test • October 26 or October 28. You choose • Consensus: Tuesday October 26.
Paper topics • Still need to get your topics • (only received one email from Majd)
topics • Layal – Thursday (carbon dioxide in the oceans – sink vs source; healthy components?) – October 14 • Lilliane – Tuesday (Marine algae and dimethyl sulfide) – October 19 • Majd – Thursday (gulf stream – what is happening and why?) – October 21 • Choose dates
EVSC 305: Climate Change – the Science and Local Impact on a Global Environmental Crisis Climate Change: Chapter 1, Book 2 History of Climate Science and Science of Climate History
Climate and Biology • Climate is a fundamental factor influencing biology • Thus… • Can use biology to learn about certain aspects of climate • And • Biology can influence climate
For most of the past 2-3 million years, the Earth has been quite cold Evidence from the distribution of oxygen isotopes in cores taken from deep ocean floor as many as 16 glacial cycles, each lasting up to 125,000 years with intervals of only 10,000 to 20,000 years From cold climate…
… to a warmer climate • During the 20,000 years since the peak of the last glaciation, global temperatures have risen by ~ 8 C • Analysis of buried pollen can show how vegetation has changed during this period • Migrations of trees in eastern North America from 18,000 years ago to present are known from pollen grains deposited in bogs and lakes: • the compositions of communities shifted as species migrated across the landscape • in particular, the composition of forests during the past 18,000 years has: • included combinations of species that do not occur today • lacked combinations of species that do occur at present
Changes in Climate 1 (c) 2001 by W. H. Freeman and Company
Climate change… • Naturally – with the change in plants change in animals • Even in regions never glaciated, pollen deposits record complex changes in distribution • In the mountains of Nevada – woody species show different patterns of change in elevational range • Species composition of vegetation is continually changing – and is still changing • So what could happen in the next 100 years? • Temperatures predicted to rise between 2 to 7 C in 100 years • Postglacial warming of 8 C occurred over 20,000 years • Now: trees will have to move at 300-500 km/100 years • Typically: trees move 20 – 40 km/100 years
“On every continent except Antarctica there are examples of deserted settlements and evidence of long-extinct civilizations. These are societies that once flourished but have now gone, due primarily to a change in climate.”
Tyndall… • 1861 – • described the greenhouse role of some gases and he quantified their heat-absorbing properties • Also suggested what would happen if their [ ] in the atmosphere changed – if the greenhouse gases decreased
Relationship between energy and light • Max Planck, 1902 • Simple equation: • E = hv • E = energy measured in joules • V = frequency in hertz • The energy of eletromagnetic radiation (light, thermal radiation and other rays) is proportional to its frequency (v) or color, with the constant of proportionality being Planck’s constant (h) • Atmosphere is transparent to some frequencies of light but not others some higher-energy light is mixed into the blanket of atmosphere surrounding our planet, but lower-energy infrared wavelengths hindered from getting out
Different warming contributions of each greenhouse gas • Concentrations and human additions to the atmosphere of each gas are different (as discussed) • Each gas has a different global warming potential (GWP) • GWP: comparative index for a unit mass of each gas measured against the warming potential of a unit mass of carbon dioxide over a specific period of time • Carbon dioxide: GWP of 1 • Need to take into consideration the atmospheric residence times of each gas
Atmospheric residence time • Methane: Atmospheric residence time (ART): 12 years • All of a kg of methane will still be in the atmosphere after 1 year • Half of it after 12 years • A quarter after 24 years • Nitrous oxide: ART – over a century • Comparing GWPs of methane and nitrous oxide over 10 years will give different warming figures compared with the same comparison over 100 years • Plus: uncertainty (evolving..) of GWP estimates • Plus: IPCC – science by committee
Carbon uncertainties • Carbon cycle: dynamic • Where does roughly half of the CO2 released into the atmosphere by human action end up? • Net imbalance: estimates of carbon dioxide entering and those accumulating and leaving the atmosphere (table 1.3) • Has some route of carbon not been identified? • Is one or more of the carbon-flow estimates off the mark?
Missing carbon • Problem seems to be associated with one or more of the other carbon sinks • Accumulation of carbon by terrestrial plants • By absorption into oceans Estimates of deforestation – how accurate? Official estimates are typically under-estimates Deforestation probably accounts for a greater contribution to atmospheric CO2 –not less Could oceans be accumulating more carbon than we think? Could the increased atmospheric CO2 + increased temp -> encourage terrestrial photosynthesis, drawing down carbon into plants? What about carbon stored in soils and detritus?– currently – soil acts as a global net carbon sink Driving force photosynthesis
Missing carbon • Isotopes of carbon may hold a key to determining the source of the increased carbon in the atmosphere • Studies are based on the ratio of the three different carbon isotopes in atmospheric CO2. Carbon has three possible isotopes: - C-12, C-13, and C-14 • C-12 - has 6 neutrons - most prevalent carbon isotope and is a stable isotope. • Carbon 13 also a stable isotope, but plants prefer Carbon 12 and therefore photosynthetic CO2 (fossil fuel or wood fuels) is much lower in C-13 than CO2 that comes from other sources (e.g.: animal respiration) ; ~ 1% C-13 • Carbon-14 is radioactive.
Rubsico enzyme evolved to handle the almost universal C-12 isotope • 1% is C-13 • If photosynthetic activity increases (each summer, or due to CC) then increase in atmospheric C-13 left behind can be measured • But: C-12 and C-13 dissolve =ly well in sea water; C-13 a bit better => so detecting atmospheric C-13
2006 discovery • Plants in aerobic conditions produce methane • Amounts detected small; globally – can amount to a significant source • Could be between 1/12 and 1/3 of annual amount
Research on carbon cycle to measure or infer carbon sinks • Global budgets based on atmospheric data and models • Global budgets based on models of oceanic carbon uptake • Regional carbon budgets from forest inventories • Direct measurements of carbon dioxide above ecosystems • Earth-system science modelling using ecosystem physiology • Carbon models based on changes in land use
Pacemaker of the glacial-interglacial cycles • The Milankovitch or astronomical theory of climate change is an explanation for the changes in the seasons which result from changes in the earth's orbit around the sun.
Evidence? • Not until the advent of deep-ocean cores and a seminal paper, "Variations in the Earth's Orbit: Pacemaker of the Ice Ages", in Science 1976, did the theory attain its present state.
1970s: ice cores revealed: last glacial lasted for 100,000 years; previous interglacial 10,000; change between the two was sudden. Current interglacial already lasted 100,000. new ice age? • 1980s: facts revealed that planet was warming • ?: how great a warming could we expect from our fossil-fuel generation of carbon dioxide and how would this compare against the current range of other climatic factors? • First IPCC report: 1990