2010 Diary week 44
Climate Change
Book Review
Below you will find Part 3 of the review of Climate Change: Turning up the Heat by A. Barrie Pittock. These are some snippets from the conclusions from the past record in Chapter 2: Learning From the Past: “Now we are forcing changes on the climate system due to large greenhouse gas emissions on a timescale of decades to a century. These are equivalent to changes which occurred previously over thousands of years. Therefore we might well expect similar impacts on natural systems to those which occurred in the past over thousands of years, but telescoped into a much faster time frame, leading to rapid and possibly catastrophic changes.” “At the end of the last glaciation, average global warming occurred at a rate of about 1°C or less per thousand years, although there were short periods during which warming was much faster. The last of these was at the end of the so-called ‘Younger Dryas’ reversal, about 11,500 years ago. Since then, and certainly since the dawn of civilisation, rates of warming have never exceeded about 0.5°C per century (0.05°C per decade) for periods of more than a few decades.” “Pollen changes show that in response to warming after the end of the last glaciation around 15,000 to 10,000 years ago, forests migrated at rates of, at most, tens of metres per century. Over the next century we can expect climate to change so rapidly that forests would need to migrate at rates of hundreds of kilometers per century to remain in their optimal climatic zones. This is clearly unlikely. What is far more likely is that forests that no longer are located in their correct climatic zones will die from heat stress, drought, disease and fire. Similarly, many crops will no longer yield well in their present locations, and will have to be re-located hundreds of kilometers away to provide equivalent climate conditions. But often the crops will be on different soils, on land owned by other people, and even in different countries. Dislocations to society will therefore be large, far larger than was the case for the small numbers of hunters and gatherers who existed tens of thousands of years ago.”
CLIMATE CHANGE
TURNING UP THE HEAT
A. BARRIE PITTOCK
EARTHSCA/CSIRO PUBLISHING 2005
PART III
Chapter 2: Learning From the Past (Continued)
Conclusions from the past record
Past climatic changes are relevant because they demonstrate what is possible in the natural climate system, when forces occur such as volcanic eruptions or variations in the Earth’s orbit around the Sun. Orbital variations act slowly, on timescales of thousands of years, while volcanic eruptions act in a matter of days or weeks. Now we are forcing changes on the climate system due to large greenhouse gas emissions on a timescale of decades to a century. These are equivalent to changes which occurred previously over thousands of years. Therefore we might well expect similar impacts on natural systems to those which occurred in the past over thousands of years, but telescoped into a much faster time frame, leading to rapid and possibly catastrophic changes.
Climate change has occurred naturally in the past due to internal fluctuations in the climate system consisting of the atmosphere (air, water vapour, constituent gases, clouds and particles), the hydrosphere (oceans, lakes, rivers and groundwater), and the cryosphere (continental ice sheets, mountain glaciers, sea ice and surface snow cover). External changes such as volcanic eruptions, variations in the Sun’s output and the Earth’s orbital variations and changes in the solid Earth (continental drift, mountain building, erosion and siltation) have also driven changes in climate.
At the end of the last glaciation, average global warming occurred at a rate of about 1°C or less per thousand years, although there were short periods during which warming was much faster. The last of these was at the end of the so-called ‘Younger Dryas’ reversal, about 11,500 years ago. Since then, and certainly since the dawn of civilisation, rates of warming have never exceeded about 0.5°C per century (0.05°C per decade) for periods of more than a few decades.
Our interest in the past is not only in what sorts of climate changes can happen, but also in what sort of impacts they had on natural systems such as plants, animals and landscapes. However, in interpreting paleo-climate induced changes, we must think carefully about rates of change, rates of adaptation, and changed circumstances as regards human populations and societies.
Pollen changes show that in response to warming after the end of the last glaciation around 15,000 to 10,000 years ago, forests migrated at rates of, at most, tens of metres per century. Over the next century we can expect climate to change so rapidly that forests would need to migrate at rates of hundreds of kilometers per century to remain in their optimal climatic zones. This is clearly unlikely. What is far more likely is that forests that no longer are located in their correct climatic zones will die from heat stress, drought, disease and fire. Similarly, many crops will no longer yield well in their present locations, and will have to be re-located hundreds of kilometers away to provide equivalent climate conditions. But often the crops will be on different soils, on land owned by other people, and even in different countries. Dislocations to society will therefore be large, far larger than was the case for the small numbers of hunters and gatherers who existed tens of thousands of years ago.
