>So, exactly what is the source of skepticism?

We should define climate skepticism, to avoid indicting a strawman. I'd start with my definition, as someone with unorthodox views on climate that often place me at odds with progressives.

It may be easier to start with the elements we agree on. Is the climate changing? Yes, obviously, visibly, measurably. Do human activities, including burning of coal and hydrocarbons, likely have a causal, contributory impact? Absolutely. Is the adoption of cleaner sources of energy: solar, hydro, geothermal, wind, nuclear, as well as investment in transmission and storage upgrades, a good thing? Unquestionably. Is climate change causing a growth in a class of threat to human life and prosperity (e.g. heat deaths, coastal flooding, extreme weather events, etc.)? Of course.

As for the areas where I diverge from progressives: Do I expect any amount of reduction in human activity, including reduction of coal and hydrocarbon combustion, reduction of overall energy usage, reduction of living standards and growth targets, to make any difference in the magnitude of the coming climate change at all in the long run? No.

The earth has both heated and cooled by orders of magnitude more than worst-case projections before humans started burning hydrocarbons.

Earth's climate is changing, yes, but historically, over the last 500 million years, the global average temperature has been as low as ~11° C at times; as high as ~34°C at others. You're reading that correctly: strictly natural processes that predate humanity itself have repeatedly changed the global averge temperature by as much as ~23°C. Ice ages occurred with zero human impact, just as the Cretaceous Thermal Maximum and global atmospheric CO2 levels exceeding 1000ppm occurred with zero human impact.

If you were to measure the full range of earth's climate variation over the history of the earth, and attempt to assign and attribute causality to all sources of that climate variation, you'd find that both the presence of all of humanity and the sum impact of all of human activity is an insignificant footnote. If this duration were a football field, humanity itself would be the last centimeter of grass in the distance of that football field; the period in which we've been measuring the climate is a thin slice of a single blade of grass.

The potential and capacity of natural processes to raise global average temperatures by 23° C has always been present, and nothing we can do will eliminate that potential and capacity.

The focus of human climate concern, accordingly, should be preservation of human life and wealth through adaptation to a changing climate, not futile efforts to prevent change itself, or an irrational alarmism that seeks to instill a widespread sense of anxiety over a process that cannot (and never could be) stopped, and for which the sum of humanity is not responsible for.

Build AC in Seattle. Set up better floodgates in New York City. Winterize the grid in Texas. Fix building codes to make houses more safe from hurricanes in Florida, and develop better solutions to stop the destruction of homes from wildfires in Colorado.

And yeah, do invest in alternative sources and production of energy. Energy is good. Energy is prosperity - it's causally linked to GDP, it's a direct requirement for quality of life / comfort / happiness. We need renewable energy. We need dispatchable energy. We need zero-emissions energy. We need energy that works at night, when it's cloudy, when we run out of oil, and when the wind's not blowing. We need better storage, better transmission. More energy, more sources, and lower costs for all of humanity.

We can't stop the world from changing, and trying to is foolish; we should accept that it is changing whether we try to prevent that or not, and focus on protecting and improving quality of life for all of humanity in the face of this always-changing environment on this little blue dot instead.