Last Friday the government released the draft of the third National Climate Assessment public comment. As so often happens in these episodes, the report is full of scientific diagnoses of a problem, and then jumps to a “solution” that won’t even work on the terms set forth by the report. If the worst-case scenarios are correct, then even very strong action by the federal, state, and local governments in the United States will do very little to alter the global climate, but will definitely cause great damage to the American economy, reducing the annual income of American family household by almost $2,000. Although the draft report’s wording would lead the reader to believe otherwise, even the “consensus” projections show that the U.S. will only contribute about 6 percent of the total global warming through 2100. This is an “inconvenient truth” that the proponents of intervention in the energy sector refuse to acknowledge.

The National Climate Assessment Wants Government to Act NOW

The full report is a whopping 147 Mb file, but an Executive Summary gives its flavor—and this is the only portion of the report that analysts and policymakers will read. The report doesn’t merely report on the natural sciences, but also gives a great deal of attention to government policy responses. Here’s a quote from the Executive Summary, where the numbers are the line numbers embedded in the draft:

“10 …Mitigation and adaptation are linked, in that effective mitigation reduces the need

11 for adaptation. Both are essential parts of a comprehensive response strategy. The threat of

12 irreversible impacts makes the timing of mitigation efforts particularly critical. This report

13 includes chapters on Mitigation, Adaptation, and Decision Support that offer an overview of the

14 kinds of options and activities being planned or implemented around the country as governments

15 at local, state, federal, and tribal levels, businesses, other organizations, and individuals begin to

16 respond to climate change (Ch. 26, 27, 28).

17 Large reductions in global emissions, similar to the lower emissions scenario (B1) analyzed in

18 this assessment, would be necessary to avoid some of the worst impacts and risks of climate

19 change. The targets called for in international agreements would require even larger reductions

20 than those outlined in scenario B1 (Figure 1). Meanwhile, global emissions are still rising, and

21 are on track to be even higher than the high emissions scenario (A2) analyzed in this report. The

22 current U.S. contribution to global emissions is about 20%. Voluntary efforts, the recent shift

23 from coal to natural gas for electricity generation, and governmental actions in city, state,

24 regional, and federal programs under way and have contributed to reducing U.S. emissions in

25 the last few years. Some of these actions are motivated by climate concerns, sometimes with

26 non-climate co-benefits, while others are motivated primarily by non-climate objectives. These

27 U.S. actions and others that might be undertaken in the future are described in the Mitigation

28 chapter of this report; at present they are not sufficient to reduce total U.S. emissions to a level

29 that would be consistent with scenario B1 or the targets in international agreements…”

We have underlined key elements of the excerpt above, which beautifully illustrate the tone of urgency and calls for drastic action by government at all levels. It is no wonder that the loudest climate alarmists welcome the draft with open arms, because it fits their messaging perfectly.

Unilateral U.S. Action Will Have Very Little Influence on Climate Change

There are well-known debates about the underlying physical science of manmade climate change. As an economist, I will put these issues to one side, and accept the standard results as reported in the International Panel on Climate Change (IPCC) at face value. Using the IPCC’s own projections, we can see that popular policy ideas such as a carbon tax would do very little to mitigate projected damages.

Recently climate scientist Chip Knappenberger walked through the IPCC emission scenarios and calculated how much of the total projected warming through the year 2100 would be due to US emissions from this point forward. His answer is shockingly low:

In other words, how much of the IPCC’s projected 1.1°C to 6.4°C of warming will the U.S. be responsible for in the next century? The answer is about 0.08°C of the low end estimate and about 0.35°C of the high end… Using the IPCC’s mid-range scenario, carbon dioxide emissions from the U.S. contribute about 0.19°C of the total 2.96°C global temperature rise.

Yep, that is it. For all the incessant talk as to how the highly consumptive U.S. lifestyle—from SUVs, to air conditioners, to big screen TVs and huge portion sizes—is leading climate catastrophe, the sum total of our contribution to “global warming” this century will amount to the neighborhood of about 0.2°C. Not five degrees. Not two degrees. But about two-tenths of a degree Celsius. And even this number may be on the high side if the climate sensitivity is lower than about 3°C (see here for more on recent findings concerning the climate sensitivity).

So all the U.S. carbon dioxide emissions restriction tactics—EPA regulations, cap and trade schemes, carbon taxes, efficiency programs, guilt-inducing ad campaigns, etc.—are aimed at chipping away at this already tiny 0.2°C. Big deal. [Emphasis in original.]

Thus we see that it was very misleading when the new National Climate Assessment draft said that the “current U.S. contribution to global emissions is about 20%.” In context, it led the reader to believe that the United States has the power to avert up to one-fifth of the potentially severe climate change the report says could be coming. Yet as Knappenberger’s analysis shows, this is wrong. China and India, with their growing economies, are projected to have much greater increases in emissions than the United States in the coming decades, meaning the U.S. share of the “blame” for future warming is more like 6 percent, not 20. Furthermore, even very aggressive U.S. government action wouldn’t eliminate all of this share, but the point is, even a total cessation of U.S. economic activity would at most avert 6 percent of the projected rise in global temperatures, according to the IPCC’s own mid-range scenario.

In this context, it’s worth pointing out that the draft report comes on the heels of the Doha round of discussions relating to the Kyoto Protocol, which even Kyoto’s host country, Japan, no longer supports. In fact, despite alarmist attempts to convince Americans of the errors of our energy ways, the number of countries agreeing to limit their own carbon dioxide emissions has shrunk dramatically, and now represents less than 15% of total world emissions.

US Policies Can Hurt Domestic Economy

But if the U.S., state, and local governments can’t do much to stop global warming, they can put a serious dent in economic growth. For example, the Heritage Foundation’s recent analysis quotes the government’s own assessment that a hypothetical $25/ton carbon tax would reduce the income of a family of four $1,900 in 2016, and cause large increases in gasoline and electricity prices.

The real irony is that a strong enough carbon tax to seriously reduce US emissions would spur increased emissions elsewhere, as industry relocated to jurisdictions that didn’t have penalties on emissions. The whole issue shows the futility of dealing with what the alarmists themselves recognize is a “global problem” with actions by individual governments. It is extremely unlikely that the poorer regions of the world will be content to remain in their current deficiency of energy development because of warnings about future climate change.


Even on its own terms, the newly released draft of the National Climate Assessment does not make the cost/benefit case for drastic U.S. government intervention in the name of mitigating future climate change. These policies would harm U.S. competitiveness while doing little to slow global emissions. To point out these facts isn’t to be a “climate denier,” it is simply to ask that policymakers base their decisions on sensible arguments.

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