Abrupt Climate Change R.B. Alley et al. (2003) Early Warning of Climate Tipping Points Timothy M. Lenton (2011) Eric Birney Atmospheric Science

Dr. Richard AlleyDr. Tim Lenton Professor at Penn State University BS and MS from Ohio State PhD from University of Wisconsin-Madison Professor at University of Exeter BA from University of Cambridge PhD from University of East Anglia

Abrupt Climate Change Alley et al. (2003)

What “Abrupt” Actually Means  “A climate ‘tipping point’ occurs when a small change in forcing triggers a strongly nonlinear response in the internal dynamics of part of the climate system, qualitatively changing its future state.”  Temperature may change 10°C or more in just a decade.  Can be both anthropogenic and natural.

An Introduction Into Abrupt Climate Change  Climate is Ever-Changing  Abrupt Change takes climate from one state to another.  “Abrupt” Change isn’t new Ice Core Records show a rapid change from one climate to another over thousands of years.

Akkadian Empire and Other Historical Events  Akkadian Empire collapsed due to multicentennial drought.  Other instances found in the Paleoclimatic records from the Holocene – Shifts in hurricance frequency, changes in flooding, especially severe droughts.

Mayan Civilization and Akkadian Empire  Mayan civilization collapsed due to multidecadal drought.

Causes – Rocking the Boat  Canoe Analogy  For an abrupt change to take place, 4 things are required: 1) Trigger 2) Amplifier 3) Globalizer 4) Source of Persistence

Examples of Triggers, Amplifiers, and Persistence  Triggers – Sahara drying: Dansgaard-Oeschger oscillation(abrupt warming) and orbital forcing. Triggers may be quick, slow, or anywhere in between.  Amplifiers – Positive feedback loops. For example, ice- albedo feedback.  Persistence – Loss of vegetation; thickening ice sheet.

What are the Implications?  More variability in climate.  Changes in precipitation quantity and location.  Changes in temperature: some locations may experience a great warming, others a dramatic cooling.

So what now?  Much more research is necessary.  Learn about stabilizing feedbacks.  More complex models to learn about the human impacts.  Develop effective strategies in preparing for, and adapting to, abrupt climate change.

Early Warning of Climate Tipping Points Tim Lenton (2011)

Most Susceptible Areas to Collapse  Abrupt climate change occurs naturally, the earth doesn’t need our help pushing it past a tipping point.  Atlantic thermohaline circulation, West Antarctic Ice Sheet, Greenland Ice Sheet, Amazon rainforest, boreal forests, West African monsoon, Indian summer monsoon, and the El Niño/Southern Oscillation. GENIE-1 GENIE-2

Importance of Early Warning  If an early warning system is developed, it may provide an opportunity to prepare and get ready to adapt to a new environment.  Potential to save lives, preserve ways of life, and keep the economy from crumbling.

How to Predict Tipping Points  Processed-based understanding, model predictions, and paleoclimate data are all used understand and predict tipping points.  It is estimated that individual thresholds for tipping points will be reached when an increase of 0.5 to 6 °C is reached.  Research and testing suggests that one in five tipping points will be passed with an increase of >4 °C.  GCMs are weak in predicting tipping points.

Crossing a Threshold Bifurcation Noise-induced tipping point

Perturbation Recovery

Amplification of Signals  Because of the lack of recovery from the various perturbations, there may be an amplification of the fluctuations due to the strengthening of positive feedback – this gives an early indication that bifurcation is approaching.  Noise-induced transitions – Fundamentally unpredictable. There should be no change in potential, no early warning visible. Example: Dansgaard–Oeschger events during last ice age. If it can be determined how stable a system is, it can also be determined how vulnerable it is to noise-induced transitions.

Testing Early Warning Indicators  Climate models – tested detection in simple, intermediate complexity, and full 3D models. Models focused on the potential for the collapse of the Atlantic THC. The 3D model was the most indicative of real-world possibilities.  Paleorecord tests – Paleoclimate data tests showed critical slowing down during the end of the last ice age in data from the Greenland Ice Sheet.

Early Detection Limitations  Potential for False Alarms and Missed Alarms. False Alarm (False Positive) – Bifurcation is expected, however, signals thought to be indicating bifurcation were caused by another source. Missed Alarm (False Negative) – Noise-induced transition may cause a system to be abruptly pushed past its tipping point.

Major Systems of Concern

What’s Next?  More dynamical models, to model changes and noise- induced transitions.  Longer Paleorecords for slow climate systems, such as the Atlantic THC, to determine its natural behavior.  Policy making to slow down human-caused forcing.

Early Warning System Status  The state of early warning systems is certainly heading in the right direction. Tests have shown that some early warning signals do exist.  Risk assessment, scientific prediction, careful warning formulation, effective communication and an appropriate response capability are all in needed in place in order to formulate a system.

Summery and Conclusion  Science is working towards detection, prediction and warning of tipping points and their various triggers that push them over the edge.  Many advances are being made, but there is still a long way to go before an actual prediction and warning system is in place.

Questions?