Aggregating part of a 2d array in a column in said array - arrays

Question

I have a 2d array, with flexible dimensions:
arr_emissions(1 to n, 0 to m)
Where n is 22 or larger, and m is 6 or larger.
In the smallest case column m = 6 should contain the sum of columns m = 2 - 5.
I could ofcourse simply add them, but as the dimensions of the array are flexible I would like to implement a more robust method, that preferly doesn't loop over the entire array.
I was hoping to implement the native application.WorksheetFormula.Sum(). I saw an implementation in this answer, but that only works for complete rows or columns.
Example:
I have arr_emissions(0 to 111,1 to 6). It is populated in a loop from 1 to 111.
The data in the array is as follows:
(1,1) #3-4-2020# 'a date value
(1,2) 1,379777
(1,3) 0
(1,4) Empty
(1,5) Empty

Answer 1

Don't know if this helps, but this takes a source array v and then populates a new array w with the sum of columns 2-4 of the corresponding row of v.
Sub x()
Dim v, i As Long, w()
'just to populate source array
v = Range("A1").CurrentRegion.Value
ReDim w(1 To UBound(v, 1))
For i = 1 To UBound(w)
'each element of w is sum of columns 2-4 of corresponding row of v
w(i) = Application.Sum(Application.Index(v, i, Array(2, 3, 4)))
Next i
'write w to sheet
Range("G1").Resize(UBound(w)) = Application.Transpose(w)
End Sub

Answer 2

Thanks to the answer from SJR I found myself a working solution. This is all within a larger piece of code, but for this example I filled some variables with fixed numbers to match my example from my question.
Dim days as Integer
days = 111
Dim emissions_rows as Integer
emissions_cols = 6
ReDim arr_emissions(0 To days, 1 To emissions_cols) As Variant
Dim arr_sum As Variant
Dim sum_str As String
sum_str = "Transpose(row(2:" & emissions_rows - 1 & "))"
arr_sum = Application.Evaluate(sum_str) '= Array(2,3,4,5)
arr_emissions(emissions_index, emissions_cols) = Application.Sum(Application.Index(arr_emissions, emissions_index + 1, arr_sum))
The code writes a string to include the variables, so to take the second column untill the second to last column, which is then evaluated into an array.
That array is then used within the sum function, to only sum over those columns.
The result is then written to the last column of arr_emissions().
emissions_index is an index that is used to loop over the array.