High-Resolution Records of Climate: Motivation and Challengeswiscsims/HiRes2015/pdfs/...Figure 6.14....

G. Comer Founda.on

High-Resolution Records of Climate: Motivation and Challenges

Richard B. AlleyPenn State HiRes 2015 University of Wisconsin June 1, 2015 Please note: I work for Penn State University, And help UN IPCC, NRC, etc., But I am not representing them, Just me.

With thanks to John Valley, who among many other efforts served on my advisory commi?ee when I was a student here. (I hope I came out OK!)

G. Comer Foundation

Making our science useful •  Takes more and more time for many of us •  And raises interesting questions •  So let me try something… •  The IPCC doesn’t really summarize itself •  My reading—reducing the tens of thousands

of pages to one sentence might give: “Humanity would be better off if we started soon to efficiently but slowly reduce emissions of fossil-fuel CO2”

Let’s look a bit more at… “Humanity would be better off if we started soon to efficiently but slowly reduce emissions of fossil-fuel CO2” •  The “slowly” is partly from economics à Economy will grow almost unhindered à So grandkids will be much richer than us à We don’t like giving money to richer people à We’re more important than them anyway àStill, invest a little now to reduce climate change, but mostly let them deal with it

From W. Nordhaus, leader in field (e.g., his A Ques'on of Balance, Yale University Press, 2008): Economically opDmal path: à Spend $2 trillion to avoid $5 trillion in damages (hence, a very good return on investment) à But, allow $17 trillion in damages to occur (could reduce those damages, too, but economic opDmizaDon uses that money in other ways) Our work affects decisions about LOTS of money!

Let’s look a bit more at… “Humanity would be better off if we started soon to efficiently but slowly reduce emissions of fossil-fuel CO2” •  But “slowly” is also from our science à Most-likely projected warming smooth, and

toward the lower end of what is possible à Impacts slow, small, and expected—no

“tipping points” or other abrupt jumps à Our responses economically efficient—no

“tipping points” in human systems, either

Knutti and Hegerl, Nature Geosci, 2008

“Charney” (fast) climate sensitivity (in K/W/m2) of 0.3–1.9 or 0.6–1.3 at 95% or 68% probability, respectively. The latter implies a warming of 2.2–4.8 K per doubling of atmospheric CO2, which agrees with IPCC estimates.

IPCC range 1.5-4.5oC

Horton, et al., 2014, QSR

Many think it is coming faster than IPCC expects…

Year 2000 2100

5

4

3

2

1

0

Sea

-leve

l ris

e (m

)

Compilation of the back of the envelope estimates of sea level rise that I’ve seen.

????????

Quantified IPCC range

Maybe more sensible?

What we don’t know can hurt us… •  Building is hard—takes many tools; •  Breaking is easier—just need a big hammer; •  Virtually no chance that CO2 makes Eden—

need to get much more right than just CO2

•  But can break things we value •  If don’t trust climate science, might worry

a lot about “hammer” of ~40,000 pounds of CO2 per person per year in USA

Prob

abili

ty

How much warming? How much damage? How much cost? Distribution of possibilities skewed, something like this.

Zero Low Medium High Really High

Prob

abili

ty

And that in turn points to “How much is wise to do?” distribution something like this (although I haven’t seen any IPCC analyses actually present it this way)

Ignore Do some, slowly Do more, rapidly

Optimal effort to reduce CO2?

Prob

abili

ty

And that in turn points towards “how much is wise to do” having a distribution something like this (although I haven’t seen any IPCC analyses actually put it this way)


Recent reports from IMF, IEA indicate current policies accelerate CO2 emissions, with fossil fuels subsidized much more than renewables

Optimal effort to reduce CO2?

Prob

abili

ty



Recent reports from IMF, IEA indicate current policies accelerate CO2 emissions, with fossil fuels subsidized much more than renewables

So, people supporting policies consistent with economic models for most-likely future are on the same “side” as the most extreme environmentalists

Prob

abili

ty



But, suppose policies move to here over the next decades…

How confident are we of the science, really? If the changes will be slow, small and expected, that is fantastic, because we don’t need to do a lot. But will they be?

