In recent comments submitted to EPA, University of Alabama in Huntsville atmospheric scientist John Christy challenges the physical science basis of the agency’s Clean Power Plan.
EPA assumes that anthropogenic emissions of greenhouse gases, especially carbon dioxide (CO2) from energy use, are the driving force behind recent climate change. It thus further assumes that regulating CO2 emissions can mitigate future climate change, providing substantial health benefits to the American people.
Christy does not dispute the reality of climate change. The climate is always changing on multiple time scales. However, the Earth has experienced climatic “fluctuations in the past centuries similar to and even greater than what has occurred in the past 50 years.” Scientific instruments measure what the climate is doing; they don’t tell us why it behaves as it does.
To understand what drives climate change, scientists must test hypotheses against data. EPA assumes CO2 emissions are the chief driver because that’s what state-of-the-art IPCC climate models assume.
But, Christy points out, data from six independent global temperature monitoring systems “demonstrate that the models do not yet have the ability to discern ‘why’ a climate variation may have occurred simply because they cannot even reproduce ‘what’ has occurred.” The chart below compares climate model projections with observed temperatures over 35 years in the tropical troposphere, the portion of the atmosphere where models project a “highly consistent and significant” warming response to rising CO2 concentrations.
Here is the same comparison of model projections vs. observations but shown in five-year running averages rather than linear trends, and for 32 model ensembles rather than individual models. The dashed red line depicts the average projection of U.S. climate models.
The models clearly “overcook the atmosphere.”
You might think such discrepancies only cast doubt on the IPPC’s climate sensitivity estimates (how much warming to expect from a given increase in atmospheric CO2 concentrations), not on the detection of anthropogenic global warming. In fact, Christy argues, the divergence shows that “CO2 has had no discernable impact in the atmospheric region where models assert greenhouse gas impacts should be largest.”
To demonstrate that point, Christy magnifies part of a chart ‘buried without comment’ in IPCC supplementary material. The area bounded by the white lines, which depicts the range of temperature observations during 1979-2011, falls within the blue area, which depicts the range of climate simulations from models run with “natural forcings” only (i.e. with no extra anthropogenic forcing).
Thus, it is possible that all the warming since the start of the satellite record is due to natural variability. Christy draws out the obvious policy implications.
Thus, we should have little confidence that the future will play out as the models suggest. . . .The EPA cannot conclude it knows “why” the climate system changes and thus cannot assert it will control “what” the climate will do . . .
Even if the models were accurate, the Clean Power Plan cannot produce measurable climate impacts. The Plan’s hoped-for 750 million metric ton reduction in CO2 emissions is only 1/7th of total U.S. emissions and is “miniscule” compared to global emissions. “As such, climate impacts of these reductions will also be minuscule and thus undetectable and un-attributable.”
MAGICC, an IPCC-approved climate change calculator developed with EPA support, estimates that the Clean Power Plan will avert only 0.02°C of warming by 2100. Christy comments:
The direct, measureable impact of CO2 emission reductions on public health due to climate change mitigation will be zero. Because the rule has no discernible efficacy regarding the impact of CO2 on climate, there is no rational basis to insist it be adopted.
Christy sensibly advises EPA to “step back and re-examine the fundamental basis” for its climate policy regulations:
The EPA should constitute a “Red Team” of analysts, independent from the climate modeling industry, to judge the current state of knowledge, i.e. the current state of how much we know about the “why” of climate variations. Such an examination would provide transparency to the process and give confidence to the public that the agency values open examination of its methodology.