1. Earth’s Changing Climate
CO2 Trends
Earth’s Changing Climate
Instructor: Dr. Steven M. Lazarus
October 20, 2015
Some say the world will end in fire, Some say in ice. From what I've tasted of desire I hold with those who favor fire. But if it had to perish twice, I think I know enough of hate To say that for destruction ice Is also great And would suffice. Robert Frost

2. Talk Outline
Based on what we know, is the change in recent climate significant? Proxies and observations
Why does the climate change: Natural Causes
Degassing and Weathering – Rock Cycle
Milankovitch Theory (orbital)
Solar Output
Ocean Circulation

3. Is current climate change unusual compared to changes in Earth’s past?
TIME SCALES are CRITICAL!
SPATIAL SCALES: DO NOT confuse “local” changes with “global”
Only very large-scale climate averages can be expected to reflect global forcings over recent millennia
Time scales Relevant Proxy
Long Term – millions of years
Intermediate – 100,000 years
Short term – 10’s to 1000’s of years
sediments
ice core
tree rings, pollen, ice core,
direct observations

4. Based on different compilations of proxy
Proxy records of climate
Based on different compilations of proxy
Records published reconstructions and their uncertainty estimates indicate, with high confidence, that the mean NH temperature
of the last 30 or 50 years very likely exceeded any previous 30- or 50-year mean during the past 800 years (IPCC/AR5 2013).
global or regional events?
??? ?
instrumental (black curve)
relative stability of the current interglacial ?
See Fig page 387 BP
year

5. Compare Scales! DCO2 ~ 100 ppm/200 yrs
~ 70% fossil fuels
~ 10-30% deforestation
Compare Scales!
Ice cores from Greenland and Antarctica indicate that there is a close link between greenhouse gases and temperature
100 yrs
CH4 abundance is
more than double its
pre-industrial value.
year
1000
1000
year
1500
2000
2000
Holocene
Note + correlation
w.r.t. temperature
EARTH: The operators’ manual
DCO2 ~ 100 ppm/15000 yrs

6. What about our current level of warmth?
cooling
Cambrian
CURRENT WARMTH IS UNUSUAL ON MILLENIAL TIME SCALE NOT GEOLOGIC (plate movement) TIME SCALES!
Fig pg. 399 BP
Fig. 14.7pg. 426 BP

7. What about our current rate of warming?
BP Fig
~ 5-10 Ky years to warm
about 5 oC!!! oC/yr
Largest DT is during the glacial-to-interglacial transition periods
If we were to keep warming at the current rate (say at the middle of the projection ~3 C per century)…
There is no evidence that this rate of climate change has ever been matched by any comparable global temperature increase in the last 50 million years!

8. NATURAL VARIABILITY
DEFINITION: On top of the natural, chaotic “free” (non-anthropogenic) variability of weather and climate are changes brought about by changing forcing which is usually considered to involve factors that are not themselves affected by climate.
Radiative forcing (W/m2) is a measure of how the energy balance of the Earth-atmosphere system is influenced when factors that affect climate are altered. The word radiative arises because these factors change the balance between incoming solar radiation (IN) and outgoing infrared radiation (OUT) within the Earth’s atmosphere. This radiative balance controls the Earth’s surface temperature. The term forcing is used to indicate that Earth’s radiative balance is being pushed away from its normal state.

9. How can the radiation balance of Earth change?
by changing the incoming solar radiation (e.g., by changes in Earth’s orbit or in the Sun itself);
(1-a)Spr2 = 4pr2esT4
2) by changing the fraction of solar radiation that is reflected (called ‘albedo’; e.g., by changes in cloud cover, atmospheric particles or vegetation); and
(1-a)Spr2 = 4pr2esT4
3) by altering the longwave radiation from Earth back towards space (e.g., by changing greenhouse gas concentrations).
(1-a)Spr2 = 4pr2esT4

10. Is this a positive or negative feedback?
LONG TERM VARIABILITY (aka ‘A Geosphere moment’)
Fig. 5.4c
Is this a positive or negative feedback?
Silicate Weathering Thermostat CaSiO3 + CO2  CaCO3 + SiO2
“Urey Reaction” simplified formula shown above
Weathering direction  dissolution of silicate rock into sedimentary
Peak to peak on the order of 1 million years or so!!!
Degassing vs. Weathering
Weathering depends on precipitation!
volcanic outgassing
atmospheric CO2 (or temperature)
Cold (warm) climate – lesss (more) weathering!
weathering > outgassing
weathering < outgassing
In a cold climate – less CO2 uptake (so it builds up in atm  increasing the temperature and weathering  pushing degassing and weathering fluxes back into balance).

11. Milankovitch Cycles (intermediate time scales)
Fig pg. 401 BP
Milankovitch Cycles (intermediate time scales)
EARTH: The operators’ manual
Fig pg. 402 BP ? ?

12. Seasons/Orbital
Which orbital parameter is responsible for the seasons?
How long did it take for the precession shown? N
summer solstice
winter solstice
Spring
Fall
Equinox N N
146 x 106 km
156 x 106 km N
351 W m-2
329 W m-2 + 2
= 340
Does annual insolation change much with eccentricity changes?
If the orbit is circular (zero eccentricity) – will precession impact seasonal insolation?