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

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

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

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. 13.6 page 387 BP year http://www.globalwarmingart.com/wiki/Image:2000_Year_Temperature_Comparison_png#Copyright

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

What about our current level of warmth? cooling Cambrian CURRENT WARMTH IS UNUSUAL ON MILLENIAL TIME SCALE NOT GEOLOGIC (plate movement) TIME SCALES! Fig. 13.18 pg. 399 BP Fig. 14.7pg. 426 BP

What about our current rate of warming? BP Fig. 13.21 ~ 5-10 Ky years to warm about 5 oC!!! 0.001 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!

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. http://icp.giss.nasa.gov/education/modules/eccm/model/

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

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).

Milankovitch Cycles (intermediate time scales) Fig. 13.19 pg. 401 BP Milankovitch Cycles (intermediate time scales) EARTH: The operators’ manual Fig. 13.20 pg. 402 BP ? ?

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? http://cimss.ssec.wisc.edu/wxfest/Milankovitch/earthorbit.html