London scoping - ukcip

Final Report
82
of air pollution concentrations (Ashmore et al., 1985;) and water stress, with major reductions in
the crown density of beech coinciding with droughts in southern Britain (Cannell and Sparks,
1999). Natural woodlands suffering from drier summer conditions in the future may become
more susceptible to insect pests, disease and windthrow during the stormier winter conditions.
However, drought stress during summer can also afford protection from ozone damage by
enforcing stomatal narrowing or closure (Zierl, 2002). Conversely, grass productivity is
substantially reduced during hotter, drier summers (Sparks and Potts, 1999), pointing to
increased water demand for lawn irrigation under the UKCIP02 scenarios.
Bird populations are sensitive to many types of environmental change and, because they occupy
a position at or near the top of the food-chain, give indications of overall ecosystem functioning.
For example, the recent increase in grey heron numbers in London has been attributed to the
improvement in water quality (leading to higher natural fish populations) and the absence of
severe winters (Marchant et al., 1990). Small birds, like the wren, are particularly prone to
prolonged spells of cold, wet or snowy weather, and therefore provide an excellent index of
very cold winters. Records of the wren population on farmland and woodland since 1962 are
strongly related to mean winter temperatures in central England, and have maintained relatively
high numbers since the 1990s (Crick, 1999). Similarly, annual variations in the first laying
dates are often strongly correlated with variations in spring temperatures (Crick et al., 1997), but
mismatches in the timing of laying relative to food supplies can reduce bird populations (Visser,
1998). Changes in migratory patterns and arrival dates have also been noted but this will
depend on the specific trigger(s) for migration. For example, a 1ºC increase in spring
temperature is associated with a 2-3 day earlier appearance of the swallow in the UK (Sparks
and Loxton, 2001).
Thus, climate change has the potential to affect future bird migration, winter survival, and egglaying.
The MONARCH project assessed the impacts of six bioclimatic variables on the
distribution of ten breeding birds at 10 x 10 km resolution under the UKCIP98 Low and High
scenarios by the 2020s and 2050s (Berry et al., 2001). (Habitat, however, was not included in
the training of the model and the ten birds studied are not all appropriate to London’s avifauna).
Under the High scenario the most significant reductions in southeast England climate space
occur for the willow tit, nuthatch and nightingale, due to warmer and drier conditions affecting
woodlands and insects. Since woodland is the second most extensive natural habitat of London,
these reductions could be reflected in the range of birds visiting the back gardens of suburban
London. Conversely, the potential distribution of the reed warbler increases nationally, along
with the yellow wagtail and turtle dove (which is contrary to the current decline in the latter
two), probably reflecting an affinity for a warmer, drier climate. These results should, however,
be treated with caution because the science underlying the MONARCH assumptions is less than
complete.
Insect distributions and the timing of insect activity are also highly weather dependent (Burt,
2002). For example, the ranges of butterflies in North America and Europe have shifted
poleward in response to rising temperatures (Parmesan, 1999). Extensive records of insects
throughout Britain since the 1960s and 1970s indicate that a 1ºC increase in temperature is
associated with a 16-day advancement in the first appearance of the peach-potato aphid, a 6-day
advance in peak flight time of the orange tip butterfly, and an 8-day advancement in the time of
activity of the common footman moth (Sparks and Woiwod, 1999). Finally, it is recognised that
climate plays a dominant role in vector-borne diseases – directly through its effects on insect
development, and indirectly through its effects on host plants and animals. Although it has been
suggested that the most lethal form of malaria can not be transmitted by mosquitoes in the UK