If it wasn't for the greenhouse effect our planet would be a frozen ball of ice. But there is one, and human beings had the chance to build a civilization on it. Unfortunately we are abusing it. And there's a reason why climate scientists are very worried.
My background is in statistical methods, about 40 years of experience, and I would like to bring some of that to bear on global warming. I am not a climate scientist but I do have the background to comment on the statistical modelling.
First, it is important to distinguish between the observations, i.e., the actual measurements, and the secular trend. The measurements that we see are variations around an underlying trend. That underlying trend is hard to see because the measurements bounce around a lot from what we call random, or independent shocks affecting it. A very significant "random shock" affecting temperature is ENSO, the La Nina and El Nino oscillations. These ocean processes have dramatic affects on global temperatures, La Nina negatively, and El Nino positively. But these processes are on top of the secular trend, hiding it. What is really important for our future is knowing the secular trend. When an El Nino happens, temperatures rise and people become very concerned about global warming The 1997-98 El Nino was record breaking. But that concern should be reserved for the secular trend, not the momentary bubble.
When La Nina dominates, the planet's temperature cools down. This fact, that 1998 was very hot year from the El Nino, and succeeding years cooled down from a La Nina, is often used by global warming deniers to "prove" that there isn't any global warming. But they are not measuring the underlying trend, but instead are abusing statistics by "cherry-picking" observations to show a decline in global temperature. The problem is they are basing their analysis on irrelevant facts, the ENSO oscillations that are independent of the secular trend.
The real issue is the secular trend. The effects of greenhouse gases, like CO2 and methane on our atmosphere and on our global temperatures (which includes not just our atmosphere but also our oceans) has been well known for more than a hundred years. The underlying secular trend is a strict function of the quantity of these gases in our atmosphere. Here is a plot of CO2 in our atmosphere,
This plot does not include methane, which is significant, but the nonlinear trend is unmistakable, i.e., the underlying secular trend, a function of the concentration of atmospheric greenhouse gasses, is actually accelerating, it is not linear, and any methane makes it more nonlinear. Independent factors affecting our global temperature, ENSO, the Sun, volcanic eruptions, are masking an accelerating force on the underlying secular trend of the global temperature.
Independent factors could possibly dominate over the underlying trend. Volcanoes could go either way, make things far worse, or maybe better by cooling us down. The Sun is not likely to affect us very much either way. But there is something that could make things really worse, methane stored in arctic permafrost. As the atmosphere warms up, and it appears that the Arctic is warming faster then the rest of the planet, the methane stored in the permafrost could be released. This would have a dramatically increasing affect on the underlying trend.
There is always a possibility that some volcanic eruption could shroud our planet with ash shielding us from the sun. We could hope for that, but in the meantime, to preserve some kind of future for our children and grandchildren, for the future of our civilization, we must emphatically stop pouring CO2 into our atmosphere.
And I must say, from observing current global warming politics, I'm not very hopeful.