When looking at reducing the carbon footprint of an application — the carbon dioxide emissions caused indirectly by running the software — attention is usually directed at making the software more efficient. The thinking is clear: more efficient software needs less electricity and fewer servers, reducing the emissions from electricity generation and manufacturing of the servers. An additional strategy is to make the application carbon aware. This is because the same workload does not always have the same carbon footprint. For example, when run in a data center in a cooler climate, less power for air conditioning is needed; or, when run at a time when more renewable energy is available (more sunshine, stronger winds), less electricity from carbon-based sources is required. With the Carbon Aware SDK, software engineers can query data sources to discover less carbon-intensive options for a given workload and then move it to a different location or run it at a different time. This makes sense for large workloads that are neither time nor latency sensitive, such as training a machine-learning model. Although the SDK and available data sources are not very comprehensive yet, we believe it's time to start looking at how we can make our systems carbon aware.