Two related events occurred recently which affect the world of energy and climate science. A group of British climate researchers met in Oxford to discuss 4 Degrees And Beyond—

Despite 17 years of negotiations since the 1992 Rio Earth Summit, global greenhouse gas emissions have continued to rise. Since 2000 the rates of annual emissions growth have increased at rates at the upper end of the IPCC scenarios, presenting the global community with a stark challenge: either instigate an immediate and radical reversal in existing emission trends or accept global temperature rises well beyond 4°...

The aim of this conference is therefore to: (i) assess the consequences of a change in global temperature above 4°C (centigrade) for a range of systems and sectors, and (ii) explore the options that are open for avoiding climate changes of this magnitude...

The second event was the publication of a comment in the science journal Nature called The End Of Cheap Coal. The authors Richard Heinberg and David Fridley give their rationale for sounding a warning—

World energy policy is gripped by a fallacy — the idea that coal is destined to stay cheap for decades to come. This assumption supports investment in ‘clean-coal’ technology and trumps serious efforts to increase energy conservation and develop alternative energy sources. It is an important enough assumption about our energy future that it demands closer examination.

There are two reasons to believe that coal prices are likely to soar in the years ahead. First, a spate of recent studies suggests that available, useful coal may be less abundant than has been assumed — indeed that the peak of world coal production may be only years away. One pessimistic study1 published in 2010 concluded that global energy derived from coal could peak as early as 2011.

Second, global demand is growing rapidly, largely driven by China. Demand rose modestly in the 1990s (0.45% per year), but since 2000 it has been surging at 3.8% per year. China is both the world’s biggest producer of coal (40% of global production) and its biggest consumer. Its influence on future coal prices should not be underestimated. Economic shocks from rising coal prices will be felt by every sector of society. Better data on global coal supplies is long overdue and energy policies that assume a bottomless coal pit need rethinking urgently.

Obviously what unites these two events is coal. Coal burning will be by far the largest source of CO₂ (carbon dioxide) emissions in future decades, and thus the chief determinant of how much the average surface temperature of the Earth will rise in the 21st century. In the past decade, coal burning in China and India has grown by leaps and bounds. The energy derived supports their explosive economic growth, but the increased CO₂ emissions add to anthropogenic climate change.

Both graphics are from Heinberg and Fridley

The UK climate scientists are rightfully fearful of a 4°C rise in the Earth's surface temperature—this would be a planetary disaster. However, the argument that such a thing is possible rests mostly on a continuation of "business-as-usual" as far as economic growth and the concomitant burning of fossil fuels are concerned. (I say "mostly" because there's likely a relatively small but still significant chance that so-called positive feedbacks in the climate system and the Earth's carbon cycle could cause such a change absent huge increases in our fossil fuel consumption.)

Here's the abstract for When could global warming reach 4°C? by Richard A. Betts, et. al. A1FI is the worst (from a climate perspective) of a suite of "business-as-usual" scenarios.

The Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) assessed a range of scenarios of future greenhouse-gas emissions without policies to specifically reduce emissions, and concluded that these would lead to an increase in global mean temperatures of between 1.6°C and 6.9°C by the end of the twenty-first century, relative to pre-industrial.

While much political attention is focused on the potential for global warming of 2°C relative to pre-industrial, the AR4 projections clearly suggest that much greater levels of warming are possible by the end of the twenty-first century in the absence of mitigation. The centre of the range of AR4-projected global warming was approximately 4°C. The higher end of the projected warming was associated with the higher emissions scenarios and models, which included stronger carbon-cycle feedbacks.

The highest emissions scenario considered in the AR4 (scenario A1FI) was not examined with complex general circulation models (GCMs) in the AR4, and similarly the uncertainties in climate–carbon-cycle feedbacks were not included in the main set of GCMs. Consequently, the projections of warming for A1FI and/or with different strengths of carbon-cycle feedbacks are often not included in a wider discussion of the AR4 conclusions.

While it is still too early to say whether any particular scenario is being tracked by current emissions, A1FI is considered to be as plausible as other non-mitigation scenarios and cannot be ruled out. (A1FI is a part of the A1 family of scenarios, with ‘FI’ standing for ‘fossil intensive’. This is sometimes erroneously written as A1F1, with number 1 instead of letter I.)

