And it was done without uttering an untruth!
Arguably the most influential graphic from the latest IPCC report is Figure SPM.2 from the IPCC WG 2’s Summary for Policy Makers (on the impacts, vulnerability and adaptation to climate change). This figure, titled “Key impacts as a function of increasing global average temperature change”, also appears as Figure SPM.7 and Figure 3.6 of the IPCC Synthesis Report (available at http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf). Versions also appear as Table 20.8 of the WG 2 report, and Table TS.3 in the WG 2 Technical Summary. Yet other versions are also available from the IPCC WG2’s Graphics Presentations & Speeches, as well as in the WG 2’s “official” Power Point presentations, e.g., the presentation at the UNFCCC in Bonn, May 2007 (available at http://www.ipcc.ch/graphics/pr-ar4-2007-05-briefing-bonn.htm).
Notably the SPMs, Technical Summary, Synthesis Report, and the versions made available as presentations are primarily for consumption by policy makers and other intelligent lay persons. As such, they are meant to be jargon-free, easy to understand, and should be designed to shed light rather than to mislead even as they stay faithful to the science.
Let’s focus on what Figure SPM.2 tells us about the impacts of climate change on water.
The third statement in the panel devoted to water impacts states, “Hundreds of millions of people exposed to increased water stress.” If one traces from whence this statement came, one is led to Arnell (2004). [Figure SPM.2 misidentifies one of the sources as Table 3.3 of the IPCC WG 2 report. It ought to be Table 3.2. ]
What is evident is that while this third statement is correct, Figure SPM.2 neglects to inform us that water stress could be reduced for many hundreds of millions more — see Table 10 from the original reference, Arnell (2004). As a result, the net global population at risk of water stress might actually be reduced. And, that is precisely what Table 9 from Arnell (2004) shows. In fact, by the 2080s the net global population at risk declines by up to 2.1 billion people (depending on which scenario one wants to emphasize)!
And that is how a net positive impact of climate change is portrayed in Figure SPM.2 as a large negative impact. The recipe: provide numbers for the negative impact, but stay silent on the positive impact. That way no untruths are uttered, and only someone who has studied the original studies in depth will know what the true story is. It also reminds us as to why prior to testifying in court one swears to “tell the truth, the whole truth and nothing but the truth.”
Figure SPM.2 fails to tell us the whole truth.
Hints of the whole truth, however, are buried in the body of the IPCC WG 2 Report as evidenced by the following quote from Section 3.5.1, p. 194, of that report. Note that Arnell (2004b) and Arnell (2004) are identical.
In the 2050s, differences in the population projections of the four SRES scenarios would have a greater impact on the number of people living in water-stressed river basins (defined as basins with per capita water resources of less than 1,000 m3/year) than the differences in the emissions scenarios (Arnell, 2004b). The number of people living in severely stressed river basins would increase significantly (Table 3.2). The population at risk of increasing water stress for the full range of SRES scenarios is projected to be: 0.4 to 1.7 billion, 1.0 to 2.0 billion, and 1.1 to 3.2 billion, in the 2020s, 2050s, and 2080s, respectively (Arnell, 2004b). In the 2050s (SRES A2 scenario), 262-983 million people would move into the water stressed category (Arnell, 2004b). However, using the per capita water availability indicator, climate change would appear to reduce global water stress. This is because increases in runoff are heavily concentrated in the most populous parts of the world, mainly in East and South-East Asia, and mainly occur during high flow seasons (Arnell, 2004b). Therefore, they may not alleviate dry season problems if the extra water is not stored and would not ease water stress in other regions of the world. [Emphasis added]
But even this acknowledgment seems grudging, and leaves a misleading impression, as can be seen by the following annotated version of the above quote. [My annotations are indicated within the quote in square brackets and are in bold.]
In the 2050s, differences in the population projections of the four SRES scenarios would have a greater impact on the number of people living in water-stressed river basins (defined as basins with per capita water resources of less than 1,000 m3/year) than the differences in the emissions scenarios (Arnell, 2004b). The number of people living in severely stressed river basins would increase significantly (Table 3.2). The population at risk of increasing water stress for the full range of SRES scenarios is projected to be: 0.4 to 1.7 billion, 1.0 to 2.0 billion, and 1.1 to 3.2 billion, in the 2020s, 2050s, and 2080s, respectively (Arnell, 2004b). [COMMENT: note that the IPCC text fails to mention that the reductions in populations at risk of water stress due to climate change are projected to be substantially higher — 0.6 to 2.4 billion, 1.8 to 4.3 billion, and 1.7 to 6.0 billion in the 2020s, 2050s and 2080s, respectively. See Table 10 from the original source.] In the 2050s (SRES A2 scenario), 262-983 million people would move into the water stressed category (Arnell, 2004b). [COMMENT: The corresponding figures for the population moving out of water stress category are 191 to 1,493 million. See Table 9 from the original source.] However, using the per capita water availability indicator, climate change would appear to reduce global water stress. This is because increases in runoff are heavily concentrated in the most populous parts of the world, mainly in East and South-East Asia, and mainly occur during high flow seasons (Arnell, 2004b). Therefore, they may not alleviate dry season problems if the extra water is not stored and would not ease water stress in other regions of the world. [COMMENT: One should expect that societies would take action to store water if that’s what is necessary to avoid water stress. Such actions are not rocket science; they are probably as old as humanity itself, and have a successful track record going back for millennia. Moreover, if the IPCC’s emission scenarios, and the economic growth rates they assume are to be believed, these societies would be much wealthier in the future and should, therefore, have access to more capital to help adapt to such problems. See here (pp. 1034-1036, Tables 1 and 10).]
[Note that the Arnell paper is discussed in some detail here (pp. 1034-1036; Table 4), among other places.]
To summarize, with respect to water resources, Figure SPM.2 — and its clones — don’t make any false statements, but by withholding information that might place climate change in a positive light, they have perpetrated a fraud on the readers.