The Current Wisdom is a series of monthly articles in which Patrick J. Michaels and Paul C. “Chip” Knappenberger, from Cato’s Center for the Study of Science, review interesting items on global warming in the scientific literature that may not have received the media attention that they deserved, or have been misinterpreted in the popular press.

With all the stern talk about global warming and widespread concern over climate change, you would think that we humans would have a propensity for cooler temperatures. Everywhere you look, the misery that rising temperatures (and the associated evils) will supposedly heap upon us seems to dominate reports about the coming climate. But do patterns of population movement really support the idea that we prefer cooler locations?

Increased Mobility

Since 1900, the population of the United States increased from about 76 million people to about 309 million people in 2010. Accompanying that population growth were major advances in technology and industry, including vast improvements in our nation’s system of transportation. As planes, trains, and automobiles replaced the horse and buggy, Americans became more mobile, and where we live was no longer connected primarily with proximity to where we were born. Instead, we became much freer to choose our place of residence based on considerations other than ease of getting there.

Where has our new-found freedom of mobility led us? Figure 1 shows the rate of population change from 1900 to 2010 for each of the contiguous 48 states. Notice the increases in states with warm climates such as Florida, Texas, and California, and also in states with big industry (that is, jobs), such as New York, Michigan, and Ohio for example.

Figure 1. The state-by-state population trend (people/year) from 1900 to 2010 (data from U.S. Census Bureau).

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To make fun of big efforts that produce small results, the Roman poet Horace wrote, “The mountains will be in labor, and a ridiculous mouse will be brought forth.”

That line sums up my view of the new tax reform plan introduced by Rep. Dave Camp (R-Mich.), chairman of the House Ways and Means Committee.

To his credit, Chairman Camp put in a lot of work. But I can’t help but wonder why he went through the time and trouble. To understand why I’m so underwhelmed, let’s first go back in time.

Back in 1995, tax reform was a hot issue. The House Majority Leader, Dick Armey, had proposed a flat tax. Congressman Billy Tauzin was pushing a version of a national sales tax. And there were several additional proposals jockeying for attention.

To make sense of the clutter, I wrote a paper for the Heritage Foundation that demonstrated how to grade the various proposals that had been proposed.

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Global Science Report is a feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

We have two new entries to the long (and growing) list of papers appearing the in recent scientific literature that argue that the earth’s climate sensitivity—the ultimate rise in the earth’s average surface temperature from a doubling of the atmospheric carbon dioxide content—is close to 2°C, or near the low end of the range of possible values presented by the U.N.’s Intergovernmental Panel on Climate Change (IPCC).  With a low-end warming comes low-end impacts and an overall lack of urgency for federal rules and regulations (such as those outlined in the President’s Climate Action Plan) to limit carbon dioxide emissions and limit our energy choices.

The first is the result of a research effort conducted by Craig Loehle and published in the journal Ecological Modelling. The paper is a pretty straightforward determination of the climate sensitivity.  Loehle first uses a model of natural modulations to remove the influence of natural variability (such as solar activity and ocean circulation cycles) from the observed temperature history since 1850. The linear trend in the post-1950 residuals from Loehle’s natural variability model was then assumed to be largely the result, in net, of human carbon dioxide emissions.  By dividing the total temperature change (as indicated by the best-fit linear trend) by the observed rise in atmospheric carbon dioxide content, and then applying that relationship to a doubling of the carbon dioxide content, Loehle arrives at an estimate of the earth’s transient climate sensitivity—transient, in the sense that at the time of CO2 doubling, the earth has yet to reach a state of equilibrium and some warming is still to come. 

Loehle estimated the equilibrium climate sensitivity from his transient calculation based on the average transient:equilibrium ratio projected by the collection of climate models used in the IPCC’s most recent Assessment Report. In doing so, he arrived at an equilibrium climate sensitivity estimate of 1.99°C with a 95% confidence range of it being between 1.75°C and 2.23°C.

Compare Loehle’s estimate to the IPCC’s latest assessment of the earth’s equilibrium climate sensitivity which assigns a 66 percent or greater likelihood that it lies somewhere in the range from 1.5°C to 4.5°C. Loehle’s determination is more precise and decidedly towards the low end of the range.

The second entry to our list of low climate sensitivity estimates comes from  Roy Spencer and William Braswell and published in the Asia-Pacific Journal of Atmospheric Sciences. Spencer and Braswell used a very simple climate model to simulate the global temperature variations averaged over the top 2000 meters of the global ocean during the period 1955-2011. They first ran the simulation using only volcanic and anthropogenic influences on the climate. They ran the simulation again adding a simple take on the natural variability contributed by the El Niño/La Niña process. And they ran the simulation a final time adding in a more complex situation involving a feedback from El Niño/La Niña onto natural cloud characteristics. They then compared their model results with the set of real-world observations.

What the found, was the that the complex situation involving El Niño/La Niña feedbacks onto cloud properties produced the best match to the observations.  And this situation also produced the lowest estimate for the earth’s climate sensitivity to carbon dioxide emissions—a value of 1.3°C.

Spencer and Braswell freely admit that using their simple model is just the first step in a complicated diagnosis, but also point out that the results from simple models provide insight that should help guide the development of more complex models, and ultimately could help unravel some of the mystery as to why full climate models produce  high estimates of the earth’s equilibrium climate sensitivity, while estimates based in real-world observations are much lower.

Our Figure below helps to illustrate the discrepancy between climate model estimates and real-world estimates of the earth’s equilibrium climate sensitivity. It shows Loehle’s determination as well as that of Spencer and Braswell along with 16 other estimates reported in the scientific literature, beginning in 2011. Also included in our Figure is both the IPCC’s latest assessment of the literature as well as the characteristics of the equilibrium climate sensitivity from the collection of climate models that the IPCC uses to base its impacts assessment.

Figure 1. Climate sensitivity estimates from new research beginning in 2011 (colored), compared with the assessed range given in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) and the collection of climate models used in the IPCC AR5. The “likely” (greater than a 66% likelihood of occurrence)range in the IPCC Assessment is indicated by the gray bar. The arrows indicate the 5 to 95 percent confidence bounds for each estimate along with the best estimate (median of each probability density function; or the mean of multiple estimates; colored vertical line). Ring et al. (2012) present four estimates of the climate sensitivity and the red box encompasses those estimates. The right-hand side of the IPCC AR5 range is actually the 90% upper bound (the IPCC does not actually state the value for the upper 95 percent confidence bound of their estimate). Spencer and Braswell (2013) produce a single ECS value best-matched to ocean heat content observations and internal radiative forcing.

Quite obviously, the IPCC is rapidly losing is credibility.

As a result, the Obama Administration would do better to come to grips with this fact and stop deferring to the IPCC findings when trying to justify increasingly  burdensome  federal regulation of  carbon dioxide emissions, with the combined effects of manipulating markets and restricting energy choices.

References:

Loehle, C., 2014. A minimal model for estimating climate sensitivity. Ecological Modelling, 276, 80-84.

Spencer, R.W., and W. D. Braswell, 2013. The role of ENSO in global ocean temperature changes during 1955-2011 simulated with a 1D climate model. Asia-Pacific Journal of Atmospheric Sciences, doi:10.1007/s13143-014-0011-z.