1. The current warming trend of ~ 0.5 degrees C per ~ 30 years, IF it
were to continue for just another 150 years, would lead to global
temperatures as high or higher than they have been at almost any time
during the last 400,000 years (~3 degrees C above "average"). Of
course it is debatable whether or not the current trend will
continue since there was a modest cooling trend of ~ 0.1 degrees C
per ~30 years in the period from 1940 to 1970. On the other hand
there are perfectly credible reasons to believe that the current
trend could accelerate.
2. We know that CO2 has historically been very closely correlated
with global temperatures and we also know that the current level of
CO2 in the atmosphere is about 30% higher than it has previously been
at any time during the last 400,000 years and that that is a result
of human activity. Of course, it is debatable whether CO2 causes
global warming and, even if it does, it is further debatable whether
the markedly higher CO2 levels that we have will cause even
noticeably increased temperatures. But, again, there are perfectly
credible reasons to think both things.
3. We know that sea levels change enormously--e.g. by more than one
hundred meters during just the last 20,000 years so that a change of
10 meters hardly seems out of the question.
5. The overriding bad news for humanity may be that all the records
point to the last 10,000 years as a highly unusual island of
stability in almost every aspect. Thus, it seems likely to me that,
even if we ONLY have to cope with natural variability, we have some
VERY challenging times ahead on the scale, probably, of thousands of
years.
(See all of the above.)
So, I understand that there are economic considerations involved in
deciding what constitutes prudent safeguards to undertake.
Nevertheless, it seems to me that the evidence is compelling enough
and the potential downside devastating enough that one might expect
the leader of the richest country on Earth AT LEAST to be using his
bully pulpit to insure against recurrences of headlines like this