Carbon dioxide release

Retorting of oil shales will generate more carbon dioxide per unit of useable energy produced than any other synfuel

development. Methods utilizing highture retorting (above 600°C) will cause more C0₂ to be released through decomposi- tion of carbonate rocks than will subsequently be generated by burning the oil produced. The amount of C0₂ produced by re- torting oil shale varies greatly depending on differences in mineralogy of the rock, organic content, and retorting techni- que.

Shale oil produced by low-temperature (near 500°C) re- torting yields about 30 kg of carbon as C0₂ for every million Btu of usable energy. This figure includes retorting and burning the oil and is significantly higher than the amount of C0₂ released when conventional fuels are burned (about 15 kg C/MBtu for natural gas, 21 kg C/MBtu for crude oil, and 25 kg C/MBtu for bituminous coal). Processing other synfuels and burning the products also generates about 30 kg C/MBtu. Retorting and burning shale oil by high temperature retorting could generate 70 kg Cl MBtu for shale that yields 25 gallons of oil per ton and 110 kg C/MBtu for yields of 10 gallons of oil per ton. It is possible that some of these estimates are on the high side (particularly for high-temperature retorting) because they assume that all of the carbon in the carbonate rock is released at high temperature.

Undoubtedly, this is not true. However, there are no mea- sured values with which to compare the estimates.

Because the global increase of atmospheric C0₂ appears to be the direct result of burning fossil fuels, it is of some interest to estimate how much C0₂ will be added to the atmosphere by shale oil production. An industry in the Piceance Creek basin producing 1 million barrels of oil per day would eject into the atmosphere from 0.06 to 0.17 x 109 tons of carbon per year.

Oil spills

Oil spills can have serious effects on marine life. A science- based appraisal of the effects reveals that whilst damage occurs and may be profound at the level of individual orga- nisms, populations are more resilient and natural recovery

processes are capable of repairing the damage and returning the system to normal functions. The first stage on the road to recovery is usually a well conducted clean-up operation but in some specific habitats aggressive clean-up methods can cause more harm than good and then it is better to let natural clea- ning processes take their course.

Many spill impacts have been documented in the scientific and technical literature, and although not all the effects of oil pollution are completely understood, an indication of the likely scale and duration of damage can usually be deduced from the information available. However, it can be difficult to present a balanced view of the realities of spill effects, given the often highly charged and emotional nature of a spill and its after- math. The scientific community can become polarised into op- posing camps with one side intent on quantifying every aspect of damage, and the other emphasising the capacity of the environment to recover naturally. The simple reality is that sometimes significant damage occurs, sometimes not and the aim of these pages is to draw together what general informa- tion is known about spill effects and their longevity.

The marine ecosystem is highly complex and natural fluc- tuations in species composition, abundance and distribution are a basic feature of its normal function. The extent of dama- ge can therefore be difficult to detect against this background variability. Nevertheless, the key to understanding damage and its importance is whether spill effects result in a downturn in breeding success, productivity, diversity and the overall functioning of the system.

Spills are not the only pressure on marine habitats; chronic urban and industrial contamination or the exploitation of the resources they provide are also serious threats. The following sections consider some of the types of damage caused by oil spills as well as some of the benefits of conducting post-spill studies.