It takes thousands and thousands of years to have
any substantial melting of ice sheets!
As intriguing a concept as it is, a «tipping point» is less useful if poorly defined quantitatively or largely unknown, as apparently is the case with two key examples that you cite: thermohaline circulation and
substantial melting of ice sheets leading to «dangerous» sea level rise.
Not exact matches
This is
of course some positive news for the Greenland
ice sheet, but the warming there is already
substantial enough to cause significant net
melting.
There are no
substantial glacial lakes forming today that could produce comparable amounts
of water (although a few hundred years
of melting of the Greenland
ice sheet could change that situation).
The impacts
of ice shelf collapse and ensuing glacier acceleration are
substantial, but in general, the effects
of ocean
melt are proving to be far more important in controlling
ice sheet mass balance.
Not only is this the earliest
substantial melt on record, but the refreezing
of the rain and meltwater soaking into the
ice sheet sets it up for even more
melting in the future.
Easterbrook criticized Gore's claims that the
melting of ice sheets in Greenland and Antarctica could lead to
substantial increases in sea levels, that the concentration
of carbon dioxide in the atmosphere is increasing, and that Bush administration officials have attempted to tamper with official reports on the threat posed by climate change.