Climate Forcing of Natural Hazards PDF

CLIMATE FORCING OF NATURAL HAZARDS © Dana Naldrett  Introduction Natural hazards a significant present risk May become an increased future risk Climate change forces altered conditions that create or strengthen hazards To assess increased risk we must look a...

CLIMATE FORCING OF NATURAL HAZARDS © Dana Naldrett  Introduction Natural hazards a significant present risk May become an increased future risk Climate change forces altered conditions that create or strengthen hazards To assess increased risk we must look at past and present climate change Need to look at how climate change is measured  What is Climate Forcing? Climate forcing is where changes in climate force a response from systems that would not happen if climate did not change Particularly concerned when this forcing creates potential for hazards or catastrophes, actually creates them, or increases the risk of existing hazards Usually, climate forcing is far too strong for people to change the forcing mechanism, so we must learn to adapt to the resulting hazards instead  Climate Forcing Concerns Concern based on five lines of evidence: 1. Periods of exceptional climate change are associated with dynamic and dangerous responses 2. Changes in environmental conditions make mechanisms that can create responses in the Earth’s crust and sometimes deeper  Climate Forcing Concerns 3. We need to identify links between climate forcing and environmental responses (the hazards) 4. Modelling and projection of current warming trends point towards increased risk with a range of hazards 5. The ongoing rise in global temperatures may already be creating a hazardous response from the Earth  How Climate Changes Through time, Earth has experienced cycles of climate change, many driven by the geometric orientation of Earth relative to the Sun and described by the Milanković Cycles 3 geometric variations, 3 cycle lengths: – Eccentricity (100,000 year cycle) – Obliquity (41,000 year cycle) – Precession (22-26,000 year cycle) Eccentricity: How egg-shaped the orbit is Obliquity: How much the Earth axis tilts Precession: How much the Earth axis wobbles  Milanković Cycles Precession (22-26 ky) Obliquity (41 ky) Eccentricity (100 ky) Temperature 1000 800 600 400 200 0 Age (kya)  Measuring Climate Change Two very different methods: one for ancient change and one for modern change Modern change is measured by direct methods using sensitive instruments – Disadvantage: extrapolation into future is difficult because we have such a short period of observation – Advantage: measurements can be calibrated so they are both accurate and precise  Measuring Climate Change Ancient change measured by indirect or proxy methods (use variety of evidence) – For any change older than the period of instrumental measurement Unfortunately, evidence may or may not be present in geographic areas or times that people want to investigate Many types of proxy evidence: physical, chemical and biological; each with their own degree of reliability Comparison of age limits and reliability of direct, historical and proxy climate records  Historical Proxies Written records of climate-related conditions long before we had accurate instruments to measure climate directly For example, the Hudson Bay Company records  How Do Proxies Work? Biological proxies rely on an ancient species being the ancestor of the modern species which is assumed to live in the same environment – Modern species can give a range of parameters (temperature, precipitation, etc.) in which the species lives – Each species will have a different range of parameters in which it can live, so the more proxies for a given environment, the closer we can determine the exact conditions  16 14 Tree 1 12 Tree 2 Temperature (°C) 10 Tree 3 8 Beetle 1 Beetle 2 6 4 = environment overlap T = 8.50 to 9.25°C 2 P = 625 to 700 mm 200 400 600 800 1000 1200 1400 Precipitation (mm) Use of overlapping proxies: by taking a group of proxy organisms, the exact environment will be shown by their overlap END OF CONTENT FOR TERM TEST 1  How Do Proxies Work? Chemical proxies exist in very specific environments which can be tested and confirmed in laboratories Since chemical laws have remained the same through time, these proxies can be used for both modern and ancient environments  How Do Proxies Work? Physical or geological proxies are used when we know that a specific type of climate change in the past produces characteristic features that could not be produced in any other way e.g. when ground gets cold, it cracks from cold causing materials to contract (called thermal contraction cracking) – We know that mean annual air temperature must be below -15°C for this to occur  1 winter 2 spring 3 summer 4 winter 5 spring 6 Seasonal changes in ground cracking to produce ice wedges  Relict ice wedge, Hunker Creek Yukon Territory. When such large bodies of ice melt, ground collapses and water causes slumping in soil. © Dana Naldrett  Steps in Using Proxies Collect proxy data Date the proxy data (e.g. match tree growth rings to calendar years) Calibration – relate the proxy measurement to known climatic conditions (confirms accuracy and precision) Validation – tests the reliability of the calibration Reconstruction – once the proxy/climate relationship is established, use statistics to predict what past climate was like  Accuracy vs Precision Accuracy: the degree to which a measurement conforms to a standard – Is the 1m tape measure really 1 m long? – Is 1 second on the stopwatch really 1 second long? – Can you hit the target bullseye? Precision: The degree to which a repeated measurement varies from other repetitions – How close together are your shots?  High accuracy High precision  Important Considerations Each proxy indicator will have a different calibration – We can use modern species to show how sensitive ancient species were to climate Once calibrated, then we have to validate (check) the calibration – Usually need to have something of known origin to validate  Proxy Climate Indicators Beetles Cave deposits (speleothems) Corals Foraminifera and Ostracoda Glaciers and Heinrich events Ice and sand wedges and casts (soils) Oxygen isotopes (ice cores and shells) Pollen Tree rings Beetles are a variety of shapes and sizes, so are relatively easy to identify © Wikipedia Various types of speleothems commonly found in caves  Corals Oxygen in calcite (CaCO3) can be used for oxygen isotope analysis of temperature Healthy coral reef in Hawaii. Unhealthy corals show bleaching effects and lose their colour. © DeepDive  Benthic foraminifera Planktonic foraminifera Scale bars are 25 μm long Scale bars are 100 μm long Examples of marine and fresh water ostracoda Scale bar is 400 μm or 0.4 mm Examples of marine ostracoda Glaciers and Heinrich Events Episodic release of icebergs from northern hemisphere glaciers in a sudden climate warming 60,000 to 16,800 years ago Evidence is the high amount of abnormally coarse rock pieces on the Atlantic Ocean floor (dropped from floating icebergs) Rock types and amounts suggest icebergs originated on the North American side and floated east to the European side of ocean Location of Heinrich event debris on ocean floor (blue). Light gray shows glaciers, dark gray no glaciers. Modified from Research Gate.  