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Water Cycle: Global Circulation. Energy input is not uniform over Earth’s surface. more heating at equator, less at poles. Latitudinal Energy Balance. Energy input&loss nonuniform over Earth’s surface. atmosphere+ocean circulation transport heat towards poles. Blackbody Radiation 1.
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Water Cycle: Global Circulation • Energy input is not uniform over Earth’s surface more heating at equator, less at poles
Latitudinal Energy Balance • Energy input&loss nonuniform over Earth’s surface atmosphere+ocean circulation transport heat towards poles
Blackbody Radiation 1 Radiation energy R a function of the temperature of the body emitting it: R = ( — Stefan-Boltzmann constant) & Energy is emitted in different proportions at different frequencies (wavelengths) that also depend on the temperature of the body emitting it [Hottest bodies emit shortest wavelength radiation (x-rays, etc.), while coolest bodies have their peak emissions in long-wavelength microwave or radiofrequencies (e.g. 2.7K big-bang relic blackbody cosmic radiation)]
Greenhouse Effect Atmosphere ‘transparent’ to solar radiation at main wavelengths of sunlight (‘high-T blackbody radiation’) Atmosphere absorbs radiation at infrared (‘Earth heat’) wavelengths at which the Earth emits radiation Of the radiation energy that the atmosphere absorbs, half is re-emitted back towards the Earth’s surface, thereby warming it. (e.g. clear nights -> cold nights, cloudy nights -> warmer nights) No reason this couldn’t work in reverse (e.g. a material that reflected optical energy but was transparent to infrared would be cooled by an ‘inverse greenhouse’ effect)
Mean Annual Heat Balance Atmosphere blocks incoming solar radiation AND creates greenhouse effect 23% of incoming solar energy goes into evaporating water (~1 ton/m2-year)
Zoomable Art PCMac 23_Featured_Art.jpg
Caution! • What we can now accurately measure back in time are 18O/16O and 12C/13C anomalies in fossil shells. • These proxies can be used to ‘determine’ past temperatures and atmospheric CO2 levels that are extremely precise — but not necessarily nearly as accurate as they are precise… • Recent glaciations can be well correlated with minor changes in the amount of sunlight reaching the northern latitudes in summer (e.g. how much winter snow can melt in the summer) • CO2 was historically low during recent glacial times — cause or effect? • We are now rapidly raising the global CO2 level — is this likely to be bad, good or neutral for the planet?
22_46.jpg Caution! Proxy & Model-based curves!
23_21.jpg Arctic Sea-Ice area down 10% last 50yrs. Sea-Ice thickness down 40% last 50 yrs Winter sea-ice critical to arctic bottom-water formation (ice-freezing expels cold+salty brine which sinks to seafloor) False hockey-stick? (Wall Street Journal, Fall 2005)
Borehole T-increase Measurement (2) Warming 1°C over past 5 centuries 50% of warming over past century 80% over past 2 centuries
Causation Correlation BUT Correlation Causation SEVERAL PROPOSED CAUSES FOR WARMING: Solar Variability Human-induced Greenhouse gases (generally believed by climate scientists to be the dominant cause — and still passing ever-improving tests…) Correlation vs. Causation Pitfall
‘Political Agenda’ Pitfall Real Money is at stake (Climate Change affects Wall St.) e.g. Global Warming is only a theory, predicted effects are highly uncertain, scientists are not unanimous, data are in error, more research is needed….. AND meanwhile we should try to keep on doing business as usual… ALTERNATIVE (environmentally conservative program) Acknowledge uncertainty is inherent Recognize it is usually easier to prevent damage than repair it later — it will cost a lot less to start now to mitigate problems than to start only when problems are becoming catastrophic... What if only a 20% chance of ‘disaster’? 10%? How would we react to this threat if it was a military threat? By doing nothing because the risk is low? Shift burden of proof away from those advocating protection to those proposing an action that may be harmful
14C, 10Be: Proxies for solar activity? 15N + p (from cosmic ray) 14C + p + p (14C has 5750yr halflife) 14N + cosmic ray 10Be + 4He (10Be has 1.51My halflife) Both 14C and 10Be rapidly rain out of atmosphere once produced in upper atmosphere. Both are not produced by any decay processes in Earth’s interior
10Be vs. 18O? Does Be anomaly reflect a cause or consequence of the process causing the 18O anomaly?