Prob

abili

ty



But, suppose policies move to here over the next decades…

My OPINION—models not up to assessing fat tail. Climate history, on human timescale (High-Res) needed. Literally tens of trillions of $$ involved

Downplayed risk. Earthquake happened. Sent to jail. Later acquitted, but it might give some people pause…

My reading of climate history: àCO2 most important control àVery large influences on life àModels maybe conserva.ve àSurprises do happen àLOTS of uncertain.es s.ll

What can control Earth’s temperature?

•  Regional, LOTS of things. Global average:

à Brightness of Sun

à Distance of Earth from Sun

à Blockage of sunlight on its way to us

à Reflection of sunlight by Earth (albedo)

à Greenhouse effect


•  Global Average

à Brightness of Sun—Fast changes small (whew!); slow ones offset by thermostat





Figure 6.14. Simulated temperatures during the last 1 kyr with and without anthropogenic forcing, and also with weak or strong solar irradiance variations. Global mean radiative forcing (W m–2) used to drive climate model simulations due to (a) volcanic activity, (b) strong (blue) and weak (brown) solar irradiance variations, and (c) all other forcings, including greenhouse gases and tropospheric sulphate aerosols (the thin flat line after 1765 indicates the fixed anthropogenic forcing used in the ‘Nat’ simulations). (d) Annual mean NH temperature (°C) simulated by three climate models under the forcings shown in (a) to (c), compared with the concentration of overlapping NH temperature reconstructions (shown by grey shading, modified from Figure 6.10c to account for the 1500 to 1899 reference period used here). ‘All’ (thick lines) used anthropogenic and natural forcings; ‘Nat’ (thin lines) used only natural forcings. All forcings and temperatures are expressed as anomalies from their 1500 to 1899 means; the temperatures were then smoothed with a Gaussian-weighted filter to remove fluctuations on time scales less than 30 years. Note the different vertical scale used for the volcanic forcing compared with the other forcings. The individual series are identified in Table 6.3.

Figure 6.14. Simulated temperatures during the last 1 kyr with and without anthropogenic forcing, and also with weak or strong solar irradiance variations. Global mean radiative forcing (W m–2) used to drive climate model simulations due to (a) volcanic activity, (b) strong (blue) and weak (brown) solar irradiance variations, and (c) all other forcings, including greenhouse gases and tropospheric sulphate aerosols (the thin flat line after 1765 indicates the fixed anthropogenic forcing used in the ‘Nat’ simulations). (d) Annual mean NH temperature (°C) simulated by three climate models under the forcings shown in (a) to (c), compared with the concentration of overlapping NH temperature reconstructions (shown by grey shading, modified from Figure 6.10c to account for the 1500 to 1899 reference period used here). ‘All’ (thick lines) used anthropogenic and natural forcings; ‘Nat’ (thin lines) used only natural forcings. All forcings and temperatures are expressed as anomalies from their 1500 to 1899 means; the temperatures were then smoothed with a Gaussian-weighted filter to remove fluctuations on time scales less than 30 years. Note the different vertical scale used for the volcanic forcing compared with the other forcings. The individual series are identified in Table 6.3.

Can improve much; e.g., E. Bard’s group finds 10Be flux spikes to ice cores with fallout of stratospheric volcanic erup.ons… (e.g., Baroni et al., 2011, GCA and others)




à Distance of Earth from Sun—No worry!—dino-killer moved Earth less than 1” (2.5 cm)








à Blockage of sun on way to us—not enough to matter (except dinosaur-killer 65 million yr)



Changes in space dust have been small, and haven’t affected climate much. Helium-3 is mostly from space dust.

If space dust changed a lot, that might affect climate some.

But there has been little change in space dust over last 30,000 years (ice-core data shown here) and beyond (other data not shown).

(Very rarely, a big meteorite does matter, such as the one that killed the dinosaurs 65 million years ago.)

