@ jake @ Anonymous Coward
'Yes. The world is getting warmer. When was the last time the Thames froze over?'
Since you ask it was the winter of 1962 - 63 when it froze as far downstream as Teddington Lock. If you're asking when was the last Frost Fair then it was 1813 - 14 which is recognised as an exceptionally cold winter even for the Little Ice Age, possibly as a result of the colossal eruption of Tambora in Indonesia. It's questionable whether frost fairs were possible much later, not just because of a general warming trend, but also because the construction of London Bridge from 1825 and the Embankment changed the flow of the river, making it faster and much less likely to freeze.
'It's still not as warm as it was in Roman times. When was the last time you drank wine from grapes grown along Hadrian's Wall?'
Actually you could grow vines at Hadrian's Wall today, it's just that it doesn't make economic sense. I've heard this story about Romans and Northumberland wine a number of times, but I can't find a definitive source apart from Freddie Forsyth blustering on 'Question Time', so I wonder if the Romans ever did have vineyards that far north.
As for temperatures changing. Yes they do, it is the RATE of change in the current warming phase that is abnormal compared to other changes in the Holocene.
@ Anonymous Coward said:
'One problem we have is that severe volcanic activity a couple of centuries ago threw a lot of ash into the air and resulted in wonderful sunsets (no you don't see sunsets like Turner painted, but you did back then)'
Already factored into the calculations and we have plenty of empirical evidence from eruptions such as El Chichon and Pinatubo to know the amount of cooling these eruptions would cause.
As for not seeing sunsets like Turner's ummmm - perhaps some of Turner's paintings are impressionistic?
'Then of course we had the industrial revolution, you should therefore have seen all those CO2 emissions producing significant global warming over the 18th and 19th centuries - but that doesn't seem to be the case from the data we have.'
We're burning an order of magnitude more carbon than we were in the 18th and 19th Century when only a tiny minority of the population were consuming fossil fuels and even then only consuming a small fraction of the energy we use today.