loop performance in global namespace (python-2.6.1)

[Poor Yorick]

In the following snippet, the loop in the global namespace takes twice as long
as the loop in the function namespace. Why?

limit = 50000000

def f1():
counter = 0
while counter < limit:
counter += 1
time1 = time.time()
f1()
print(time.time() - time1)
print('number of locals: ', len(locals()))

time1 = time.time()
counter = 0
while counter < limit:
counter += 1
print(time.time() - time1)
print('number of locals: ', len(locals()))