After millions of years of the Earth orbiting the Sun, Earth had reached a radiative equilibrium. This means that the Earth is warmed by incoming absorbed solar radiation, and Earth was cooled by an equal amount of infrared radiation. Since there is no conductive heat transfer through space, this radiative heat transfer between Earth, Space, and the Sun is what has given the Earth an average temperature that has been conducive to life.
Due to the Earth being much cooler than the Sun, Earth mostly radiates in the infrared region, whereas the Sun mostly radiates in the visible region. Since we humans don't see in the infrared, this is not obvious to us. But it is why it cools down at night.
CO2 happens to have four strong absorptive bands in the infrared region. One of those absortive bands unfortunately overlaps with the infrared band within which the Earth radiates. This band is from 8 to 13 microns. So, what happens is that CO2 absorbs infrared radiation that would otherwise pass through the air into space - cooling the Earth. The CO2 molecules warm when they absorb, which warms the air through conduction, which warms everything else. Warmer air also increases in radiative emittance, of which approximately half is emitted back to the Earth's surface.
It’s not simply that CO2 is warming us, so much as it is that it doesn’t let the Earth cool as much as the Earth was warmed during the day from the Sun. Unfortunately, we are no longer in thermal equilibrium with the Sun.
This is all due to fossil fuels dramatically increasing the amount and concentration of CO2 and other greenhouse gases in the atmosphere. The Earth no longer emits into space the infrared radiation it should. The implications are that, yes, the Earth is warming. But it is the byproduct of the richest industry on Earth, and they are poisoning our planet. While what exactly is going to happen, and when, is complicated, the basic science behind manmade climate change is not.
If you are skeptical, then I suggest that you have been influenced by the disinformation the fossil fuel industry promotes. The fossil fuel industry would like you to believe that CO2 is a natural molecule that life depends on. It is. But it is the concentration in air that is the problem, not the molecule itself. They want you to believe that plants will increase and absorb the CO2 we generate. Plants will - to a degree. But the staggering rise in measured CO2 concentration in the atmosphere over the years leaves no doubt that plants can’t and haven’t kept up. They also would like you to believe that there will be positive benefits to a warming planet. That is also true. But the planet is changing faster than life is evolving, and the negatives vastly outweigh the positives. What they most want is for you to believe their disinformation, particularly when it comes from their candidates that stand up and tell what they want you to believe, regardless of truth.
The fossil fuel industry can only avoid extinction if they fund disinformation. Truth kills them. The most fundamental problem we face is the success of their denial, and the professional denial industry. The changes to our Earth are happening slowly. One disaster at a time is easy to explain away as bad luck. Now the scary thing here is that they can’t avoid extinction, they can only delay it until deniability becomes impossible. But the question remains: is that point beyond the tipping point where we eventually all go extinct.
Regarding polar ice:
Warmer water picks up more moisture. So right now, glaciers are growing closest to the poles, as more moisture means more snow where it is still really cold. But near the edge of of the polar ice caps, ice is melting. Due to this effect, the surface of the oceans is only about seven inches higher over the last century. But as anyone who lives in snow country knows, ice gets dirtier as it melts. That dirt absorbs the radiant energy from the sun and the snow and ice melt ever faster.
Also, snow happens to be a rare selective surface. It is one of the best known to man. What this means is that it is incredibly reflective to visible light from the Sun reflecting a really large percentage back into space. But snow also is an excellent emitter of infrared radiation. What this means is that snow radiates a lot of heat into space. So, while rising sea levels is a very real threat in the future, it is far from the only problem.
Ice increasing right at the poles is somewhat offsetting ice lost at the edges. But it is not so much the amount of ice that matters to global temperatures, it is the surface area of the ice caps that matters. Due to ice being a selective surface, ice is a planet cooler. Less surface area means warmer global temperatures, which of course leads to more ice area loss. It is a positive feedback loop, which is incredibly dangerous!
Here is a simple analogy: If a scoop of ice cream is placed on a plate, one could measure the temperature for a period of time and it wouldn't change. Ice cream is just like ice. It undergoes a phase change, and during the phase change the temperature does not change. So a warming denier through confirmation bias could use this to state that this is evidence that the ice cream is not warming. A denier could also point out that the ice cream is extending farther out into the plate with time. If one were to assume that increasing distance of spread indicates a growing mass, as did some with glaciers that started extending farther out into the sea, then an argument could be made that the mass of the ice cream is increasing - indicating cooling. But, of course, that is all nonsense. Once the ice cream is melted, its stops moderating the temperature, just as the polar caps will do eventually.