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Notes
- Summary:
- The outlook for global climate change has deteriorated, and the scientific understanding of the associated dynamics and risks has improved, since the IPCC scenarios which remain in force were prepared in the late 1990s and published in the Special Report on Emissions Scenarios (Nakicenovic et al. 2000). This was documented in the Fourth Assessment Report (Pachauri and Reisinger 2007), but the outlook has continued to worsen since then.
Plans are underway to develop scenarios – both on emissions and the underlying narratives – in time for the fifth assessment in 2014. Meanwhile, however, we are stuck with decade‐old scenarios, and the crucial question is how (a) the storylines, (b) the emissions scenarios and (c) the economic and social implications can be developed to remain internally consistent. This has been a major hurdle in the preparation of this report, which was not fully anticipated when the scoping report was written (Hoegh‐Guldberg 2005).
It was a main challenge for the Florida Keys project. We needed to develop a set of four plausible scenarios from an updated set of IPCC scenarios, starting globally and then pursuing the course via the United States towards ultimate scenarios for the Keys (where we have the added benefits of insights through the five scenario‐planning workshops conducted in June 2008, and further feedback through meetings in August 2009). These scenario stories could then be supplemented with quantitative estimates of key physical and economic variables, along the lines of the Great Barrier Reef report which provided the initial model for the Keys study (Hoegh‐Guldberg and Hoegh‐Guldberg 2004).
In the effort to update the scenario basis, we selected a number of recent global scenarios and descriptions which imply certain scenarios. They all indicate that the need for action has become more urgent since 2000. The selection ranges from the ongoing work on the United Nations Millennium Development Goals and the comprehensive review of the science contained in Mark Lynas’s Six Degrees, to contributions by economists and others which prescribe a way out of the problem over the 21st century and describe the dire effects of “business‐as‐usual” or “BAU” scenarios.
The final selection is based on one prominent scientist’s continued efforts to warn the world. James Hansen of NASA’s Goddard Institute for Space Studies has maintained a high profile as a climatologist since the 1970s. He continues to provide compelling evidence, based on a combination of contemporary and paleoclimate data, that the need to correct for climate change has become significantly more urgent – the tipping point is here, or near. During 2009, many others joined Hansen’s advocacy to keep the level of atmospheric CO2 below 350 ppm to limit the rise in average temperatures to a “reasonably safe” 2OC in the 21st century. The concluding sections of this background paper reflect this.
While this task has become generally more critical, there is a deepening understanding of the need to mitigate against increasing greenhouse gas emissions, both at national and international level, as well as in many local settings. There is hope, but no certainty, that international action will eventuate in time to avoid disaster. Crucial to this is international cooperation, and the full engagement of the United States in a leadership role. Unfortunately, the global economic crisis interfered with public and political perceptions during 2009 and climate change took a backseat while “climate denialism” became prominent.
An “endnote” to the main scenario analysis is based on a small empirical study of one popular science journal, New Scientist. It could be extended to other journals but is likely to be typical. The object was to measure, through the journal’s internal search engine, whether there has been an increase in the number of items dealing with climate change over the past two decades, as an indication that climate change has become a more urgent problem, recognized by a widely read and respected popular science publication. It shows convincingly that there has been a strong increase in the number of climate change‐related items in the last few years (with a leap in the second half of 2009, leading up to the Copenhagen COP‐15 meeting in December), which provides some reassurance that comprehensive action will follow sometime in the not too distant future.
Finally, the link from global scenarios through the United States to the Florida Keys needs to be established. The main Florida Keys report refers to the state‐of‐knowledge report by the US Global Change Research Program (USGCRP) under the auspices of the Office of Science and Technology Policy and NOAA (Karl et al. 2009). As background for the US analysis, this document contains a powerful synthesis of global climate change prefaced by the evidence from Antarctic ice core data that the concentration of carbon dioxide never in 800,000 years exceeded 300 parts per million – until 1911. In 1959 when the present Mauna Loa data begin, the level was 316 ppm, from which it reached 387 ppm in 2009, 30% above the past maximum level in that has been measured in geological time.
The USGCRP graph shows a “lower‐emissions scenario” reaching 550 ppm by 2100, and a “higher emissions scenario” reaching 900 ppm. Even the lower level is far too high, a view shared by the authors of the USGCRP report and the accumulated evidence in this paper, which concludes that the atmospheric content of CO2 must be reduced if global temperatures have any reasonable chance of staying within 2OC above pre‐industrial levels.
Another link from global to local concerns the scenario storyline. Chapter 7 in the main report (Hoegh‐Guldberg 2010)ends with Keys‐specific scenarios preceded by a brief outline of possible US‐wide futures based on Cullen Murphy’s The New Rome? (2007), including the “Titus Livius hundred‐year workout plan,” which would fit in with the global B1 scenario (adding a “green tinge”). Murphy also outlines three “all too plausible” American scenarios, summarized in the final addendum to this background paper.
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