Transcript archer6
Chapter 6: Weather & Climate Midterm Exam 9:33 8: 22335778 7 : 5788 6:2335778 Average Score = 77 2 Topics before Chapter 6 Material 1. Keeling Curve 2. How scientists approach Climate Change Keeling Curve +400 ppm Keeling Curve Keeling Curve Shows atm. CO2 rising at unprecedented rates Driven by burning of fossil fuels past 200 yrs. Pioneered in 1958 by scientist Charles Keeling. Longest-running tally of carbon dioxide levels in atm. Maintained by Scripps Institution of Oceanography. Up 22 points from a decade ago. Many scientists have warned that carbon dioxide readings must be brought down to 350 ppm to avoid severe climate impacts and stall "feedback loops" that will exacerbate the rise. Keeling Curve Previous 800,000 years, CO2 levels never exceeded 300 ppm There is no known geologic period in which rates of increase have been so sharp. Was about 280 ppm at the advent of Industrial Revolution “I wish it weren't true, but it looks like the world is going to blow through the 400-ppm level without losing a beat," said Scripps geochemist Ralph Keeling, who has taken over the Keeling curve measurements from his late father. "At this pace we'll hit 450 ppm within a few decades." Large body of evidence supports conclusion that human activity is primary driver of recent warming. 1. Our understanding of how gh gases trap heat, how climate system responds to increases, and how other human and natural factors influence climate. 2. Many indirect estimates of climate changes over the last 1,000 to 2,000 years. Ice cores, tree rings and corals - show recent T rise is unusual Large body of evidence… 3. Comparisons of actual climate with computer models. When models are run with historical inc. in gh gases show gradual warming of Earth, increases in ocean heat content, rise in sea level, retreat of sea ice and snow cover. In agreement with observations. Climate Model Indications & the Observed Climate Global climate models clearly show effect of human-induced changes on global T. blue band shows how global T would have changed due to natural forces only . pink band shows model projections of effects of human and natural forces combined. black line shows actual observed global average temperatures. Global climate models clearly show effect of human-induced changes on global T. Close match between black line and the pink band indicates that observed warming over last half-century cannot be explained by natural factors alone, and is instead caused primarily by human factors. 800,000 Year Record of CO2 Concentrations Measured from trapped air bubbles in Antarctic ice core Energy from the Sun Has Not Increased Solar energy has been measured by satellites since 1978. Now, Chapter 6 Our layer model to date assumes that that surface temperature is the same everywhere on Earth! But, we know this is not true. So, we have to add yet more complexity to our climate change model! 1. Daily & Seasonal cycles - drive surface temperatures above and below average values. 2. Energy budgets DO NOT balance locally. – net heat input at low latitudes, transport to high latitudes. turbulent flows of air and water. requires complex computer climate models. Daily Variability: Simplified Surface Energy Balance NET R = +SW (insolation) –SW (reflection) +LW (infrared) –LW (infrared) Figure 6.2 Radiation Budgets El Mirage, CA Pitt Meadows, BC Seasonal Variability Earth’s tilt is responsible for seasons. Earth’s tilt determines how much heat the surface receives from the Sun each day as a function of latitude (y axis) and time of year (x axis). net heat input at low latitudes, transport to high latitudes Global Latent Heat Figure 4.19 Global Sensible Heat Figure 4.20 So we have to simulate the weather. In order to forecast global warming we have to simulate the time and space variations and imbalances in the energy budget. And the way the Earth’s climate responds by storing or transporting heat around. Our original layer model can’t do this. Physics that simulate flows of air/water is complex and difficult to simulate. Global Circulation without Rotation Coriolis effect - an inertial force described by 19thcentury French engineermathematician GustaveGaspard Coriolis in 1835. Effect is an apparent deflection of the path of an object that moves within a rotating coordinate system. The object does not actually deviate from its path, but it appears to do so because of the motion of the coordinate system. Global Circulation With Rotation With Coriolis Effect 1. Energy Budget of the Earth fluctuates on daily & seasonal timescales (in contrast to the layer model). 2. Annual Energy Budget doesn’t balance locally because excess heat is carried to higher latitudes by winds and ocean currents. 3. Global warming forecast requires simulation the weather – computational challenge.