Michael,

I read a helpful article that touched on this exact topic yesterday. It's https://www.searchenginejournal.com/mobile-first-index-actually-mean/178017/ . As you've already pointed out, a responsive solution is best, but if the website's mobile and desktop content are the same, you may not have to do anything right away.

Check it out.

Give them two options in a grid format:

(1) do nothing;

(2) redirect mobile to desktop

To the right of that, use two columns to convey pros and cons.

I guess you could do nothing and measure the impact for a few months, comparing this year to last. If things don't look good, then execute option 2. Might be hard to isolate the impact of the mobile index versus anything else though, but it's probably the best you can do.

And then there's the 3rd option... go responsive, but as you've said, you don't have time or budget for that unfortunately.

What is a realistic timeline to increase a website's domain authority by 20 points?

Years. Domain authority uses a logarithmic scale like the Richter scale used to measure earthquakes. Every notch you move up the rung takes exponentially more time, discipline, creativity, outreach, and energy.

If you're asking the question b/c you have to set expectations with someone, I'm with Gaston and would suggest you set business goals and a realistic timeline to reach them versus relying on a metric that correlates with high rankings. Think leads and downloads. If it's an e-commerce site, think sales. Things that are easier to measure and explain to the business.

What are the most important factors to increase a website's domain authority?

Someone from Moz would have to answer that. Here is the page on their site that best explains it. My understanding is the domain authority metric tries to mirror Google's interpretation of a website's importance and would expect incoming links and their sources to be given considerable weight in the calculation.

I agree with Kevin. Ahref has that capability assuming you don't run into size constraints. Here's a quick post that explains where to find it. (See https://ahrefs.com/blog/turning-broken-links-site-powerful-links-ahrefs-broken-link-checker/.)

Very hard to say what's going on Kingalan1 without a detailed analysis. You've done a domain and https migration at the same time. It could just be a result of the transition given Google will have indexed multiple versions of the same content. Give it some more time. After that, if things don't improve you'll need to do a detailed analysis to diagnose what the problem is.

ColesNathan,

Have you seen what Google has to say about canonicals? https://support.google.com/webmasters/answer/139066?hl=en

You might find it helpful. They list reasons why you might want to use a canonical tag including those identified above and a few others, for example, for letting Google know your priorities when it comes to crawl budget and SERP display.

Canonicals can also help undermine plagiarism. If scrapers leave your self-referencing canonical intact, it will tell Google you are the originator of that content and consolidate link signals into your URL.