In terms of painting a picture of the complexity of the living earth, the direct C02 effect serves as a final brush stroke, on top of everything else. If there is an overall message from this book, it is that the earth system is immensely subtle and complex, and that life has a key role in just about every aspect of it. And yet, as we marvel at the elegance of the mechanisms that we can see at work, we should not expect to know exactly how they will behave as we tinker with our planet.
The more effort—and the more money—that goes into research on the earth system, the more light will be shed on these processes and how they interact. This can allow us to consider a range of possibilities with more confidence, to spot new possible scenarios that had never been noticed before, and give either more or less credence to each of the various scenarios we already have. But, given the sheer complexity of what we are dealing with here, science can never provide the detailed certainty that politicians crave.
And so we enter a vast experiment, raising greenhouse gas levels beyond anything that has occurred in tens of millions of years. All science can do is offer a range of plausible scenarios, and then try to lay out these possibilities in an accessible way. It is up to people around the world to decide whether to take the gamble on any particular scenario coming true.
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