Winckler & Fischer, 2006, Science

Winckler & Fischer, 2006, Science

Students assigned to research key climate events almost always report on a cause from space, that almost surely is wrong—End-‐Permian, Younger Dryas, PETM, …, GOOD data on what really came from space, and what didn’t, are of value.






à Reflection of sunlight by Earth (albedo)—can matter; hard to change much by itself


From Muschler et al., 2005, QSR. δ18O (proxy for temperature) from GRIP core (top), the concentration of 10Be (middle), and the flux of 10Be (bottom). The Laschamp event of near-zero magnetic field (red arrow) allowed increased cosmic-ray flux producing more 10Be, but with no apparent effect on climate.

Climate didn’t change

When more cosmic rays reached Earth


Today

War

mer

Cosmic rays, magnetic field don’t matter much to climate.


When more cosmic rays reached Earth


Today

War

mer

Cosmic rays, magnetic field don’t matter much to climate. Addi.onal work rela.ng climate to cosmic rays could be quite interes.ng—There MIGHT be something there, although we’re pre?y sure it isn’t big







à Greenhouse effect—can matter a lot (Venus…), and easy to change, as we’ll see







à Greenhouse effect—can matter a lot (Venus…), and easy to change, as we’ll see

More, higher-‐resolu.on paleo-‐CO2 data would be really nice…If we remember the large changes in <10 ka for ice-‐age cycles, and events such as the OAEs in the Cretaceous that must have impacted CO2, available data are undersampling the likely varia.ons

Faint Young Sun “Paradox” •  Sun’s output ~70% of modern 4.6 billion

years ago—fusing hydrogen to helium increases solar core’s density, so faster fusion occurs, balancing gravity;

•  Yet liquid water on Earth as far back as records go (~4.4 billion years; Valley et al);

•  Earth reflects ~30% of sun now, so would need perfectly black early Earth (didn’t happen) to offset changing sun;

•  So, physics plus data point to stronger early greenhouse (Sagan, C. and G. Mullen, 1972).

CO2 (gas)

CaSiO3 (solid)

Volcanoes supply CO2 to air—rate (nearly) independent of climate

Rock Weathering removes CO2 from air—CaSiO3+3H2O+2CO2à Ca+2+H4SiO4+2HCO3

- Faster when warmer

Shell Growth— Ca+2+H4SiO4+2HCO3

- à CaCO3+SiO2+3H2O+CO2

Shell subduction CaCO3+SiO2

Walker, J.C.G., P.B. Hays and J.F. Kasting, 1981

Rock-Weathering Thermostat—When Earth cold, CO2 builds up in air, warming; when Earth warm, CO2 removed from air, cooling

Rock (CaSiO3) +CO2

Walker, J.C.G., P.B. Hays and J.F. Kasting, 1981

Rock-Weathering Thermostat—Simpler Version

Rock or shell CaCO3+SiO2

At surface, faster when warmer

Deep, doesn’t care about surface temperature

Rock Weathering Thermostat

•  Enough to solve faint young sun paradox (Halevy, I., R.T. Pierrehumbert and D.P. Schrag, 2009);

•  Supported by physical/chemical understanding; •  Maybe other greenhouse gases, etc. involved; •  If others failed, CO2 there to do the job; •  Is there any evidence for this other than

physical/chemical unavoidability? •  Probably…Snowball Earth cap carbonates…

Where the ice was at different times (colors of stars relate to geologic setting) (Hoffman and Li, 2009, Paleo3)

Snowball Earth •  Extensive low-elevation, low-latitude glacial

deposits from some times on middle-aged Earth; •  Physical understanding: if CO2 warms & rock-

weathering thermostat works, then à Can get into a snowball with a faint sun if fast

(thermostat takes ~0.5 million years to work); à Then high snow albedo needs lots of CO2 to thaw; à Then lots of warming and rapid weathering should

have deposited carbonate rocks rapidly •  And, cap carbonates sit atop snowball deposits.

