Updated, Jan. 29, 10:50 p.m. | David Roberts, the progressive environmental blogger who coined the phrase “climate hawk,” has done the environmental community a great service with a Grist post stressing the difference between a vision of a climate-safe energy future and a strategy for making that vision a reality.

One of his core lines is:

[M]ost decarbonization scenarios are thought experiments, not practical roadmaps. But when they are reported to the public, that distinction is often lost.

Marking the difference is essential unless you want to give the public a false sense that it’ll be easy to satisfy the world’s energy needs without overheating the planet.

This is particularly true given the “super wicked” nature of this issue, which is complicated by competing societal concerns, embedded special interests, huge gaps between human energy needs and clean-energy menus and other impediments to swift change.

The piece, titled “We can solve climate change, but it won’t be cheap or easy,” is important in many ways. One is that he’s created an opening for constructive crosstalk between camps that too often seem to be at each others’ throats — progressive environmentalists and people associated with the innovation-focused Breakthrough Institute, founded by the “Death of Environmentalism” authors Michael Shellenberger and Ted Nordhaus.

He centers the piece on a recent paper — “A critical review of global decarbonization scenarios: what do they tell us about feasibility?” — by four authors including Jesse D. Jenkins, an energy policy analyst long associated with Breakthrough who’s currently pursuing his doctorate at the Massachusetts Institute of Technology. I’m glad Roberts sees value in varied approaches to energy and climate progress. (For the record, I’ve participated in Breakthrough meetings and hung out with Grist staff.)

But the prime value lies in Roberts’s simple reminder, amid floods of glossy optimistic rhetoric, that taking the climate-warming carbon out of a growing global energy menu is a challenge requiring far more than better messaging or political tactics. My guess is he’d agree with my notion that energy progress will only come with an odd combination of “urgency and patience.”

The piece starts with Roberts’s critique of those, including Paul Krugman of The Times and Joe Romm of the Center for American Progress, who embraced a finding in last year’s Intergovernmental Panel on Climate Change report that even a very aggressive global push to cut carbon dioxide emissions would trim a barely perceptible 0.06 percentage points per year from global economic growth.

As with all such analyses, fine print matters and just one panel caveat such enthusiasts didn’t mention was this:

Under the absence or limited availability of technologies, mitigation costs can increase substantially depending on the technology considered.

One of the technologies the scenarios took as necessary was rapid global adoption of systems that capture and store carbon dioxide from power plants — none of which have been tested at anything remotely close to a scale the atmosphere would notice. (See “Scaling up carbon dioxide capture and storage: From megatons to gigatons,” a 2009 paper by Howard J. Herzog at the Massachusetts Institute of Technology, for just one of many sobering takes on what’s needed.)

On Twitter and in a Grist comment, I cheered Roberts on. I’ve long said (and I’ve often been punished for saying) such thought experiments are valuable ways to delineate how something might get done, but that’s just a starting point. It’s up to citizens, communities and experts on energy and innovation policy, human behavior and politics to dig in on how it might get done.

Here are three more examples showing the tough realities hidden by breezy bullet points.

In 2011, I posted two pieces on California’s ambitious plan to cut greenhouse gas emissions 80 percent by 2050.

Is it a road map or thought experiment?

See what you think after reading what Nate Lewis, a solar energy researcher at the California Institute of Technology, said in one of the posts:

California could get roughly halfway to that goal in a perfect world – one without impediments such as higher costs, nimby fights and resistance from consumers and industries wedded to fossil fuels.

But even in that perfect world, Lewis says, citing the reviewed literature, fundamental leaps in basic energy sciences would be required to get all the way – and the nation and world are not investing at anywhere the level that would be required in the related sciences and in development and demonstration of promising technologies.

Looking beyond California to the nation, Lewis cited a National Academy of Sciences report he co-authored with 40 experts in energy technology on a path to getting more than half of the country’s electricity from renewable sources by mid-century:

“Everybody agreed that if we were going to get more than half of our electricity in our country from renewables by 2050 we were going to have to do things that we simply don’t know how to do today at all and fundamentally change the way we use, generate and consume energy [relevant section here]. That’s completely in agreement with the California report. And it’s different than people who would tell you that we have all the technology we need and we just need the political will and let’s be done with it. That’s not what any technically knowledgeable panel concludes.”

