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wg:ptof:papers [2018/09/28 17:44]
brierley [Using paleo-climate comparisons to constrain future projections in CMIP5]
wg:ptof:papers [2020/07/30 12:50] (current)
jules [Future climate forcing potentially without precedent in the last 420 million years]
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 Chronological by publication date, most recent first: Chronological by publication date, most recent first:
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 +==== An assessment of Earth'​s climate sensitivity using multiple lines of evidence ====
 +S. Sherwood ​ M. J. Webb  J. D. Annan  K. C. Armour ​ P. M. Forster ​ J. C. Hargreaves ​ G. Hegerl ​ S. A. Klein  K. D. Marvel ​ E. J. Rohling ​ M. Watanabe ​ T. Andrews ​ P. Braconnot ​ C. S. Bretherton ​ G. L. Foster ​ Z. Hausfather ​ A. S. von der Heydt  R. Knutti ​ T. Mauritsen ​ J. R. Norris ​ C. Proistosescu ​ M. Rugenstein ​ G. A. Schmidt ​ K. B. Tokarska ​ M. D. Zelinka https://​agupubs.onlinelibrary.wiley.com/​doi/​epdf/​10.1029/​2019RG000678
 +Preprint: https://​climateextremes.org.au/​wp-content/​uploads/​2020/​07/​WCRP_ECS_Final_manuscript_2019RG000678R_FINAL_200720.pdf
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 +(It's still 3 plus or minus a bit. -Ed)
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 +Abstract: ''​We assess evidence relevant to Earth'​s equilibrium climate sensitivity per doubling of atmospheric CO2, characterized by an effective sensitivity S . This evidence includes feedback process understanding,​ the historical climate record, and the paleoclimate record. An S value lower than 2 K is difficult to reconcile with any of the three lines of evidence. The amount of cooling during the Last Glacial Maximum provides strong evidence against values of S greater than 4.5 K. Other lines of evidence in combination also show that this is relatively unlikely. We use a Bayesian approach to produce a probability density (PDF) for S given all the evidence, including tests of robustness to difficult‐to‐quantify uncertainties and different priors. The 66% range is 2.6‐3.9 K for our Baseline calculation,​ and remains within 2.3‐4.5 K under the robustness tests; corresponding 5‐95% ranges are 2.3‐4.7 K, bounded by 2.0‐5.7 K (although such high‐confidence ranges should be regarded more cautiously). This indicates a stronger constraint on S than reported in past assessments,​ by lifting the low end of the range. This narrowing occurs because the three lines of evidence agree and are judged to be largely independent,​ and because of greater confidence in understanding feedback processes and in combining evidence. We identify promising avenues for further narrowing the range in S , in particular using comprehensive models and process understanding to address limitations in the traditional forcing‐feedback paradigm for interpreting past changes.''​
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 ==== Future climate forcing potentially without precedent in the last 420 million years ==== ==== Future climate forcing potentially without precedent in the last 420 million years ====
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 Abstract: ''​The evolution of Earth’s climate on geological timescales is largely driven by variations in the magnitude of total solar irradiance (TSI) and changes in the greenhouse gas content of the atmosphere. Here we show that the slow B50 Wm   2 increase in TSI over the last B420 million years (an increase of B9 Wm   2 of radiative forcing) was almost completely negated by a long-term decline in atmospheric CO2. This was likely due to the silicate weathering- negative feedback and the expansion of land plants that together ensured Earth’s long-term habitability. Humanity’s fossil-fuel use, if unabated, risks taking us, by the middle of the twenty-first century, to values of CO2 not seen since the early Eocene (50 million years ago). If CO2 continues to rise further into the twenty-third century, then the associated large increase in radiative forcing, and how the Earth system would respond, would likely be without geological precedent in the last half a billion years.''​ Abstract: ''​The evolution of Earth’s climate on geological timescales is largely driven by variations in the magnitude of total solar irradiance (TSI) and changes in the greenhouse gas content of the atmosphere. Here we show that the slow B50 Wm   2 increase in TSI over the last B420 million years (an increase of B9 Wm   2 of radiative forcing) was almost completely negated by a long-term decline in atmospheric CO2. This was likely due to the silicate weathering- negative feedback and the expansion of land plants that together ensured Earth’s long-term habitability. Humanity’s fossil-fuel use, if unabated, risks taking us, by the middle of the twenty-first century, to values of CO2 not seen since the early Eocene (50 million years ago). If CO2 continues to rise further into the twenty-third century, then the associated large increase in radiative forcing, and how the Earth system would respond, would likely be without geological precedent in the last half a billion years.''​
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 ==== The University of Victoria Cloud Feedback Emulator (UVic-CFE): cloud radiative feedbacks in an intermediate complexity model ==== ==== The University of Victoria Cloud Feedback Emulator (UVic-CFE): cloud radiative feedbacks in an intermediate complexity model ====