AFAIK that is impossible

Definitely not impossible. Microsoft offers a pay-as-you-go Bing Search API (https://azure.microsoft.com/en-us/pricing/details/cognitive-...).

I can only assume ecosia share this data with Microsoft because doing so has allowed them to land a more lucrative deal.

I would assume they send the IP so that Bing will return location specific search results for weather, local businesses and such. I see no reason to assume malicious intent.

What’s stopping them from performing an offline IP location lookup and requesting location specific search results without sharing the IP with Microsoft?

I'm not sure if that is a feature that the Bing API supports. I couldn't find anything about looking up coordinates in the docs: https://docs.microsoft.com/en-us/azure/cognitive-services/bi....

Yeah their documentation is dreadful, but they could just append loc:countryCode to the query before making the API request: e.g. ‘attractions loc:dk’.. at least that works for me despite some people mentioning this filter is no longer supported.

Not sure how DDG and other search engines that rely on Bing does it, but it’s certainly possible without sharing the users’ IP with Microsoft.

StartPage does it with Google and is explained here: https://support.startpage.com/index.php?/Knowledgebase/Artic...

So it is probably possible.