I would greatly appreciate if you could help me to obtain access to reliable and up-to-date data on world economic growth or the GDP growth rates at both the quarterly and monthly levels. This is just annually.
Not monthly, but You can get both annually and quarterly past, current as well as forecasted GDP data along with several other factors. Data IMF Org. have service named GDP and components where you can get data for all countries. You can export data very easily from here in csv, xlsx and other formats.