For all those people hand-wringing about what 400 ppm of CO2 will do to all life on earth, here is a historical footnote:
In Earth's geological history, there have been periods when atmospheric carbon dioxide (CO2) levels were much higher than they are today, and during these times, Earth supported massive trees and plants. One notable period was the Carboniferous Period, approximately 360 to 300 million years ago.
During the Carboniferous Period, atmospheric CO2 levels were significantly higher than they are today, possibly reaching levels as high as 2000 to 3000 parts per million (ppm), or even higher. These elevated CO2 levels, combined with other favorable environmental conditions such as warmth and moisture, created an optimal environment for plant growth.
As a result, the Carboniferous Period is sometimes referred to as the "Age of Ferns and Giant Trees." Forests dominated by tree-sized ferns, horsetails, club mosses, and early conifers covered large portions of the Earth's landmasses. Some of the trees that grew during this time, such as the lycopods and tree-sized ferns, could reach impressive heights, with some estimates suggesting they may have exceeded 30 meters (100 feet) in height.
The dense vegetation of the Carboniferous Period played a crucial role in sequestering atmospheric carbon, with large amounts of organic material accumulating and eventually forming coal deposits. These coal deposits, which are mined for their fossilized plant remains, are evidence of the abundance and size of the plants that existed during this period.
Overall, the Carboniferous Period serves as a prime example of how elevated CO2 levels in Earth's past have supported the growth of massive trees and plants, shaping the planet's ecosystems and leaving behind significant geological and biological legacies.
In other words, we have a lot more fossil fuel to burn before we can get back to the golden age of life on Earth.