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Frequently Asked Questions about the Science of Climate Change – 2008 Update

E. Impacts of Climate Change

E.1 Global temperatures have warmed by less than 0.8°C in the last 100 years. Such a change is much less than we get from one year to the next. What’s the big deal?

Response: Natural variability in climate can cause large differences in conditions from one year to the next and one region to the next. However, the observed 0.74°C warming between 1906 and 2005 is a long-term trend in the global average of all these variations in space and time. Experts indicate the average Northern Hemispheric temperature during the past 50 years has likely been higher than at any other time during at least the past 1300 years. By comparison, it took only about 4 to 7°C of warming to cause the Earth to slowly change from the last glacial period some 15,000 years ago, when large volumes of ice covered what is now Canada, to the interglacial conditions that exist today.

Explanation: Natural variability in climate can cause one region of the world to warm several degrees relative to the preceding year, while another cools a similar amount. However, when such variability is averaged globally, much of this spatial variability is removed from the measurements. Likewise, averaging weather conditions over time also reduces the season-to-season and year-to-year variability of climate. The reported trends in temperature represent a long-term and global change. Experts indicate that the average Northern Hemispheric temperature over the past 50 years is now very likely higher than any similar period of the past 500 years, and likely without precedence in at least the past 1300 years (see Figure C.4). By comparison, the change in temperature between the last glacial maximum, which ended about 15,000 years ago, and today was about 4 to 7°C. That temperature change caused a transformation of the Canadian landscape from a large ice sheet several kilometres thick to today's mosaic of productive ecosystems.

Reference: Jansen et al., 2007.

E.2 What are the potential consequences of a few degrees of warming?

Response: Even a modest warming of global temperatures would significantly change global wind and precipitation patterns, and hence alter local weather behaviour around the world from that which we are used to. Some of these changes would be effectively irreversible. Since both ecosystems and human societies have adapted to the climates of today and the recent past, they will be ill-prepared to deal with the changes if these are too rapid to allow ecosystems and societies to adapt. For many developing countries, this may have very harmful effects on basic human needs for a place to live, food to eat and clean water to drink and on their ability to live healthy lives. For all countries, increased frequency of severe weather events will enhance the risk of weather-related disasters.

Explanation: Ecosystems evolve slowly in response to changes in the average conditions and variability of past weather. Many species, like most trees, respond very slowly, while others with shorter lifespans can respond and evolve more quickly. Since individual species will respond at different rates to changing environmental conditions, ecosystem function is likely to be disturbed since the relationships among species within ecosystems may be disrupted. Some species have unique climate niches that may disappear, leaving them vulnerable to extinction. Likewise, the socio-economic infrastructure and culture of human societies are closely adapted to the climate within which these evolved, and rapid climate change would make it difficult to adapt quickly. Experts also predict longer and more frequent extreme weather events such as heavy rains, droughts, floods, and severe storms that would significantly impact humans and natural ecosystems and increase the risk of weather-related economic disasters. For example, longer and more frequent heat waves will likely increase heatstress-related deaths. More frequent and severe droughts are likely to increase the risk of famine, particularly in semi-arid and arid regions of the tropics and subtropics. Global warming is also expected to increase the potential transmission of infectious diseases such as malaria, dengue, and yellow fever through the expansion of the range in which disease-carrying organisms can survive.

The IPCC synthesized knowledge about the vulnerability of societies and ecosystems to the impacts of climate change into five 'reasons for concern' (see Figure E.2). Although there is uncertainty about temperature change thresholds at which different types of impacts will occur, there is, nonetheless, a lot of confidence in the general relationship of impacts becoming increasingly negative with increasing temperatures. Recent scientific evidence has strengthened the reasons for concern about climate change and provided support for some negative impacts occurring at lower thresholds of temperature change than previously thought.

References: IPCC 2007d.

Figure E.2. Modest warming could provide some benefits in some regions, but as global temperature increases, impacts are expected to become increasingly negative at all scales. Refer to caption beneath image for description.

Figure E.2 Some negative impacts have already occurred in some regions in response to warming to date (e.g. increases in human mortality, loss of glaciers, increases in the frequency and/or intensity of extreme events). Modest warming could provide some benefits in some regions, but as global temperature increases, impacts are expected to become increasingly negative at all scales. (IPCC 2001, WGII Figure SPM-2, RH panel).