Oxygen Isotopes Determine ancient temperatures using any material containing oxygen (O) atoms Isotope : Atoms of the same element with varied number of neutrons – e.g. O16, O17, O18 Can be used in any shell material because it is made of CaCO3 so the O can be used for isotope analysis Also commonly used in glacier ice cores where water (H2O) gives the O © National Snow and Ice Data Center Extraction of an ice core from the Antarctic Ice Sheet © WAIS Divide Ice Core Project Cutting an ice core for 18O/16O sampling © British Antarctic Survey Example of Various Pollen Types © Wikipedia  Example of a Pollen Diagram climate stage Example of Tree Ring Indicators  What Does Changing Climate Do? For anything driven by the atmosphere or ocean, there will be much more energy available to drive storms – Hurricanes, tornadoes, typhoons will be stronger and probably more widespread Most surface processes will intensify, so landslides, avalanches, floods, fires and droughts will get stronger and more frequent Climate change will raise sea level, melt permafrost and glaciers, alter agriculture and ecology so plants and animals are threatened  Hazards Affected by Climate Avalanches Earthquakes and volcanoes Floods Forest fires Glacial lake outbursts Ground subsidence and karst Hurricanes and tornadoes Landslides Thermokarst  Avalanches Rising temperatures make avalanches bigger, they trigger earlier in the year and they travel farther once triggered Snowfall starts earlier, providing more material to avalanche Warmer weather makes it harder for the snowpack to stick together, increasing the risk of weak layers starting avalanches This is seen in Europe, Iceland, and western North America Earthquakes and Volcanoes Melting of glaciers may take enough pressure off fault zones to allow slippage and new earthquakes Changes is sea surface temperatures in El Niño-Southern Oscillation cycles may contribute to triggering earthquakes in the Pacific Rim zone Some volcanoes collapsed in pluvial periods (rain when colder areas had glaciation) Melting ice and snow appears to be responsible for volcanic eruptions in Iceland  Floods With global warming, there is more energy in the atmosphere and storms will become stronger and harder to predict We will have more rain and this will cause more flooding for several reasons: – Ground will saturate faster – Snow pack will not usually melt early in spring, so when rain falls it will be warm and melt the snow  Forest Fires Forest fires are most likely to occur when conditions favour the 30/30/30 rule: –30% or less relative humidity –Temperatures greater than 30°C –Winds greater than 30 km/hr Lightning is a common initiator of forest fires, and will increase significantly with warmer atmosphere  Glacial Lake Outbursts A glacial lake outburst flood (GLOF) occurs when the dam holding back a glacial lake fails: the sudden and intense flooding can be catastrophic for nearby communities – Not all dams are the same: some are ice, some sediment, so global warming effects are not clear or simple – Ground under glacial lakes is not the same so some areas are more prone to outbursts because of warmer ground melting ice dams  Glacial Lake Outbursts As glaciers melt, more water accumulates in dammed lakes, posing a higher risk Some areas more prone to GLOF than others – Himalaya, because of high altitude, cold climate and thick glaciers High slopes and runout areas very dangerous if outbursts occur Ground Subsidence and Karst Karst refers to the dissolving of bedrock, leaving large void spaces where solid rock once existed With rising temperatures, more rock will dissolve and there will be more water to dissolve the rock Hazards such as sinkholes will become more common and will be as difficult to predict in the future as they are today  © Christian Science Monitor Tropical storm Agatha caused this huge sinkhole in Guatemala City, Guatemala in June 2020. Several people were buried alive and there was a lot of property damage.  Hurricanes and Tornadoes Hurricanes (or cyclones or typhoons) are getting larger and stronger, more damaging, have a longer season and are in more places than ever before It is not clear if there are more now or not The tornado story is more complex: – There is no increase in strong tornadoes – Tornadoes have become more clustered and so are more damaging  Hurricanes and Tornadoes A hurricane system can have tornadoes spin off it, so if storm systems are getting stronger, we can expect more and stronger tornadoes  Landslides With increased rainfall, there will be more water on slopes causing failure from: – More weight on the slope – Wetter soils keeps particles farther apart No water: grain-grain contact Little/no movement- high friction With water: no grain-grain contact Movement- no friction  Thermokarst Permafrost with large amounts of ice starts to melt (the thermokarst process) and the ground above sinks The higher the ice content of the soil, the more potential sinking can happen Particularly hazardous in highways that were originally built on solid ground and now have turned to soup with sinking roads (e.g. Dempster Highway YT and NWT) © NWT Government Thermokarst-induced slumping near the Dempster Highway, NWT © Scott Zolos Thermokarst-induced slumping near the Dempster Highway. The slump has doubled in size in one year.  Summary Climate forcing of hazards can be direct and unequivocal, or can be indirect and difficult to establish The first problem is establishing past climate history using proxy evidence, which is variable in reliability The second problem is noticing enough hazards to be able to establish a causal relationship with climate – Must be able to show cause and effect rather than just a correlation  Summary Future safety will depend on establishing these factors more clearly and being able to take action to prevent hazards from having adverse effects on people  Next: Volcanoes