State of Art in the Field

Future climate scenario

The global climate has experienced great changes over a long geological time span. The global climate system, although highly complex, is modelled with increasing accuracy and effectiveness on time scales up to a century. Such models offer considerable insight into the details of the type of European climate that will be experienced by future generations. Although there are still dissenting voices within the scientific community, it is clear that the consensus viewpoint is that human-induced global climate change is now occurring and will continue to affect the global climate for at least the next one or two centuries.

Some of the consequences of global climate change for the natural and human environment have received wide attention in the literature. Scientists concerned with building deterioration, while aware of the importance of climate change, have been preoccupied in the short term deterioration caused by pollutants and acid rain. Improved knowledge of pollutant deposition on cultural heritage has revealed the likely importance of novel climatic factors that affect buildings on a longer timescale. It is important that the care of buildings and cultural heritage in general takes a long term view, if they are to have long life cycles.

Atmospheric concentrations of greenhouse gases have increased since the pre-industrial era due to human activities, primarily the combustion of fossil fuels and changes in land-use and land-cover. For the wide range of emissions scenarios foreseen by the Intergovernmental Panel on Climate Change (IPCC), it is predicted that the Earth's mean surface temperature will warm by 1.4 to 5.8°C by the end of the 21st century, with land areas warming more than the oceans, and high latitudes warming more than the tropics. In general, precipitation is predicted to increase in high-latitude and equatorial areas, and decrease in the subtropics, with an increase in heavy precipitation events [1] .

Climate models in their basic form only provide temperature, wind and precipitation climate data with any degree of certainty. The focus on damage to cultural heritage means that specific parameters need also to be considered, among them: freeze-thaw cycles, wind-driven rain/sand, diurnal humidity cycles, solar radiation, gas and particle concentration, pH precipitation, water table level, and sea level.

The project will develop appropriate methods for calculating such parameters. From the climate model output (e.g. under ARCHEO (ENV4-CT95-0092) freeze-thaw cycles were calculated on century long timescales using the daily maximum and minimum).

For some parameters, a range of special sub-models for specific purposes has already been developed in different countries. As an example, models for pH and chloride have been set up. However, the large grid size of the global model currently available reduces the chance of predicting impacts in detail.

For many parameters, including all sub-daily parameters, it will not be possible to use climate model output directly for calculating the climate indicators. Nevertheless the use of alternative "proxy" indicators will be explored, together with statistical downscaling methods (such as weather generators). Water table level is likely to be one of the more problematic variables. It should be possible to construct a simple meteorological subsidence hazard index based on the balance between total monthly precipitation and potential evapotranspiration (PET) and the water-loading capacity of the soil.

In the case of sea level changes and accompanying changes in storminess, considerable information is available from previous and ongoing projects funded by the EU and national bodies. Given the major modelling efforts required to address such issues, it is not considered appropriate for Noah's Ark to undertake new work in this area. However, existing data and information will be pooled and mapped in a common format.

For as many of the climate indicators as possible, European-wide scenario maps will be produced predicting changes for the late 21st century (2070-2100) with respect to the present day (1961-1990).

The maps will take into account some of the uncertainties associated with the construction of climate scenarios, related to:

1. Emissions or radiative forcing scenarios, i.e. inter-scenario variability.
2. The use of different climate models, i.e. inter-model variability.
3. Different realisations under a given emissions scenario with a given climate model, i.e., internal model variability (which is, in part, a reflection of natural climate variability).

Uncertainties due to (1) will be addressed by using more than one emissions scenario (i.e. the A1F1, and A2, IPCC SRES emissions scenarios) [1] . Those due to (2) will be addressed by using output from more than one RCM (obtained via the UK Climate Impacts LINK project and the FP5 EU-funded PRUDENCE project). Finally, uncertainties due to (3) will be addressed by using output from ensemble simulations performed with the same RCM (e.g., three ensemble simulations performed with the Hadley Centre's HadRM3H model, using the A2 emissions scenario).

A weather generator set up by the Climatic Research Unit at the University of East Anglia (UK) for projects funded by the European Union and EPSRC will be used to develop and test some of the climate indicators. It will also be used to produce site-specific scenario time series for selected case-study locations. Daily and hourly time series will be produced for the following meteorological variables: precipitation, mean temperature, diurnal temperature range, vapour pressure/relative humidity, sunshine duration, wind speed and potential evapotranspiration.