Friday, March 8, 2013

To Boldly Go Where None Have Been Before...

The amazing image of the day here is is Figure S3 from the supplementary material of Marcott et al, A Reconstruction of Regional and Global Temperature for the Past 11,300 Years, in the current issue of Science.  They combined 73 proxy records of temperature from around the globe - mainly from marine sediments - and used a Monte Carlo analysis to estimate the uncertainties.  The result is the above picture of the entire Holocene - the period in which agriculture and civilization have arisen on this planet for the first time - together with the spike of the Anthropocene on the right - the period of major human impact on the climate.

Note that the authors' work suggests that global temperature has not yet exceeded the mid-Holocene optimum, but obviously that is going to change in a hurry:
Our results indicate that global mean temperature for the decade 2000–2009 has not yet exceeded the warmest temperatures of the early Holocene (5000 to 10,000 yr B.P.). These temperatures are, however, warmer than 82% of the Holocene distribution as represented by the Standard5×5 stack, or 72% after making plausible corrections for inherent smoothing of the high frequencies in the stack (Fig. 3). In contrast, the decadal mean global temperature of the early 20th century (1900–1909) was cooler than >95% of the Holocene distribution under both the Standard5×5 and high-frequency corrected scenarios. Global temperature, therefore, has risen from near the coldest to the warmest levels of the Holocene within the past century, reversing the long-term cooling trend that began ~5000 yr B.P. Climate models project that temperatures are likely to exceed the full distribution of Holocene warmth by 2100 for all versions of the temperature stack (Fig. 3), regardless of the greenhouse gas emission scenario considered (excluding the year 2000 constant composition scenario, which has already been exceeded). By 2100, global average temperatures will probably be 5 to 12 standard deviations above the Holocene temperature mean for the A1B scenario based on our Standard5×5 plus high-frequency addition stack.


Manolo said...

Fascinating found, Stuart ! Really !

Now for "civilization have arisen on this planet for the first time" in the Holocene , I would venture this might not be absolutely proven and true.
Way to many inconsistencies in archaeological findings and mythology/legends.
Vast subject, lots of controversies, however, the facts remain: we had a major cataclysm by the end of the last ice age, namely the sudden and utter collapse of the Laurentide Ice sheet by 129000 BP (maybe an out of space impact of a cosmic wreck-train à la Shoemaker-Levy 9,which had 21 impactors and made a hell of a show on Saturn in 1994). The debate is on anyway.
Consequences of this collapse: a rather extremely fast sea level rise (best estimate: by about 42 meters in what legends say was happening "in one day and one night". This is reported in mythology by about 600 cultures around the globe.
Between 18000 and 12900 Years BP (before present)sea levels did rise by about 120 to 150 meters, in several pulses.
Given our human taste for warm and sunny weather, I would venture a lot of our smart ancestors lived by the sea: food was easy there as well, remember, it was a pristine world at that time. There where very few humans living at that time, but City-States are a real possibility, way before the Holocene.
After that last Cataclysmic, which must have been utterly devastating, in all, we had lost to the sea a tremendous surface of the best land available, estimated to be as big as Europe and China combined.
Very little archaeology is actually done underwater, despite the fact that incredible findings prove the existence of structures and even complete towns in several places around the globe.
IMVHO, the last chapter on our civilization beginnings is still wide open...

PS: A little to ponder ;) what happened then could still happen any day in our world. Just imagine what would become of us, if some very big rock smashes into East Antarctica. OK, the odds are indeed very, very small, but still, not impossible. Say goodbye the the world as we know it...

Aaron said...

Or, perhaps, "to boldly re-establish the status quo" would be more apt...

It's no wonder we're so adept at walking since we evolved on a planet with a continually changing climate requiring regular migrations - at least until recently when we settled into an agricultural lifestyle and developed civilizations. So I'm not so sure that we're entering a novel planetary space as much as we're returning to an older one.

kjmclark said...

"Say goodbye the the world as we know it..."

You might want to look at that chart a little more closely. That gets our current temps to the highest in the past (at least) 6,000 years, and rising rapidly.

Aren't we already saying goodbye to the world as we knew it?

Manolo said...

Ouups, a little typo correction: "collapse of the Laurentide Ice sheet by 129000 BP" should read: 12'900 BP of course !

@ Aaron: I always wonder how come that we suddenly had such a stable climate during the last 10'000 years. Such a singularity! Understanding this could really be key.

@ kjmclark: of course you are right :) ... my point was rather to be a bit sarcastic. Things can go even faster than what we witness now, things can indeed change in 1 day and one night ;)
None of this makes me feel better.

Winn said...

Good graphic Aaron, I'd be curious to hear Stuart's response.

Stephen B. said...

Aaron, thanks for linking to that graphic. I had forgotten where I'd seen it previously.