E.3 How will rising global sea levels affect people?

Response: Experts project that the average global sea level will rise 18 to 59cm by 2100 (see D.10). Because 50 to 70% of the world's population lives in low-lying coastal areas, millions of people are already vulnerable to coastal flooding due to storm surges. A sea-level rise within the above range would affect many millions more. Protective measures, such as dike building, can help to reduce the risks in some but not all areas, but would be costly

Explanation: Today, many millions of people are already at risk from flooding in low-lying coastal areas, where 50 to 70% of the world's population lives. The combined effects of a significant rise in sea level and population growth in coastal areas would substantially increase this number. Adaptation measures, such as the installation or enhancement of protective sea walls and dikes, could help reduce the impacts on people. However, such measures would be costly. Estimates for protection of U.S. coastlines, for example, range from US$20 billion to US$150 billion.

Furthermore, even with the adoption of such protective measures, a modest sea-level rise of 40cm would still leave an estimated 80 million additional people vulnerable to coastal flooding during storm surges.

While Canadian coastlines are relatively rugged and hence less vulnerable to the impacts of sea-level rise than those of many other countries, some of the 240 000km of ocean coastline are low lying and/or soft and vulnerable to erosion. Highly sensitive regions of the Canadian coastline include much of the Maritime Provinces, a large part of the Beaufort Sea Coast and the Fraser Delta region of British Columbia.

References: Nichols et al., 2007; Natural Resources Canada, 2004.

E.4 The frequency and intensity of disasters related to extreme weather events appear to be increasing. Is this linked to climate change?

Response: It is very difficult to establish trends in weather-related disasters or to attribute recent disasters to specific causes. That is, the perceived increase in disasters in some parts of the world in recent years may be inaccurate or may be entirely natural. There is no clear evidence to suggest that recent disasters are already a consequence of global warming. However, studies suggest that the frequency and severity of many types of extreme weather events will change as the climate warms. Therefore, many of the current weather-related disasters may be viewed as examples of what can be expected more often in the future as the global climate continues to warm.

Explanation: A weather-related disaster can occur when society and/or ecosystems are unable to effectively cope with an extreme weather event. That is, both the extreme nature of the weather event and the sensitivity of ecosystems or society to that event are factors. The dramatic rise in damages in recent years due to such disasters may therefore be at least partly attributed to demographic factors, such as increased human population in vulnerable regions and increased wealth.

On the other hand, there are indications that there have also been increases in various types of extreme weather events, at least in some regions of the world. Yet, since these events, by definition, occur infrequently and irregularly, they are difficult to link to global causes. They may simply be the result of natural variations in climate. Experts agree it is still too early to be confident about a direct link between climate change and these extreme events. Furthermore, few events are without historical precedence. Most historical records of such events prior to the past few decades are also not very accurate.

However, in many respects, the trends towards more intense and unusual extremes for some types of weather and climate events in some regions in recent years are broadly similar to those projected by climate models and related studies. Therefore, while there is no hard proof to link recent disaster trends to climate change, many of these events can be considered as examples of what could happen more frequently in the future.

Reference: Hegerl et al., 2007.

E.5 Why would global warming lead to more frequent and extreme weather events?

Response: Higher temperatures lead to higher rates of evaporation and precipitation, more frequent heat waves, less frequent cold extremes, and generally more energy for storms. Model results can provide useful clues as to the direction and significance of such changes. However, the processes involved are complex and the changes in extremes are therefore still difficult to predict accurately.

Explanation: Most extreme events are complex responses to a number of factors, and hence their responses to warmer climates are difficult to assess. However, as the Earth warms, experts expect more frequent high temperature extremes and less frequent cold extremes, and that more precipitation will fall over shorter periods of time. This will likely increase the frequency of very heavy and extreme precipitation events, and of local flooding. Tornadoes and the intensity of thunderstorms and related extreme wind and hail events will also increase in some areas. It is also expected that many regions of the world will experience more frequent, prolonged, or more intense droughts due to more rapid evaporation from plants, soils, lakes, and reservoirs. Increasing atmospheric moisture could also increase the intensity and frequency of blizzards and snow storms in some colder locations. In more temperate latitudes, their frequency will likely decrease, but their intensity may rise. In effect, climate change will 'load the dice' with respect to the probability of occurrence of such extreme weather events. There is as yet little consensus on how global warming will affect other extreme weather events such as tropical storms, cyclones and typhoons, although the potential maximum intensity of such storms is expected to increase.

