Climate change is a complex and increasingly important environmental stressor, with implications for Earth and human systems. There are many observing systems currently available that capture elements of how climate is changing, for example, direct measurements of atmosphere and ocean temperature. The purpose of this report is to look beyond the existing observing approaches that focus primarily on physical attributes (even as these remain important) to provide more information about the human dimensions and impacts of climate change.
This report is not an exhaustive analysis of all the human-environment interactions that will be stressed by a changing climate, but instead it attempts to provide representative lists of metrics that appear likely to be affected by foreseeable disruptions over the next 20-25 years. The committee’s challenge was to sort through the many possible metrics and identify some subset within key sectors where observations over time could help project climate-related changes in the human-environment system and their impacts.
As the committee deliberated and examined potentially useful metrics, it became apparent that key indicators of environmental sustainability, in a climate change context, are found at the intersection of how the climate is changing and how those changes will affect the five domains of human vulnerability: food, water, energy, shelter, and health. It will be a challenge to advance the understanding and ability to observe and analyze these points of intersection. It is understood that the Earth is a complex system. As public policy in response to climate change evolves, it will be increasingly important to think with a systems perspective in order to understand the components and their interconnections.
The committee finds that observations of global-scale processes are especially valuable from an indicators perspective. They reflect both the impacts of climate change as well as the feedbacks and forcings that change the directions, scale, or timeframe of impacts. An emphasis on global-scale processes provides insights on linkages within the Earth system because these linkages extend from the cryosphere to the hydrosphere, from the atmosphere to the oceans, and include the land-surface and natural disasters.
Several metrics appear in multiple tables, such as sea level rise, seasonal snow cover, and air quality. In part, this is simply a result of the fundamental linkages across the components of the Earth system. Sea level rise is a function of oceanic, land ice, and hydrological processes, but it also acts as an “amplifier” for natural disasters such as tropical cyclones by increasing the risk of harm. For example, subsidence in the Gulf Coast increased the damage from Hurricane Katrina, which serves as an example of the intersection of Earth and human systems in the context of climate change. Thus the metrics of climate change presented in this report cross many disciplines.
Identifying metrics of climate change that intersect with human systems is a difficult but important task. Clearly, there is a sense of urgency behind this task. The climate is changing simultaneously with an increase in the global human population, which in turn makes humans more vulnerable to environmental stresses and disasters. More than ever before, it is critical to think about metrics of climate change through an environmental sustainability lens, and identify those indicators that will provide human society sufficient time to act.