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AR5 Attribution Studies

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Dr. Clive Best reviews the IPCC fifth assessment report (AR5) attribution statement, which is based on comparing climate models to the global temperature record before this century. The statement "depends critically on them [models] being able to simulate both anthropogenic forcing and natural variability. Chapter 9 of the IPCC report shows that models are tuned so as to describe past observations. The model control runs exhibit long-term drifts. Any ‘natural’ trends generated by models in the temperature data are assumed to be an artifact and simply removed. The procedure assumes there in no natural climate change despite the recovery from the little ice age. However, the Atlantic Multidecadel Oscillation alone added 0.2 C warming to the 1950 - 2010 trend. The result is that the AR5 attribution statement is useless.

IPCC AR5 Climate Sensitivity?

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The IPCC fifth assessment report failed to provide a best estimate of equillibrium climate sensitivity. Christopher Monckton of Brenchley uses the feedback parameters published in the report to determine realistic estimates expected global warming to the year 2100. He finds that global temperature could rise by up to 2.1 C by 2100 if the reported feedback parameters are correct, which is much less that the 3.7 C estimated to the RCP 8.5 emissions scenario. Monckton's best estimate is that the feedbacks are net zero, giving a temperature rise of just 3/4 of a degree Celsius by 2100.

Comparing Models and Observations in the Tropical Troposphere

Climate models and observations were compared over a 55-year span (1958-2012) in the tropical troposphere. The paper finds that climate models are inconsistent with three weather balloon series. The models not only predict far too much warming, but they get the nature of the change wrong. Models show a smooth upward trend but the observations show all the warming occurred in a single step-change in the late 1970s, known as the Pacific Climate Shift, and no significant trend before or after. Dr. Ross McKitrick explains the new paper is this Climate Audit post. Over the 1979-2009 interval climate models on average predict 2x and 4x too much warming in the tropical lower- and mid- troposphere layers, respectively.

The Global Warming Hiatus

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While the Intergovernmental Panel on Climate Change (IPCC) still uses the iconic word “unequivocal” to describe warming of the climate system over the past century, a new word has slipped into its lexicon: the “hiatus.” They have begun referring, with a bit of hesitant throat-clearing, to “the warming hiatus since 1998.” Cracked-beakerBoth satellites and surface records show that sometime around 2000, temperature data ceased its upward path and leveled off. Over the past 100 years there is a statistically significant upward trend in the data amounting to about 0.7 oC per century. If one looks only at the past 15 years though, there is no trend.

A Sensitive Matter: How the IPCC Buried Evidence

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The IPCC's recently published report suppressed evidence that the climate is much less sensitive to greenhouse gases than indicated by climate models according to this report by Nicholas Lewis and Marcel Crok. The report says, "In AR5, many studies still use inappropriate data and/or statistical methodology. However, there is now a body of empirical estimates of climate sensitivity, prepared using sound methodology and appropriate data, that give substantially lower values - than climate model simulations." Estimate of the cooling effects of aerosols have been cut, which reduces the estimate of greenhouse gas warming, but this is not included in climate models.

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