Thanks for being patient, I am finally on a computer.
The current CO2 ppm is about 417ppm. But yes, currently 0.04% of our atmosphere.
A few things you must also consider. There is a time lag, as well as positive feedbacks, so even if we stopped all human CO2 output tomorrow, there would still be increases in temperature for years/decades. Happy to go find some papers to show this, but I'm sure a quick google will turn something up if you're interested.
Climate Change and Food Systems (https://link.springer.com/chapter/10.1007/978-3-031-15703-5_27#:~:text=Considerable%20evidence%20has%20by%20now,2021).
I posted this source last week which goes through in depth about climate change and food systems and productivity. You'll notice its not as simple as more CO2 = more plants = more produce. Shifting rainfall patterns, higher rates of desiccation, environmental stability, etc etc show that whilst some regions may have some higher yields, there are also many more regions with lower yields.
One thing that often gets overlooked is the rate at which the climate is changing. In the past, the climate has warmed (or cooled) over thousands, tens of thousands, or hundreds of thousands of years. This gave many systems the opportunity to adapt. Now, we are seeing the same change over the span of decades/centuries, and those systems cannot adapt that quickly.
The fact that CO2 is a relatively low trace compound in our atmosphere doesn't automatically mean its effect must also be low. Humans can tolerate, say, anywhere from 5 to 50 parts per billion of arsenic in water. Turn that up to 150 parts per billion, and it can start to become fatal. We're talking about 0.000015%
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