Gardening in the Global Greenhouse The Impacts of Climate Change on Gardens in the UK Gardening in the Global Greenhouse was funded by the following organisations: Research was carried out by: The UK Climate Impacts Programme The UK Climate Impacts Programme (UKCIP) is based at the University of Oxford and funded by DEFRA to coordinate an assessment of how climate change will affect the UK, and help organisations assess how they might be affected. UKCIP, Union House, 12–16 St. Michael’s Street, Oxford, OX1 2DU, UK; [email protected]. Tel: +44(0)1865 432076; Fax: +44(0)1865 432077. Summary report written by Dr Phil Gates, University of Durham. Cover images (from top): Protea longiflora (NT); Hardy’s Cottage (Eric Chrichton, NTPL); Nymans (Patsy Fagan, NTPL). Printed on 50% recycled paper. Published in November 2002 under the UK Climate Impacts Programme. Summary Report Gardening in the Global Greenhouse: Summary Report Introduction Introduction: The British and their gardens The British are noted for their love of gardens. As an art form, gardening is an essential part of our culture. It is one of the leading hobbies in Britain, with an estimated 27 million gardeners (41 per cent of the population) participating in some way. Gardeners sustain a multi-million pound horticultural retail industry. Our heritage gardens and their plant collections, representing 500 years of garden history, attract 24 million visitors each year, contributing an estimated £300 million to the tourism industry. A wake up call from the weather Gardeners are more aware than many how organisations, commercial horticulturists, the weather affects them and their interests. landscape consultants, the horticultural press, Over the last four decades, extreme weather and representatives from local and national events have severely damaged many gardens government, universities and research and resulted in major economic losses. These organisations, to consider how gardens would events include: be affected by climate change. • severe winter weather in 1962/63 that The primary outcome of the meeting was killed many hardy plants; the commissioning of a technical report, entitled ‘The Impacts of Climate Change • drought in 1976, which weakened trees Drought dried out lakes and reservoirs in 1976 on Gardens in the UK’, by Richard Bisgrove and dried out lakes; (Mike Sleigh, RHS) and Professor Paul Hadley, of the University • storms in 1987 and 1990 that felled of Reading (2002). The authors assembled millions of trees; and evaluated evidence on how plants and garden components respond to altered • torrential and prolonged rain leading to climatic conditions, and assessed the likely soil erosion, flooding and drowning of impact of the UKCIP1 climate change plant roots in 2000 and 2001. scenarios on gardens in the United Kingdom. These events highlight the vulnerability of This document summarises their report. It gardens to the vagaries of weather and describes effects on garden plants, domestic climate. A workshop was held in London in gardens, nationally important heritage April 2000, attended by gardening gardens, the landscape industry and the retail Trees at Chartwell, Kent felled by the storm in 1987 horticultural industry. It discusses aspects of (Peter Baistow, NTPL) gardening that might benefit from climate change and identifies techniques and practices that might reduce undesirable effects of climate change on gardens. It also highlights the important role that gardens can 1 The UKCIP02 scenarios describe how the climate of play in raising awareness of environmentally the UK is likely to change over the course of the 21st century. They were produced for the UK Climate sustainable practices which can minimise the Impacts Programme by the Hadley Centre at the Met. effects of climate change, and identifies areas Office and by the Tyndall Centre for Climate Change Research with funding from the Government’s for further research. Department for Environment, Food and Rural Affairs. Flooding at Westbury Court, Glos. in 2000/01 (NT) 1 Gardening in the Global Greenhouse: Summary Report What is happening to our climate? Gardening in the Global Greenhouse: Summary Report What is happening to our climate? What is happening to our climate? The current phase of climate change is part of a continuous warming of the climate Change in average winter and summer temperature for the low and high emissions scenarios. recorded over the last 150 years and is being caused primarily by industrial activities that have raised levels of greenhouse gases which retain heat within the atmosphere. Winter Summer 2020s 2050s 2080s 2020s 2050s 2080s There is overwhelming evidence that the rate In the low emissions scenario, at the current • mean annual rainfall may decrease by deg C of warming is increasing, although rate of 0.1°- 0.3°C rise per decade annual 10-20 per cent, but with 10-30 per cent 4.5 projections for the rate and extent of average temperatures will increase by more falling in winter and 20-50 per cent 4 Low Emissions warming vary, depending on predictions of 1° - 2.5°C by the 