Climate Variability and Extremes: Is Global Warming Responsible? Chip Konrad Associate Professor Department of Geography, UNC – Chapel Hill Director of the Southeast Regional Climate Center

Talk Outline 1.Introduction: Recent weather and climate extremes 2.Climate change vs. climate variability Challenges in the measurement of the earth’s temperature 3. What is the greenhouse effect? 4. What is the impact of greenhouse warming on our climate? How accurately can we assess this?

1.Recent weather and climate extremes Dec – Jan : Daily min temp ≤ 3240/46 days (Normal 22 days) Apr – Oct :Daily max temp ≥ 9091/214 days (Normal 46 days) From Climate Perspectives: Ranking of the coldness of the mean temperature: Dec – Jan 15, 2010

How did these cold temperatures compare with the rest of the world? This information and much more is available for any month at:

Why was it so cold? The North Atlantic Oscillation was in a highly negative mode.

How did the warmth in summers of 2010 & 2011 compare with the rest of the world?

What about recent temperature patterns?

Peaks: El Nino years Subsequent troughs: La Nina years Global temperature departures from normal 2. Climate change vs. climate variability Climate change Climate variability: Short-term variations in the climate. There are inter-annual and inter-decadal components.

There is much natural temperature variability and change in our atmosphere Some climatologists argue that we’re still coming out of the Little Ice Age

What mechanisms drive climate variability and change? Climate variability 1. Volcanism 2. Large scale circulation variations: North Atlantic Oscillation Also, El Nino-Southern Oscillation (ENSO) - These relate to changes in ocean forcing

Mechanisms that drive climate variability and change (con’d) Climate change Changes in atmospheric chemistry Changes in earth-sun geometry

How do we take the temperature of the Earth? Temperature measurements are often bias by the local environment around the thermometer. Must take into account the following: 1.Effects of local environment. Land cover type: urban heat island, proximity to water 2. Station density. 3. What about the oceans?

3. What is the greenhouse effect and its role in recent warming?

G.H. Gases Sources CO 2 burning fossil fuels Methane rice paddies, cattle flatulence H 2 O oceans Ozone burning fossil fuels (indirect) Most significant Greenhouse gases and their sources

CO 2 concentrations are increasing Explain the annual cycle

Human addition to natural background greenhouse gases is very small. However there is still a significant impact. Why? a. Contribution greatest with Co 2 and methane, which are the strongest greenhouse gases. b. The natural greenhouse gases bring the temperature of the earth from -23°C to 13°C

4. What is the impact of greenhouse warming on our climate? How accurately can we assess this? The earth – atmosphere system is very complicated. We must consider numerous interactions amongst components in the system.

1. Feedbacks Positive feedbacks – Ice-albedo feedback mechanism i.GH gases  warming  ice caps melt  lower albedo ii. GH gases  warming  more evaporation  more w. vapor Negative feedbacks – Examples: i. GH gases  warming  more evaporation  more clouds  higher albedo cooling

2. Clouds are smaller scale systems that can have a strong influence on the larger atmospheric system. Clouds reflect away visible light but also absorb outgoing longwave radiation from the earth. Convection as a scaling up process Cirrus vs. cumulus clouds: Different radiative properties.

How do we understand and account for these complexities in global warming scenarios? Global circulation models (GCM) How does a GCM work?

Shortcomings of models 1. Incomplete understanding of the earth-atmosphere system Example: GCMs cannot replicate El Nino events or the North Atlantic Oscillation. 2. Computer memory and processing speeds are getting much faster but are still limited. Mainframe 1967 Laptop 2007

How are these shortcomings dealt with? a.Parameterize smaller scale processes (e.g. convection) b.Coupled models approach What about chaos in the system? Can it be effectively modeled?

Conclusions There is much confidence in the fact that earth is warming up and will continue to do so, especially in the polar regions. However much uncertainty in the details. There is some confidence in their being more flooding and more droughts, but again much uncertainty in how much and where.

How should we handle this uncertainty? Example: Sea level rise  coastal flooding. Largely from thermal expansion of water. Amount of ice cap melting is big unknown (e.g. Antarctica) 3’ 4’ ’ 1.3’ Which scenario is most likely? Would you select the scenario in the middle of the envelope?