Human civilization is inextricably linked with the Earth system and the ecosystem services it provides. The sustainability of both human and Earth systems depends in large part on their vulnerability and resilience to system threats. Climate change is a significant component of the people-environment link. Because changes in climate threaten multiple Earth systems, such as the atmosphere and oceans, it also threatens many human systems.
The stresses associated with climate change are expected to be felt keenly as human population grows to a projected 9 billion by the middle of this century, increasing the demand for resources and supporting infrastructure. Therefore, information to assess vulnerabilities to climate change is needed to support policies and investments designed to increase resilience in human and Earth systems.
There are currently many observing systems that capture elements of how climate is changing, for example, direct measurements of atmospheric and ocean temperature. Although those measurements are essential for understanding the scale and nature of climate change, they do not necessarily provide information about the impacts of climate change on humans that are especially relevant for political and economic planning and decision making.
The challenge to the report’s authoring committee was to develop an illustrative suite of indicators, measurements (and the locations around the globe where the measurements can be applied), and metrics that are important for understanding global climate change and providing insight into environmental sustainability (Box S-1 for definitions). Eight panels provided input on: cryosphere, land-surface and terrestrial ecosystems, hydrology and water resources, atmosphere, human health and other dimensions, oceans (both physical and biological/chemical), and natural disasters. The committee developed an illustrative set of metrics (Chapter 3 tables) that are likely to be affected by climate change over the next 20-25 years and, when taken together, can potentially give advance warning of climate-related changes to the human and environment systems.
Definitions of Key Terms
Measurement: A quantitative, physical attribute.
Metric: A category that reflects a combination of individual measurements and that can be used to provide a large-scale view of a system and gauge system performance. It may be quantitative or qualitative.
Indicator: A selected subset of metrics that is judged helpful for projecting future performance of a system.
This report is envisioned as a technical document for use by analysts in the intelligence community, as well as researchers, as they delve more deeply into climate change and its ramifications worldwide. Developing interdisciplinary metrics that intersect with environmental sustainability and human well-being, as done in this report, is an important step in thinking about how to monitor the impacts of climate change.
DOMAINS OF HUMAN VULNERABILITY
The committee began by identifying examples of domains of human vulnerability where change is likely to occur in the near term and where climate change impacts on humans begin to be significant. Each domain is an area of critical importance to society, is vulnerable to the impacts of climate change, and highlights the intersection of human needs and climate change. This report concludes that indicators of environmental sustainability, in a climate change context, can be found at the intersection of how the climate is changing and how those changes will affect five domains of human vulnerability.
These five domains are:
Food: Climate change impacts may result in competition for declining food resources (both fisheries and agriculture) as well as shifting patterns of harvest. This could lead to food shortages and famines in less developed countries, as well as a variety of economic ramifications.
Water: Climate change stands to affect future water distribution, quantity, and quality. This could lead to lack of water, water of poor quality, or too much water at the wrong time in many locations around the globe.
Energy: Anthropogenic input of CO2 to the atmosphere is well established as a cause of climate change. The pressure to “decarbonize” over the next few decades will inevitably result in new approaches to energy use, which will, in turn, have potentially unforeseen environmental impacts.
Shelter: Humans need shelter as a basic element for quality of life. Natural disasters such as flood, drought, and wildfire both threaten existing shelter and increase the need for shelter. Many of these extreme events may be exacerbated by climate change.
Health: A changing climate may affect any health outcome that is influenced by environmental conditions, such as an increase in mosquito- and water- borne diseases.
CLIMATE CHANGE METRICS AT THE INTERSECTION OF THE HUMAN AND EARTH SYSTEMS
A global-scale process is one that is manifested in all regions of the planet, such as the biogeochemical cycles of carbon and nitrogen or the hydrologic cycle. The committee finds that observations of global-scale processes are especially valuable from
an indicators perspective, because they link the impacts of climate change to the feedbacks and forcings that can change the direction, scale, or timeframe of those impacts. The linkages extend across the Earth system, from the atmosphere to the oceans, from the cryosphere to the hydrosphere, and include the land-surface and natural disasters.
Chapter 3 presents tables of metrics, measurements, and locations by topical areas of human and Earth systems. The metrics vary, with some being clearly quantifiable and others being more qualitative. Some metrics are indicators of distinctly measurable change, whereas others are more exploratory and offer new perspectives.
Several metrics such as sea level rise, seasonal snow cover, and air quality appear in multiple tables because of the fundamental linkages across systems. 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 potential. Thus the metrics of climate change presented in this report cross many disciplines.
A broad array of indicators, based on a great diversity of measurements, could to some degree provide advance warning of the impacts of global climate change. But because it is uneconomical and, indeed, fundamentally impossible to measure everything, it is important to develop priorities—to select a finite suite of indicators that, taken together, provide a generally accurate and informative basis for anticipating problems.
The committee concluded that certain characteristics tend to make a metric particularly useful, including the following:
Direct (e.g., loss of mass of an ice sheet leads to rising sea level)
Significant (i.e., represents a large change in one or more resources including water, energy, shelter, health, and food)
Dominant (i.e., outweighs other factors and processes)
Measurable (i.e., capable of being quantified)
Historical (i.e., provides the foundation of understanding and measurement)
Well documented (i.e., data are complete and consistent)
Given the diverse nature of metrics, a uniform process for categorizing and prioritizing the metrics presented in this report is not possible. Therefore, each panel, in addition to considering the criteria described above, explains in the text preceding each table the processes and criteria it used when categorizing or prioritizing its metrics.
CONSIDERATIONS FOR THE FUTURE
Having metrics that illustrate how climate change is affecting human systems will prove useful as climate change impacts become more prominent. Climate is changing simultaneously with an increase in the global human population, which in turn increases environmental stresses and reduces human resilience1. Increasing information about climate change when its impacts most affect human needs is a logical step in informing decision makers and improving our ability to adapt and/or embrace societal resilience.