LECTURE 2: WHAT IS NATURAL? Why is studying the past important? Met Office Mean Central England Temperature Annual anomalies, 1772 to 11" Oct 2014 3.0 2.5 - It allows us to validate climate models 2.0 - Provides longer term climate datasets which can put current climate change into context. 1.5 1.0 - What temperatures, greenhouse gas levels, sea leves are 'naturls'? 0.5 Difference ("C) from 1961-90 0.0 - Produces 'analogues' that may be useful for understanding the impact of future climate change. -0.5 -1.0 -1.5 - Most argue that climate change began with the onset of the industrial revolution, or as we started to farm. -2.0 2.5 - Longest climate data based on weather stations goes back 200 years. -3.0 - 1950s - start of measuring CO2 in atmosphere (1958) - tree rings, corals, ice cores and other proxies. Based on Parker et al (1992) 1780 1800 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000 NORTHERN HEMISPHERE 0.5 Placing current change into context: - 1750 industrial revolution starts - our records do not go back far enough. 0.0 - It is important to show understanding through discussion and critiquing. Departures in temperature (?) from the 1961 to 1990 average 0.5 - Average temperature from 1960-1990. - Past climates are important as they allow us to validate climate models and allow us to put current climate change into context. -1.0 - - 'Analogue' - climate system of the past may be similar to today in parts. 1000 Data from thermometers (red) and from tree rings, corals, ice cores and historical records (blue). 1200 1400 1600 1800 - Mann 'Hockey Stick curve' of the Northern Hemisphere temperature - Mann et al., 1999. What is "natural"? - The current level of GHGs is completely different to the past. - Peaks are all at 800 ppm but NO higher. - CO2 concentration has been increasing. - What are natural levels - ice cores are the only way of directly measuring past atmosphere. - In 1800, CO2 at 300 ppm starts to rise. 2000 Carbon Dioxide Variations Year 400 400 350 The Industrial Revolution Has Caused A Dramatic Rise in CO, 300 +350 1000 1200 1400 1600 1800 Year (AD) 2000 CO2 Concentration (ppmv) 300 Ice Age Cycles 250 200 400 300 200 100 0 Thousands of Years Ago - Steady gradual warming? - Relatively constant and then suddenly increases? Do some periods of time offer analogues for the future? Petit et al., 1999 b forcing System change - Can we actually look at periods in the past for analogues? - Temperatures from Antarctic ice core - approximately 400,000 years ago - interglacial - factors that drove climate are similar to today. - MIS 11 - a warm period in our climate? - Northern Hemisphere in high latitudes show evidence that climate was warmer than present day. response Time Time d System change thresholds Time Time System change Time
- Turney and Jones (2010) - looked at the last IG with temperature evidence