I am not a climate scientist, not even a garden-variety generic scientist, so what I am about to say is all speculative horseshit.
NOAA (the National Oceanic and Atmospheric Administration) said today (May 6th, 2015): “Global carbon dioxide concentrations surpass 400 parts per million for the first month since measurements began.”
Some climate scientists, notably James Hansen (a NASA climate scientist for 46 years until 2013), arguably the most important climate scientist in the Global Warming controversy, warns us that there is a tipping point in the concentration of CO2 in our atmosphere and that that tipping point is 400 PPM (parts per million). A “tipping point” is a level of concentration (x PPM) above which a positive feedback takes over. A “positive feedback loop” is the name for a situation where phenomenon X drives up the measure of phenomenon Y which in turn drives up the measure of phenomenon X, in a runaway fashion that is unstoppable without introducing a new factor. So, when the concentration of CO2 in the atmosphere reaches that tipping point, without a new outside factor to keep it in check or reverse it, it will explode unstoppably. The planet Venus is 2/3 of the distance from the Sun as is planet Earth, yet its surface temperature averages 462° C or 863° F (lead’s melting point is 327 °C or 621 °F). That is hot! Too hot for life on land and too hot for any oceans or indeed any water in a liquid state. The reason that Venus is so hot, whether at noon or at midnight, is NOT that it is closer to the Sun than we are; the entire reason for Venus being SO hot is that it has an atmosphere composed mostly of CO2, one of the greenhouse gasses (a greenhouse gas is an atmospheric gas that absorbs heat and radiates it back to a planet’s surface instead of letting it radiate harmlessly back into space).
Hansen suggests that the tipping point for a runaway positive feedback loop that would propel our own atmosphere to levels impossible to imagine is 400 PPM. One can only hope he is wrong, or else our goose is cooked. How long will it take before living conditions on the Earth’s surface become 100% impossible? No telling. But we are cooked.
One can argue from now to the Rapture what the tipping point really is. One can argue that when it begins in earnest we will figure out how to suck all those greenhouse gasses out of the atmosphere and sequester them in a way that they cannot escape once again into the atmosphere.
But in the meanwhile we are just asking for trouble.
The problem with the climate deniers’ argument is that they believe that if they are wrong and we just keep adding more CO2 to the atmosphere, we will just get a little warmer. They don’t see or don’t understand that the down-side is extinction, not inconvenience.
That’s it. As I say I am not a climate scientist but at least I hear what they are talking about. Extinction may take a while, but it ain’t just an inconvenience. And, really, what is the downside in migrating sooner to a cheaper, cleaner, more inexhaustible source of energy than filthy finite fossil fuels anyway?