Climate change is one of the biggest challenges humankind has ever faced, because it is clear we are creating a slow-motion catastrophe for ourselves and fellow travelers (fauna and flora) on Earth's journey. A big part of the challenge is the orchestrated denial and well-funded opposition, designed to slow action that would adversely affects some of the world's biggest industries. Thus, progress has been insufficient to halt the predicted, and already observed, warming, weather disruptions, and rising sea levels.

It is well acknowledged that climate change will have numerous major effects on health, and these negative effects will be concentrated among populations which have the least resources to cope. What does climate change have to do with active living? Though warming temperatures may discourage people in some areas from being active, I believe the main connection is that promoting active living and creating activity-friendly communities can be an important part of the solution. The transportation sector generates a large share of total greenhouse gases, with automobiles being major contributors.

Carbon emission reduction goals from transportation are unlikely to be met unless many more people are walking, bicycling, and taking transit. We have a great opportunity to simultaneously advance carbon and public health goals by increasing active travel. Of course, this will require more investments in, and better design of, pedestrian, bicycling, and transit facilities and other intervention strategies.

Like many people, I have been concerned about climate change but not involved enough to feel like I was making a contribution. Thus, I was very pleased to receive an invitation from Janet Rankin to participate in a "side event" on climate change and health a day before the United Nations Summit on Climate Change. This meeting was one of several highlighting the connection between climate change and health, and the focus was on solutions and co-benefits. Janet is a past president of the American College of Sports Medicine (ACSM) whose signature initiative was announced at the meeting. "ActivEarth" aims to reduce carbon emissions by increasing physical activity. See the website for more information and upcoming events: www.activearth.org.

The September 22, 2014 gathering was co-hosted by ACSM, the Public Health Institute, and two other groups, plus several more co-sponsors. The list of keynotes was impressive, befitting the significance of the topic: Richard Horton (editor of The Lancet), Boris Lushniak (Acting Surgeon General), and Gena McCarthy (Administrator of the Environmental Protection Agency). The audience of about 120 were all invited, with representatives of many important groups, including several from the World Health Organization. There were panels on sustainable agriculture, active transportation, and air pollution, all dealing with the joint agendas of climate change and public health. My role was on the active transport panel. A video will be made with highlights of the event, accompanied by a set of recommendations. Check the ACSM and ActivEarth websites for the release date and other follow-ups.

On Sunday September 21, I had the pleasure to be among 400,000 people marching through Manhattan to demonstrate to world leaders the strong support for meaningful action to reduce carbon emissions. There were similar marches in hundreds of cities around the world. This event was well-organized, massive, peaceful, and uplifting. All age groups were well-represented, but there was an especially strong contingent of young people. All of us hope the march and climate change activities throughout the week are a turning point in global commitment to action.

Here are some of my favorite photos from the panel and people's march.

The active transportation panel, plus Jim Whitehead, Executive Director of ACSM.

Just to show I was there. Note my t-shirt showing children doing some active travel. This is street art from Penang, Malaysia.

Many aspects of climate change were spotlighted during the march.

We got to see fellow marchers around the world.

A human river of 400,000 commmitted people.

The young people speak.