Dear Mr. President:
Take climate change seriously.
The US has to end the use of fossil fuels in electricity production; transportation; and heating of space, water and industrial processes.
Decarbonizing power production is actually easier than most people think. Renewable energy is less expensive than coal or gas, so we can save money by switching. Provide some incentives to adopt renewables – such as production tax credits and renewable portfolio standards – and the market will take care of this at little cost to the taxpayer. Don't spend a lot of money here because it's not needed and can be used better elsewhere (see below).
The car market is about to decarbonize by switching to electric vehicles. The government should accelerate this by strengthening the CAFE standards and subsidizing the installation of electric charging outlets and giving a tax deduction on electric vehicles. All of this will promote rapid decarbonization of the car market and again at little cost to taxpayers.
Aviation and shipping are more problematic. They will need some governmental encouragement: they can switch to biofuels or hydrogen. We need R&D here.
Decarbonization of heating is probably the hardest task we face in combatting climate change. New buildings can use heat pumps at no extra cost from conventional systems and should be required to do so, but retrofitting existing buildings is costly. The Federal government will need to provide incentives for this.
Climate change is a major threat to our way of life. Most of the population recognizes this and will give you credit for tackling it.