Uncertain road to ozone recovery

Depletion of the Earth's ozone layer is being tackled through the Montreal Protocol, which puts limits on the production of ozone-depleting halogen chemicals. The Protocol is effective, but its aims are threatened by production and emission of chlorofluorocarbon-12 (a refrigerant) and halon-1211 (a fire-fighting chemical) in particular.

and Schultz 1 adds a new dimension to characterization of the orbitofrontal neuronal activity -the relative attraction of the incentive.
It is important to place these results into the broader context of the part played by the prefrontal cortex in cognition. Studies of the prefrontal cortex have focused on the lateral prefrontal cortex in relation to working memory 5,6 . Current debates centre on whether dorsal and ventral parts of the lateral prefrontal cortex are functionally segregated according to what information is retained in working memory, or how that information is kept there 5,6 . But the orbitofrontal cortex -which occupies quite a large proportion of the prefrontal cortex -is not essential for working memory. If this area of the brain is damaged, working-memory tasks are not impaired. Moreover, clinical and noninvasive studies indicate that the orbitofrontal cortex is important for estimating the pleasantness or value of objects, emotional reactions 3,7 and motivational operations such as expectation of reward 8,9 . The lateral prefrontal cortex, which is considered to be more involved in cognitive operations, is also implicated in reward expectancy 8,9 . It is clear, then, that theories to describe the functions of the primate prefrontal cortex will have to include the motivational parameters that underlie much of our behaviour 10 . is presumably even larger now. The combined effect of these emissions is continuing growth of CFC-12 in the atmosphere (Fig.  1a, overleaf), and this is the biggest single long-term threat to ozone recovery.
Fortunately, HCFC emissions to date have been only 50% of those permitted under the Protocol; in large part this is because HCFCs are due to be phased out by 2030, and some parts of the refrigeration and air-conditioning industry have hesitated to invest in short-term HCFC technologies. Likewise, HCFCs have not replaced CFCs in aerosols or foam plastics, where hydrocarbons or 'not-in-kind' substitutes have filled these niches. Yet HCFC useand therefore emissions and atmospheric concentrations -are predicted to increase substantially, and legally, under the Protocol over the next decade 4 as HCFCs continue to be used as CFC substitutes in refrigeration (Fig. 1b).
Another emerging player is halon-1211 (CBrClF 2 ), a fire-fighting chemical used increasingly in developing countries such as China and Korea, which now account for over 95% of global production of halons 3 . Under the Protocol, emissions of halon-1211 were thought to have peaked in the late 1980s (ref. 4), but atmospheric observations indicate near constant 2,5 or possibly growing 6 emissions ( Fig. 1c and d). Using inventories based on atmospheric observations, emissions in the late 1990s are 50-60% higher than those predicted from global production data 6 . Presumably global production has been underestimated, or emissions from the bank are larger than assumed (or both). Studies by Montzka et al. 2 and a group involving one of us 6 conclude that, in the near term (as opposed to CFC-12 in the long term), halon-1211 emissions pose the largest threat to ozone recovery.
Prompt and continuing progress towards ozone recovery requires that emissions of halocarbons must be reduced faster than is apparent from current observations of the atmosphere. The United Nations Environmental Programme is facilitating such an accelerated phasing out of halon use in China, with production of halon-1211 scheduled to end by 2006, four years ahead of the Protocol 7 . In addition, the technology exists to recycle or destroy the bank of CFC refrigerants that would otherwise vent to the atmosphere when refrigeration systems are scrapped. The uses of HCFCs could be restricted to refrigeration, where their identification and recycling is again possible, and emphasis could be placed on use of very short-lived gases such as HCFC-123 (CHCl 2 CF 3 ) that pose a minor risk to the ozone layer 8 . All in all, it is possible that ozone depletion can be halted in the next decade. But it will require a level of global stewardship that still poses a substantial challenge to all parties to the Montreal Protocol. T he manufacture and emission of chlorofluorocarbons (CFCs), our inadvertent global experiment in modifying the Earth's stratosphere, has damaged the ozone layer for decades to come. The Montreal Protocol, which was agreed in 1987 and revised several times in the 1990s, and has the aim of reducing global emissions of ozone-depleting chemicals, has gone a significant way to solving the 'ozone problem' 1 . However, as described by Montzka and colleagues on page 690 of this issue 2 , the road to ozone recovery remains uncertain.
