The G20 is expected to give its political endorsement to plans for new rules on where and how much companies are taxed which were backed last week by 130 countries
Zucman calculates that a 25 percent rate would collect an extra 170 billion euros ($208 billion) this year -- or half of Europe's total current corporate tax revenue.
A robust price on carbon was needed to ensure that global carbon emissions were reduced in line with the goals of the 2015 Paris climate accord, she said, noting that over 60 pricing schemes had already been implemented.
Setting a price floor could avoid less efficient and contentious border carbon adjustments if some countries moved ahead with robust pricing and others did not.