Since I like to read scientific articles and scientific magazines fairly regularly, I have to say that the overwhelming majority view of scientists seems to be that global warming is real, and that it is caused at least partly by humanity.
There are other causes for climate change, too. The most important of these is variations in the energy output of the Sun. It is easy to think that the Sun shines steadily and unchangingly at all times, but it doesn't. For example, it is well known that the 17th and 18th centuries were unusually cold in Europe, and probably in most of the Northern hemisphere. The period is known as The Little Ice Age. Astronomical observations of the Sun from that time show that the Sun had very few sunspots at that time. It has been established that the more sunspots the Sun has, the more active it it, and the more energy it puts out. In other words, the Sun was in fact a little colder in the 17th and 18th century than it is now, which affected the climate of the Earth.
However, the last, oh, twenty years or so has seen the Earth grow steadily warmer. Is that because the Sun is getting hotter? It might be, and if so, that is clearly going to affect the climate of the Earth. Does that mean we can happily release all sorts of known greenhouse gases into the Earth's atmosphere with impunity? Can we say that if the Sun is doing most of the additional warming of the Earth, then we don't have to worry about the part we play ourselves? Can we say that what we are doing to the Earth, such as changing the composition of the atmosphere, isn't affecting the temperature of the Earth?
I don't think we can. I want to point out, too, that to the best of the understanding of astronomers, the Sun is going to grow slowly but inexorably warmer (that is to say, it is going to release ever more energy) as it grows older. In other words, the long term effect of the Sun on the Earth is going to make it progressively hotter. Does that mean that we ourselves should be careful so that we don't add to any general climate changing trend? Yes, in my opinon, we should.
Ann