The authors report the good news that, by 1997, the lower-atmospheric burden of ozone-depleting halogen compounds (chloro-and bromocarbons) had declined by 3% from its 1993-94 peak; and they provide a reminder that this decline is almost entirely due to the rapid atmospheric removal of the solvent methyl chloroform (CH 3 CCl 3 ), global emissions of which are now virtually zero. But concentrations of other halocarbons -carbon tetrachloride (CCl 4 ) and CFC-11 (CCl 3 F), for instanceare falling more slowly, and those of others such as CFC-12 (CCl 2 F 2 ) are still rising. If the decline in emissions of these other halocarbon species does not gather pace, the overall fall in halogen concentrations in the atmosphere will stall sometime during the next decade.
What are the barriers to ozone recovery? Montzka et al. have identified several, namely, emissions of refrigerant CFCs, of HCFCs (hydrochlorofluorocarbons) as interim CFC replacements, and of halons (bromocarbons) as fire-fighting chemicals. In the developed world, a large 'bank' of CFC-12 in old refrigeration and vehicle air-conditioning systems continues to leak slowly into the atmosphere. Although new CFC production declined by a factor of 4-5 from 1986 to 1995 in accord with the Montreal Protocol, the developing world (China, India, Mexico) has increased production by 2-3 fold (largely of CFC-12), so that in 1995 it accounted for 45% of global CFC production 3 . This figure Ozone depletion is the dark side of the CFC experiment. But, for science, there is a bright side -the great progress in atmospheric chemistry, made over the past 25 years, which stems in part from the scientific and political drive to understand CFCs and ozone depletion, and in part from the study of the rapid yet transient rise of the synthetic halocarbons. For example, the earliest measurements of CFC-11 envisaged its use as a tracer of air motions 9 , and it has become a standard test of global models of atmospheric chemistry 10 (and also a diagnostic indicator of ocean circulation); the first meaningful measure of the mean tropospheric concentration of hydroxyl radicals (OH), which destroy CH 3 CCl 3 and HCFCs, is derived from observations of CH 3 CCl 3 (refs 11, 12); CFC pollution events in Ireland are used to calibrate European emissions of other greenhouse gases 13 ; and study of CH 3 Br (a crop and soil fumigant) has shown us the importance of the ocean in determining the atmospheric residence time of a soluble trace gas, and has resulted in revision of the concept of ozone-depletion potential for short-lived gases 14 .
What new opportunities will the second phase of the CFC experiment provide? Through its latitudinal gradient, the decay of CH 3 CCl 3 will give us a measure of the north-south hemispheric difference in OH concentrations, plus a long-term record of possible OH trends. And, after sources of CFC-11 have diminished sufficiently, its atmospheric decay will provide us with the first accurate lifetime for a CFC, and the north-south differences at the surface will measure hemispheric asymmetry in stratosphere-troposphere exchange. It is serendipitous indeed that CFCs and related halocarbons have provided, and will continue to provide, some of the benchmarks of progress in atmospheric chemistry. news and views 664 NATURE | VOL 398 | 22 APRIL 1999 | www.nature.com 100 YEARS AGO The Groundwork of Science; a Study of Epistemology. By St. George Mivart. The chief definite conclusions which are drawn are that it (the universe) cannot consist of one kind of energy only, that it is impossible that intellect can have been evolved from mere physical force, and that animals show no signs of latent intellectuality. It is further insisted "that the portion of truth which we are able to attain to in our investigations of the cosmos, is but an unimaginably small portion of the whole"; a statement which will, we imagine, not be seriously challenged by workers in science. To the latter, viz. the science workers, Dr. Mivart devotes some attention in the concluding pages of his book. The narrowing effect of extreme specialism upon the mind is an undoubted evil ... . But there is the opposite evil of becoming diffuse to the extent of a practically useless attenuation of the mental faculties.
From Nature 20 April 1899. 50  His teaching equipment at Kidderminster was largely of his own making, and it would seem that this gave physics an added attraction to his students.
We regret to announce the following death: Mr. Will Hay, well known as an actor and also a distinguished amateur astronomer, on April 18, aged sixty.