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Why should we care about biodiversity?

Two ASU scientists have the answers

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December 07, 2020

The loss of biodiversity is occurring at an unprecedented rate across Earth. Approximately 1 million species are threatened with extinction, and many species have gone extinct in the past decade. The recent Intergovernmental Panel on Biodiversity and Ecosystem Services (IPBES) report offers an overview of where the world stands in relation to key international goals on climate change, including the U.N. Sustainable Development Goals (SDGs), the Aichi Biodiversity Targets and the Paris Agreement.

ASU Now sat down with Leah Gerber, a lead author of the IPBES report and founding director of ASU’s Center for Biodiversity Outcomes, and Steffen Eikenberry, a postdoctoral fellow in ASU’s School of Mathematical and Statistical Sciences, to discuss why a loss of biodiversity is important, how species are accounted for now and in the past, and what issues are swirling around climate change and global warming when it comes to mitigating their effects.

Editor's note: Gerber and Eikenberry collaborated on the following responses.

Question: How do you know that past measurements of extinction are accurate, and how does that relate to the accuracy of today's measurements?

Answer: We are interested in estimating extinction rates as a way of understanding human impacts such as habitat loss, and compare that to our best estimates of the “background rate” of extinction; that is, the expected extinction rate based on nonhuman factors. We have found that the rate of extinction today is higher than ever before. For example, a recent study provides evidence for exceptionally rapid loss of biodiversity over the last few centuries, coinciding with the rise of the Industrial Revolution and human ingenuity, indicating that a sixth mass extinction is already under way.

Q: How can you reconcile human-caused climate change with natural causes for elevated carbon dioxide?

A: No doubt there are those who do not believe that what we experience today is the effect of human activity on Earth. However, there is significant consensus in the scientific literature and direct surveys of scientists that show at least a 97% consensus that humans are the primary cause of global warming. Some surveys put that consensus higher, as high as 99.9%, and anthropogenic climate change is so widely accepted that most scientists don’t even bother explicitly endorsing the notion. The Intergovernmental Panel on Climate Change coordinates with thousands of scientists to produce large assessment reports reflecting the scientific consensus, which now states that humans are causing unprecedented global warming.

Q: So, are the Earth’s increasing temperatures caused by humans?

A: Carbon dioxide is increasing, in both the atmosphere and ocean, with the only possible sources being the burning of fossil fuel and human land clearing and deforestation. Global mean temperatures have increased by about 1°C (almost 2°F) since the Industrial Revolution — the dawn of burning fossil fuels. Direct measurements, a wide range of climate models, and data from past climates and atmosphere (paleoclimate) all indicate that a doubling of atmospheric carbon dioxide will cause a 3 degrees to 4 degrees C (5.4 degrees to 7.2 degrees F) increase in average global temperatures. Climate models that do not include human carbon dioxide emissions cannot reproduce observed warming trends.

Q: Do scientists agree that humans activity is behind global warming?

A: None of this is to say that there is no disagreement in the field of climate science. The whole idea of science is that there are unanswered questions that we are trying to answer by studying the world. But the basic science of climate change, in that elevated carbon dioxide increases Earth’s temperature by about 3 degrees to 5 degrees C (5.4 degrees to 9 degrees F) with every doubling of carbon dioxide, is no longer in question. The main questions now are ones like what will the effects of climate change be on agriculture and cities, or when will climate change cause tipping points in other systems, like large scale forest die-backs and out of control wildfires or rapid ice shelf collapses. It is natural that as we study these problems, there is disagreement and uncertainty, but generally speaking the worst-case predictions from just a few decades ago are coming true.

Q: Why do we believe humans are changing the climate?

A: We know the atmosphere and climate are changing from direct measurements: Measurements of the carbon dioxide concentration in the atmosphere show an almost 50% increase (from 280 ppm to 410 ppm) since about 1750. Furthermore, since carbon in the ocean is also increasing, this cannot be explained as a shift from ocean to atmosphere. Some of this carbon is from humans clearing vast tracts of land for agriculture and cities — a shift from biomass to atmosphere — but this accounts for only a fraction of the increase. Therefore, burning fossil fuels is the only possible explanation for the observed increase in carbon.

Reliable measurements across the globe also show that the average surface temperature on Earth has increased by about 1 degree C (1.8 degree F). This represents a global increase in the amount of heat stored in the Earth system, and so either more heat must be coming in, or less going out. With no significant variation in the sun’s output, volcanic activity, or reflectivity of Earth’s surface, the only explanation is an enhanced greenhouse effect trapping heat in Earth’s atmosphere. By the 1970s, it was clear from observational data and scientific models that not only was atmospheric carbon dioxide increasing, but that Earth was likely on the brink of a pronounced “global warming,” with this term appearing in print for the first time in 1975.

Q: Why should we care about biodiversity?

A: Biodiversity indicates the health of an ecosystem. Having biodiversity improves the health of Earth. It shows it is thriving. And healthy ecosystems clean our water, purify our air, maintain our soil, regulate the climate, recycle nutrients and provide us with food. Biodiversity provides raw materials and resources for medicines and other purposes. The loss of biodiversity has an effect on humans, as we are part of that biodiversity. Biodiversity is the foundation of our economy and our well-being.

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