GC 170 1st EditionExam # 4 Study Guide Lectures: 14-17Lecture 14: climate variability and climate change, natural forcingsWhat is the difference between Global Warming and Climate Change? - Climate change: Significant change in measures of climate (temp, precipitation) that lasts for an extended period of time - Global warming: Average increase in temperature in the atmosphere. It is only a PART of climate change (a big one). o Climate change that is related to human activities (fossil fuel emissions)What is the difference between Climate Change and Climate variability?- Climate Change: Long-term changes in the regional climate or earth’s average temperature occurring over decades to centuries - Climate variability: Short-term changes in the climate occurring over years to decades, usually related to natural climate forcings/influencesWhat is a paleoclimate reconstruction?- Paleoclimate reconstructions: thousands of years are developed from proxy records (tree-rings, ice cores, pollen records)o Key to future: understanding past o Historical information provides a context for recent warming o Help us to predict the future environmental conditionsWhy is it important to study paleoclimate? - Key to future: understanding past - Historical information provides a context for recent warming - Help us to predict the future environmental conditionsWhat is significant about 20th century warming compared with the past ~2,000 years? - Major warming over the past few decades o 20th century warming is unpredictableWhat is the Medieval Warm Period, and what is the evidence from this time?- Medieval warm periodo A period from 900 – 1300 ADo When average temperature in the northern Hemisphere was warmer (~ 0.5 degrees) than the 20th centuryo Evidence from Northern Europe (Vikings in Europe settled in Greenland for 400 years)o Medieval Period in Europe was a time of growth, many castles were built during the MWPWhat happened in the southwestern US during the Medieval Warm Period?- Western USo Arid and warmer across the western US o Several long and severe droughts lasting around 20 years in the Southwesto Large communities of Native Americans dispersed (Hard to sustain large communities)What is the evidence of the Little Ice Age?- Cool period from 1400 – 1800 AD- Glaciers more advanced in some places than they are today - Holland had a lot of continuous Ice- Periods of cooler temperatures, glacial advances and more freezing temperaturesNatural Climate ForcingsWhat is the climate effect of a large, explosive volcanic eruption?- Volcanic eruptions inject large amounts of ash into atmosphere o Blocks amount of incoming solar radiation reaching the earth surface and cools the climate. Explosive volcanic eruptions emit black ash & SO2 gas,  reaches the stratosphere SO2 converts to sulfate aerosols (Fine particles that reflect incoming solar radiation) remain in the stratosphere for 1 – 2 years (stratosphere is dry & sulfate aerosols are not rained out)o Cool the global climate for 1 – 2 yearso Volcanoes near equator cool more effectively Upper-level winds transport volcanic gases and ash to cover both hemispheres Higher latitudes winds transport the ash and gases to cover a smaller area (ex: only within the northern hemisphere)How do volcanoes cool the climate? o Blocks amount of incoming solar radiation reaching the earth surface and cools the climate. Explosive volcanic eruptions emit black ash & SO2 gas,  reaches the stratosphere SO2 converts to sulfate aerosols (Fine particles that reflect incoming solar radiation) remain in the stratosphere for 1 – 2 years (stratosphere is dry & sulfate aerosols are not rained out)How long is the climate cooled following a volcanic eruption?- 1-2 yearsWhy are volcanoes near the equator the most effective at cooling the climate globally? o Volcanoes near equator cool more effectively Upper-level winds transport volcanic gases and ash to cover both hemispheres Higher latitudes winds transport the ash and gases to cover a smaller area (ex: only within the northern hemisphere)How do sunspots affect climate, specifically, how is the energy budget affected?- In terms of the energy budgeto More solar radiation is absorbed at the earth surface o Earth’s surface temperature increasesHow long does the climate effect last?- 10 yearsDid sunspot activity contribute to the cooler period of the Little Ice Age?- The combination of volcanoes and decreased sunspot activity may be partly responsible for cooler climates during Little Ice AgeDoes sunspot activity contribute to recent warming of the past few decades?- Partially, because there are natural forcing (volcanoes and sun spots) but also human forcing (use of fossil fuels etc…) According to the Global Climate Models, would there be warming without human influences on climate?- YesLecture 15: Proxy methods (ice cores, tree rings)What is proxy data?a. Data that represents past environments and climates (levels of CO2)i. Before 1958 (Keeling Project)1. Found levels of CO2 in ice cores2. Contain old layers of ice with air bubbles, containing CO2 levelsin pastii. Used to develop paleoclimate reconstructions 1. Key to the future is understanding the past 2. Historical information provides context for recent warming 3. Help predict future environmental conditionsWhat are some examples of natural archives which contain proxy data?i. Tree-ringsii. Ice coresiii. Pollen recordsHow are ice cores are collected, and what happens in the lab to measure the proxy data? - In the lab o Ice is cut into sections (10 cm – 1 m) o Ice is melted o Gas bubbles are released o Water is collected Scientists measure: o Gas  Samples of the atmosphere reconstruct past greenhouse gas concentrations- CO2- Methane - Nitrous Oxideo Water  Temperature (Hydrogen isotopes)o Dust and Particulates in the ice Dust/ash from past volcanic eruptions and pollution- Shows repetitive cycles or fluctuations in CO2 - Shows unprecedented CO2 levels in recent decadesWhat proxy information can be obtained from ice cores?- Dust and Particulates in the iceo Dust/ash from past volcanic eruptions and pollution Shows repetitive cycles or fluctuations in CO2  Shows unprecedented CO2 levels in recent decadesWhat modern measurements do scientists make in order to have a modern analog for an ice core?- In order to interpret the past conditions, scientists need to understand how ice accumulates and