I like trees. I even just this week went out of my way to plant about as many trees as I reasonably could in my backyard. Did I do any real good for the planet or just arrange for a nice place to hang a hammock or two in a couple of decades? If you successfully planted -- and kept planted despite them being made out of a useful resource -- 100 billion trees by 2050 you'd offset roughly 0.6% of the carbon emissions produced in the same timeframe. If you planted, and kept planted, a trillion trees it would only handle about 6% of the carbon emissions by 2050, reducing change in the temperature of Earth by 0.15 degrees Celsius. climateinteractive.org/blog/… Note: Planting a trillion trees would represent increasing the amount of trees _everywhere on Earth_ by something like 33%. If we sum over the different tree planting projects, we seem to be only track for something like 250 million trees / year. If we keep that pace we offset roughly 0.1%-0.2% of the produced carbon. One problem is deforestation currently massively outpaces that. We seem to be losing about 10 billion trees net per year due to clear cutting. (+5 billion -15 billion). nature.com/articles/nature14… That is to say, that reforestation efforts aren't currently even enough to amount to a meaningful net reduction in the loss of trees. Aiming for the trillion tree target by 2050, planted 1 trillion trees, we'd lose ~250 billion of those to current deforestation. Okay, so let's say you get everyone everywhere to stop cutting down trees, so that you're not just feeding later clear cutting efforts, and that everyone everywhere in all developing countries will by treaty choose not to use this local resource, despite historical precedent, because they totally won't think this is some effort by the developed countries to keep them down. Even with that, the above just wasn't anywhere near enough to keep up, even if we keep scaling up current efforts like One Tree Planted, the Amazon Project, etc. But let's say we went all in! Successfully offsetting all carbon production in that timeframe with trees would take something like ~16 trillion additional trees, multiplying the number of trees on earth by a bit over 6x. Taking 1,000 trees per hectare as a reasonable average tree density, just the _new_ trees required by this effort would take 160 million square kilometers. Unfortunately this is ~7% more land than _exists_ on Earth, (149 million square kilometers) even ignoring the fact that much of Earth has large unusable areas like deserts that exist, and there's already ~3 trillion trees sitting on that land today taking up space, as well as people, and this would require us to increase sequestration efforts by well over 1000-fold, sustained for the better part of a century, AND stop all net deforestation cold today. Trees as much as I like them just aren't a sufficient carbon sequestration technology. They may help on the margin, and their loss definitely hurts, but they don't come close to being the solution to climate change on their own, and most reforestation efforts seem more about slightly slowing the bleeding than being remotely sufficient to the task of actually making a difference. I think that is probably why Bill is so dismissive of planting trees as a solution.