When they are serious about doing something to address global climate change, you will be able to tell because you will see them launching orbital solar shades / reflectors.

We don't really understand exactly how atmospheric chemistry effects the climate yet, and we can't accurately predict the weather beyond a week or so, but there is something that has been well understood for over a century, and that is thermal-dynamics. Atmospheric chemistry and weather prediction are both extremely complicated, but thermal-dynamics is extremely simple. It is an easy concept to understand... if you block some of the sunlight that reaches the Earth, the temperature goes down... and if you reflect more sunlight onto the Earth, the temperature will go up. It's quite simple.

So, when they are serious about doing something about global climate change, you will know because you will see them launching orbital solar shades / reflectors.

It really is just that simple, and it will work regardless of the cause, or the direction, of the global temperature changes. (until then, all you're looking at... is business as usual)