Another example is the 2012 Renewable Electricity Futures study by the National Renewable Energy Laboratory. The study is waved around frequently by campaigners for wind and solar power. And why not, given the main bullet point:

Renewable electricity generation from technologies that are commercially available today, in combination with a more flexible electric system, is more than adequate to supply 80% of total U.S. electricity generation in 2050 while meeting electricity demand on an hourly basis in every region of the country.

But then there’s that darned fine print, including this disclaimer:

[A]lthough RE Futures describes the system characteristics needed to accommodate high levels of renewable generation, it does not address the institutional, market, and regulatory changes that may be needed to facilitate such a transformation.

That’s precisely the gap Roberts says needs to be the focus. I agree.

Finally, there was the Intergovernmental Panel on Climate Change synthesis report last fall. Here’s one (widely quoted) bullet point: “Greater use of low-carbon and no-carbon energy – many of these technologies exist today.”

As I wrote at the time, you’d have to dig deep and long in the background chapters to learn that “many of these technologies exist today” hides huge gaps, particularly at the scale that would be needed to blunt emissions of greenhouse gases.

For a far better description of the challenge and gaps, see Pathways to Deep Decarbonization, a report released last fall by two groups trying to help the United Nations advance sustainable development.

Here’s one blunt bullet point:

Very few countries have looked seriously at the operational implications of staying within the 2°C limit.

The word “operational” denotes the difference between a thought map and a plan.

And the executive summary included this sobering statement on an issue I first explored in a front-page article in The Times in 2006:

[T]he technical feasibility of deep decarbonization rests on the large-scale deployment of several low-carbon technologies, some of which are not yet fully commercialized or affordable. For this reason, countries and the international community as a whole must undertake a major research, development, demonstration, and diffusion (RDD&D) effort to develop low-carbon technologies and ensure their widespread availability and their cost-competitiveness with high-carbon alternatives, when the social cost of carbon is taken into account by means of carbon pricing, which, however, need not be uniform across countries.

Let’s circle back to the climate panel’s November report. As I wrote at the time, with all the graphics and lists and other content attending the report release, “Somehow the panel failed to fit in a single graph like this one from the International Energy Agency showing how utterly inconsequential energy research is in advanced democracies (the O.E.C.D.) compared to budgets for science on other things we care about”:

There are plenty of other examples, of course. Read this post for my look at a zero-carbon vision of my home state: “Can Wind, Water and Sunlight Power New York by 2050?” Thought experiment or road map? I’m sure views will vary.

I’ll give David Roberts the last word. Please read his post and explore the paper he cites, which was written by Peter Loftus of Primaira LLC, Armond Cohen of Clean Air Task Force, Jane Long, formerly of Lawrence Livermore National Laboratory, and Jesse Jenkins.

Here’s Roberts’s kicker, which sums things up well:

[W]e are past the time when thought experiments are enough. We need to start thinking in practical terms about how to get the technologies we need ready — as the authors say, “deep energy system decarbonization is likely to require an ambitious, focused agenda of rapid innovation and improvement in every critical technology area, even those commercially available today, as well as substantial ‘demand pull’ efforts and policies to ensure early demonstration, industry maturation, scale-up, and ‘learning by doing.’”

We need to think about the costs and who is going to pay them; even if the benefits outweigh the costs, the costs are going to be enormous. We need to think about the systemic changes required to integrate a large amount of variable renewables into an infrastructure that wasn’t designed for it. And most of all, we need serious, realistic thinking about the social and political buy-in necessary to drive wholesale energy transformation. In the fallen world we live in, such social and political barriers are likely to be more difficult to overcome than technology or modeling challenges.

It’s great to have these studies in our back pocket, as they refute the conservative mantra that a clean-energy transition is impossible. It is possible. But possible is a long way from practical or likely, and farther yet from “cheap” or “easy.” Let’s not fool ourselves about the huge task ahead.

Update, Jan. 29, 10:50 p.m. | Joe Romm, has posted part one of a rebuttal to Roberts’s post and mine, insisting that “solving climate change is ‘cheap'” — in relation to the long-term cost of inaction.

He does concur it won’t be “easy,” adding: “I have striven to avoid using that word. When I talk about this I usually say it is ‘not easy, but straightforward.'”

I focused, in fact, not on the economics nearly as much as the difficulties posed by inertia (just one example is the Bloomberg Administration estimate that 80 percent of the buildings in New York City in 2050 already exist today) and factors like the primacy of energy policy over carbon policy in the countries where nearly all emissions growth is coming.