Why Carbon Footprint Tool emissions in different regions seems unexplainably higher?

It depends on the method used to generate electricity - workloads backed by solar- or hydro-generated electricity will have a smaller footprint than workloads on coal-generated electricity.

This is addressed directly in https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/ccft-estimation.html#ccft-estimation-billing

There are some Regions where high usage result in relatively low emissions. There are others where the low usage results in higher emissions. For carbon reports, EMEA Regions are often shown as under represented in estimates since there are more renewables on the grid. APAC Regions are often shown over represented in estimates. This is because sourcing renewable energy is difficult.

Great question. The electricity grids across the globe vary in the carbon-intensity of their sources of power. For example, some grids may have high reliance on coal while others may rely more on wind and solar.

Some APAC electricity grids are more carbon-intense and can cause the carbon emission from that region to appear over-represented in the Carbon Footprint Tool. Some areas in EMEA have high levels of renewable energy sources and usage there can sometimes appear to be under-represented.

One other thing you can look out for is purchases of upfront Reserved Instances which show additional spend on your AWS bill but there is not actually increased usage at that time. If you use AWS Cost Explorer, you can choose the "Unblended Costs" or "Net Unblended Costs" settings so that a one-time Reserved Instance purchase will be clearly visible on the day of purchase. If you are set to "Amortized" or "Net-Amortized," it will spread those purchases out over the life of the reservation.

There are 19 AWS regions that the energy consumption has been 100% attributable to renewable energy since January 2022. The list of those regions is here:

https://sustainability.aboutamazon.com/products-services/the-cloud

You can check the AWS Regions that you use and see if they are in the list of 19 regions that are 100% attributable to renewable energy. You can then better evaluate your usage in each of the super-regions (APAC, EMEA, Americas) in the Carbon Footprint Tool to determine why one super-region may have higher emissions that the other.

I hope this is helpful,

Richard