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Lecture 3

Week 3 lecture 1.docx

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Wilfrid Laurier University
Environmental Studies
Robert Mc Leman

Week 3: Impacts of climate change Where did all these greenhouse gases come from? • Fossil fuels • Removal of carbon sinks (most importantly, forests) • Cement production Key CO2 source: Fossil fuels • Burning 1 kg of carbon creates 3.67 kg of carbon dioxide (C + O + O) • Humans began burning large amounts of carbon-based fossil fuels in the late 1700s • Consumption has been accelerating in the last 50 years CO2 source: Cement production • Akey ingredient in cement is limestone (CaCO3) • To make cement requires removing the carbon from the limestone, to get at the calcium • In the process, it releases CO2 CaCO3→ CaO + C2 • Process probably accounts for <5% of anthropogenic CO2 emissions Reduction of carbon sinks: Deforestation • An estimated 1.6 billion tonnes of forest material is burned each year • The annual net loss of forests worldwide each year is roughly an area the size of New Brunswick Carbon sinks • The term ‘sink’refers to a mechanism that removes CO2 from the air Key sinks are: • Land vegetation • Ocean direct absorption • Phytoplankton Land vegetation • Humans have been steadily removing forest cover and replacing it with other forms of vegetation that store far less carbon Does additional CO2 in the air stimulate plant growth? • Recall that CO2 is required for photosynthesis • Recall that CO2 is required for photosynthesis • Therefore, if there is more CO2 in the air, you could get more plant growth, right? Key term: “limiting factor” ** (midterm and exam questions) • Any factor in the environment that controls the growth, abundance or distribution of a population of organisms in an ecosystem • Plant growth & distribution is influenced by numerous factors: sunlight, water, temperature, carbon dioxide, nitrogen, phosphorus, and other soil nutrients... • The one that is in shortest supply relative to a particular plant’s needs is its key limiting factor Does additional CO2 in the air stimulate plant growth? • It can where CO2 is the limiting factor • Where is this the case? • Typically, where all other plant requirements are in sufficient supply Does additional CO2 in the air stimulate plant growth? • Theories often based on studies of plant behaviour in greenhouses • Because of poor air circulation & ability to apply artificial fertilizers, CO2 concentrations within a greenhouse can indeed be a key limiting factor • If you pump in artificially high levels of CO2 into greenhouse (especially during daytime) you do indeed increase plant growth/biomass Not all plants are alike • They use different photosynthetic methods to acquire carbon • Some are more efficient at collecting carbon from the air than are others • We distinguish these based on their cellular structure • C3 versus C4 (TWO different types of plants, know the difference) Does additional CO2 in the air stimulate plant growth? • C4 plants don’t benefit from extra CO2 because they are already able to mobilize large numbers of C atoms during photosynthesis, and don’t need extra help (e.g. corn) • Most plants are C3 plants, which are less efficient photo synthesizers, and some can benefit from extra CO if nutrients and soil moisture are plentiful • The effect is not universal; some plants do not do well under higher CO2 concentrations, regardless of type Is CO2 a limiting factor for plant growth in nature? • For terrestrial plants, it is more often the availability of soil nutrients (especially N) that limits plant growth, not CO2 • This is particularly the case for agricultural crops • So, higher CO2 levels will increase plant growth globally, but the rates may not be as high as we hope for, especially for many food crops Carbon sink: Direct atmosphere-ocean transfer of carbon • CO2 can dissolve into seawater directly under certain conditions • Very slow process Does dying plankton “sink” CO2 into the deep ocean? • Yes, but probably not as much as we would like to think (Pollard et al. Nature 2009) • Nonetheless, some propose dumping large amounts of iron into the ocean to fertilize plankton (iron availability is believed to be a limiting factor in plankton growth) Are elevated CO2 levels beneficial for plankton? • It has in the past been theorized that for ocean surface organisms (e.g. phytoplankton, diatoms) CO2 availability may be a limiting factor (Riebesell et al., Nature 1993) • Therefore, it was speculated that higher levels of atmospheric CO2 could stimulate higher phytoplankton that would then remove the excess CO2 from the air and “correct” the balance Are elevated CO2 levels beneficial for plankton? • Not necessarily; it maybe the opposite • In actuality, it appears that ocean temperatures are the key limiting factor in phytoplankton productivity • Warmer sea surface temperatures discourage water from mixing, thereby limiting the availability of essential nutrients • During recent ElNino when Pacific surface temperatures increased, phytoplankton activity declined Summarizing sinks • There are many natural processes that absorb CO2 from the atmosphere • The important question: is the rate at which they cumulatively absorb CO2 from the atmosphere greater than the rate at which humans put CO2 into the atmosphere? • At present, it appears: human production > efficiency of sinks Summary of the underlying science • Particular trace gases in the atmosphere (H2O, CO2 CH4, N2O, CFCs) trap infrared radiation and exert a “greenhouse effect” • Concentrations of CO2, CH4 and N2O are growing rapidly, and have been over past century; human activity is the primary source of increase • Human activity has reduced a key carbon sink (forests); other sinks are not likely to make up for the loss Implications of elevated atmospheric concentrations of GHGs • Increase Earth's average temperature • Influence the patterns and amounts of precipitation • Reduce ice and snow cover, as well as permafrost • Raise sea level • Increase the acidity of the ocea Future temperature changes • Will not be evenly distributed across the Earth • Higher latitudes, altitudes will warm more rapidly In the future: more extreme storm events • Why? • Tropical cyclones/hurricanes form over oceans • Their intensity is positively related to the sea surface temperature • Sea surface temperatures are rising In the future: more severe droughts over continental areas Why? • Seasonal precipitation shortfalls are linked to sea surface temperatures, either directly or through monsoon behaviour • Higher average temperatures increase evapotranspiration rates, putting plants under greater stress Why does sea level rise with global warming? • The volume of water increases as it gets warmer • If you heat up the oceans they will grow in size (called “thermal expansion”) • Melting of land-based ice also contributes to ocean volume Agreat unknown • As northern land areas thaw, it is expected they will begin releasing large amounts of methane, a powerful GHG • They will also have higher rates of photosynthesis than at present • What will the net effect be? Will the CO2 sink effect be greater than the CH4 source effect? Vulnerability to climate change Vulnerability = potential for harm or loss Is a function of: • The nature of the physical changes to which a population is exposed • The sensitivity
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