AGCI Insight

What is global change?

September 27, 2023

This is the first in an occasional series of blog posts exploring how AGCI approaches global change science and solutions.

What’s in a name? Oftentimes when I introduce myself as the executive director of the Aspen Global Change Institute, I’m asked a very reasonable question: What, exactly, is global change?

Global change refers to the reality that our home planet is made up of many constantly changing and connected systems. Earth’s so-called “natural” systems include the biosphere (any place where life exists), as well as oceans, land, ice, and the atmosphere, all tied together across space and time through exchanges of energy, water, and nutrients.

Over time, humanity, with our collective ideas and technologies, has become one of Earth’s systems. We are now a driver of global change, capable of influencing all other Earth systems at a planetary scale—and, in turn, being impacted by these altered systems in new and often alarming ways.

Through a growing awareness of global change, we are invited to think more holistically about how people and planet interact in order to chart a more sustainable path for all life on Earth.

Human systems, Earth impacts

Take, for example, one element: nitrogen. The largest component of our atmosphere, nitrogen is also a key nutrient for living systems as it cycles through Earth’s soil, water, air, and living things. Beginning in the early 20th century, humans accelerated this cycle by developing new technologies that enabled vast quantities of nitrogen to be taken from the atmosphere and fixed to hydrogen, forming ammonia to use as agricultural fertilizer.

As this technology was deployed at industrial scales, different kinds of global changes emerged. The advent of fast and cheap ways to produce fertilizer significantly improved agricultural efficiency and helped feed a rapidly growing human population. Yet nitrogen runoff into rivers and oceans has also overstimulated algae growth, disrupting freshwater and marine ecosystems. And producing artificial nitrogen fertilizer emits carbon dioxide, which exacerbates climate change.

In this satellite image taken near the Mississippi River Delta in the Gulf of Mexico, nutrients from agricultural runoff, such as nitrogen, iron, and phosphorus, cause algal blooms that may contribute to the blue-green color near the coastline. Source: NASA Earth Observatory.

The story of nitrogen shows just one way human activities—represented by the sum of our economies, technologies, cultures, and political systems—have come to dominate the Earth system. Other examples of global change where human activity has played a causal role include climate change, land-use change (including deforestation), ocean acidification, ozone hole depletion, and biodiversity loss.

Mind the “safe operating space”

One well-known way to represent the various forms of global change is the planetary boundaries framework developed by the Stockholm Resilience Centre (pictured below; Richardson et al., 2023), which quantifies the magnitude of human-driven changes across many biophysical thresholds crucial to sustaining life on Earth. According to this framework, we have successfully remained within some boundaries, such as stratospheric ozone depletion, but have exceeded the “safe operating space” of several others.

And climate change is hardly the only global change of concern. Indeed, human impacts on biodiversity and biogeochemical cycles (e.g., nitrogen) have transgressed sustainable limits slightly more than climate change. The framework also reflects growing concern about the risks posed by poorly understood “novel entities,” which can include human-made compounds, like microplastics and endocrine disruptors, that circulate widely throughout our environments and bodies with unknown consequences.

The 2023 update to the planetary boundaries framework. Source: Azote for Stockholm Resilience Centre, based on analysis in Richardson et al., 2023. CC BY-NC-ND 3.0.

What’s remarkable is not just the variety and global extent of these changes, but also how fast they are appearing. The late researcher and futurist Alex Steffen, together with colleagues, coined this temporal aspect of global change “the Great Acceleration,” depicted with data for a wide range of Earth and socioeconomic trends in the figure below.

The Great Acceleration. Data for each variable is plotted from the time at which data is available (as early as 1750). Nearly all variables exhibit a notable uptick around 1950. Credit: Steffen et al. 2015. and F. Pharand-Deschênes/Globaia. Source: International Geosphere-Biosphere Programme.

The dawn of “global change”

A stamp released by the United States during the 1957-1958 International Geophysical Year. Source: National Postal Museum

The concept of global change emerged over the course of the 20th century, when scientists, citizens, and international leaders started to take the study and state of our home planet seriously. Scientific developments included coordinated international campaigns to monitor the Earth, starting in 1957-58 with the inaugural International Geophysical Year, and later via satellites with the dawning of the space age. Civic and political developments include the rise of the environmental movement, marked by the establishment of Earth Day in 1970; the United Nations Conference on the Human Environment in Stockholm in 1972, which led to the development of the United Nations Environment Programme; and the emergence of the concept of sustainable development, advanced through the 1987 United Nations publication Our Common Future, also known as the Brundtland Report

According to Google Ngram Viewer, which reports on the prevalence of words used within its large archive of texts, use of the term “global change” started in the 1980s. During this period, in the United States, interest in global change fused into federal agency research agendas on Earth Systems Science (NAS 1988), culminating in the establishment of the U.S. Global Change Research Program in 1990.

Internationally, coordinated programs emerged on the study of Earth systems, notably the International Geosphere-Biosphere Programme. So much research was produced from these activities that additional efforts were formed to assess the emerging science and draw conclusions for policy makers, such as the Intergovernmental Panel on Climate Change, which continues to this day.

Google’s NGram Viewer also shows that starting around the 1990s, usage of “climate change” eclipsed “global change.” Not surprisingly, this has corresponded with confusion about whether climate change is synonymous with global change. I like to think of global change as an umbrella term that encompasses climate change and many other examples of alterations to Earth systems. Even so, climate change has become a primary, if not singular, interest of many organizations concerned generally with global change.

Where does “sustainability” fit in?

Another common question I hear is: How does global change relate to sustainability? After all, if we’re interested in staying within planetary boundaries, don’t we also need to ensure the well-being of current and future generations? Sustainability is a deeply value-oriented concept broadly concerned with improving the quality of life for humans and other living beings today and long into the future. The 17 Sustainable Development Goals adopted by the UN illustrate the broad range of issues involved in pursuing sustainability in an actionable way, from ensuring adequate food supplies to strengthening institutions that maintain peace and justice.

Source: United Nations­

Encouragingly, the unanimous adoption of these goals by UN member nations has spurred many citizens and political leaders to embrace sustainability agendas and start taking action to achieve real change. Knowledge of global change is closely related to sustainability since in an age of global change, understanding Earth and human systems is essential for the continued flourishing of human activities within planetary boundaries.

Needed: solutions at speed and scale

Although global change has existed for millennia, we have only awakened to it over the last several decades. And just as alarming as the global scale of these changes is the speed at which they are unraveling. The growing body of research on global change has alerted societies around the globe to the need for swift implementation of solutions that consider the myriad and now unavoidable ways Earth and human systems are connected.

Adopting a global change mindset allows us to recognize that people can influence the actions of others at a global scale. Some of this influence is frightening: witness, for example, the speed at which social media can spread rumors or false claims. More encouragingly, however, international political processes like the one that produced the 2015 Paris Accords signaled the possibility of global collective action to reverse the harmful impacts of climate change.

Ultimately, the definition of global change is not as important as the scientific and solution-seeking activity it has mobilized since the last quarter of the 20th century. Taken together, global change as a means for understanding the future of Earth and human systems and sustainability as a set of values for organizing human priorities can and must inform the urgent work needed to chart a safe and just future for people and nature.