London scoping - ukcip

Final Report
61
5. The Potential Environmental Impacts of
Climate Change in London
5.1 Introduction
There are several approaches to climate change impact assessment. These include:
extrapolating findings from existing literature; fully quantitative, model-based simulations of
the system(s) of interest; or eliciting the opinions of experts and stakeholders. All three
approaches will be implemented in this section by a) reviewing the formal literature where
appropriate, b) undertaking exemplar impacts modelling for specific issues identified through c)
dialogue with stakeholders. Two workshops were held in May 2002 in order to engage expert
and stakeholder opinion regarding the most pressing potential climate change impacts facing
London. Following stakeholder consultation, five environmental areas were highlighted: 1)
urban heat island effects (including London Underground temperatures); 2) air quality; 3) water
resources ; 4) tidal and riverine flood risk and 5) biodiversity. Although these are addressed in
turn – and where appropriate, case studies have been included – it is also acknowledged that
many of these are cross-cutting (for example, river water quality impacts relate to flood risk,
water resources and biodiversity). The final section delivers a summary of the most significant
environmental impacts of climate change for London. Policy responses are addressed
elsewhere.
5.2 Higher Temperatures
5.2.1 Context
Throughout this section the reader is invited to refer to the downscaling case study provided in
Section 4.7). Heat waves may increase in frequency and severity in a warmer world. Urban
heat islands exacerbate the effects of heat waves by increasing summer temperatures by several
more degrees Celsius relative to rural locations (see Figure 3.2b). This can lead directly to
increases in mortality amongst sensitive members of the population (Kunst et al., 1993;
Laschewski and Jendritzky, 2002). For example, the heat waves in the summers of 1976 and
1995 were associated with a 15% increase in mortality in greater London (Rooney et al., 1998).
Conversely, it has been estimated that 9000 wintertime deaths per year could be avoided by
2025 in England and Wales under a 2.5ºC increase in average winter temperatures (Langford
and Bentham, 1995).
5.2.2 Stakeholder Concerns
Rising ambient air temperatures in central London may have significant impacts on air
temperatures experienced across the London Underground network. However, projecting future
summer temperatures in the network is not straightforward because the outcome depends on
assumptions about the number of passengers, frequency of trains, station design and depth
below the surface, as well as on air humidity and levels of ventilation (typically low, with
mixing ratios ~10%). Furthermore, passenger comfort often reflects the difference in