Place sugar, water, ginger and rosemary in a small pan over medium-high. Stir and bring to a boil, reduce heat to medium-low.
Simmer uncovered for 10 minutes, stirring occasionally to thicken and infuse flavors. Remove from heat and cool completely. Strain into a jar or container.
To make drinks: Fill glasses with ice. To each add a tablespoon of the ginger rosemary simple syrup, 1/3 cup ginger ale and 1/3 cup pear nectar. Stir and enjoy immediately. Extra simple syrup can be stored sealed in the fridge.