First of all, I'm a science writer, not a meteorologist. But I was trained as a scientist. I believe in the scientific method and am a skeptic by nature, as good scientists ought to be. Hence my first reaction to all the doomsayers about Global Warming is to be skeptical. But... what if they are right? The short answer to your questions:
1. I think the burning of fossil fuels at the current rate is crazy. I do not know for certain if it is having an effect on global average temperatures, but one thing I do know: it is having an effect on how much oil is left. I think we've used about half of it and only in about 100 years--most has been burned in the last 20 or 30 years. Maybe it's having an effect on the temperature, but that is beside the point. We need to slow down the rate of burning.
2. Yes. The general view of the scientific community is that human burning of fossil fuels is having an effect on global temperatures. But see below for how they more accurately express it.
THE WAY WE ARE BURNING FOSSIL FUELS IS INSANE
Here is the first point and THE MOST IMPORTANT POINT regardless of anything else anyone says about climate change and global warming. WE ARE BURNING OIL AND OTHER FOSSIL FUELS AT AN INSANE RATE. It is totally crazy to burn all this stuff so fast. [Edit 2015: and the rate of increase of burning is increasing which is even more crazy.] Oil is a resource that took hundreds of millions of years to be made by Nature. Now it appears we humans will burn it all in a few hundred years. That is totally stupid, ignorant, short sighted, and like I said: insane. The burning must be reduced and it must be reduced by a great deal and soon. Instead, the exact opposite is happening. As fast as we can we are burning it faster and faster. Each year I see bigger and more cars on the road. It's rather sad. All I can say is: do everything you personally can to burn less fossil fuels, and convince all your friends to do the same. Make sure your car has a 4 cylinder 1.5L engine at the most, and preferably smaller--much smaller. Walk, bus and bicycle more. Also, write to your political and industry leaders and get them to change the laws and the way they do business so we burn less. By the way, this includes things like the manufacture of paper, cement, aluminum and countless other things that require a huge amount of energy to produce.
WHAT HAS ALREADY BEEN SAID ON SCIENCE.CA
My answer to a question Nov 2004 about how will they make plastic when the oil runs out.
My answer (Jan 2006) to the question about whether volcanoes are contributing very much to CO2 in the atmosphere.
My Nov 2004 discussion about Earth's climate generally headed for warmer times.
How scientists figure out what the temperature was on Earth thousands of years ago before we had records.
Something I wrote in Feb 2006 on fossil fuels and global warming.
Here are my key thoughts on this issue, but don't forget the most important one at the top of the list: REDUCE THE BURNING!
IS IT SCIENCE OR SPECULATION?
Science is based on experimentally proven observable facts. For instance, you can measure the electromotive potential of elements exactly. Based on that you can predict with exact knowledge the electrical potential of, say, a battery made of the elements nickel and cadmium (a NiCad battery). That is science. To then say how long that battery will last in a particular toy or radio is speculation. You can make a good guess based on what you know about the power requirements of the toy, but there are too many variables to know for sure how long the battery will last. So it's a guess. A guess is not science. A guess is imaginary. It's not a fact.
Here is exactly what we know for sure about Global Warming--the facts. The global average mean temperature near the Earth's surface rose by 0.74 +/- 0.18 degrees C in the last 100 years. The uncertainty (+/-) part is due to the limits of our measuring tools. So that means the rise might have been as low as .56 of a degree or as high as .92 of a degree. We cannot say for sure. CO2 in the atmosphere has increased from about 300 parts per million (ppm) to 383ppm in the last couple hundred years.
[Edit 2015: As of January 2015 global average CO2 concentrations are about 400 parts per million or 0.04%, an increas of 4.4% since this question was first answered in 2007. The rate of increase is increasing because the burning has been increasing. Wikipedia page on CO2 concentration.]
400 parts per million is not a very big portion of the atmosphere, and in any case, scientists guess that it accounts for between 9 - 26% of global warming. The majority comes from water vapour. Those are the facts and the only facts. Everything else that is stated about climate change is guesswork. Is the rise caused by humans? Is it something to be worried about? Will there be dire results? Who knows? Granted, experts can make educated guesses and they should be respected, but I do not believe these guesses are any better than a good weather forecast. They are not facts. They are guesses. Everything after the two facts given above (.7 degree rise in temperature and about a 33% increase in CO2) is guesswork.
