Gardening in a Changing Climate Acknowledgements The RHS and University of Reading would like to acknowledge the support provided by Innovate UK through the short Knowledge Transfer Partnership KTP 1000769 from November 2012 to September 2013. The RHS is grateful to the Trustees of Spencer Horticultural Trust, who supported the project to revise the Gardening in the Global Greenhouse report. The RHS would also like to thank: The authors of the 2002 report, Richard Bisgrove and Professor Paul Hadley, for building the foundations for this updated report. The contributors of this report: Dr John David (RHS), Dr Ross Cameron (University of Sheffield), Dr Alastair Culham (University of Reading), Kathy Maskell (Walker Institute, University of Reading) and Dr Claudia Bernardini (KTP Research Associate). Dr Mark McCarthy (Met Office) and Professor Tim Sparks (Coventry University) for their expert consultation on the climate projections and phenology chapters, respectively. This document is available to download as a free PDF at: www.rhs.org.uk/climate-change Citation Webster E, Cameron RWF and Culham A (2017) Gardening in a Changing Climate, Royal Horticultural Society, UK. About the authors Dr Eleanor Webster is a Climate Scientist at the Royal Horticultural Society Dr Ross Cameron is a Senior Lecturer in Landscape Management, Ecology & Design at the University of Sheffield Dr Alastair Culham is an Associate Professor of Botany at the University of Reading Gardening in a Changing Climate 2 Gardening in a Changing Climate Eleanor Webster, Ross Cameron and Alastair Culham RHS 3 Contents Acknowledgements ............................................................................................................................................................................. 2 Contents page ....................................................................................................................................................................................... 4 Executive Summary ........................................................................................................................................................................... 8 A summary of climate projections .............................................................................................................................................. 8 Implications for gardeners .............................................................................................................................................................. 8 What can you do? ............................................................................................................................................................................... 9 Preface ..................................................................................................................................................................................................10 1. INTRODUCTION ...........................................................................................................................................................................11 2. CLIMATE CHANGE: THE GLOBAL PERSPECTIVE ...............................................................................................................13 2.1 Changes in the global climate system ............................................................................................................................................. 15 2.1.1 The interaction between the atmosphere and the ocean ............................................................................................................... 15 2.2 Causes of climate change ..................................................................................................................................................................... 17 2.3 Projections of future climate ............................................................................................................................................................... 19 2.3.1 Simulating the global climate system ...................................................................................................................................................... 19 2.3.2 Future climate change .................................................................................................................................................................................... 19 2.4 Global action to address human–induced climate change .................................................................................................... 21 2.5 Summary ..................................................................................................................................................................................................... 22 3. THE FUTURE CLIMATE OF THE UK ........................................................................................................................................23 3.1 Characteristics of UK climate .............................................................................................................................................................. 23 3.2 How is UK climate changing? .............................................................................................................................................................. 23 3.2.1 Temperature ........................................................................................................................................................................................................ 23 3.2.2 Rainfall ................................................................................................................................................................................................................... 24 3.2.3 Frost ........................................................................................................................................................................................................................ 24 3.2.4 Sea–level rise ....................................................................................................................................................................................................... 25 3.2.5 Storms/windiness .............................................................................................................................................................................................. 25 3.3 How will the climate of the UK change in the future? .............................................................................................................. 26 3.3.1 Changes in temperature and rainfall ........................................................................................................................................................ 26 3.3.2 Heat–waves, dry spells and frosts .............................................................................................................................................................. 26 3.3.3 Soil moisture ....................................................................................................................................................................................................... 29 3.3.4 Sea–level rise ....................................................................................................................................................................................................... 30 3.3.5 Changes in storminess .................................................................................................................................................................................... 30 3.3.6 Solar radiation and cloudiness .................................................................................................................................................................... 30 Gardening in a Changing Climate 4 3.4 The UK’s variable weather and its implications for projections of future climate ........................................................ 31 3.4.1 The effect of year to year variability......................................................................................................................................................... 31 3.4.2 The influence of the Gulf Stream............................................................................................................................................................... 32 3.4.3 The Jet Stream ................................................................................................................................................................................................... 32 3.5 Recent extreme weather events and seasons............................................................................................................................... 33 3.6 Summary and discussion ...................................................................................................................................................................... 35 3.6.1 Current and near term (present to the 2040s) ..................................................................................................................................... 35 3.6.2 Medium and longer term (2050 to 2100) ............................................................................................................................................. 35 3.6.3 What does this mean for gardening? ......................................................................................................................................................