2008 ECSA Junior Faculty Forum on Future Scientific Directions


The Thermohaline Circulation and Tropical Cyclones
in Past, Present and Future Climates

July 8th-10th, 2008, NCAR, Boulder, CO

This year the ECSA presents two topics of fast and slow extreme events in the climate system that may be subject to abrupt or long-term changes. The first process is the oceanic overturning circulation, a slow process. Second, atmospheric tropical cyclones, a fast process that may still change rapidly. The workshop will have two sessions looking separately at their past, present and future from observations and models. There will also be a joint session to look at common interactions and/or techniques in understanding past, present and future variations of the coupled ocean-atmosphere system using both paleo-climate proxies and models.

Link to early release of Meeting Summary (Bulletin of the American Meteorological Society)

Topic 1: The role of the Thermohaline Circulation in abrupt climate change: past, present and future from observations and modeling

Chairs: Aixue Hu (NCAR), Jianjun Yin (FSU)

The Thermohaline circulation (THC, or also called Meridional Overturning Circulation, MOC) has the potential to cause abrupt climate change (and not just in Hollywood movies). Because of the lack of long-term observations of the THC, it is difficult to assess the state and variability of this circulation over the past century or two, and its potential impact on future climate. Model predictions indicate that the THC will not collapse due to greenhouse-gas-induced warming in the 21st century. However, these model projections have potentially significant uncertainties. More fundamentally, none of the coupled climate simulations of the THC are able to adequately represent THC characteristics such as bistability, bifurcation, hysteresis and irreversibility. Those behaviors are thought to be essential to abrupt past climate changes. The purpose of this forum is to gather junior scientists from both observational and modeling fields to work on the most difficult issues outlined as follows regarding the role of the THC in abrupt climate change:

1. What is the observed and modeled contribution of the THC to past abrupt climate change?

2. What is the impact of melting ice sheets, glaciers and ice caps on future changes of the THC?

3. What observations can improve understanding about the past variability of the THC?

4. How well is the THC represented in models and what improvements are needed?

Topic 2: Combining Models and Geological Data to Explore Past, Present, and Future Tropical Cyclone Activity

Chairs: James Done (NCAR), Christa Farmer (Hofstra)

Exploration of tropical cyclone activity under past climate variability can provide useful information towards reducing the current uncertainty surrounding future variability in tropical cyclones due to natural climate variability and anthropogenic climate change. A robust historical record of tropical cyclone activity has significant practical applications and societal relevance. Understanding the climatology and especially landfall probabilities of these destructive events is not only of interest to climate researchers but also to policy-makers, socio-economic planners, emergency response and risk managers and the reinsurance industry. This workshop aims to bring together computer modelers, climatologists, and earth scientists to examine the temporal and spatial patterns of past, present, and future tropical cyclone activity focusing on paleo-climate records and extending hurricane modeling.

The satellite record of global tropical cyclone frequency only goes back a few decades and is therefore sufficient only to capture high-frequency ranges of variability. Paleoclimate (or paleo-tempest) records in geological proxy data can extend the record of past tropical cyclone activity back up to 5000 years, enabling the analysis of lower-frequency variability.  Several geological proxies of tropical cyclones have been explored, including tree rings, pollen concentrations, oxygen isotopes in corals and cave deposits, and overwash deposits in the sediments of coastal lakes and marshes.

Statistical hurricane models have shown success in generating distributions of tropical cyclone activity that are statistically indistinguishable from the observed record. Many such 'samples' can be generated to provide populated distributions of hurricane activity, including samples driven by paleo-climate records. The workshop will explore opportunities to use models with paleo-climate proxies to extend the observed climatology of tropical cyclones to past climates, and also to future climate scenarios.

Powerpoint presentations of talks
These are rather large files, please be patient while they download.

Group Photo at NCAR Mesa Lab

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