Climate Variability and Change

1. Climate Variability and Change Lab 10

2. Is our climate changing? • Natural climate variability vs. human-induced variability • Human-induced global warming being the ‘hot topic’ • Difficult to determine the specific causes of climate change • Uncertainty

3. Climate Data Statistical Analysis • Time series (e.g., temperature observations over time) • The life of a climate scientist: • Break data into component parts to identify significant aspects/trends (i.e., sudden change, upward trend, etc.) • Then, look for forcing factors that may account for observed aspects (e.g., trends) found in the time series data (e.g., volcano eruption, industrial revolution, etc.) • Note: forcing factors result from events or conditions that significantly change the radiation budget – hence the climate response (e.g., increase or decrease in temps.) • Speculate about the future and scare people

4. Statistical Analysis • Studying climate change: look for patterns • Cyclical, e.g.: • Daily changes, diurnal • Seasonal changes • Upward trend, e.g.: • Changes between sunrise & sunset • Over the course of hundred + years • Sudden changes, e.g.: • Rapid average temperature change due to volcano eruption

5. Patterns: cycles, trends, and sudden shifts

6. Radiative forcing: • Measure of the influence that climatic factor (ice albedo, tropospheric aerosols) has in altering the balance of incoming & outgoing energy in the Earth-atmosphere system. • Positive = warming the surface • Negative = cooling the surface • Expressed in watts per square meter.

7. Forcings: human vs. natural influence

8. Climate Change Projections • Scenario-driven (hypothetical forcing condition) • That is, what if amount x of GHG emissions occurred instead of amount y? What would be the climate response? • Scenarios are usually described in terms of human behavior (e.g., carbon emission policies, economic trends, etc.)

9. NPCC Climate Change Scenarios A2: Relatively rapid population growth and limited sharing of technological change combine to produce high greenhouse gas levels by the end of the 21st century, with emissions growing throughout the entire century. A1B: Effects of economic growth are partially offset by introduction of new technologies and decreases in global population after 2050. This trajectory is associated with relatively rapid increases in greenhouse gas emissions and the highest overall CO2 levels for the first half of the 21st century, followed by a gradual decrease in emissions after 2050. B1: This scenario combines the A1 population trajectory with societal changes tending to reduce greenhouse gas emissions growth. The net result is the lowest greenhouse gas emissions of the three scenarios, with emissions beginning to decrease by 2040.