Reference: Meehl et al., 2007.

E.6 Will global warming take place gradually or rapidly?

Response: Most climate model studies suggest that the response of the climate to human influences will be gradual. However, there is evidence that the Earth's climate has undergone abrupt shifts in the past, primarily during periods of glacial climates or during major transitions of climate from one state to another. Similar abrupt changes, although unlikely within the next century, cannot be ruled out (see D.11).

Explanation: There is clear evidence from paleoclimate data that the climate system underwent large-scale abrupt changes in climate during the past glacial maximum and the deglaciation process between 10,000 and 15,000 years ago. These appear to occur when the climate system is in an unstable mode, and to have had major impacts on regional climates. Temperatures over Greenland, for example, have changed by as much as 10°C within a few decades. Such large, abrupt changes have not occurred during the past 10,000 years of stable Holocene climate. Some scientists, however, have expressed concern that a rapid, human-induced climate change could return the climate to an unstable condition and once again trigger such abrupt events. While such events are unlikely within at least the next century, that possibility cannot be ruled out. Abrupt events appear to be linked to changes in ocean circulation, and the risk of occurrence appears to increase with increasing rates of change in global climate. The consequences, should they occur, could be catastrophic, since rapid change allows little time for adaptation.

Reference: Jansen et al., 2007.

E.7 Wouldn’t Canadians be much better off with a warmer climate?

Response: For cold countries such as Canada, climate change can indeed provide some significant benefits. For example, warmer temperatures would reduce space heating costs and provide for longer, warmer growing seasons. When averaged over the entire country of Canada, these benefits could help offset some of the harmful effects caused by climate change provided the rate and magnitude of climate change are modest. However, if climate change is rapid or large, the risks of danger increase significantly, and the overall effect on countries like Canada would be increasingly negative, simply because it is more difficult to adapt to large or rapid change. Moreover, major negative impacts are projected for many of the developing countries of the world, even for modest changes in climate. These off-shore impacts can also have indirect yet significant negative consequences for Canadians (see E.8).

Explanation: Moderately warmer climates could provide benefits to some sectors of the economy or society, and to some regions of the world. For example, providing there is adequate moisture, longer and warmer growing seasons will increase productivity of agricultural crops, and warmer winters will reduce space heating costs in such countries and make it easier to navigate through ice-covered waters. Most of these benefits are due to changes in average temperatures.

However, other consequences of climate change are expected to be very harmful. These include: the combined effects of sea-level rise and ocean storm surges, which could be economically and ecologically devastating to some of Canada's coastal regions; enhanced summer drought conditions that could threaten agricultural production and natural ecosystems, and increase competition for water; increased intensity of summer rainfall, that would increase heavy flooding and erosion, sometimes in the same regions otherwise plagued by drought; and increased frequency of high summer temperature extremes that could stress both ecosystems and human populations.

The larger or more rapid the change in climate, the more difficult it will be to take advantage of the potential benefits, and the greater the risk of danger due to extreme events and other harmful changes. Thus, the concern is not about climate change of any particular kind, but about the possibility that rates and magnitudes of change will exceed human and ecological tolerance thresholds.

References: Field et al., 2007; Anisimov et al., 2007; Natural Resources Canada, 2004.

E.8 What are the primary reasons why Canadians should be concerned about climate change?

Response: While climate change will affect Canadian ecosystems and societies in many complex ways, the primary reasons why Canadians should be concerned are the effects of a warmer world on our northern environment and ecosystems, the economic and ecological consequences of longer and more severe droughts and the implications for life and property of more frequent and/or intense extreme weather events. Furthermore, Canadians should also be concerned about the impacts that climate change will have on other countries, especially those already exposed to severe problems of poverty, hunger and other health risks.

