Are the great lakes large enough to moderate temperature extremes near the coast to the degree we need?
Sure. Until they dry up, that is. See great salt lake, and death valley for how that works, longer term. See Lake Mead for how that looks short term.
The world will be warmer. That's not so hard to work out. Look at a map. The temps down south will move north. California will be more like Mexico, PNW will be more like Cali. Eastern Washington will be more like Eastern Cali. This is because there will still be an ocean and mountains. Warm air moving across water will still pick up humidity, and dump it over land. But the gentle drizzle I am used to, will be replaced by monsoon like storms. Warmer just means more energy in the system, so bigger, more sudden storms and less mist and clouds, locally. Shifts in predominant winds will affect coastal range areas, but not likely to be a big concern inland.
The great plains is even easier, as the rivers go south and away, rather than in. Less rain will mean less water going into the lakes until evaporation exceeds rainfall. Then the lakes will receed for a generation or 2. Eventually, WI looks more like Tx. You see any big lakes in Tx? LA? AR? It's not that they don't get rain, it's that they evaporate faster than they accumulate.
Now go into Google maps, and look at the coast of moracco. Or better, look for African towns before fossil fuels. This can be done by scrolling into towns, and looking for the area that clearly wasn't laid out in a grid. Now scroll back out a bit. All that grid area is fossil fuels growth. Try it again in other parts of the globe. Get comfortable with it. Try to imagine how the reversal of that trend will look. When you have 1000 people where there are resources for 20, and no more resources coming in, you get a good grasp on the scale of the issue. Now think of how well the itinerant band of ERE Gypies suggested above will be received.
The problem isn't carbon, and never was. The problem is fecundity. And nobody is even willing to face that, let alone deal with it. A human population of one million doesn't need a carbon tax, and a carbon tax won't help a population of 7+ billion.
Again, this isn't a problem we can address thru politics.