The increase in the concentration of CO   in the atmosphere, from 1750 to today. This greenhouse gas has increased from a 2,000-year baseline concentration of 280 ppm to 412 ppm today, thanks to the burning of fossil fuels and other human activities.

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The number of years left, emitting at 2021's rate, before we reach the total cumulative greenhouse gas emissions consistent with limiting global warming to 1.5 degrees Celsius.

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The estimated percentage of excess greenhouse gasses (created by human activities) that are absorbed by the world’s terrestrial ecosystems. That is, terrestrial ecosystems have been mitigating climate change quite substantially, preventing the change from being more rapid.

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The percentage of greenhouse gas emissions reductions committed in the Paris Climate Agreement that are supposed to come from forest-related activities (afforestation, reforestation, improved forest management, reduced deforestation). In other words, we’re planning on relying heavily on forests to get ourselves out of this mess.

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Level of uncertainty about the future of the land carbon sink. We have a poor understanding of the feedback between terrestrial ecosystems and the Earth’s climate system. Different models predict different futures. At the same time humanity is planning on relying heavily on forests to solve the climate crisis, we don’t understand how the effects of climate change are changing—and will continue to change—the ability of forest ecosystems to absorb CO   .