Saving rainforest is hugely cost effective to mitigate climate change: prevent 1000 tons of CO2 emissions for cost of coffee
An acre of rainforest contains about 200 tons of carbon. If deforested, at least half of that carbon is converted to CO2, say 100 tons of C which translates to 366 tons of CO2. Direct conservation can save an acre of Amazon rainforest for about $100 to $200 per acre via land purchase and as little at about $1 per acre via other methods, including titling of indigenous lands and formation of government preserves and parks. At $1 per acre of rainforest saved from deforestation, 1000 tons of CO2 emissions thus can be avoided for the cost of a cup of coffee.
Of course, to combat climate change effectively, we must reduce or eliminate use of fossil fuels. But saving rainforest is the low-hanging fruit in the effort to combat climate change, given the cost-effectiveness described above. If you compare the cost effectiveness of putting solar panels on the roof of your home, or buying an electric car (rather than a lower priced gas car), saving rainforest for $1 per acre is about 1000x more cost effective than putting solar panels on your home or buying an electric car. Each of these options (solar panels, or electric car) cost over $10,000 (versus the alternatives) but do less to reduce CO2 emissions than saving a single acre of rainforest, perhaps 4 tons of avoided CO2 emissions for each of 20 years.
Here is an example of a project that costs only 50 cents to save an acre of rainforest, and is already underway (and in which anyone can participate):
Full disclosure: I am a board member of the Rainforest Trust and a major donor to this charity. I also contribute substantial amounts to other charities focused on saving rainforest. I have funded projects in the last year that will save over 1,000,000 acres of rainforest.