Climate change will replace land use change as the major driver of changes in Earth’s biosphere in the 21st century if greenhouse gas emissions aren’t curbed, new research suggests.
Historically, human land use change, like urban development and agricultural expansion, has been the primary cause of anthropogenic ecosystem change. For example, more than 4.5 billion hectares (17.4 million square miles) of the planet has been converted into land for growing crops and feeding livestock, roughly 30 percent of Earth’s land surface area.
But now, due to rising greenhouse gas levels, climate change has become a growing threat to ecosystems. The rapid pace of climate change is making it difficult for species to adapt to changes in temperature, water cycles, and other environmental conditions that affect life on Earth.
To address the risk of climate change, the world’s nations adopted the Paris Agreement in 2015, an international pledge to limit global warming below 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels. In a new study accepted for publication in Earth’s Future, a journal of the American Geophysical Union, researchers developed computer simulations that illustrate how the success or failure of the Paris Agreement would impact Earth’s land ecosystems.
According to this new research, if the international community fails to reach their regulatory goal, climate change will likely replace land use change as the biggest catalyst for major changes to the planet’s ecological landscape.
Land use change has already interfered with important ecological systems and put species at risk of extinction. Scientists are concerned that climate change’s growing contribution to landscape change will deal even more damage to Earth’s biosphere.
“Think of the impacts that have already been caused by land use change. Now imagine that climate change impacts will likely be even bigger than that by the end of this century,” said Sebastian Ostberg, a geoecologist at the Potsdam Institute for Climate Impact Research in Potsdam, Germany and lead author of the new study.
A Changing Environment
Climate change can alter Earth’s ecosystems in several different ways. For instance, increasing temperatures can disrupt important time-sensitive ecological interactions that many species rely on for survival. Although every species reacts differently to these changes, a change in temperature could cause some plants and animals to start their activities earlier in spring, and cause some plants to shed their leaves later in autumn, Ostberg said.
The increased carbon dioxide levels associated with climate change can also drive ecosystem change, acting as fertilizer for vegetation growth and consequently causing a ‘greening effect’ across Earth. This kind of change presents a problem for regions normally devoid of plants, as increased vegetation can make ecosystems more vulnerable to fires and other major ecological changes.
Scientists have already seen evidence of some of these changes, and researchers predict these impacts will only increase if climate change isn’t controlled. “There are already observations of changes in ecosystems from all continents and all climate zones,” Ostberg said.
Modeling Global Impact
Several studies have examined how climate change and land use change have individually impacted or will impact Earth’s various ecosystems, but the new study seeks to understand how the interaction of these factors influences terrestrial biomes.
To fully assess how climate change and land use change will impact Earth’s ecosystems, the researchers created biosphere simulations for three scenarios. In the first scenario, the world reaches the Paris Agreement goal by limiting global warming to well below 2 degrees Celsius above pre-industrial levels. In the second scenario, the world reduces greenhouse gas emissions, but not enough to achieve the Paris Agreement goal, and in the third scenario, the world completely fails to control greenhouse gas emissions.
The researchers used climate change and land use projections based on four greenhouse gas concentration trajectories, known as representative concentration pathways (RCPs). Like the Paris Agreement scenarios, the RCPs represent varying degrees of greenhouse gas regulation success. Ostberg and his colleagues used each greenhouse gas pathway as a proxy to represent one of the three Paris Agreement scenarios.
The researchers ran computer simulations that demonstrated how climate change and land use change have already influenced the biosphere and how the two factors might influence the planet’s biosphere under the three Paris Agreement scenarios.
Their models suggest that by the start of the 21st century, climate change and land use change had already caused major ecosystem changes to 25 to 30 percent of Earth’s land surface, with land use change responsible for roughly twice as much land surface change compared to climate change.
If the international community successfully limits global warming to their agreed upon goal, the researchers say land use change will be responsible for major impacts to 23 percent of the Earth’s land surface, and climate change will account for major impacts to 22 percent of Earth’s land surface by the end of the century.
In the case that the world reduces greenhouse gas emissions, but is unable to limit global warming to 2 degrees Celsius above pre-industrial levels, the researchers’ model projects climate change will cause major changes to 34 percent of Earth’s biosphere while land use change will impact 11 to 13 percent of the global land surface by 2100.
If the world fails to reduce carbon emissions, climate change and land use change will bring major changes to 73 percent of the global landscape by the end of the century, according to the model. In this scenario, the researchers predict climate change alone would account for almost three-quarters of this change.
“It’s hard to know what the future world will actually be like, but this is a valuable first attempt to draw attention to the fact that climate change in the future could become more important as a driver of land cover change than anthropogenic land use change,” said Jed Kaplan, an expert on land cover at the Environmental Change Institute of the University of Oxford in the United Kingdom who was not involved in the study.