Climate at a Glance: Climate Sensitivity

(click to enlarge) Climate sensitivity estimates from new research beginning in 2009. Note that in blue, two studies using actual real-world data to infer climate sensitivity values between 0.8 and 1.3°C, far lower than model-based estimates. Diagram by Anthony Watts.

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Key Takeaways:

  • Predictions of substantial global warming assume high climate sensitivity to a doubling of carbon dioxide emissions in the atmosphere.
  • For decades, scientists have debated the effect of climate sensitivity, due to the uncertain nature of climate feedback in various models.
  • Estimates in peer reviewed studies range from 0.8°C warming to almost 6.0°C warming by 2100.
  • Such a large range of  uncertainty means climate model temperature projections remain dubious, at best.
  • The best evidence indicates climate sensitivity is at the low end of the range, unlikely to exceed 1.5°C in the 21st century.

Short Summary:

Climate sensitivity is a measure of how much the Earth’s climate will cool or warm after a change in the climate’s system. In scientific circles, climate sensitivity is usually linked to the degree to which temperature will be affected by a doubling in carbon dioxide concentrations in the atmosphere.1 (See Figure 1.)

Figure 1. Factors that Determine Climate Sensitivity

Figure 1. After increasing carbon dioxide levels, there is an initial warming. This warming could be amplified or reduced by the net effect of various feedbacks (weather processes that change the characteristics of the planet). Diagram by Femkemilene from WikiMedia Commons.

Declaring future predictions of global warming as “settled science” requires a fairly precise calculation of future temperatures. However, since climate sensitivity gained scientific visibility more than 40 years ago, scientists and climate models have produced a very broad range of potential future temperature patterns, strongly indicating
that no one model can be deemed reliable enough for policymakers to depend upon.2

Mainstream calculations for a doubling of atmospheric carbon dioxide range from eight-tenths of a degree Celsius warming to almost 6 degrees C of warming by 2100.3


If climate scientists don’t understand the Earth’s atmosphere well enough to nail down a true climate sensitivity estimate for increased carbon dioxide, how can we trust climate model projections of future warming that rely on such an uncertain value?

Further, dire estimates about climate sensitivity have been undercut by real-world data. Climate sensitivity estimates from real-world atmospheric observation data suggest global warming occurring this century is unlikely to exceed 1.5 degrees C.

References:

  1. David L. Chandler, “Explained: Climate Sensitivity,” MIT News, March 19, 2010, http://
    news.mit.edu/2010/explained-climate-sensitivity
  2. Carbon Dioxide and Climate: A Scientific Assessment, a report of an Ad Hoc Study
    Group on Carbon Dioxide and Climate, Climate Research Board of the National
    Research Council, published by the National Academy of Sciences, July 1979, accessed
    August 19, 2021, doi:10.17226/12181, https://web.archive.org/web/20110813231807/
    http://www.atmos.ucla.edu/~brianpm/download/charney_report.pdf
  3. Schwartz et. al, “Earth’s Climate Sensitivity: Apparent Inconsistencies in Recent
    Assessments,” Earth’s Future, Volume 2, Issue 12, November 7, 2014, https://agupubs.
    onlinelibrary.wiley.com/doi/full/10.1002/2014EF000273
  4. Richard S. Lindzen and Yong-Sang Choi, “On the Observational Determination of
    Climate Sensitivity and Its Implications,” Asia-Pacific Journal of Atmospheric Science,
    article number 377, August 28, 2011, doi:10.1007/s13143-011-0023-x, https://link.
    springer.com/article/10.1007%2Fs13143-011-0023-x
  5. Roy Spencer and William Braswell, “On the Misdiagnosis of Surface Temperature
    Feedbacks from Variations in Earth’s Radiant Energy Balance,” Remote Sensing, July
    25, 2011, doi:10.3390/rs3081603, http://www.drroyspencer.com/wp-content/uploads/
    Spencer_Misdiagnos_11.pdf
  6. David Herring, “Are There Positive Benefits from Global Warming?,” climate.gov,
    National Oceanic and Atmospheric Administration, October 29, 2020, https://www.
    climate.gov/news-features/climate-qa/are-there-positive-benefits-global-warming

Climate At A Glance is a Project of The Heartland Institute

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