It's obviously easier to "fart around with" the Earth's climate considering we're doing it now to some extent.
Assuming you meant the much higher bar of improving the Earth's climate (sidestepping the obvious question of what we mean by improve), I'm still not convinced colonizing another planet is easier. There's a number of theoretical plans for reducing CO2, or decreasing surface temperature by reflecting some of the sun's light. These plans are much less sci-fi fanciful than building a viable colony (especially if you mean largely self-supporting) on other planets.
"sidestepping the obvious question of what we mean by improve"
This, by the way, is rather a massive problem with current discourse. Anyone who wants to talk about "damage" to Earth's environment ought to be required to specify their definition of "optimal". It turns out to be rather tricky, but without it a lot of this debate is politics, not science or engineering.
Point being that making a mess on another planet is more preferable than making a mess of the only one we have - and I have much more faith in our ability to make a mess of things than I do in our ability to "improve" the Earth's climate.
That's odd since the evidence we have so far points to humanity adapting our environment and improving our living conditions with breathtaking success.
Well yes and no - great short term success (of the order of decades or centuries), but we still don't know what the longer term impact of our activities will be; that's one of the big questions of climate science.
Assuming you meant the much higher bar of improving the Earth's climate (sidestepping the obvious question of what we mean by improve), I'm still not convinced colonizing another planet is easier. There's a number of theoretical plans for reducing CO2, or decreasing surface temperature by reflecting some of the sun's light. These plans are much less sci-fi fanciful than building a viable colony (especially if you mean largely self-supporting) on other planets.