Human Impact on Climate does the data support that there is an effect?

Looking at more data to find significance or not:

Another Case: US Tornado Frequency:

This is the distribution of verified tornadoes in the American Midwest from the period of 1953--1993:

Is the apparent recent increase significant?

- Excluding the last 4 years, the mean number of tornadoes is 747 with a dispersion of 162 and a mean error of 27
- For the last 4 years, the mean number of tornadoes is
1172 with a disperion of 76 and a mean error of 38 (the mean error
is larger because N is smaller)
Again the means are similar so we get

- M1-M2 = 1172 -747 = 425
- 1.5E1 = 1.5*27 which is around 45
- 425/45 = 9 --> EXTREMELY SIGNIFICANT indicating a real effect has increased the tornado frequency --> observation or physical?

Another Case: Urbanization and the Weather

Does Urbanization produce a microclimate in the sense that urban areas are getting warmer.

Here are some results for Washington DC average Tempearture:

- 1960-1990: 14.78 +/- 8.5 N=360
- 1960-1970: 14.26 +/- 8.8 N=120
- 1970-1980: 15.25 +/- 8.3 N=120
- 1980-1990: 15.01 +/- 8.5 N=120

Note that the dispersions are all very similar in these periods. The square root of 120 (number of data samples) = 11.

Let's look at the case for Berkeley CA:

- 1960-1970: 13.67 +/- 3.1 N=120
- 1980-1990: 14.32 +/- 3.0 N=120

So for Berkeley we have: 14.32-13.67/1.5(.27) = .65/.40 = 1.65 --> still not significant but a lot more significant than the case for Washington DC.

This indicates that Berkeley is a better site for this study than Washington DC since the natural climate variations in DC are more severe and hence the signature of a small effect will be much more difficult to get out of the data.

Now, what do you make of this data?