Paleo-climatic analogies to our present predicament confuse many people. They argue that if large changes occurred before, and humans and other species survived, then life, and even humans, can survive today, so there is not much to be concerned about. This fails to consider the different time scales, the very different place of humanity in the ecosystems then compared to now, and the many restrictions that exist today which limit our ability to adapt to such large and rapid changes. These include national boundaries, mass reliance on relatively few crops for food, and other environmental stresses caused by some six billion people. Human beings and their societies may well be threatened, not with extinction, but with severe disruption, and possible catastrophic economic and social effects. This is especially so if we happen to cross a threshold which leads to rapid climate change of a magnitude and speed unparalleled since the Younger Dryas event, and one which cannot be quickly reversed.
The upshot of all these studies is that climate change of the magnitude we are expecting in the next 100 years and beyond has happened before, although usually at a much slower rate and from a cooler starting point. Projected changes in climate by 2100 are comparable to those from the last glaciation (20,000 years ago) to the present, which led to large sea rises in sea level, massive changes in plant and animal numbers and distribution, and changes in the land-sea borders. Some places changed from tundra to temperate forests, and others from forests to desert. Today we face similar change, but much faster, and from a base climate which is already as warm as any experienced since human societies began.
Chapter 3: Projecting the Future
• There is a whole range of aspects of climate change, with some much more certain than others. There are uncertainties and possibilities we are aware of, and may even be able to quantify in terms of risk. But, there is also a possibility that there are things about climate that we simply do not know, and which may totally surprise us.
• The Intergovernmental Panel on Climate Change (IPCC) was formed to provide foresight in relation to the possible human impacts on climate, with a view to helping governments formulate wiser policy options and decisions in relation to climate change.
• Prudent people use foresight to decide or plan their actions so as to improve their future prospects. Foresight requires some estimate of future conditions.
• The purpose, from a policy perspective, is not to predict which of the possible futures will occur, but rather to inform us so that we might choose which one we would prefer and attempt to bring to reality.
Predictions, scenarios and projections
• A prediction is a statement that something will happen in the future, based on known conditions at the time the prediction is made, and assumptions as to the physical or other processes that will lead to change. Predictions are best expressed with probabilities attached.
• A scenario is a plausible description of some future state, with no statement of probability. It is used to enable people to explore the question ‘What if such and such were to happen?’ They are alternative pictures of how the future might develop and are used to assess consequences, and thus to provide a basis that might influence future developments, or enable businesses or governments to cope with the future situation if and when it occurs.
• Predictions are sets of future conditions, or consequences, based on explicit assumptions, such as scenarios. Even for a given scenario or set of assumptions, projections introduce further uncertainties due to the use of inexact rules or ‘models’ connecting the scenario conditions to the projected outcomes.
• A key issue in projecting the future on the basis of a scenario is the plausibility of the scenario. Scenario plausibility has several elements: that the scenario must be logically, physically, biologically, and historically possible.
• Plausible scenarios are useful for asking ‘What if …’ questions, and thus for helping to make policy choices that may influence which of the ‘what ifs’ actually comes to pass.
• In the climate change context they are useful for influencing policy regarding the need to reduce greenhouse gas emissions.
• Climate change projections based on high-emission scenarios for greenhouse gases may, hopefully, be seen in retrospect as self-denying prophecies: if high emissions demonstrably lead to disastrous impacts, they may well be avoided through policy settings aimed at lowering emissions.
The emissions scenarios used by the IPCC
IN order to provide policy-relevant advice on the consequences of human-induced climate change in the 21st century, the IPCC commissioned a range of scenarios of greenhouse gas and sulphate aerosol emissions up to the year 2100.These emission scenarios were developed by a panel of authors, with wide consultation, and an open process of review and comment by experts and governments, followed by subsequent revisions. The scenarios were reported in the Special Report on Emissions Scenarios (SRES), published in 2000. They were intended to feed into projections of climate change in the Third Assessment Report in 2001, and to enable a discussion of the potential impacts, adaptations and vulnerability of sectors, regions and countries.
Future emissions are the product of complex interacting systems driven by population change, socio-economic development, and technological change. All of which are highly uncertain, especially when extended as far as the year 2100.
