Gardening in a Changing Climate
Implications for Allotment Owners
22 November 2007
• Introduction to UKCIP
• Climate change in the UK
• Impacts on gardening
• Practical adaptation
What is UKCIP?
The UK Climate Impacts Programme (UKCIP)
“helps organisations to assess how they might be affected by climate
change, so that they can prepare for its impacts”.
• Set up by UK Government in 1997.
• Funded by DEFRA.
• Based at University of Oxford.
How do we go about this?
• Provide common tools and datasets for climate impacts and adaptation
assessments, all for free (www.ukcip.org.uk)
• Conduct stakeholder-led research projects.
• Establish partnerships in regions or sectors.
• Build capacity on climate change, impacts and adaptation – NOT mitigation.
Some climate change is unavoidable
Expected climate changes in the UK
• The UK will continue to get warmer.
• Summers will continue to get hotter and drier.
• Winters will continue to get milder and wetter.
• Sea levels will continue to rise.
• Some extremes will become more common other less common.
• More very hot days.
• Fewer very cold days.
• More frequent heavy winter precipitation.
• More frequent winter storms.
Changes in average temperature in UK
Changes in seasonal average precipitation in UK
Seasonal rainfall changes in the UK (observed)
% of 1931-90 average
Summer 2003 ‘Heat wave’ could be normal by
2040s, cool by 2080s
European Medium-High emissions (modelled)
Source: Peter Stott, Hadley Centre
Observed and projected frost trend, central England
Average number of days per year
1850 1900 1950 2000 2050 2100
By the 2080s, frosts may only occur in Cornwall
In one year in 10.
Summary of climate changes by 2050s & 2080s
• Hotter drier summers; milder wetter winters
• Extreme high temperatures more frequent
• Extreme winter precipitation more frequent
• Significant decrease in soil moisture content
• Significant increase in thermal growing season
• Net sea level rise and increased occurrence of
extreme high-water levels
Impacts (1): Higher CO2 concentrations
• CO2 levels are expected to rise from the current level of c.
380ppm to between 500 and 800ppm by the 2080s
• Increased CO2 levels:
o Increase the rate of photosynthesis
o Increase plant growth rates – by as much as 50% in experimental conditions,
depending on the species (though this may only be a short term response)
o Result in more efficient use of water and nitrogen
o Accelerate bud burst, flowering and fruiting
Impacts (2): Warmer temperatures
• Longer growing season - a 1oC temp increase will increase the growing season by
3 weeks in SE England
• Higher temperatures increase growth rates
• Precocious flowering could make spring frosts more damaging; Frost damage in
autumn may become more serious
• In hotter, sunnier conditions, damage possible in greenhouses if not shaded and
• Higher temps AND CO2 have mixed effects:
• Increases yields of vegetables harvested early in development (carrots), but not those
harvested close to maturity (cauliflower, broccoli and onions).
• increases yields in potatoes, but higher temps hasten foliage death, so plant earlier to
• If winter chilling requirements not met, flowering can be delayed, compromised, or
fail (eg apples, raspberries, blackberries)
Impacts (3): More variable rainfall
• Increased drought risk in
• Increased flood risks in
winter – and also other times
of year (eg. summer 2007)
Impacts (4): Soils
Warmer, drier summers will:
• increase evaporation - a 3oC increase in soil temperature can
decrease soil moisture by 25%
• increase in activity of micro-orgs, leading to more rapid
breakdown of soil organic matter and faster nutrient release
o More nutrients available to plants, but without the addition of organic matter
and mulching, soils will become leached in the long term
Wetter winters could mean flooding (eg. summer 2007) and
waterlogging (OCC received several requests for compensation)
Impacts (5): Pests and diseases
• Warmer temps will mean pests can complete life cycles faster so
populations can increase (eg. thrips, aphids and spider mites)
• Longer growing seasons mean pests active earlier:
o Cabbage aphid attacks begin 2 weeks earlier for every 1oC temp increase
o An 2oC increase in spring temp means cabbage root fly becomes active 1
• Faster plant growth reduces nutrition in leaves and can increase
pest feeding by 20-40%.
Impacts (5): Pests and diseases cont.
• Glasshouse pests could establish in the open (eg. Tomato spotted wilt
virus and Impatiens necrotic spot viruses)
• Could see alien pests become established, but at present few do
• Diseases are complex so more difficult to predict, but:
o Warmer, wetter winters could favour spread of water-borne diseases and root rot
(Phytophthora), and wood and bark invading fungi
o Warmer, drier summer will favour powdery mildew and rusts
o Drought increase susceptibility of perennials to disease
• Weeds will grow faster and earlier; slow growth in dry summers will
reduce effectiveness of common herbicides
What can you do?
You need to mitigate and ADAPT:
• Look after your soil:
• understand your soil type, its properties and behaviour, and work within its limits
• maintain or improve organic matter by mulching
• Prepare for the need to irrigate: store winter rainfall for use in summer
• Protect against water-logging: add grit to heavy soils, raise beds
• Monitor change: build on your own experience of past extreme weather
(2003 heatwaves; summer 2007 floods) and review planting regimes
• Tell us about your experience: impacts database
• Consider growing different varieties / species; experiment
Find out more
• National Trust
• Royal Horticultural Society
• UKCIP – loads of information and resources
Natural factors cannot explain recent
Temperature change ºC
1850 1900 1950 2000
Most of the observed increase in global average temperatures since
the mid-20th century is very likely (>90% probability) due to the
observed increase in anthropogenic greenhouse gas concentrations
Temperature change ºC
1850 1900 1950 2000
Will the Gulf Stream collapse?
Climate models show a 20% reduction, but not a switch-off
Circulation strength (Sverdrups)
No change in emissions