Explanation: Canadian ecological and social systems are well adapted to today's climate and weather patterns. Climate change will therefore affect almost every aspect of Canadian society and significantly alter the ecological patterns across the country. There are several aspects of such change that are of particular concern. First, warmer climates will melt snow, permafrost and sea ice across Canada's northern regions, dramatically altering the environment that current ecosystems and northern residents depend upon. While Arctic marine transportation may eventually become easier, over-land transportation that relies on frozen grounds will be increasingly curtailed, traditional cultures that rely on sea ice and frozen ground for pursuing hunting activities will be jeopardized, and ice-dependent animal species may become increasingly threatened with decline and possible extinction. In southern Canada, the primary concerns are related to extreme climate and weather events, particularly extended droughts, increased severe local floods and major wind events.

Canada also has had a long and admirable history of helping those in need in other countries of the world. Experts argue that the global need for assistance will increase dramatically under warmer climates, even for modest rises in temperature (see E.2 and E.3). Hence, Canada will likely be called upon to extend help to these victims through direct aid, through assistance in resolving related conflicts within and between countries, and by accepting those people who are displaced from their home countries because of the loss of property and homes or by related social unrest.

References: Field et al., 2007; Anisimov et al., 2007; Natural Resources Canada, 2004.

E.9 It has been suggested that, within 50 years, warmer climates will cause Halifax’s climate to be similar to that of Boston today, Toronto’s like that of Kentucky, and Vancouver’s like that of San Francisco. What’s so bad about that?

Response: Ecosystems, culture and socioeconomic infrastructures in Canada have been shaped by the local climate of today and the recent past. Changing infrastructure to suit warmer climates and associated changes in weather may be very costly. If climate change occurs rapidly, the process of adaptation becomes increasingly difficult, costly, and potentially unsuccessful, leading to risks of major disasters. The same is true for the natural environment.

Explanation: The past development of the infrastructure of Canadian cities, transportation systems, agricultural practices and other social and economic well-being activities have been significantly influenced by the past conditions of local climates. For example, most Canadian winter sport facilities and activities are dependent on the presence of snow and ice. Storm sewers and drainage systems in Canadian cities are based on, among other things, local rainfall characteristics, and residential and commercial buildings are designed for temperate to cold climates. Likewise, agriculture, water resource management and flood control infrastructures are based on current growing season and water resource characteristics. Many of these structures and activities require long lead times in order to prepare for future changes in climate. Hence, the more rapid the change in climate, the greater the potential mismatch of cultural, social and economic infrastructures with altered climate conditions, and the greater the risk of failure to adapt, and of negative consequences of climate change.

E.10 Reports indicate that warmer global temperatures will cause some of the largest changes in northern countries such as Canada. Does this mean we are much more at risk of danger than countries near the equator?

Response: No. Climate models, indeed, indicate that the magnitude of climate change in Canada will probably be greater than in many other countries. However, because our current Canadian climate regularly undergoes large changes from week to week, season to season, and year to year, Canadians may be better prepared to deal with climate variability and climate change than those living in less variable climates. Furthermore, modest warming will give us some benefits that will help offset some of the harmful effects (although the benefits and harm may be experienced by different regions, economic
sectors or communities). As a people, we may be less vulnerable to climate change than many others, particularly those living in poor tropical countries. However, within every country, there are communities and sectors of the economy more vulnerable than the population or economy as a whole.

Explanation: Models suggest that changes in temperature will be greatest at high continental latitudes and in winter. However, natural climate fluctuations are also greatest in these regions, and in winter. Hence, ecosystems and societies which have developed in these regions, in general, also have a greater tolerance for change, and may be more adaptable to the large changes predicted for future decades. As in any other region, the rate of climate change will be a key determinant in our ability to adapt to the coming changes. Since cold temperatures are a limitation to many ecosystems and socioeconomic activities in Canada, warmer climates are expected to bring many benefits. That said, the warming of the Arctic is expected to bring about such dramatic changes that residents of the North, and species within northern ecosystems, are expected to face many serious challenges in the coming years. Canada is a relatively wealthy nation, however, with a social infrastructure that can help Canadians to adapt more readily. By contrast, societies of many developing countries in low latitudes already have a marginal existence and have less access to such resources. This can make them vulnerable to even very small changes in climate. Thus, while the large changes for Canada projected by models may result in significant impacts within Canada, many of which will be negative, Canadians may be better able to cope with the consequences of climate change than residents of many developing countries.