The original 40 SRES scenarios were based on four different ‘storylines’ of internally consistent developments across different driving forces (see Box 3), and multiple modeling approaches. This led to a reduced total of 35 scenarios containing data on all gases required to force climate models. Resulting accumulated emissions by 2100, expressed in units of thousands of millions of tones of carbon equivalent (GtC) range from a low of 770 GtC to approximately2540 GtC. This range compares with previous IPCC projections from 1992 and 1995 (based on what is known as the IS92 scenarios), which range from 770 to 2140 GtC, so the upper end of the projected range is now greater than before. Accumulated emissions are an important indicator of eventual climatic effects because the effective lifetime of carbon dioxide in the atmosphere is so long that this figure largely determines eventual carbon dioxide concentrations and the resulting global warming.
Corresponding projected carbon dioxide concentrations for the illustrative scenarios in the year range from 540 to 970 ppm, that is, roughly 2 to 3.5 times the pre-industrial levels. As the scenarios only went to 2100 and concentrations had not stabilized by then, stabilized concentrations are likely to be well in excess of these numbers….
Box 3: The SRES emissions scenarios
A1. The A1 storyline and group of related scenarios describe a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income. The A1 group scenario is split into three groups that describe alternative directions of technological change in the energy system. The three A1 groups are distinguished by their technological emphasis: fossil intensive (A1F1), non-fossil energy sources (A1T), or a balance across all sources (A1B) (where balance is defined as not relying too heavily on one particular energy source, on the assumption that similar improvement rates apply to all energy supply and the end-use technologies).
A2. The A2 storyline and group of related scenarios describe a very heterogeneous world. The underlying theme is self-reliance and preservation of local identities. Fertility patterns across regions converge very slowly, which results in continuously increasing population. Economic development is primarily oriented to particular regions and per capita economic growth and technological change more fragmented and slower that other storylines.
B1. The B1 storyline and group of related scenarios describe a convergent world with the same global population that peaks in mid-century and declines thereafter, as in the A1 storyline but with rapid change in economic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource-efficient technologies. The emphasis is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives.
B2. The B2 storyline and group of related scenarios describe a world in which the emphasis is on local solutions to economic, social and environmental sustainability. It is a world with continuously increasing global population, at a rate lower than A2, intermediate levels of economic development, and less rapid and more diverse technological change than in the A1 and B1 storylines. While the scenario is also oriented toward environmental protection and social equity, it focuses on local and regional levels.
• The SRES scenarios are not predictions, but merely a plausible range of emissions, used to bound discussion of climate change impacts. Moreover, the climate models used to produce the projections of climate change that underlie the IPCC assessment are developed and validated separately from the emissions scenarios.
• Any re-assessment of the range of the SRES scenarios may affect the upper and/or lower bounds of the projected climate change over the next 100 years, but are most unlikely to alter the main conclusions that significant climate change is likely to occur, with significant impacts.
• Due to their late publication, the SRES scenarios were not applied in any detailed studies of impacts globally or regionally in time for inclusion in the IPCC report in 2001.
Projections of socio-economic futures
• An important consideration in estimating potential impacts of climate change is the future exposure of populations, human systems and ecosystems to climatically induced stresses, and the capacity of those so exposed to adapt to the stresses.
• The global SRES socio-economic scenarios have been reduced to a national scale by Stuart Gaffin for the United States and Wolfgang Lutz for Austria. Additionally, the UK ‘Fast Track’ project went on to produce finer resolution data at a sub-national scale in order to estimate and map global impacts of climate change on a number of industrial and societal sectors.
• In the case of coastal exposure to sea-level rise and storm surges, existing trends make it reasonable to assume greater growth rates in population and investment in coastal areas than in national averages. This affects not only the exposure, but also the rate of localized sea-level rise, since greater coastal populations tend to withdraw more ground water, leading to greater local subsidence.
• The United Nations Environment Programme has published a series of Global Environment Outlooks, taking four contrasting socio-economic scenarios: Markets first; Policy first; Security first; and Sustainability first.
• The effect in relation to greenhouse gas emissions is that the first and third scenarios, lacking effective environmental policies, lead to significant increases in greenhouse gases over the next 30 years.
• An ongoing Australian study by the Resources Futures program of CSIRO Sustainable Ecosystems has an integrated approach where interactions between the environment and population are simulated.
• Among the conclusions of their 2002 report was a need to recognize that: Australia’s social, economic and physical systems are linked over very long time scales; Short-term decisions have long-term consequences, and; There is inbuilt inertia in our institutional systems, requiring time for change to take effect.
• These conclusions apply in many places besides Australia, and are themes reflected in the IPCC Third Assessment Report.
• They suggest that any realistic assessment of the overall impacts of climate change on any local or national community, and of its capacity to cope with or adapt to climate change, will need to integrate studies of socio-economic futures with climate change studies. They are all part of an interconnected future.