abrupt climate change scenario would led to food shortages, decreased water supplies in key regions, and disruption to energy supplies, with likely downstream risks for the US national security, including border management, global conflict and economic malaise.
• Given a major theme of this book is risk management in the face of possible climate change, such possibilities deserve some careful, albeit critical, attention.
Rapid sea-level rise from melting ice sheets
• The ideas discussed in Chapter 5 regarding possible rapid melting of the Greenland and West Antarctic ice sheets suggest an outside chance that sea-level rise may be more rapid than suggested by the IPCC 2001 range of 9 to 88 centimetres by 2100.
• The growing evidence that surface meltwater penetration through crevices in outlet glaciers leads to lubrication and acceleration of outflow, suggests that more rapid outflow melting is possible.
• While the time scale for complete disintegration of Greenland and the West Antarctic ice sheets under these faster scenarios is still uncertain, the above ideas suggest that sea-level rises of the order of a metre in the 21st century, and several metres in the following centuries are possible.
• Martin Parry of the Jackson Environmental Institute, University of East Anglia, and others estimate that for the more modest sea-level rises expected by 2100 under the IPCC 2001 report scenarios, 50 to 100 million people may be subject to coastal flooding.
• For the faster sea-level rise scenarios, the number affected by 2100 could be twice as large, and of course ongoing sea-level rise in the following century would at least double it again.
• The internal disruption in many populous developing countries such as China, Indonesia, Bangladesh, Egypt and Nigeria would be enormous, with the likelihood of internal conflicts, poverty and disease.
• Large regions that are low-lying and in some cases subsiding will be threatened, for example eastern parts of England, the Low Countries of Western Europe, Venice and other parts of the Adriatic coast, Florida, parts of the Gulf Coast, the Chesapeake Bay region and much of the Atlantic coast in the US, and parts of coastal cities in Australia.
• At what level of global warming these rapid melting and ice sheet disintegration processes will get underway is not clear, but once started they are likely top be unstoppable, leaving the world with a sea-level rise of up to 12 metres lasting for millennia. This would be quite a legacy for our descendents.
Runaway carbon dynamics
• As discussed in Chapter 5, runaway carbon dynamics (rapid increases in carbon dioxide concentrations in the atmosphere due to positive feedbacks) would lead to an acceleration in global warming.
Stabilisation of greenhouse gas concentrations
• All the ‘five reasons for concern’ about global warming increase in severity with the amount of warming.
• The big question for climate change policy is at what degree of warming does this become unacceptable, and therefore what concentration of greenhouse gases in the atmosphere should be considered the upper limit? This will determine what emissions reduction strategies must be put into place.
• A study published in 2002 by a consortium of UK scientists concluded ‘While this study shows that mitigation avoids many impacts, particularly in the longer-term (beyond the 2080s), stabilisation at 550 ppm appears to be necessary to avoid or significantly reduce most of the projected impacts in the unmitigated case.’
Growing reasons for concern
• Despite acknowledged uncertainties, it is clear from this review of the potential impacts of climate change that there are substantial reasons for concern, which increase with global warming.
• There is growing concern that the risk of substantial and potentially catastrophic changes in the climate system, which may be unstoppable once they commence, will rise greatly for larger warmings.
• Warmings of only about 2 to 3°C may set such largely irreversible changes to the climate system in motion, and this may not become apparent until it is too late to avoid the consequences.
• We may be able to adapt to small changes in climate, but in some cases this may be costly or have unwelcome side effects.
• We examine the capacity to adapt in Chapter 7, and the costs and benefits of reducing the rate and magnitude of climate change in Chapter 8.
• The message for now is that the projected climate changes are large enough and rapid enough to cause some pretty big problems which we need to take very seriously indeed.
Chapter 7: Adaptation: Living With Climate Change