Answer to Question 1
Answers should include the laws and actions brought about by the following international agreements: the Earth Summit in Rio de Janeiro (1992), the Kyoto Protocol in 1997, and the Durban Accord in 2011.
Answer to Question 2
The carbonate-silicate cycle contains a negative feedback loop that would have mitigated the impacts of the decreased solar luminosity. If the Earth was relatively cool 4 billion years ago, then silicate weathering would have slowed down and the rate of drawdown of CO2 from the atmosphere into the oceans would have also decreased. Slowing down the removal of CO2 from the atmosphere allows CO2 concentrations to increase, thus creating a greater greenhouse effect that compensates for the lower solar luminosity.