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The most recent global icehouse-hothouse climate transition in Earth history occurred in the Permian. Warmer polar conditions relative to today existed from the middle Permian through the Mesozoic and into the Cenozoic. We focus here on one particularly well-correlated middle Permian stage that postdated the deglaciation, the Wordian (267-264 Ma), integrating floral and lithological date to determine Wordian climates globally. Paleobotanical date provide the best means of interpreting terrestrial paleoclimates, often revealing important information in the continuum between 'dry' and 'wet' end-member lithological indicators such as evaporites and coals. New statistical analyses of Wordian floras worldwide have enabled a greater understanding or original vegetation patterns and prevailing climate conditions. The derived climate interpretations are compared with new Wordian atmospheric general circulation model simulations. The model matches the data well in the tropics and northern high latitudes, but predicts colder conditions in southern high latitudes. We discuss possible reasons for this discrepancy.

The authors examine the silicate chemical erosion rates due to changes in the climate. Topics include chemical weathering, atmospheric variations, and research models.

The Late Ordovician glaciation differs from other major Phanerozoic glaciations because of its short duration ([approximately]1 m.y.). A satisfactory explanation for this glaciation must be able to account for its sudden initiation, short duration, and rapid termination; mechanisms operating on tectonic time scales appear to be precluded. Given recent studies of a major perturbation in the carbon cycle during the glaciation, a climate model investigation of the sensitivity of the Late Ordovician climate to changes in atmospheric pCO2 was undertaken. Under the condition of a 4.5 % reduction in solar luminosity, permanent snow cover (taken as a key indicator of potential for glaciation) is dramatically different between five experiments. The range of 18X present atmospheric level C[O.sub.2] (ice free) to 8X ('runaway' icehouse) lies within the uncertainty of previous geochemical estimates of Late Ordovician atmospheric pC[O.sub.2]. The strong sensitivity to the modest direct forcing from pC[O.sub.2] changes is due to the ice-albedo feedback. A plausible increase in organic carbon burial could have drawn down enough atmospheric C[O.sub.2] to have briefly lowered the climate system below a critical glacial inception threshold at the end of the Ordovician. Conversely, a high pC[O.sub.2] is required for the rest of the early Paleozoic, which was essentially ice free.

At any time, the condition of ecological infrastructure is related to the availability of funds to support operational management programmes. Environmental management outcomes are therefore often coupled to general economic conditions. When general economic conditions are favourable, investment in environmental management is often greater. This implies that environmental management frameworks need to be able to cope with the waxing and waning of economic conditions while still delivering acceptable environmental management and service delivery outcomes. At the onset of budget cuts, environmental managers therefore need effective ways of assessing the near and far future trade-offs of curtailing particular programmes in a defensible and internally consistent manner. Operators of large civil infrastructure assets face the same problem. In response, the asset management community has developed the State of Good Repair approach. The objective of the preliminary consideration presented here was to determine whether this engineering management approach has any merit in environmental management. [ABSTRACT FROM PUBLISHER]