A wide range of environmental processes threaten the preservation of heritage assets, whether built or buried. These can be characterised as physical (e.g. severe precipitation, wind, changes in relative temperature or humidity, compression, dewatering), chemical (pollutants, acidification, corrosion etc.), or biological (microbial, invasive plants, insects and invertebrates, larger, burrowing and roosting animals). Climate change is accelerating many of these impacts (and perhaps retarding others) [80].
Met Office 50-year forecasts for climate change in the north of England predict mean temperature rises of around 2 degrees in both winter and summer. Inherent uncertainty in the models and over how we will act in future, mean that this rise in mean temperature could be as much as 5 degrees.
Rainfall predictions for the same period are subject to less certainty, with some model scenarios showing less rain in summer, and some substantially more (see Met Office website for current UK climate scenarios). However the changes to mean temperature and precipitation mask the likelihood, in a climate which is heating, of more extreme events including heavier rainfall events, higher wind speeds, longer periods of rain and longer periods of drought and extreme heat.
For the historic environment in the North Pennines the main threats would appear to be from:
Desiccation of water-logged archaeological deposits during prolonged drought.
Increasing storm intensity & frequency leading to more tree upheaval – damaging underground archaeology and potentially damaging above ground structures.
Increased flooding intensity and frequencies washing away in-river or riparian structures.
Slope failure from saturation of soils / conversely shrinking of soils from desiccation leading to subsidence.
It is also recognised that the work undertaken to alleviate threats (particularly from water) might also threaten the historic environment.