Unsustainable Energy Demands

Vaclav Smil, who is Professor in the Faculty of Environment at the University of Manitoba,
has a thorough study of the pessimistic outlook for the popular solar-based "renewable energy" strategies, at

http://www.vaclavsmil.com/wp-content/uploads/docs/smil-articles-science-energy-ethics-civilization.pdf

His conclusions are more pessimistic than mine, although he quotes conclusions more pessimistic than his.
I have extracted some of his more trenchant observations in the following,

With the abbreviations:

Energy Consumption Acceleration

In 1800, a New England farmer using two oxen to plow his stony field controlled about 500 W of animate energy.
In 1900, a prosperous Great Plains farmer controlled 5 kW of sustained animate power as he held the reins of six large horses when plowing his fields.
In 2000, his great-grandson performed the same task in the air-conditioned comfort of the insulated cabin on a huge tractor capable of 300 kW.

In 1800, a coach driver controlled about 2.5 kW of horse power on an intercity route.
In 1900, an engineer operated a steam locomotive along the same route, commanding about 1 MW of steam power.
In 2000, a captain of a Boeing 737 flying between the same two cities could leave it to onboard microprocessors to control two jet engines whose aggregate cruise power added up to about 10 MW.


Biomass Fallacies

Terrestrial net primary productivity (NPP) of 55–60 TW is nearly five times as large as was the global TPES in 2005, but proposals of massive biomass energy schemes are among the most regrettable examples of wishful thinking and ignorance of ecosystemic realities and necessities. Their proponents are either unaware of (or deliberately ignore) three fundamental findings of modern biospheric studies.

First, as the Millennium Ecosystem Assessment (2005) demonstrated, essential ecosystemic services (without which there can be no viable economies) have already been modified, reduced, and compromised to a worrisome degree. Massive, intensive monocultural plantings of energy crops could only accelerate their decline.

Second, humans already appropriate 30%–40% of all NPP as food, feed, fiber, and fuel, with wood and crop residues supplying about 10% of the TPES (Rojstaczer et al., 2001).

Moreover, highly unequal distribution of the human use of NPP means that the phytomass appropriation ratios are more than 60% in east Asia and more than 70% in western Europe (Imhoff et al., 2004).

Claims that simple and cost-effective biomass approaches could provide 50% of the world's TPES by 2050 or that one or two Gt of crop residues can be burned every year would put the human appropriation of phytomass close to or above 50% of terrestrial photosynthesis.

This would further reduce the phytomass available for microbes and wild heterotrophs, eliminate or irreparably weaken many ecosystemic services, and reduce the recycling of organic matter in agriculture.

Only an utterly biologically illiterate mind could recommend such action.

Finally, nitrogen is almost always the critical growth-limiting macronutrient in intensively cultivated agroecosystems as well as in silviculture.

Mass production of phytomass for conversion to liquid fuels, gases, or electricity would necessitate a substantial increase in continuous application of this element.

Proponents of massive bioenergy schemes appear to be unaware of the fact that the human interference in the global nitrogen cycle has already vastly surpassed the proportional anthropogenic change in carbon cycle.

The surfeit of reactive nitrogen – dissolved in precipitation, dry deposited, causing spreading contamination and eutrophication of fresh and coastal waters, escaping as N2O via denitrification, and changing the specific composition of sensitive ecosystems – is already the cause of an undesirable biosphere-wide change (Smil, 2002).

Until we create engineered organisms capable of superior enzymatic conversion or photosynthetic efficiencies, or at least until we have affordable, efficient direct photovoltaic solar-energy conversion, there are two fundamental reasons why we cannot substitute for fossil fuels by harnessing renewable energy flows.

First, except for prospects to tap direct insolation, global aggregates of all proposed renewable energy sources are smaller than current global energy use. Second, none are available at suitably high power densities sufficient to deliver the high energy throughputs required by the existing global civilization.

Pessimism

Truly long-range forecasts are impossible, albeit increasingly common.
Two prominent physicists, Martin Rees and Stephen Hawking, have recently joined the catastrophist school. They believe there is a high probability of civilization's demise before 2050.

Not Vaclav Smil's View

Prof. Smil proceeds to recommend serious behavioral changes that might remedy our profligacy, but he ignores what I believe to be the truly renewable, sustainable alternative of total conversion of quite small amounts of uranium and thorium to fission products and usable industrial energy.