A warming climate is changing the pace of spring green-up. Using remote sensing and a new approach that quantifies the rate of green-up, Seyednasrollah et al show that green-up is fast in the mountains and relatively insensitive to temperature anomalies, while slow development in warm, coastal forests can respond to temperature swings. Confirming experimental evidence, this study shows that spring is compressed in cold climates, delayed in onset but then rapidly progressing to full leaf expansion. Conversely, mountainous forest green-up is more susceptible to intensifying drought and moisture deficit, while coastal areas are relatively resilient. Canopy thermal stress slows leaf development following dry years, but accelerates it following wet years. The study is published in Remote Sensing of Environment.