2080s. This lower rate of less in summer by the 2080s. Rain will 3.5 economic growth, human population levels increase would depend on the use of clean tend to fall with greater intensity; 3 and compliance with international and efficient technologies, reduced use of • by the 2080s summer droughts will be 2.5 agreements to regulate emissions of carbon natural resources that generate carbon more frequent, as will very wet winters, 2 dioxide, the most important greenhouse gas. dioxide, and global solutions to problems but autumns will be drier. Higher 1.5 of social and economic stability and In the UKCIP02 high emissions scenario, with temperatures and less cloud cover in 1 equity between developed and High rapid economic growth in developed and less summer will lead to greater evaporative Emissions 0.5 developing countries. developed countries and a market driven loss from soils and leaves, reliance on fossil fuels, by the 2080s Climate change is already occurring and worsening drought conditions; average temperatures are likely to rise by further change is inevitable, with common • although predictions for extreme weather 2°- 4.5°C, at a rate of between 0.3°- 0.5°C consequences for climate in the UK. These are: events are less certain than for per decade. This is between two and three • higher mean annual temperatures, which temperature, weather patterns are likely to times faster than the current rate of will increase the length of the growing become more erratic, with greater temperature increase. season for many plants. A 1°C increase in frequency of torrential rain, temperature mean temperature will increase the extremes and storms. Percentage change in average winter and summer precipitation for the 2020s, 2050s and 2080s growing season by three weeks in south Within these overall trends there will be east England and by 10 days in the for the low and high emissions scenarios pronounced regional differences, with the north west; lowest rainfall and highest temperatures • greater warming in summer and autumn occurring in south east England. The reduction Winter Summer than in winter, with summer maximums of soil moisture will therefore be greatest in 2020s 2050s 2080s 2020s 2050s 2080s per cent rising faster than summer minimums, areas where water supplies are already low. 30 leading to increased frequency of hot By the 2050s sea levels are expected to rise 25 summer days. By the 2080s temperatures by 14-18 cm, and by the 2080s by 23-36 cm. 20 may exceed 42°C about once per decade Low 15 The effects will be greatest in the south east, Emissions Traditional scenes such as this at Bodnant, Gwynedd in lowland England; 10 where the land mass is naturally subsiding. will become a rarity (Christopher Gallagher, NTPL) 0 • winter minimum temperatures rising faster Coastal flooding could damage some -10 than winter maximums, leading to milder domestic and major heritage gardens. -20 winters with a reduced temperature range These climate changes will have major -30 and fewer frosts. In many parts of the UK, -40 effects on plant growth and on the especially in the south west, frosts will be High -50 ways in which we design, plant and Emissions rare and might occur in Cornwall only maintain gardens. Changes within about once every 10 years by the 2080s, 'natural' variability although local variations will occur. Snowfall will decrease everywhere in lowland and coastal regions by as much as Source: UKCIP02 Climate Change Scenarios 90 per cent by the 2080s, and by 60 per cent in high snowfall areas such as the Droughts will become more frequent (NT) Scottish Highlands; 2 3 Gardening in the Global Greenhouse: Summary Report Plants in a warmer world Gardening in the Global Greenhouse: Summary Report Plants in a warmer world Plants in a warmer world: how climate affects plant growth and development Plants are influenced by extreme weather events and by gradual climate changes, the effects of “Grape cultivation could extend Failure of plants to shut down metabolic as far north as Scotland during activity in winter might increase frost damage, which are more insidious but potentially dramatic. A small change in average annual temperature the second half of the but higher sugar levels generated in tissues of, say, 0.1°C has a cumulative effect through the growing season, with a large net impact. An of evergreen species by winter growth might 21st century.“ have the reverse effect. Species-specific effects analogy would be a small change in bank interest rate, which might have little immediate effect Bisgrove and Hadley (2002) are likely, and further research is needed. on the daily economy but would have a profound impact on annual accounts. Interactions between higher carbon dioxide levels and higher temperatures Grapes could be grown in Scotland in future (RHS) Effects of individual elements of climate so although plants will grow more rapidly, As temperatures rise, plants respond more change have been tested in controlled fertiliser requirements do not necessarily flower earlier, but others such as honesty vigorously to higher carbon dioxide levels.