I've explained it, in detailed, with citations, several times in this thread. If you are truly curious, you can find it or seek out other sources of knowledge. Someone isn't paying attention, otherwise, you would know that our climate data goes back way past human record keeping (humans have only been good at keeping climate records for ~156 years).
For fun, I will simplify it as much as possible (again):
Science can very accurately trace atmospheric CO2 going back ~800,000 years.
Science can very accurately measure temperatures continuously going back ~2,000,000 years (and back 3 million, but not continuously).
There is strong correlation between increased CO2 levels and temperature in the records.
There is separate strong scientific evidence for CO2 as a greenhouse gas.
Combining these data points, scientists conclude that CO2 causes warming.
CO2 and temperature both fluctuated back and forth slowly over millennium (average cycle ~8500 years).
Humans have pumped ever increasing amounts of CO2 into the atmosphere in measurable amounts.
The current rapid rise in CO2 levels is a historic anomaly and corresponds with the industrial revolution (rise equal to a cycle in 50 years).
The last time CO2 levels were this high, humans did not exist.
https://climate.nasa.gov/evidence/In a typical cycle, the average temperature rose 4-7 degrees C over thousands of years.
In the recent past, we have experienced warming at a rate of 1 degree per 100 years.
Studies have shown an unambiguous one way causality between the recent man-made rise in CO2 and temperature.
https://www.nature.com/articles/srep21691That's all done. It's a scientific conclusion, like gravity. We should always seek more data and refine the theory, but the basic conclusion has been reached and will not be overturned without extraordinary data. The questions being asked now are:
1. How much CO2 can the oceans absorb?
2. Will the oceans moderate the increase in air temperature?
3. What regional changes will it bring about?
4. For how long will change continue? and
5. What can be done to minimize the impact?
As far as I can tell, there isn't a consensus on these things. If the global average changes 2 C uniformly, we have a solid idea of what that means (bye Miami). But if the gulf stream is disrupted, the jet stream moves, or other massive ocean/air currents shift - serious problems emerge. Ever notice that Tulsa and Baghdad have similar latitudes or that London is north of Winnipeg? Turns out currents really matter.
For my own ignorance, I've never understood what caused CO2 levels to drop previously. I assume a shift in floral/fauna over millennia (which would be bad for us), but I've never really looked into it. So don't think I'm operating with complete (let alone perfect) knowledge.
But as long as we continue to have the same debate over and over and over and over on matters already decided, its hard to press forward with the other questions. And yes, science should ALWAYS be an open question. The problem is when the questions have been answered and people still refuse to accept the data. If no new evidence is presented, then at a certain point, you have to write them off as refusing to accept reality and move on.
I'm looking at you, flat earthers.
