Global warming is not just a short term problem . Barring catastrophe , human energy generation from fusion and non-solar sources will within a few centuries exceed the solar influx . We will need planetary air-conditioning .
(See Larry Niven's Puppeteer Planets)
At first , the simplest way is to put up an umbrella .
A simple solar Umbrella can be created by injecting Lunar reflecting dust into a hyperbolic orbit between the sun and Earth by mass-drivers on Luna .
The space elements of a moonbase and mass-drivers an be done with existing technology .
The Terran climate models needed for effective climate-control also exists , but can do with some refining .
The political control of an effective climate control system still needs some work .
The money , paradoxically , is the easiest . Big insurance companies (like Swiss Re , etc ) can easily fork up the estimated $60 billion this will cost . ( One big hurricane can cost $20 billion in damages .)
Later on it gets trickier .
At higher levels of planetary energy generation , Hilsch-tube lasers could directly pump energy out . A model that springs to mind is a fairly massive object (a few billion tons) in a perpetually skipping orbit . Propulsion would be by Hilsch-tube lasers (existing technology) and fusion (Orion-type existing tech.) More elegantly , the lasers would be boosted by fusion processes in the laser . This could be made made fairly fail-safe , so that there would be a nett energy loss to the planet . The matter-loss would have to be topped up ( comets?)
Of course , the same technology could be used to strip-mine a planet or sun .
Cascaded Hilsch-tubes were used in the South-African Uranium235-enrichment process for weapons purposes . A large physical or magnetic Hisch-tube cascade can be used like a mass-spectrometer to separate elements .
It would make a great booster for light-sails , or an awesome weapon . Also , cheap , pure elements
Time horizen : since all the above elements are based on standard physics , it can be done . Whether it will be , depends on humans .
Reusable reaction mass.
Imagine a 50 ton solar-powered launching satelite with a set of mass-driver rings in LEO at 18 000 mph in a West-to-East Low Earth Orbit .
Let it accellerate a 50 ton payload via mass-driver to 36 000 mph in some tangential direction .
In reaction , the Launching satelite will now orbit at 18 000 mph in an East-to-West direction .
Of course it is a bit more complicated than this , but the orbital mechanics are well within present technology (and really old maths) .
Docking new craft with the Launching satelite is also proven technology (ref International Space Station). This can then be relaunched in the opposite direction .
Essentially , the same reaction mass can be used over and over again , as long as it has been in orbit and an energy source is available (solar power , nuclear , etc).
All you need to do is get off-planet . Later on , the most valuable real-estate becomes in-vacuo mass (because you can use mass-drivers cheaply).
The orbit can be around any planet or sun .
The station need never decay .
One can imagine a Solar System ( at various ages ) with literally millions of millennia-old booster-stations in various solar and planetary orbits , each of various technological levels of development . They are inhabited , of course . Throw in some collapses and a singularity or two .
The political system and races will be quite fragmented .
Alien invaders would only consider a system with a developed transport infrastructure and fragmented culture .
This stellar signature should be quite distinct . The end result should be a Dyson-sphere or Ringworlds . But the intermediate stages will vary considerably .
They should also be observed more easily .
Jupiter class worlds will be moved closer to the sun for more efficient dismantling .
Planetary blobs and ringworlds should be observable by striations . Technological ramp-ups up waste-energy dispersal should be measurable if there are handy gas-clouds of various distances nearby . Reflections of planetary laser-heat dispersals varying over time might give a clue .
As can be seen , arriving at the optimum Dyson sphere stage will be outmatched by the number of civilizations either en-route or become agley .
To quote a Sol humanoid , each happy civilization is the same , but each unhappy one is unhappy in its own way .
Happy universes !