h?p://www.sno

wballearth.org/capcarbs.html

Glacial deposit

CaCO3= CaO.CO2

h?p://www.sno

wballearth.org/capcarbs.html

Glacial deposit

CaCO3= CaO.CO2

Fascina.ng work is being done on cap carbonates, but more good s.ll to come. Best story now is that this is the CO2 that thawed the snowball… but LOTS of implica.ons and hypotheses from that…

Resetting the Thermostat •  More CO2 from volcanoes (e.g., more volcanism,

or shallower oceanic subduction zones so more shells subducted rather than dissolved);

•  Slower weathering—colder or drier climate, or less-weatherable materials (e.g., shale at surface, vs. basalt), or less plant activity (e.g., pre-land-plants less CO2 in soil);

•  Less fossil-fuel burial, or more fossil-fuel burning (e.g., higher-oxygen oceans because colder or less-fertilized);

•  Change greatly over time-scales of plate tectonics and evolution—100 million years or so.

Figure 4.24 Atmospheric CO2 and conDnental glaciaDon 400 Ma to present. VerDcal blue bars, .ming and palaeola.tudinal extent of ice sheets (ager Crowley, 1998). Plo?ed CO2 records represent five-‐point running averages from each of four major proxies (see Royer, 2006 for details of compila.on). Also plo?ed are the plausible ranges of CO2 derived from the geochemical carbon cycle model GEOCARB III (Berner and Kothavala, 2001). All data adjusted to the Gradstein et al. (2004) .me scale. Con.nental ice sheets grow extensively when CO2 is low. (ager Jansen, 2007, that report’s Figure 6.1)


High CO2 melted ice, and low CO2 grew ice, over hundreds of millions of years… and work by Jim KasDng and others shows this was cause, not effect

A beautiful view of a lot of history…

~200 years ago, geologists named time, giving new names when life changed. We now are learning that many of those life changes were from climate changes, with CO2 important.

Permian

PennsylvanianMississippian

Devonian

Cambrian

Precambrian

Events—The Great Dying •  End-Permian extinction, 251 million years, perhaps

95% of species became extinct; •  Widespread marine biomarkers of green sulfur

bacteria that use H2S for photosynthesis (100 ppm in air is immediate danger to life or health);

•  Greatest volcanism in >500 million years (Siberian traps) (slow vs. human source, but protracted);

•  CO2-induced warmth, fertilization from basalt breakdown, sulfur from volcanoes seem to have contributed to anoxia and euxinia (H2S) of ocean.

Yadong Sun et al., 2012, Lethally hot temperatures during the early Triassic greenhouse, Science 338, 366.

Too hot for marine animals


This is one of the most fascina.ng and challenging issues of all…but how relevant is it to our near-‐future? Volcanic S and P, but we’re fer.lizing and .lling…Lots of ques.ons


Time in next slide

Figure 3.8. Global compilaDon of more than 40 deep sea benthic δ18O isotopic records taken from Zachos et al. (2001), updated with high-‐resolu.on Eocene through Miocene records from Billups et al. (2002), Bohaty and Zachos (2003), and Lear et al. (2004). Dashed blue bars, .mes when glaciers came and went or were smaller than now; solid blue bars, ice sheets of modern size or larger. (Figure and text modified from IPCC Chapter 6, Paleoclimate, Jansen et al., 2007.)

~9oF ocean, 14oF land Arc.c warming, to mid-‐70s summer ocean

Zachos et al., 2001, Science, PETM

56

A

ge (M

a)

54

Warmer More CO2

Mostly organic CO2 (from sea-floor clathrates, soils, permafrost, or …?). Probably some coincidence, or we would have seen more of these.

