The Trans-Atlantic Research and Development Interchange on Sustainability Workshop (TARDIS) Workshop is essentially a three-day study session stimulated by presentations and discussion. TARDIS has been held every other year since 2004, alternating between the USA and Europe. The workshop involves 30 - 40 participants from the United States, Europe, and other parts of the World in the multi-disciplinary field of sustainability.  The group will include the participation of experts from engineering, mathematical sciences, physics, ecology, economics, and political science fields.  While there are many conferences on sustainability, TARDIS is unique in that: (1) participants are carefully selected by-invitation-only scholars from the United States, Europe and elsewhere in the World, (2) participants represent multiple disciplines, and (3) TARDIS addresses forward-looking topics in sustainability.

We propose to focus TARDIS 21 on emergent local and global challenges to sustainability. The reason why this important is that in the 21st Century, the World is highly urbanized with more than 4 billion people living in urban areas.[1] Due to efficient modern transportation by land, water, and air, there is a fast and reliable movement of people and goods between these urban centers across the globe. Besides, the World Wide Web has, in modern times, made the diffusion of information across the World almost instant and widespread, i.e., anyone with an internet connection can find almost any information. This gives rise to a hyperconnected world where any event tends to be amplified by being transmitted across the globe at the speed of modern communications and transportation.[2] The current SARS-COV-2 pandemic is a clear example of the modern form of this emergent phenomenon, but it is by no means the only or the last challenge that we will face in the 21st Century.

Historically, this same type of emergent issues was observed and documented during the Roman Empire.^[3] The Empire had established a region of relative stability across the Mediterranean Sea, making the movement of people, goods, and information easy and efficient. Hence, a drought on one part of the Empire affected the whole, and disease breaking out on any area soon spread to the whole. News of political or military events in one region tended to spread and affect other regions in the Empire and beyond, often changing the course of political and military events.

In the 21st Century, the dominant challenge to humanity is encapsulated in the concept of sustainability. This is at its core an effort to find ways that make it possible for humanity to exist in a civilized manner on the Earth for as long as possible. This is by itself a formidable challenge given the 7.97 Billion human population.[1] But this challenge must be met in the face of emergent threats such as the SARS-COV-2 pandemic, wars, climate change, and others.  At the local level, these emergent global threats can manifest at the local scale as major disruption events like floods, droughts, forest fires, economic distress, and public health challenges. We, therefore, propose the following theme for TARDIS 22:  Sustainability and Resilience in the Face of Emergent Threats. To explore this issue and to find feasible and actionable pathways to manage it, we propose the following focus questions to be addressed at TARDIS 21:

1. What are the most important threats facing the World in the 21st Century?
2. Which of these threats are critical challenges to achieving sustainability and promoting resilience locally as well as globally?
3. What may be the most practical and effective ways to mitigate these threats?
4. What is the most practical and effective path to resilience and sustainability in the face of these threats?

Given the importance and timeliness of this issue, an effort will be made by the organizers to prepare a manuscript representing all TARDIS participants for publication in a top journal.