Summary
Figure 12 (i). Index of the timing of biological spring events
in the UK, 1891 to 1947 and 1999 to 2008
This is a contextual indicator and as
such is not assessed.
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The UK Spring Index shows how changes in
climate can lead to changes in the timing of biological events and
is calculated from the annual mean observation date of the
following four biological events: first flowering of hawthorn,
first flowering of horse chestnut, first recorded flight of
orange-tip butterfly and first sight of swallow.
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The 1900 to 1947 data were collected by the
Royal Meteorological Society and the 1999 to 2008 data by the UK
Phenology Network.
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While there is year to year fluctuation, on
average spring events in the UK occurred seven days earlier in the
years between 1999 to 2008 than between 1900 to 1947. These changes
in the Spring Index are strongly linked to increases in temperature
in March and April.
Indicator assessment
This is a context indicator and as such is not
assessed.
The indicator is shown to demonstrate a
biological response to climate change and a potential pressure on
biological systems.
Description of trends
There is high, year-to-year variability, but
since 1999, biological events in the UK have occurred significantly
earlier in the spring than in the period 1900–1947 (Figure
12(i)). The advancement of spring events is strongly linked to
warmer temperatures in March and April.
The Spring Index for the UK fluctuates
markedly from year-to-year. However, since 1999, the annual Index
dates have been around 7 days in advance of the average dates in
the first part of the 20th Century. Between 1999-2008, this change
has been driven by the changes for hawthorn, horse chestnut and
orange-tip. There has been little or no overall change in mean date
for the first swallow, between these two periods.
Relevance
There is evidence that the global climate is
changing. The UK Climate Impacts Programme reports that, globally,
14 of the hottest years since 1850 have occurred since 1990. In the
UK, 9 of the 12 hottest years since 1659 have occurred since
1990.
In 2007, the Intergovernmental Panel on
Climate Change (IPCC), concluded that most of the observed increase
in global average temperatures since the mid-20th century is very
likely due to the observed increase in anthropogenic (man-made)
greenhouse gas concentrations.
Phenology is the study of the timing of
recurring natural biological events in relation to climate and such
observations provide year-on-year information on how nature is
responding to a changing climate. This indicator illustrates the
stress that one aspect of climate change (spring warming) can place
on biological systems. Differential responses among species may
cause problems for life cycles, disrupt food webs, change
competitive balance and increase vulnerability to extreme events
such as late frosts.
Background
The UK Phenology Network (UKPN) Spring Index
is based on the annual mean observation dates for four natural
events: first flowering of hawthorn (Crataegus monogyna),
first flowering of horse chestnut (Aesculus
hippocastanum), first recorded flight of orange-tip butterfly
(Anthocharis cardamines) and first sight of swallow
(Hirundo rustica). These four events were chosen for the
following reasons:
- Good UK coverage
- Well recognised and easily recorded
species
- Good historical data
- Spanning both early and later spring
events
- Included plants, a vertebrate and an
invertebrate
- Strong phenological response observed
The overall index is compiled by calculating
an annual mean across all sites where all four biological events
were recorded. The pre-1948 data were mostly collected by the Royal
Meteorological Society (RMS). In 1998 the Centre for Ecology and
Hydrology revived the Phenology Network in the UK, which was
launched by the Woodland Trust as a web-based project in 2000. The
UKPN has grown since its inception to 29,000 registered recorders
in 2008. In Spring 2005 the UKPN launched the Springwatch survey
with the BBC, the biggest ever survey into the arrival of spring,
with 70,000 people logging 157,000 records.
The Index shows a strong relationship with the
mean March and April temperature (Figure 12(ii)). There is also a
significant difference in the magnitude of change in the Spring
Index at higher temperatures. The average advance in dates for the
Spring Index is 3.2 days per oC below a mean March-April
temperature of 7oC and 7.4 days per oC above
7oC.
Figure 12 (ii). Relationship between Spring Index and Central
England Temperature, 1891-1947, 1999-2008
Further development planned
There is a growing body of evidence showing
some species that are expanding in range as climate changes whilst
others will be at risk of local extinctions as their isolated
habitat patches become less favourable. Whilst at present there is
no comprehensive dataset on the negative impacts of climate change
on UK biodiversity, further development work is likely to focus on
identifying data that are capable of demonstrating the degree of
threat to native wildlife.