Fig. 1. Representa.ve insect damage diversity on PETM leaves. (a) Dicot sp. WW007 (Fabaceae) leaf about one-‐third consumed by insect herbivores (USNM 530967). (b) Characteris.c large, circular hole-‐feeding (DT4) found only on dicot sp.WW006(530968). (c) Serpen.ne mine with a solid frass trail becoming massive (DT43) on an uniden.fiable dicot (530969). (d) Polylobate to clustered galls (DT125) on dicot sp. WW007 (Fabaceae, 530970). (e) Blotch mine with a sinusoidal frass trail (DT37) on dicot sp. WW003 (530971). ( f) Blotch mine with dis.nct coprolites and terminal chamber (DT35) on dicot sp. WW006 (530972). (g) Serpen.ne mine with a solid frass trail (DT43) on dicot sp. WW004 (530973). (h) Semilinear serpen.ne mine with terminal chamber (DT40) on dicot sp. WW005 (530974). (Scale bars: white, 1 mm; black, 5 mm.) Currano et al., 2008, PNAS (>5000 fossil leaves, Wyoming)

Fig. 1. Representa.ve insect damage diversity on PETM leaves. (a) Dicot sp. WW007 (Fabaceae) leaf about one-‐third consumed by insect herbivores (USNM 530967). (b) Characteris.c large, circular hole-‐feeding (DT4) found only on dicot sp.WW006(530968). (c) Serpen.ne mine with a solid frass trail becoming massive (DT43) on an uniden.fiable dicot (530969). (d) Polylobate to clustered galls (DT125) on dicot sp. WW007 (Fabaceae, 530970). (e) Blotch mine with a sinusoidal frass trail (DT37) on dicot sp. WW003 (530971). ( f) Blotch mine with dis.nct coprolites and terminal chamber (DT35) on dicot sp. WW006 (530972). (g) Serpen.ne mine with a solid frass trail (DT43) on dicot sp. WW004 (530973). (h) Semilinear serpen.ne mine with terminal chamber (DT40) on dicot sp. WW005 (530974). (Scale bars: white, 1 mm; black, 5 mm.) Currano et al., 2008, PNAS (>5000 fossil leaves, Wyoming)

Dwarfing of large animals, loss of C in soils, geomorphic perturbaDons, ecosystem disrupDons… much more yet to be learned

Much more recently, ice ages are caused by features of Earth’s orbit, NOT by CO2… But…

Milankovitch predicted bumps under arrows; found 50 years later.

Petit et al., 1999

Today

Ice Ages •  Forced by features of Earth’s orbit •  Those mainly redistribute sun; little net change •  Low summer sun in far north led to: à Ice growth on land à Sea-level fall, shifts in winds, currents, dust, etc. àSome raised CO2 in air, but most lowered àNet lower CO2

àAnd this globalized signal àHalf of planet cooled with more sun, warmed with less sun, mainly because of CO2

We’re here and rising…

So, where does that leave us? •  Lots of knobs control the Earth’s climate system; •  “Sun” knob not twiddled much over short times,

ineffective over long times from CO2 feedback •  Magnetic-field, cosmic-ray, space-dust, other

“space” knobs not shown to matter, and no more than fine-tuning (except dinosaur-killer)

•  Much on Earth matters regionally—drifting from equator to pole cools a continent, North Atlantic ocean circulation important, etc.

•  But, best data today show that CO2 has been “biggest control knob” on Earth’s climate

So, where does that leave us? •  The biggest of the past changes are on the same

scale as what we might do in next centuries; •  And ours is likely to be much faster than these

natural ones (except for dinosaur-killer) •  Slower, similar-sized natural changes had huge

impacts on living things, often killing them •  Nature restored diversity after natural ones, but

over millions of years…

You may hear someone say “Climate has always changed, so we don’t need to worry about changing the climate.”

That is logically equivalent to saying “Nature has always caused fires, so we don’t need to worry about arson.”

And, the more I learn about the history of natural climate changes, the more worried I am about what we’re doing.

But, for the first .me, we know how to build a sustainable energy system to power us almost forever.

Back to us, I believe we really need to narrow uncertain.es on this. The story I just told mo.vates more economic effort now to reduce CO2. But, is it right? Can we say?

Need high-‐resolu.on records, mul.ply calibrated and validated, addressing the big ques.ons at the big events, with controls at “boring” .mes, etc.

I’m sure we’ll hear a lot of those over this mee.ng. But whatever we hear, I’m sure there is room for more. Thanks!

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