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Stephen Schwartz on climate sensitivity

Posted on 22 August 2007 by John Cook

A recent paper Heat capacity, time constant and sensitivity of Earth's climate system by Stephen Schwartz determines a climate sensitivity of 1.1 ± 0.5°C. Eg - if you doubled atmospheric CO2, global temperatures would go up 1.1°C. This is about a third of the consensus view (around 3°C) and unsurprisingly has been getting some attention on skeptic websites. Consequently I've added a new skeptic argument climate sensitivity is low.

Schwartz calculates sensitivity as the quotient of the climate "time constant" and global heat capacity. The "time constant", or time for the climate system to return to equilibrium after a perturbation, is a key aspect of the paper and Schwartz estimates around 5 years.

However, as Schwartz points out in his study, climate recovers at different rates depending on the nature of the forcing causing the perturbation. Short term changes such as a volcanic eruption result in a short time constant of a few years. A long term increase in CO2 levels results in a recovery spanning decades. Schwartz rightly points out "as the duration of volcanic forcing is short, the response time may not be reflective of that which would characterize a sustained forcing such as that from increased greenhouse gases because of lack of penetration of the thermal signal into the deep ocean."

In spite of that, Schwartz filters out long term changes by detrending the time series data which has the effect of biasing the result towards a shorter time constant. The time constant for non-detrended data yields a time constant of 15 to 17 years. Consequently, the estimated time constant of 5 years is questionable - a value the final result hinges on.

More on Stephen Schwartz and climate sensitivity...

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Comments 1 to 1:

  1. One thing that is often overlooked is that irrespective of whether CO2 causes warming, [I for one, will stick with the science]. Increasing CO2 will result in acidification [reducing pH] of the ocean. There are a number of studies that show that this is likely to be bad thing. AFAIK, no peer-reviewed scientific studies have suggested it is a good idea, although I look forward to a new study - perhaps “authored” by ExxonMobil et al. What Corals are Dying to Tell Us About CO2 and Ocean Acidification - Caldeira "Emissions of carbon dioxide are causing the oceans to become more acidic. Recent experiments show that this ocean acidification threatens many ocean ecosystems. The ancient past may provide a cautionary tale, indicating what might happen if we change ocean chemistry too much too fast. end quote" Effects of carbon dioxide and climate change on ocean acidification and carbonate mineral saturation - Long Cao, Ken Caldeira, and Atul K. Jain "We use an earth system model of intermediate complexity to show how consideration of climate change affects predicted changes in ocean pH and calcium carbonate saturation state. Our results indicate that consideration of climate change produces second-order modifications to ocean chemistry predictions made with constant climate; these modifications occur primarily as a result of changes in sea surface temperature, and climate induced changes in dissolved inorganic carbon concentrations." Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms – Orr et al. "Today’s surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms—such as corals and some plankton—will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of ocean–carbon cycle to assess calcium carbonate saturation under the IS92a ‘business-as-usual’ scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of underaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously."
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    Response: Thanks for the links, I've added ocean acificiation to the list of negatives on the Global Warming is Good page.

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