The American Institute of Physics has a great resource in "The Discovery of Global Warming" -- a deep and long look at the history of climate science. If you're interested in understanding how the interdisciplinary scientific consensus on the reality of deadly human-caused climate change arose, this is the right place to start.
It is an epic story: the struggle of thousands of men and women over the course of a century for very high stakes. For some, the work required actual physical courage, a risk to life and limb in icy wastes or on the high seas. The rest needed more subtle forms of courage. They gambled decades of arduous effort on the chance of a useful discovery, and staked their reputations on what they claimed to have found. Even as they stretched their minds to the limit on intellectual problems that often proved insoluble, their attention was diverted into grueling administrative struggles to win minimal support for the great work. A few took the battle into the public arena, often getting more blame than praise; most labored to the end of their lives in obscurity. In the end they did win their goal, which was simply knowledge.The scientists who labored to understand the Earth's climate discovered that many factors influence it. Everything from volcanoes to factories shape our winds and rains. The scientific research itself was shaped by many influences, from popular misconceptions to government funding, all happening at once. A traditional history would try to squeeze the story into a linear text, one event following another like beads on a string. Inevitably some parts are left out. Yet for this sort of subject we need total history, including all the players — mathematicians and biologists, lab technicians and government bureaucrats, industrialists and politicians, newspaper reporters and the ordinary citizen. This Web site is an experiment in a new way to tell a historical story. Think of the site as an object like a sculpture or a building. You walk around, looking from this angle and that. In your head you are putting together a rounded representation, even if you don't take the time to inspect every cranny. That is the way we usually learn about anything complex.
Climate Change Economics is an excellent, thorough and ongoing look at the economics of climate change mitigation. Aimed at legislators and people interested in policy implications of climate change, CCE offers a series of well-organized directories of white papers and technical information from a variety of sources for people trying to understand why it makes good economic sense to take immediate, drastic measures to curb emissions and mitigate the effects of anthropogenic climate change.
In practice, economists' analyses of the effects of climate change and the positive and negative returns to mitigation efforts have generally come to agree that a constant discount rate is not appropriate, and that the rate must generally decline over time. They do NOT agree on a rate at which to start the calculations, nor on the way in which the rate should be reduced over time.Looking back at the table, it is obvious that the rate that applies at first - and how long it applies - will play a major role in the prevent value derived. Using a 5% rate for the first decade, for example, would leave under 62% of the FV in the PV, even if the discount rate used for the rest of time was zero. That is why many analysts claim that the discount rate for possibly catastrophic outcomes (possible but not known) should be negative relative to the known investment results, which would push calculations of PVs toward using the 0.6% rate rather than in the direction of the 7% rate.
This argument is not based on risk alone, which is what is used in investment analysis, but on the combination of risk and uncertainty, factors that combine to shape all forecasts, but especially those of processes and events about which we know relatively little, such as the processes of global climate change and species survival and extinction.
So the question of the initial discount rate used, and why it is used, is central to any analysis of the economics of climate change and alternative policies intended to slow the growth of greenhouse gasses.
A frequent shibboleth used by the climate change deniers is that the Medieval Warm Period -- a period of apparent global climate change in medieval times -- indicates that the Earth's climate rises and falls all the time, and that therefore, human beings don't cause global warming. In this paper, scientists from the National Oceanic and Atmospheric Administration investigate the best scientific findings on the Medieval Warm Period hypothesis, with special emphasis on the massive, wide-ranging, independent UN Intergovernmental Panel on Climate Change. They conclude that "the late 20th and early 21st centuries are likely the warmest period the Earth has seen in at least 1200 years."
In summary, it appears that the late 20th and early 21st centuries are likely the warmest period the Earth has seen in at least 1200 years. For a summary of the latest available research on the nature of climate during the "Medieval Warm Period", please see Box 6.4 of the IPCC 2007 Palaeoclimate chapter. To learn more about the "Medieval Warm Period", please read this review published in Climatic Change, written by M.K. Hughes and H.F. Diaz. (Click here for complete review reference). Discussion of the last 2,000 years, including the Medieval Warm Period, and regional patterns and uncertainties, appears in the National Research Council Report titled "Surface Temperature Reconstructions for the Last 2,000 Years", available from the National Academy Press.
From Nature's excellent Climate Change section, excellent summation of the year's research into anthropogenic climate change -- that is, the hard scientific evidence from unbiased, independent scientists indicating that climate change is real, caused by humans, and dangerous to the planet.
4. The hockey stick holds upA follow-up to the infamous 1998 'hockey stick' curve confirmed that the past two decades are the warmest in recent history. Climatologist Michael Mann's contentious graph has become a symbol of the fierce debates on evidence for global warming, to the extent that an independent investigation into the study was performed at the request of US Congressman Joe Barton. The 2006 report that resulted from the Barton enquiry criticized Mann and colleagues for their reliance on tree-ring data from bristlecone pines as a proxy to reconstruct Northern Hemisphere temperatures over the past 1,000 years. Although their earlier work had been largely vindicated, in September the same team revised their global surface temperature estimates for the past 2,000 years, using a greatly expanded set of proxies, including marine sediments, ice cores, coral and historical documents (Proc. Natl Acad. Sci. USA 105, 13252–13257; 2008). The team reconstructed global temperatures with and without inclusion of the tree-ring records: without their inclusion, the data showed that recent warming is greater than at any point in at least the past 1,300 years; inclusion of tree-ring data extended this period to at least 1,700 years. According to the Christian Science Monitor: "It still looks a lot like the much-battered, but still rink-ready stick of 1998. Today the handle reaches further back and it's a bit more gnarly. But the blade at the business end tells the same story."
No comments:
Post a Comment