Degrees of Change – About the Diagram
The Degrees of Change Diagram
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About the DiagramThe Degrees of Change diagram summarizes a body of scientific literature on the expected effects of climate change in Canada associated with a rise in global average temperatures over the 21st century.
It is an illustrative and representative depiction of what a changing climate could mean for Canada, citing 60 specific examples of impacts. It is based on existing published research, with examples of impacts selected to highlight direct and indirect effects of global warming. The diagram is a summary of some of the more important impacts, those we know most about, are most confident about, and those expected to occur this century. In doing so, the NRTEE seeks to inform Canadians on just how pervasive the effects of a changing climate will be. And it seeks to inform decision makers on the scope and need for adaptation measures. |
Interpreting the Degrees of Change Diagram
Degrees of Change is a simple diagram that contains abundant information. Here we draw the reader’s attention to four key elements: the global temperature scale, the “Current +0.78°C” marker, the eight impact categories and the suite of impacts of climate change represented.
The NRTEE believes the diagram is a useful tool to communicate the risks and potential opportunities of climate change for our country and to foster a national conversation on strategies that governments, businesses, communities, and households can take to manage them.
However, the diagram has limitations. We set them out here:
- The Degrees of Change diagram is not a comprehensive overview of all expected impacts for Canada — the effects of climate change are too pervasive, broad and wide-ranging for a comprehensive summary in diagram form to be possible. This means that we may be excluding poorly understood yet extremely relevant and important impacts for Canada. It also means that we exclude reinforcing impacts that could result from sustained warming of several degrees over several centuries, such as the release of large pools of carbon stored in sediments from warming of the deep ocean.
- The diagram is not a firm prediction, it is an illustration of what we think is possible and likely based on scientific literature. The impacts of climate change will occur at different times in different places, and result from a combination of changes in climate conditions, not just warmer temperatures. In addition, some of the scientific studies that we used to develop the diagram do not always specify the relationship between local and regional effects of climate change and global temperatures. As a result, we have made some interpretations and inferences of impacts reported in the literature, which can add uncertainty to some aspects of the diagram.
- The effects of climate change are not all instantaneous, and long-term impacts from warming are difficult to represent. It’s important to recognize that changes in air temperature do not trigger an immediate response in the physical environment. Even if we limit global temperatures to 2°C by 2050, climate change impacts will continue to build up for decades at a minimum, simply due to the inertia of the systems involved. For example, sea levels would continue to rise for hundreds of years because of the long time it takes for surface changes to mix through to the bottom of the ocean and for major masses of ice and snow to react to warmer air temperatures. Although very important, these lags are difficult to represent in a diagram.
- A common international view is that Canada is likely to experience both beneficial and adverse impacts from climate change, but much of the literature focuses on quantifying risks, costs, and damages rather than positive changes. The Degrees of Change diagram can only represent what exists in the current scientific literature, which mostly highlights the risks from a warming world.
- The climate change effects included in the diagram do not account for the potential to reduce or avoid harm through adaptation. Some of the effects of climate change — such as those on industries and communities — will depend on the way in which people respond to the changing climate. By taking proactive action to prepare for expected impacts, Canadians can lessen the blow of climate change and even position ourselves to benefit accordingly in some cases.
The Global Temperature Scale
In the diagram, we map climate change effects expected in Canada to a global temperature scale (see Figure 2).
We did so because, while Canada as a whole is warming faster than the global average (see Box 3), a global temperature scale places expected effects of climate change in Canada within the broader context. This broader context includes international climate change talks currently negotiating country-level commitments to prevent global temperatures from exceeding 2°C above pre-industrial levels (i.e., relative to 1850–1899 averages).
FIGURE 2: DEGREES OF CHANGE DIAGRAM – TEMPERATURE SCALE
The diagram’s global temperature scale embodies complex scientific information that merits explanation. The temperature scale starts at 0.5˚C and ends at about 6˚C. The range is significant for two reasons.
FIRST, we can benchmark the rise in global average temperatures relative to pre-industrial times that has already occurred and warming that is in the pipeline. The diagram’s “Current +0.78°C” marker captures the observed warming and tells us that the effects of climate change that line up with this marker are already taking place. From the marker at 0.78°C a further rise in global temperatures of 0.6˚C is now unavoidable due to the historic buildup of heat-trapping gases. This means that adapting to the impacts shown to about 1.5˚C is no longer optional.
SECOND, the range reflects current understanding of the possible rise in global average temperatures during this century. The range is so large because of uncertainties in future changes to the chemical makeup of the atmosphere (mainly the proportion of heat-trapping gases), and the reaction of the global climate and other components of the Earth system to these atmospheric changes.
Our focus on the trend in rising global average temperatures does not mean that temperature is the only indicator to worry about. In Canada and elsewhere, global warming affects averages of other climate indicators in addition to climate variability, resulting in changes in the amount and timing of rain and snow, air and soil moisture, wind patterns, and in the frequency, extent, and severity of climate extremes such as droughts, heat waves, and intense storms and rain events. The diagram specifically highlights some of these changes as impacts.
Impact Categories
The Degrees of Change diagram includes the eight impact categories listed below.
- Ice, snow, and sea
- Ecosystems
- Water resources
- Human health
- Communities and infrastructure
- Resource industries
- Service industries
- Security and trade
The NRTEE chose these eight impact categories to illustrate the full chain of effects of climate change, and interconnections among them from a Canadian perspective. Although inspired by formats used by the Intergovernmental Panel on Climate Change, Degrees of Change is uniquely Canadian in representing categories and impacts that are significant to our country. Categories include direct and visible impacts on our environment and then progress to indirect impacts on our economy and society. Together, these eight categories represent interconnected systems and sectors but with varying degrees of adaptive capacity:
- those incapable of adapting to the effects of higher global temperatures, such as glaciers and sea ice;
- those that can, within limits, adjust spontaneously to change, such as forests; and
- those that are capable of anticipating the effects of climate change and making changes to accommodate them, such as service industries.
In several cases, the effects of climate change in one impact category have implications for another category. Among the most obvious examples are the impacts in Ecosystems and those in Resource industries: shifts in the viability and range of fish species as oceans warm and change chemistry because of higher carbon concentrations in the atmosphere greatly influence the economic sustainability of capture fisheries.
Each category includes four or more impacts of climate change. Sixty in total are plotted on the diagram. Every impact has two components: a statement on the expected direction and quality of change and a global temperature range where we can expect the statement to be true.
A rigorous selection and validation process decided what impacts to include in the diagram and how to portray them.
The diagram includes impacts that are already evident and impacts that scientists project for the future. We can expect the former to continue into the future and probably increase (or decrease, depending on the direction) with higher global temperatures. Drawing definitive conclusions on forecasts of climate change impacts is more difficult. Confidence is a function of understanding the direction and magnitude (how much or how little) of change, the global temperature range associated with this change, the lag time between global temperature change and the response of our physical environment, and conditions under which the direction of change may flip, or the speed of change may accelerate. Issues of certainty and confidence are noted in Appendix 5.5 which highlights where and why readers should be cautious about drawing firm and fast conclusions on each and every impact at this time, over and above clear directional changes.
Overall, we have tried to present the potential impacts of climate change in a way that is balanced, informative, and compelling. We have summarized existing evidence. New evidence and more scientific research are always appearing. Having established a framework and means of communicating climate change impacts in Canada, the NRTEE’s Degrees of Change diagram can be updated to reflect this.
© 2013