So what is going on? Yes, it is true that "the IPCC implicitly assumes that the bulk of the challenge of reducing future emissions will occur in the absence of climate policies." But as we'll see, that is a semantic point. It is extremely misleading to imply that technological changes occur spontaneously or automatically.

In fact, in its scenarios, the IPCC assumes energy and environmental policies, but just isn't allowed to call them "climate policies." I kid you not.

Here is what the Special Report on Emission Scenarios (SRES), which the Nature article cites, says about the scenarios:

As required by the Terms of Reference, however, none of the scenarios in the set includes any future policies that explicitly address additional climate change initiatives, although GHG emissions are directly affected by non-climate change policies designed for a wide range of other purpose.

Let me give a specific example. Most of the IPCC scenarios are of little interest because they result in global warming of much more than 2 degrees C -- and thus make catastrophic climate impacts likely. The B1 scenario, however, is worth examining because it keeps warming close to 2 degrees C through energy efficiency and decarbonization. Does this happen spontaneously? Quite the reverse:

The central elements of the B1 future are a high level of environmental and social consciousness combined with a globally coherent approach to a more sustainable development. Heightened environmental consciousness might be brought about by clear evidence that impacts of natural resource use, such as deforestation, soil depletion, over-fishing, and global and regional pollution, pose a serious threat to the continuation of human life on Earth. In the B1 storyline, governments, businesses, the media, and the public pay increased attention to the environmental and social aspects of development.

In other words, in B1, humanity aggressively pursues sustainable development.

... Technological change plays an important role. At the same time, however, the storyline does not include any climate policies, to reflect the SRES terms of reference. Nevertheless, such a possible future cannot be ruled out.

Semantically, the scenario writers are not allowed to include climate policies -- but they are allowed to include policies that would lead to a great deal of decarbonization and energy efficiency, which is the same thing.

Particular effort is devoted to increases in resource efficiency to achieve the goals stated above. Incentive systems, combined with advances in international institutions, permit the rapid diffusion of cleaner technology. To this end, R&D is also enhanced, together with education and the capacity building for clean and equitable development. Organizational measures are adopted to reduce material wastage by maximizing reuse and recycling. The combination of technical and organizational change yields high levels of material and energy saving, as well as reductions in pollution.

That does not sound like "spontaneous technological change and related decarbonization." In fact, it sounds like an aggressive and coherent climate policy to me.

The B1 storyline sees a relatively smooth transition to alternative energy systems as conventional oil and gas resources decline. There is extensive use of conventional and unconventional gas as the cleanest fossil resource during the transition, but the major push is toward post-fossil technologies, driven in large part by environmental concerns.

And it also sounds like B1 is imagining a future where conventional oil and gas production peaks and declines, which, as we've seen, appears to be our likely future.

Given the high environmental consciousness and institutional effectiveness in the B1 storyline, environmental quality is high, as most potentially negative environmental aspects of rapid development are anticipated and effectively dealt with locally, nationally, and internationally. For example, transboundary air pollution (acid rain) is basically eliminated in the long term. Land use is managed carefully to counteract the impacts of activities potentially damaging to the environment. Cities are compact and designed for public and non-motorized transport, with suburban developments tightly controlled. Strong incentives for low-input, low-impact agriculture, along with maintenance of large areas of wilderness, contribute to high food prices with much lower levels of meat consumption than those in A1. These proactive local and regional environmental measures and policies also lead to relatively low GHG emissions, even in the absence of explicit interventions to mitigate climate change.

Pretty amazing, no? A primary conclusion of the Nature article, embodied in its title, "Dangerous Assumptions," is simply wrong.

And as we saw in part one, the recent carbonization data does not support the other central conclusion of the article, "Enormous advances in energy technology will be needed to stabilize atmospheric carbon dioxide concentrations at acceptable levels." If anything, it supports the reverse conclusion: If you want to beat 450 ppm and avoid catastrophic climate impacts, a significant price for carbon (plus aggressive technology deployment) is much more important than technology breakthroughs.

So both of the two major conclusions of the Nature article are wrong. I do remain mystified as to why Nature published it.

This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.