This paper presents simulations of climate change with an ensemble of GCMs driven by the A1FI scenario, and also assesses the implications of carbon-cycle feedbacks for the climate-change projections. Using these GCM projections along with simple climate-model projections, including uncertainties in carbon-cycle feedbacks, and also comparing against other model projections from the IPCC, our best estimate is that the A1FI emissions scenario would lead to a warming of 4◦C relative to pre-industrial during the 2070s. If carbon-cycle feedbacks are stronger, which appears less likely but still credible, then 4◦C warming could be reached by the early 2060s in projections that are consistent with the IPCC’s ‘likely range’.

Here is a more accessible discussion of the same issues—

Niel Bowerman's Oxford colleagues have calculated that to keep maximum global temperature increases below 2 degrees Celsius, humanity can spew greenhouse gases equivalent to no more than 1 trillion metric tons of carbon (or 3.67 million metric tons of carbon dioxide) by 2200. Already, he adds, regarding this carbon limit: “We’re just over halfway there"...

Climate scientist Richard Betts of the United Kingdom’s Meteorological Office in Exeter led a team that attempted to gauge how soon a global 4 degree C warming might occur. They considered seven different “business-as-usual” scenarios of energy use.

“We don’t really know which [energy use and emissions] trajectory we’re on yet,” Betts says. But by using the upper value for likely emissions into the future — based on what industrial nations are emitting and what rapidly industrializing nations like China and India probably will soon be releasing annually — “you get to this projection showing us reaching 4 degrees in the 2060s,” Betts says.

There’s plenty of uncertainty surrounding such a projection, he acknowledges. “But if our models are a good judge,” he cautions, greenhouse gas emissions will have to peak within about five years or so if humanity hopes to dodge temperature increases exceeding 2 degrees C. When Betts’ group used less extreme versions of the business-as-usual emissions trajectories, the time to excessive warming lengthened.

“But most of these business-as-usual scenarios still gave you a 4 degree warming at some point in the next century,” he reports.

Now let's talk about confusion. There's "plenty of uncertainty"—we don't really know which [energy use and emissions] trajectory we're on yet. On the one hand, we have researchers warning that coal production could peak within a few decades (and presumably decline thereafter). On the other hand, we have climate scientists running GCMs (general circulation models) using seven different "business-as-usual" scenarios. The outcome of this latter experiment is a 4°C rise in the Earth's average surface temperature by the 2060s or 2070s.

Both of these outcomes (the peak and decline of coal production within a few decades, or 4°C of surface warming) would be an unmitigated disaster for human civilization. There's no doubt about it. Running low on coal would be great for the climate, but would blow up human economies. If we have more coal than we know what to do with, we would blow-up the climate but the coal would help sustain human economies, absent a miraculous breakthrough in renewable energy. (And then there's the peak oil problem, but I don't have the time or space to talk about that today.) And what is the important information that helps us determine which, if either, of these coal disasters may occur?  

We urgently need to know how much economically and technically recoverable coal we have left to exploit. We urgently need a global geological survey to make that assessment.

Heinberg and Fridley call for better data, which only makes sense—

The poor quality of coal data globally means that uncertainty clouds every forecast. Even in the technologically advanced United States — the ‘Saudi Arabia of coal’ — most experts rely on decades-old coal surveys. These are commonly interpreted as indicating that the nation has a coal supply with a 250-year lifetime. This figure is not reliable enough for strategic energy planning...

At the very least, the USGS should urgently complete a new national coal survey. And it is essential for the security of energy supplies globally that Chinese domestic coal production and the timing of its likely decline is better understood.

We believe that it is unlikely that world energy supplies can continue to meet projected demand beyond 2020...

Unfortunately, we meet with a little more confusion here, because in the absence of a global geological survey to assess the true size of our recoverable coal reserves, you can pretty much believe anything you're inclined to believe.

In so far as the Fate Of Human Civilization very likely rests upon the answer to the question how much coal have we got, you might think that we humans would be all over this issue. But, no! — ignorance and confusion reign. We would rather live in the dark than gather the data we need to assess our energy and climate future. Maybe it's time to rename our species, to take the "sapiens" out of Homo sapiens. How about Homo obliviosus?

And I didn't even talk about petroleum today. Talk about confusion. Here's Dr. Mark New talking about 4 Degrees And Beyond.