Calculate 2d area of a polygon in wgs84

I have a polygon in wgs84. If I use the method polygon.calculateArea2D(), the result is in angular units (according to the [documentation](https://esri.github.io/geometry-api-java/javadoc/com/esri/core/geometry/MultiPath.html#calculateArea2D--)). Naturally I would like to have the results in square meters or similar.

It seems to me that the polygon has to be projected to webMercator spatial reference system. However, I cannot find such method in the Polygon's list of methods or the static methods of GeometryEngine.