INTRODUCTION

The earth’s climate is changing at a faster rate than any time during the last millennium and some amount of the change is due to anthropogenic causes (IPCC 2001).  A global surface temperature increase of 0.6°C +- 0.2°C has been recorded since the late 19^th century, with the highest temperatures occurring during the 1990s (Figure 1) (IPCC 2001).  While temperature increases have not been unidirectional, the strongest trends have been towards warming of winter nighttime temperatures in the mid and high-latitudes of the Northern Hemisphere (IPCC 2001). 

            Figure 1: Climate change over the last 1,000 years.

            Climate change in British Columbia during the last century has been consistent with these global trends.  Average annual temperature has warmed by 0.6°C on the coast, 1.1°C in the interior and 1.7°C in northern BC (Ministry of Water, Land and Air Protection 2002).  Evidence of warming in BC includes earlier ice-free status of lakes and rivers, increasing sea surface temperatures along the coast, and prominent glacial retreat (Ministry of Water, Land and Air Protection 2002).  These trends are expected to continue over the coming centuries due to the continued release of greenhouse gasses into the atmosphere through the burning of fossil fuels.  Climate models for British Columbia project an additional increase of 1°C to 4°C in mean annual temperature over the 21^st century, and a 10-20% increase in annual average precipitation (Ministry of Water, Land and Air Protection 2002).

            The details regarding how climate is changing in BC are critically important to anyone interested in resource use and conservation.  In the forest sector, specifically, climate change is already implicated in some dramatic tree growth and health trends, and much attention is being focused on projected future impacts.  A new climate model called ClimateBC has been created for the purpose of generating biologically-relevant climate variables for any location in British Columbia over the course of the 20^th century.  The outputted variables can be used to create raster images that show the coverage of the variable across British Columbia on a monthly, annual or decadal basis.  The purpose of this project was to create animated maps showing the changing values of three climate variables relevant to tree growth over the course of the 20^th century: mean annual temperature, number of frost-free days and summer heat:moisture index.