'Global warming skeptics' like to point out that previous interglacials achieved global temperatures higher than what we have yet to experience. This is true. Since it's also true that this came about without the influence of artificially high CO2 levels, we know that this was the result of the natural Milankovitch cycle. However, the kink in this reasoning is that the temperature changes induced by orbital variances don't occur so rapidly as what is now occurring. Thus, the sudden current global temperature increase is being fueled by CO2 releases. And because greenhouse gases endure for many centuries, we face the prospect of CO2 further amplifying eventual natural temperature increases induced by the Milankovitch effect. Unlike the last interglacial that saw hippos basking in England, they'll someday be able to enjoy the fjords of Norway.
interglacials Milankovitch cycles carbon dioxide
The "rest of the story":
One variable that is not receiving serious enough consideration is the
subject of "Methane Hydrate Degasification + Paleoclimatology". Read up
on this and then consider that since temperatures in the current
interglacial period will go higher than in any previous interglacial
period due to artificially higher levels of CO2 amplifying the natural
Milankovitch temperatures, that ocean temperatures will be warmer at
greater depths than they have been in over 56 million years in the
Paleocene-Eocene Thermal Maximum. That means that the oceanic methane
hydrate that has been building up without interglacial releases at these
greater depths will be released. Thus, greater amounts of oceanic
methane than ever before in any interglacial period would come into
Will this occur overnight? Certainly not. But those greenhouse
gases being released now (and will be released in the future) will play
a role in ever increasing global temperatures for many centuries.
Certainly long enough to be a factor in eventual long term 'methane
hydrate degasification'. If this then were to lead to a self sustaining
cycle, then in the worst case scenario, eventually there'd be no hippos
left anywhere --- and very few humans (if any).
are very fortunate to have detailed ice core information from Antartica
and Greenland that tell about global temperatures, etcetera. After
studying the graphs from these, it's very obvious that the temperatures
during the past ten thousand years take on an atypical pattern when
compared to previous interglacials. The variable is mankind.