Reasonably accurate weather prediction is good for a few days. Predicting the future climate for years has never been done successfully. Climate modeling is a new and poorly understood science that requires a lot of assumptions and a lot of speculation. I have interviewed a number of meteorologists, some of them very great scientists. Check out the profile of Roger Daley on science.ca the guy who is credited with creating the first computerized global climate model back in the 1970s in Montreal. Since *ALL* the predictions and speculations about global warming are based on models of the future climate, you would think this guy would know what he's talking about. Well, he was a founding member of the IPCC (International Panel on Climate Change, the group that shared the 2007 Nobel Peace prize with Al Gore). Daley *resigned* from the IPCC when he felt the group was being taken over by pseudoscientists. This was in the 1990s.
People are fond of saying ALL scientists are unanimously in agreement that global warming is real, but I'm not sure. The meteorologists I have interviewed actually say something more like this: "That humans have caused global warming is a real possibility, and it's also possible that this level of warming could cause problems, hence we should err on the side of caution and cut back on burning fossil fuels." Basically, this is like saying: "There's a possibility of showers tomorrow, but we don't know for sure, so take an umbrella just in case." I believe this is the correct attitude towards global warming. Note that this is a lot different from saying "We are positive that humans are causing global warming and that it will have dire consequences for all life as we know it on the planet today." That is NOT what good scientists say. Most don't know for sure, so they offer cautionary advice.
THE EARTH IS IN A WARMING PHASE ANYWAY
All of recorded human history is only about 6000 years. This is not even a microsecond on the cosmic scale of geological time. Earth's climate and atmosphere have varied greatly over the hundreds of millions of years life has been on Earth. Our planet has mostly been much hotter and more humid than we know it to be today, and with much more carbon dioxide in the atmosphere than exists today. Check out the attached chart that shows the planet for the last 600 million years.
Note that we are at one of the very unusual *cold* times for our planet. Normally, and I mean for hundreds of millions of years, Earth is a much warmer place. No matter what happens, we are certainly going to return to the much much warmer NORMAL conditions of planet Earth. It might take a million years, but that is a certainty. How do you think all the oil got here in the first place? It originated with tons and tons of plants that grew for hundreds of millions of years on hothouse Earth and got covered and compressed and turned into oil and coal, etc. Hot is normal. Cold as we've had for the last few tens of thousands of years, now coming out of one of the rare ice ages is NOT normal. The planet did fine for hundreds of millions of years as a hot place, so it will continue to do fine as it warms up again. No worries.
THE TIME SCALE OF GLOBAL WARMING IS NOT A HUMAN TIME SCALE
All of this is happening on a very long time scale. Even the "rapid" rate of warming that may be due to people burning too much fossil fuel is taking a couple hundred years. A couple hundred years is a VERY LONG TIME for humans. A lot can happen in only 50 years (e.g. the invention and ubiquitous proliferation of plastic, or the change of Europe from a bunch of mad warring nations to a happy peaceful union) so I would not worry too much. People talk about sea level rising and major flooding, but this won't be like a Tsunami that happens in a few minutes. It will take a hundred years. You won't even notice it. The gradualness of change will be so slow that humans will have generations to react. If you don't move, then your son or granddaughter will move farther away from the seashore to avoid flooding. Nature, including humans, can handle this rate of change very easily. We'll be OK.
SPECULATIVE GUESSES CAN BE OPTIMISTIC AS WELL AS NEGATIVE
I don't understand why all the Global Warming hype is only about doom and disaster. Flooding, storms, famine, etc. As long as you are just guessing and making things up out of thin air why not make up positive and optimistic speculations. Here are some examples that seem quite reasonable. The warmth will cause a flowering of new species. This is what happened in the past, so we have good reason to expect it will happen again. Rising sea levels could cause an increase in fish and seafood, created by whole new areas of ocean bottom that can be colonized by existing and maybe even new species of fish and other sea life. These areas will be near the shore and near human population centres. More food for humankind. More storms mean more rain and perhaps an overall increase in fertile land so more crops for more people. Why not? My point is: as long as you are speculating--you really have no observable facts--you are just making things up, why not make up nice positive optimistic things about global warming. Both the bad and the good have an equal chance of occurring. In fact, it's a certainty that both bad and good things will happen as a result of global warming.
To sum up, there is one other major fact: fossil fuels are a finite resource. Burning it all up is certainly one way we could use it. I just think there are more intelligent things to do with the stuff. That is why we need to slow down the rate of burning and conserve this precious material for future generations.