Yes, global warming, the long forgotten theoretical driving force of climate change, caused by the even longer forgotten greenhouse effect. Climate change is the first part of the truncated phrase, 'Climate change due to global warming' which is impossible not to happen if literally applied to the climate.
Global warming is divided in two parts, the theory and the resulting evidence. Maybe 80% of the majority of articles I've read on it base their evidence on theory, with the remainder being a scattering of examples to demonstrate how it 'must' therefore be happening. The theory in turn is divided in two parts, the mathematics and the projections. If you apply physics to any substance it will behave perfectly on paper and more or less perfectly in a controlled experiment. If not then they need more work to pass the level required to be a scientific theory. If you transfer these experiments from the lab to the atmosphere you suddenly multiply the influences many thousandfold. These are still more or less measurable for vast or very short term influences, but the scientists here are referring to a small additional amount of CO2 (the other gases are treated separately), claiming a few percent extra (man adds 3% to the 0.03% it currently makes up) is capable of producing a significant rise in temperature. If a volcano erupts you see the changes for a while as a sudden output of material is present and the results easily measured. But a gradual increase in a relatively poor insulating gas over centuries, combined with solar, oceanic and as yet unknown influences appears not to be capable of any such measurement.
The mechanics of chaos theory were demonstrated by the effects of tiny actions on the climate as a whole. One can reverbarate globally, so combine that by millions and you have a lot of competing influences. Every significant one must be factored into every CO2 equation, as outside a greenhouse the effect is joined by countless other effects. I doubt the combined power of the world's computers are sufficient to calculate a model of it all, in fact Philip Stott, the BBC science spokesman, says 85% of climate drivers are as yet unknown. I think had this not been the case it would have been edited from the programme before it went on air. Scientists without an agenda simply have no reason to invent figures.
The second part of the theory is projections. However, a projection is only reliable within a closed system, like astronomical movements. If you push an object with a certain force in a certain direction you can project its route. Compare that with adding some CO2 to the atmosphere, know how it interacts with water vapour, learn how long it stays there, measure the height it appears in etc, and then use all these to combine with the often unseen variations like el nino and sunspot activity and make projections around 100 years in the future. This is what the actual policies are based on. When they were made, not enough had happened (genuinely caused or otherwise) to show the greenhouse effect, but in order to prevent it from happening (the fact it was outside our lifetimes seemed to go over most people's heads) they say we must act first.
If you look at the factors driving the climate, the size of the atmosphere plus the solar changes outside it, the legal test of the reasonable man would be unlikely to believe that a small increase in a mild greenhouse gas could be measured in the present, let alone projected hundreds of years into the future.
As for the practice, this falls into a few areas. There are the general figures like sea and ice level, temperature figures and long term trends for all. These are the roots of any known effects, as the only variable we have is temperature trends. The single effect of global warming is contained in the phrase, ie warming. Besides the fact we have historical (written by men of the day) records of the range of temperature they are predicting from the past already, meaning the fear factor is basically negated as few if any of the effects dreaded by the faithful have been mentioned in history) they have to present graphs showing the continual temperature variations, and somehow connect them with the much more easily measurable greenhouse gases (ie as well as CO2). In reality the CO2 tends to be the sole figure used, despite 95% of any greenhouse effect, (33' above what it is outside the atmosphere at present) is actually water vapour which is far more powerful in effect. But these are the macro criteria which have to be used to measure the increase in temperature.
To put this further in context, the ice age cycle means the climate cools or heats half the time naturally. As we are in a heating phase, it means they theoretically have to compare what they expected the temperature rise to be with what it actually is. Remember the complications involved in predicting future temperatures and that becomes a lot tougher than it looks.