Combining that larger timescale graph with the one from the Science article suggests that if temperatures break out of the Holocene stability range to the upside then we'd really be getting into warm territory we haven't visited in over 100,000 years.

This first graphic is largely the basis for why Denialists insist that we are most likely to return to a more glaciated state. If all else were held constant, I'd agree with them, but of course, that is a big, unreachable *if* at this point.

Stuart Staniford said...

Stephen B:

I think there's little doubt that on our present course, we are headed in the 21st century for a climate as warm as the Eemian (the last interglacial), or likely warmer - the Pliocene.

There's one major caveat though - those climates were in equilibrium as the changes that bought them about were comparatively slow. Our climate is already out of equilibrium (for example, the land has warmed more the ocean) and likely to get more so. We probably have no idea what that's really going to mean.

Aaron said...

@ Aaron: I always wonder how come that we suddenly had such a stable climate during the last 10'000 years. Such a singularity! Understanding this could really be key.

I don't have any clue as to how it came about although it does seem that some climate research must be dedicated to it. My guess is that the ocean current setup in a singularly unique fashion that distributed heat from the tropics and somehow did so in a way that stabilized the climate. Probably won't occur again for hundreds of thousands of years if ever.

It's somewhat ironic that the evolutionary niche of a stable climate was best filled by the one species most adept at upsetting it. Our capacity to increase entropy by breaking hydro-carbon bonds seems almost limitless...

The Rational Pessimist said...


What we do know from the recent Vaks et al. paper is that the permafrost will melt and start to release carbon.

And this carbon cycle disequilibrium isn't included in current climate sensitivity to CO2 calculations.

Really, not good.

Stuart Staniford said...


I'm stuck on a very simple point there: when did the carbon in permafrost soils/peat etc get put there? It clearly didn't happen when it was all frozen, right? So therefore, it must have happened when the earth was warmer. So why wouldn't we think permafrost soils/peat were a sink, not a source, in a warmer world?

JohnMashey said...

1) If you t all the "normal" interglacials for which we have decent ice-core records (i.e., back to "Stage 19"):

a) By 1700AD or so, we "should" have been down to !@50 (+/-10) ppm CO2, but instead, the last 2 millennia look like this

b) Likewise, CH4 should have been way below where it was.

2) This recent article by Dan Vergano (a fine science reporter) talks about Bill Ruddiman's latest work, which has come a long way in 10 years (see the AREPS article he cites).

3) Briefly, as can be seen in Fig 2.D of Marcott, et all, about 8,000 years ago, human deforestration for agriculture first flattened the CO2 curve, then turned it back up, partially (but no completely) countering the normal Milankovitch downtrend from lower solar insolation @ 60degN.

4)About 5,000 years ago, rice paddies and ruminant livestock started doing the same thing for CH4.

5) Bill also makes a good case that some of the CO2 jiggles of the last 2 millenia came from plague+reforestration (CO2 down) + population rebuild+reforestration (CO2 up), once there got to be enough humans to matter. For example, the unique (in 2 millenia) drop into 1600AD most likely came fro ma 50M-person post-Columbus die-off in the Americas. Add volcanic activity and after that, solar minima (Maunder, etc) ... voila: Little Ice Age.

6) Anyway, Marcott, et al's results are another approximation to what the planet has been doing, but Bill's (and others') work *explains* much of this.

7) In effect, humans created a thermostat for a while that kept temperatures in a very narrow range, while we did things like building huge amounts of sea-level infrastucture (especially in US ... not as much problem for Canada, almost no problem for Russia except primarily St. Petersburg.) We have of course now set the thermostat to HIGH.

8) We may or may not have had a real ice-age inception absent humans (Bill thinks so, others argue), but in any case, read David Archer's fine book The Long Thaw. Summary: the next cool-summers period at 60degN would have been in 50,000 years, but with Business As Usual, there will be too much CO2 for that. The next time is 130,000 years off, and if we burn all the cool, that won't happen either, and then it will ~400,000+ years. In any case, if there's a technic civilzation around, all it has to do is generate SF6, a greenhouse gas 32,000X stronger than CO2.

The Rational Pessimist said...


Surprisingly, much of the carbon in these northern latitudes was put there relatively recently; i.e. over the holocene.

This paper by Yu et al gives you an idea of what was laid down when.

So certain processes gave rise to these carbon deposits over the last 14,000 years or so, but temperature was not the simplistic determinant. In other words, higher temperature does not mean more locked up carbon.

And as things warm up, we already have studies looking at the sink-source tug of war for permafrost carbon such as this by Schuur et al:

Their finding is that at initial thawing plant growth more than compensates for bacterial CO2 release, but this flips when you get extensive thawing.

And this takes us back to your original chart: it is the incredible speed of change that has the potential to completely upturn the existing carbon cycle.

The Rational Pessimist said...

And this paper is even better and certainly more accessible: a kind of 'where did permafrost-related carbon come from and where is it going':