CE 401 Climate Change Science and Engineering orbital variations and climate, aerosols, carbon cycle 25 January 2011

any questions from last time? Earth radiation budget and GHG spectra HW 3 is due today HW 4 is posted on the web – due Thursday 1/27

HW 2 average was 3.5/10 :(. Distribution was bimodal with 6 10’s and 12 < 1/10

you need to: follow directions and answer the question, use a computer, think about your answer – does it make sense?, write neatly, don’t let bad points drive your analysis (these “-99” points were clearly coded as bad), show your work please! What happened to the use of MATLAB from the computer course? solution is posted on the class website



astronomical forces drive global climate change – the Earth orbit seasons are driven by astronomical causes, as is the 24 h day/night cycle

ice ages: Earth orbital changes that vary the solar input and cause the ice ages: the Milankovich cycles – these cycles change the solar input to the Earth system

not until the second half of 19 th century was it accepted that there were indeed ice ages three main types of evidence that climate has radically changed in the past geological rock scouring moraines from glaciers valley cutting glacial erratics chemical isotope ratios in fossils and ice cores paleontological fossil distributions have been at least 5 major ice ages Earth has been in an interglacial period for about yrs – very stable climate positive feedbacks ice  increased albedo  decreased T changes in ocean currents (e.g. Gulf stream to Europe) negative feedbacks causes of the ice ages are not understood in detail atmospheric composition changes in Earth orbit that are cyclic motion of tectonic plates  changed winds, ocean currents, etc. changes in solar irradiance

changes in Earth orbit – Milankovitch cycles

shape of earth’s orbit changes during a cycle of about 100,000 years eccentricity changes varies from nearly circular to high eccentricity with mean Caused by perturbations from the other planets e = currently

axis of rotation changes from about 21.5° to 24.5° --> seasonal variations over a period of 41,000 years. Tilt is the most significant cause of seasonal temp change. Modulates the seasons, does not change climate overall. But ice sheets advance when summers are too cool axial tilt (obliquity) – increased obliquity  increased seasonal amplitude change

the earth’s rotation axis precesses (wobbles) with a period of about 26,000 years due to tidal forces exerted by sun and moon on solid Earth since Earth is not spherical affects climate extremes axial precession – trend in direction of axis of rotation in inertial space – gyroscopic motion

problems with the Milankovitch theory for ice ages: 100,000 yr problem: eccentricity variations should have a smaller impact that the other mechanisms, but this is the strongest climate signal in the data record 400,000 yr problem: eccentricity variations also show a 400,000 yr cycle but that cycle is only visible in climate records > 1My ago observations of climate changes show behavior much more intense than calculated the 23,000 yr cycle dominates, the opposite of what is observed the “reinforcement of causes” does not seem strong enough to initiate an ice age in the past 400k yrs, Milankovitch cycles match too well to ignore so the explanation is not 100% - there are still issues with the explanation

deg change obliquity=axial tilt long of perihelion precession index calc. insolation to TOA Benthic and Vostok ice cores

past and future daily average insolation at the top of the atmosphere at summer solstice, 65°N next ice age: k yrs from now.

aerosols and their effects on climate big driver – HUGE driver, both human induced and natural RF not well understood – hardly on the data sheets in 1990 not well measured – satellites and ground networks – short record of data parameters that affect aerosols and their RF not understood global effects not well understood – clouds (height and distribution)

increasing complexity of the modeling world

aerosols: solid particles or liquid particles suspended in the air size: few nanometers to microns in size: x variation in size have major impacts on climate physical properties: shape, size, chemical composition particles at the small end play a large role in cloud physics condensation nuclei EPA regulates particles in the US PM10 and PM2.5 – CEE 341, 415 key aerosol groups: sulfates organic carbon black carbon nitrates mineral dust sea salt aerosols of clump together to form complex mixtures 90% of aerosols (by mass) are natural in origin about 10% of global aerosols are generated by human activity problems in dealing with aerosol effect: diversity in size, composition and origin; spatial and temporal variability; source; injection height aerosols removed primarily through cloud processing and wet and dry deposition