Climate Change Reconsidered II: Physical Science Summary of NIPCC’s Findings • Atmospheric carbon dioxide (CO2) is a mild greenhouse gas that exerts a diminishing warming effect as its concentration increases. • Doubling the concentration of atmospheric CO2 from its pre-industrial level, in the absence of other forcings and feedbacks, would likely cause a warming of ~0.3 to 1.1°C, almost 50% of which must already have occurred. • A few tenths of a degree of additional warming, should it occur, would not represent a climate crisis. • Model outputs published in successive IPCC reports since 1990 project a doubling of CO2 could cause warming of up to 6°C by 2100. Instead, global warming ceased around the end of the twentieth century and was followed (since 1997) by 16 years of stable temperature. • Over recent geological time, Earth’s temperature has fluctuated naturally between about +4°C and -6°C with respect to twentieth century temperature. A warming of 2°C above today, should it occur, falls within the bounds of natural variability. • Though a future warming of 2°C would cause geographically varied ecological responses, no evidence exists that those changes would be net harmful to the global environment or to human well-being. • At the current level of ~400 ppm we still live in a CO2-starved world. Atmospheric levels 15 times greater existed during the Cambrian Period (about 550 million years ago) without known adverse effects. • The overall warming since about 1860 corresponds to a recovery from the Little Ice Age modulated by natural multidecadal cycles driven by ocean-atmosphere oscillations, or by solar variations at the de Vries (~208 year) and Gleissberg (~80 year) and shorter periodicities. • Earth has not warmed significantly for the past 16 years despite an 8% increase in atmospheric CO2, which represents 34% of all extra CO2 added to the atmosphere since the start of the industrial revolution. • CO2 is a vital nutrient used by plants in photosynthesis. Increasing CO2 in the atmosphere “greens” the planet and helps feed the growing human population. • No close correlation exists between temperature variation over the past 150 years and humanrelated CO2 emissions. The parallelism of temperature and CO2 increase between about 1980 and 2000 AD could be due to chance and does not necessarily indicate causation. • The causes of historic global warming remain uncertain, but significant correlations exist between climate patterning and multidecadal variation and solar activity over the past few hundred years. • Forward projections of solar cyclicity imply the next few decades may be marked by global cooling rather than warming, despite continuing CO2 emissions. Source: “Executive Summary,” Climate Change Reconsidered II: Physical Science (Chicago, IL: The Heartland Institute, 2013). �
Posted on: Wed, 25 Sep 2013 07:25:50 +0000
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