social cost of carbon

Post image for Social Cost of Carbon: Interagency Group Predictably Predicts Climate Change Worse Than Predicted

Hold the presses! A U.S. Government interagency working group has just released its updated Technical Support Document (TSD) on the social cost of carbon (SCC).

This is joyous news in some circles. “The ‘Social Cost of Carbon’ Is Almost Double What the Government Previously Thought,” Climate Progress enthuses. Why are they pleased? Because the higher the SCC, the stronger the (apparent) case for suppressing the production and export of hydrocarbon energy in general, and for blocking the Keystone XL pipeline in particular.

SCC is an estimate of how much damage an incremental ton of carbon dioxide (CO2) emissions does to humanity and the biosphere. SCC estimates are driven by assumptions about such issues as climate sensitivity (how much warming results from a given increase in CO2 concentrations), climate impacts (how warming will affect weather patterns and sea-level rise), economic impacts (how changes in global temperature, weather, and sea-level rise will affect agriculture and other climate-sensitive activities), and technological change (how adaptive capabilities will develop as climate changes).

Modelers feed the assumptions into computer programs called “integrated assessment models” (IAMs). By tweaking those values, the modeler can get pretty much any result he desires. Outcomes also vary based on the discount rate selected, i.e., how much people are assumed to value income in the future compared to income in the present.

Using three IAMs, three discount rates (2.5,% 3,% and 5%), and a fourth value representing low-probability catastrophic impacts, the interagency group calculates four SCC estimates for the year 2020. In the working group’s 2010 TSD, the SCC estimates were $7, $26, $42, and $81 (2007$). In the updated TSD, the corresponding estimates are $12, $38, $58, and $129 (2007$). Excuse me, but even for the high-impact projections, the updated estimate ($129) is 59% higher than the 2010 estimate ($81), which is more than a tad shy of “almost double.”

Let’s cut to the chase. Those who say the SCC is bigger than the government previously thought merely recycle the old saw that climate change is “worse than scientists previously thought.” They are mistaken. The climate change outlook is better than we have long been told.

One reason the updated estimates are higher is that the IAMs contain an “explicit representation” of sea-level rise “dynamics.” Are the modelers keeping up with the scientific literature? Consider two recent studies

  • King et al. (2012): The rate of Antarctic ice loss is not accelerating and translates to less than one inch of sea-level rise per century.
  • Faezeh et al. (2013): Greenland’s four main outlet glaciers are projected to contribute 19 to 30 millimeters (0.7 to 1.1 inches) to sea level rise by 2200 under a mid-range warming scenario (2.8°C by 2100) and 29 to 49 millimeters (1.1 to 1.9 inches) under a high-end warming scenario (4.5°C by 2100).

If 21st century sea-level rise is more likely to be measured in inches rather than feet or meters, shouldn’t SCC estimates decline?

And what about the 15-year period of no-net warming, which the climate science establishment did not predict and still struggles to explain? The warming pause is hard to square with the mantra of “worse than we thought.” It is evidence that the SCC is lower than they thought.

Let’s look at the disconnect between what they predicted and what happened.  The graph below comes from NASA scientist Roy Spencer[click to continue…]

Post image for Carbon Tax? Sorry, I Already Gave at the <strike>Office</strike> Gas Pump

Carbon tax advocates say Congress should slap a price penalty on fossil fuels to make consumers bear the “social cost of carbon” (SCC) — the damage carbon dioxide (CO2) emissions allegedly inflict on public health and welfare via their presumed impacts on global climate.

What is the SCC? Depends on who you ask. Climate “hot heads” like Al Gore think the SCC is huge. “Lukewarmers” like Patrick Michaels think the SCC is less than the cost of the tax or regulatory burden required to make deep cuts in CO2 emissions. “Flatliners” like Craig Idso think the SCC is negative (i.e. CO2’s net impact is beneficial), because a moderately warmer climate is healthful and CO2 emissions nourish the biosphere.

In February 2010, the EPA and 11 other agencies issued a Technical Support Document (TSD) on the SCC. The TSD’s purpose is to enable federal agencies to incorporate the “social benefit” of CO2 emission reductions into cost-benefit estimates of regulatory actions.

The TSD recommends that agencies, in their regulatory impact analyses, use four SCC estimates, ranging from $5 per ton to $65 per ton in 2010:

For 2010, these estimates are $5, $21, $35, and $65 (in 2007 dollars). The first three estimates are based on the average SCC across models and socio-economic and emissions scenarios at the 5, 3, and 2.5 percent discount rates, respectively. The fourth value is included to represent the higher-than-expected impacts from temperature change further out in the tails of the SCC distribution.

Here’s where it gets interesting. Both the federal and state governments levy taxes on motor fuel. Motor fuel taxes are not called carbon taxes but their economic effect is the same — impose a price penalty on consumption. Moreover, via simple arithmetic any carbon tax can be converted into an equivalent gasoline tax and vice versa.

The point? Americans in every state except Alaska already pay a combined federal and state gasoline tax that is higher than a carbon tax set at $5, $21, or $35 per ton. Americans in five states pay a combined gasoline tax that is higher than a $65 per ton carbon tax. Americans in several other states pay a combined gasoline tax that is nearly as high as a $65 per ton carbon tax.    [click to continue…]