Simplify the following text for a Grade 11 native English-speaking person.
Original: Political influence on the IPCC has been documented by the release of a memo by ExxonMobil to the Bush administration , and its effects on the IPCC 's leadership .
Simplified: Political influence on the IPCC has been shown by the release of a memo by ExxonMobil to the Bush administration , and its effects on the IPCCs leadership .