Figure 6 shows how [DELTA][W.sub.diff] changes during the historical simulations for various CMIP5 models using rolling 30-yr reference periods. It is clear that different models behave in very different ways, warming more or less than the observations at different times.
This is partly because optimal reference periods are typically much longer, as the variability is larger relative to forced changes (see appendix D).
The number of years (in the 1861-2005 period) that the median of HadCRUT4.3 fails outside the specified CMIP5 confidence interval for different reference periods. Reference period >95% >75% <25% <5% Number expected 7 36 36 7 1861-2005 3 35 37 4 1861-90 1 10 50 8 1911-30 13 68 10 0 1961-90 1 27 31 2 1980-99 0 21 27 1 1976-2005 1 35 19 0 1986-2005 1 25 18 1
When comparing simulations with each other and with observations, it is standard practice to compare temperature anomalies with respect to a reference period. It is not always appreciated that the choice of reference period can affect conclusions, both about the skill of simulations of past climate and about the magnitude of expected future changes in climate.
Careful consideration of sensitivities to the choice of climate reference period is required to reliably compare climate models with observations and to produce robust projections of future climate.
For five of the six reference periods the difference is statistically significant with a market capitalization loss for the stock buyback portfolio (SBP) and a market capitalization gain for all other stocks.
Panel A of Table 4, representing large capitalization stocks, shows t-statistics of market capitalization differences (from the beginning to the end of the reference periods) predominately significant in relation to the t-statistics in Panel B representing small capitalization stocks.
The market capitalization change (from the beginning to the end of the reference period) for the large capitalization stock buyback portfolio (MCDSBP) stocks in Panel A is negative for all reference periods except the 2003 to 2012 reference period.
This study focuses on shareholder wealth changes for three, five-year and three, ten-year reference periods. The evidence shows market capitalization declines for most of the reference periods for the stock buyback portfolio relative to the portfolio of all other stocks.
Many companies might do a spin-off during a long reference period and these firms might be merger and acquisition activities.
One-year reference period in certain sectors (processing industry, tourism) established in law whereas it is only authorised under collective agreements.
The reference period can be raised under legislation to 12 months.