Is Global Warming caused by us?

I suppose we are now at the point that we have to accept the science 'fact' that Global Warming is taking place. Nearly every day there is a new story in the news that supports this. The BBC has a great mini site dedicated to Climate Change. One of the most recent stories is related to the disappearing ice and snow on Kilimanjaro. However, with the recent winter being the warmest on record and the weather over the last 3 weeks being abnormally warm and dry fo this time of year - people do start to aske questions. So - we can establish that the weather is different, that we dont quite get the same winter extremes that we used to and that spring plants and butterflies, bees and wasps are all out a lot earlier. But the BIG question remains - is this caused by us or is this part of the natural cycles of world climate. Would this have happened normally even without our input and production of the so called 'greenhouse gases'? For me, that is the big question and I am not quite sure that the proof is quite there yet.
In saying that how can reducing our carbon emissions and the amount of chemicals and pollution that we pump into the atmosphere be anything but a good thing - but will it help to reduce the way that our climate changes . . . that is the big question. What do you think?
22nd April 2007

Additional

I came across this quote as I have been reading Barack Obama's book - The Audacity of Hope.

"Just about every scientist outside the White House believes that climate change is real, serious, and is accelerated by the continued release of carbon dioxide. If the prospect of melting ice caps, rising sea levels, changing weather patterns, more frequent hurricanes, more violent tornadoes, endless dust storms, decaying forests, dying coral reefs, and increases in respiratory illness and insect-borne diseases - if all that doesn't constitute a serious threat, I dont know what does."