Of mice, men, and CO2

University of Wisconsin researcher Jessica Blois crawling out of Samwell Cave in California, from where she excavated fossils that she used to determine how small mammals responded to natural climate changes. Credit: Stanford University

The temperatures predicted as a result of human-driven climate change are likely to be warmer than any that some small mammal species have seen in their evolutionary history. So suggests Jessica Blois, a University of Wisconsin researcher who has studied how the balance between these species has changed over the last 18,000 years. “Presumably, because they have survived to the present, most species can deal with the range of climate change we have seen in the past,” she tells Simple Climate. “But our inferences from the past don’t allow us to predict with as much confidence whether or how they’ll be able to deal with future climates.”

Blois’ work, recently published in the leading journal Nature, used information gathered from fossils in a cave in Northern California to assess the impacts of previous warming periods. She found that one small mammal species – the deer mouse – fared much better than others, like gophers and squirrels, which became increasingly rare. “The data in the paper show that diversity declined with post-glacial warming,” she explains.

The impact of the lost diversity is still felt today, and is likely to make it harder for the population she describes to respond to higher temperatures. “I think that continued climate warming is going to accelerate these trends and may lead to even more significant impacts,” Blois says. She emphasises that plants and animals have often moved home in response to changing climate in the past, but that humans are also making alternative locations unsuitable. “These issues may increase the risk of extinction,” she said.

Small mammals play a “crucial” role in the food chain, Blois notes, and also help distribute seeds and fulfil other roles that help plants and trees to grow. However, they also suggest how other species might react to warming. “Comparable changes are likely happening in many other communities as well and the overall ecosystem – in addition to just the small mammals – may be less resilient to major climate changes now than in the past.” Blois is now studying how rapid climate change 12,000-13,000 years ago affected plant species. She points out that this general period in history boasts comparatively good climate records and biological data, making it ripe for this kind of research.

Looking at changes over such a wide timespan gives Blois a perspective on climate change that is often overlooked. “Climate has changed through earth’s history, regulated naturally by a combination of orbital forces that determine how much sun hits the earth as well as the total concentration of different natural gases in the atmosphere,” she points out. “These natural processes are still occurring today, but with the rise of industrialism in the mid-1800s, humans started altering the balance of gases in the atmosphere, primarily by emitting a lot more CO2 due to burning fossil fuels like oil and gas. Since CO2 is a ‘greenhouse gas’ that traps heat in the atmosphere, human activities have caused temperatures to increase much, much more than naturally expected.”

For those seeking evidence that this is really the case, Blois points to the following figure, showing temperatures and atmospheric CO2 levels, says it all:

Jessica Blois suggests this graph of temperature changes and atmospheric CO2 concentrations through history strongly demonstrates the effect of humans burning fossil fuels. Credit: Pew Center on Global Climate Change

In addition, how the Intergovernmental Panel on Climate Change (IPCC) – the United Nations-sponsored body assessing global warming risks – has gathered information is a good reason to listen to what it says, Blois feels. “The IPCC process is long, exhaustive, in-depth and it consistently has concluded that rapid rates of climate change are real, and that the climate changes we see today are caused by humans,” she notes. “It is the most elegant model for consensus-based science that I know of.”

To try and bring emissions back down, Blois encourages us all to reduce our impact on the environment through actions that we can control. Her suggestions include reducing the total amount of gas used by driving less or driving more fuel-efficient vehicles, and reducing the total amount of oil used producing goods by wasting less. “Another significant action individuals can take is by pressuring government officials and industry, through their votes and their dollars, to enact scientifically-sound policies that aim to reduce the total amount of carbon emissions,” she says.

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