Paleocene/Eocene Thermal Maximum

~55 million years ago, the Paleocene/Eocene Thermal Maximum saw global temperature increase by ~5°C in ~15000 years:

zachos_2001

Zachos (2001), 'Trends, Rhythms, and Aberrations in Global Climate', Science 292, p. 686.

Today, we face a similar ~5°C temperature increase, but wrought within ~one tenth the amount of time:

solomon_2009

Solomon et al. (2009), 'Irreversible climate change due to carbon dioxide emissions', PNAS 106, p. 1704-1709.

How will the {Earth System}’s negative feedback cycles respond in the face of this unprecedented rate of change?

3 Responses to “Paleocene/Eocene Thermal Maximum”

  1. Beth! says:

    But is it truly an ‘unprecedented’ rate of change?? Records from the Greenland ice cores indicate sharp swings in temperature occurring over tens of years time as recently as a few thousand years ago (as summarized http://www.wunderground.com/education/abruptclimate.asp here, building on published data from JGR and other sources). While I am in no way trying to belittle the discussion here, and definitely do think it is important to consider how human impact may be altering ‘natural’ systems, I caution the reliance on select Earth history records to frame the debate that the rate of change happening now has never occurred before.

  2. Jelte says:

    Hi Beth! The alleged recent temperature shifts to which you refer are inferred from d18O shifts in ice-cores from Greenland. As far as I know, individual shifts have not been successfully correlated with Antarctic cores and there is no evidence that the shifts correspond to global, rather than local, events. Furthermore, there are many possible ‘non-temperature’ causes for the isotopic shifts: changes in sea-ice distribution, shifts in precipitation source area, altered weather and/or cloud patterns, … It’s also important to consider the background to your excursions: a glacial period, when sudden changes in ice volume strongly control d18O[ice].

    The Paleocene/Eocene temperature shift I’m referring to is inferred from d18O shifts in carbonates (not ice) from both marine and terrestrial records on several continents. It occurred against a background of much hotter temperatures: your large d18O variations are absent from inter-glacial periods. Drastic changes in fossil assemblages attest to the temperature changes that I called ‘unprecedented’.

    With regards to the situation today: if it were merely a question of ten hot years followed by a return to the good ol’ days, I would not be worried!

  3. Beth! says:

    dj Jelt, you bring up very good points about the validity of extrapolation of the Greenland ice core data to conditions occurring globally – thank you. (note to self: get more schooling on paleo-climate datasets).

    Addressing your original question – how the Earth’s systems will respond to the current accelerated rate of change is anyone’s guess. Models will only tell us so much, and they probably won’t take into account interference by humanity (a la maybe it will rain more somewhere else, but what if ‘we’ build more dams to catch it and prevent it from going anywhere…) But I think the more sure thing is that the level of orchestrated dependency of humanity on the artificial supports for our life-as-the-developed-world-knows-it (drill for oil to make the fertilizers to grow our food, etc.) is highly susceptible to links in the chain being broken.

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