Nail in what coffin?
No one can deny our climate is changing. But neither can anyone deny that anything that could conceivably change our lives is a really good thing for politicians who can use that shred of truth to gather supporters.
Science observes that the climate is changing but only has observations from a statistically insignificant amount of time over the earth's existence. We can infer things from archeological evidence such as ice cores and tree rings and sediments but it is not direct observation and other processes that we may not even know exist could account for the CO2 levels in ice layers or the amount and type of vegetation in a layer of sediment etc. Ice cores show about the same CO2 levels as now existed about 20 million years ago yet composition of plant leaf waxes in marine sediments in the antarctic seem to suggest temperatures more than 20 degrees F hotter than today and we don't have any other evidence that explains why. While evidence seems to suggest such high temperatures, current models show a steady growth of polar ice at that same time period. The current models for the earth's systems can't produce an accurate 10 day weather forecast and suddenly we can predict our effect on the weather will cause global catastrophe hundreds of years into the future?
Politicians have rung alarm bells whenever science comes up with a possible interpretation of observed data that could change our lives. In the 1960's acid rain was going to melt our buildings and kill our crops and send us into a global famine. It was a real thing and our industry did contribute some of the sulfur dioxide and nitrogen oxide which makes the rain acidic. Areas around major industry did see dangerous acidity increases but on a global scale rain acidity was almost normal, the vast majority of nitrogen oxides are produced naturally by lightning and sulfur dioxide is produced by volcanic eruptions. We did have a problem to be sure but it was not that acid rain would end the world. We breath easier in our cities because of the regulations on the emissions we imposed in response the impending global doom. The problem is that the average person doesn't care if someone who lives near a bunch of factories is sick all the time. But they do care if those far off factories are reaching out and melting their backyard bird bath and killing their vegetable garden. Politicians used the earliest and most alarmist of predictions they could make sound plausible to gain voter support to fix a real but different problem they could not have gotten enough support for.
In the 1970's science found the hole in the Ozone layer above the poles was expanding. The prediction was that we would all have to be Mylar coated to survive the wrath of the sun's unfiltered UV rays. Scientists theorized that chlorofluorocarbon compounds broken down by UV light from the sun both reacted with and catalyzed reactions with the ozone causing it's depletion. Those reactions do happen and it is now the generally accepted ( does not mean is considered fact ) to be the mechanism that widens the hole in summer but others point out that we can't support any of the dire predictions of the results of those reactions. We have no observational data of the actual effect over time on surface UV levels and no data at all on what the pre-industrial ozone layer looked like: Science didn't have a clue it existed . UV light is needed for the reaction we believe depletes ozone but is also the creator of ozone as well. As more light passes the "ozone layer", more ozone is created. What that means and if there are any consequences for us or the planet is still hotly debated. Some argue that the altitude of the creation vs depletion reactions are different and that changes the UV filtering effect of the ozone as well as many other factors. There is circumstantial evidence that actually suggests that DuPont Chemical may have had a hand publicizing this scare. "In spite" of a rather lackluster opposition by DuPont, the U.S. banned CFCs as an aerosol propellant in 1978. Just before DuPont's CFC patents were set to expire in 1979. Other chemical companies were all set to compete in the CFC market without licensing but that never happened. By 1986, with a new group of HCFC patents in hand, DuPont actually condemned CFCs at the Montreal Protocol hearings saying they had safe (patented) alternatives in production. DuPont went as far as to call for the world wide ban of their own product that actually worked better than the replacements of the time but would have had a significantly reduced profit margin. That's not scientific proof either. No one has proved or disproved the DuPont anti-competition theory any more than the CFCs will deplete the Ozone and cause our extinction theory. We do know that DuPont profited from the solution to the "problem" and we do know that in the presence of UV light, CFCs break down into free radicals that react with or cause reactions with ozone. We do not know whether DuPont influenced public policy nor do we know what the effect would have been if we had increased the amount of CFCs released into the atmosphere - which was definitely set to happen. As the last few developing nations stop production and recycled CFC supplies dwindle, we will get some real data on what is actually going on.
Science requires repeatability of an outcome in order to call something fact. There are no other planets we know of that have life capable of altering the atmosphere like we have and when the earth previously heated up we had a completely different biosphere. There are hot planets with high "greenhouse gas" levels but are the greenhouse gasses there the cause of the heat or the result of it? Will oceans of CO2 consuming / O2 producing plankton bloom and prevent the dire effects predicted? We do have evidence that that may be the case. We have evidence that the earth has been largely an ice sheet as well as a tropical rain forest-like planet more than once in the past and it looks like a cycle. Is it a cycle or just a random occurrence? If it is a cycle, where can we get accurate and granular enough data to even determine what the "normal" warming trend should be in a 20 year sample at our exact point in that cycle. If it isn't a self perpetuating cycle, then what has happened in the past to effect climate changes and would current conditions cause a similar event to have the same effect?
Again, politicians have popularized an alarmist - possibly plausible problem to garner support in solving other problems. So many of the "solutions" to global warming solve real problems that urgently need solving yet would be very hard to garner support for in the face of the well funded entities that would not profit from such changes. People in industrial areas aren't going to vote to eliminate their own jobs even if they are slowly being killed and industry isn't going to voluntarily reduce profits for any reason except to increase future profits.
Don't be fooled either way. We have no idea if the earth will get hot or not because of our car exhausts. BUT we do know that our own industries and products are harming us in ways that they don't or no longer need to. It is relatively easy to build broad support for preventing a doomsday projection with some way of making it plausible. Although the laws being passed right now in the name of preventing global warming may have little or no affect on the earth's climate, they are still much needed for other reasons and are opposed by those with a stake in the old way of doing things