Global Climate Stayed Warm in 1996, With Wet, Cold Regional Surprises
Climatologists rank 1996 as the fifth-warmest year ever recorded in global terms, even though North America and Europe were unusually chilly for much of the year; hold that 1990's remain the warmest decade on record, with 1980's second; some scientists demur, saying rise in temperature last two decades is too small to be statistically significant; those who do see a rise do not expect any global warming due to emission of greenhouse gases to be smooth and continuous; say heavy precipitation like that experienced by Americans in Northeast and Northwest in 1996 may be a consequence of global warming; map (M)