Answer to Question 1
Tropical deforestation reduces the complexity of the landscape so biodiversity is reduced, and tropical deforestation also adds CO2 to the atmosphere and, hence, adds to global warming.
Answer to Question 2
The temperature changes, T, were determined from measured values of the deuterium content of the Vostok ice core. The section of the Vostok ice core that has been fully analyzed is about 3.5 km deep and it extends back for almost 450,000 years. The Dome C record mentioned in the text is about 3.3 km deep and extends back about 800,000 years.