Sum() unequal number of rows

[Dave Kennedy]

 
SELECT sum(col1) AS total1
FROM t1
GROUP by col1
 
SELECT col1, sum(col2) AS total2
FROM t2
GROUP by col2
 
Table t1 contains 4 rows to sum for each value in col1 
 
Table t2 contains 8 rows to sum for each value in col2
 
If one select statement is used, the result has 8 rows and total2 is
correct but the tota11 is summed over 8 rows instead of 4 
 
How can they be joined to produce one row total1, total2