So we have measurements of temperature, compared further with the theoretical rise had the extra CO2 (3%) been absent, and then similar comparisons made with ice coverage and sea levels. In fact only ice coverage and sea levels for the whole planet count, as although they are constanly quoting (and quite controversially) specific glaciers, they are only a part of the whole and if others are growing it's only the overall amount that exists, the rest are only elements of it. The University of Illinois have produced the ice coverage graphs showing them all since records started being measured in 1979. They show an incredibly regular shape, the only variation being a 2% reduction trough in 2007 which is now rising. Individual glaciers, being part of the whole, have no value at all as if the world temperature rises the ice can't hide somewhere else from it. The sea level, rarely mentioned nowadays, is the easiest to measure, although for reasons only the experts know it's not a constant depth for all like the water in your bath, but an average. This has risen a few inches a century for centuries, and is currently rising inches a century. They can't use these figures in the media as they imply nothing's changing, as the ice melts over land and the sea expands as temperature rises, and this indicates very little has changed. The very figure which reflects more influences the most easily is serially ignored by the media.
The second type of evidence is weather, yes, weather not climate. The IPCC view from about 2008 is that severe weather incidence was not related to temperature, yet is still used by anyone who can whenever it happens as more evidence for global warming. Firstly we are warming anyway, so whatever normal weather increases in that direction is a given, which does make it that much harder to attribute to much else. If the warm weather incidents increased in such a large number it became climate then maybe there would be something to look at, but most use single events over days or less as evidence despite every freezing winter, abnormal snowfall and the like are always dismissed as weather as being in the wrong direction are treated as they should be, part of the normal variations part of the chaos theory of climate. Such selective treatment of short term weather is misleading and easier to simply not include any of it as some is clearly impossible to assign meaning to.
The third type is physical effects. These again have many causes, but if you're already looking for specific evidence (science tries to disprove a theory before confirming it when they can't), you tend to attribute anything that looks like it could be without a definite causal connection (required in law as well). Deserts are guaranteed to extend beyond the equatorial direction as temperature rises. But man does also contribute to making deserts. They drain rivers, erode soil and cut down forests. These will cause deserts to expand in months without any need to look for any other reason. Of course they fail to mention the temperate areas moving away from the equator as well towards the poles, as the changes balance the land use pretty well. No one disputes more people die from the cold than the heat but that spoils the emotional appeal if mentioned. Land being inundated by sea is another standard photo opportunity and political weapon used by those living near the sea level. But plate tectonics tell you the land moves as well as the sea. Britain tilts to one side and sinking at one side while rising on the other. The Pacific islands are also sinking which is inevitable even if the sea level dropped it could only be delayed. And building on coastal flood plains like New Orleans or Bangladesh is simply a combination of overpopulation, forcing people to live in uninhabitable areas as only temporary land, and greed of those who build there for profit. They were doomed as soon as occupied, and if we diverted efforts to reducing the population rather than CO2 as well as the poverty that forces the poorest to live there then it would be a quick solution with visible results.
To sum up the evidence, global warming is based on mathematics, lab experiments, and complex calculations looking at the possible effects a small increase in CO2 can have over time in the atmosphere. The theory works perfectly in a greenhouse, which is why it's called the greenhouse effect, and on paper or within a computer trial. The claim is man's 3% addition of CO2 to the atmosphere is both effective and measurable.
The effects are: Seal level increase, Ice coverage decreases, changing land patterns, changing weather patterns, and many less certain effects thrown in in case our extra CO2 may have caused them as well, which are so diverse it's not worth trying to keep a note of them. In fact many measurements besides the ice and sea levels are not certain. Specific glaciers are presented as evidence, yet competing measurements then appear saying they are not melting. Similarly temperature measurements are presented as a whole, but collected from satellites, air, land and sea. Each produces a different set of figures and climatologists, not surprisingly, don't actually agree on all of these. But the base year they use (but rarely mention as a figure) now has a 0.5 increase. That's not yet close to even the 1.5' rise used as some sort of tipping point, and at current rates is unlikely to happen in our lifetimes. I did my best to use the official figures and then analyse them, and not use any others or ignore any I didn't like. If I missed any it was due to volume and not design. You decide.