Where will the tall trees grow?

Reference: Nolan, Conner, Jonathan T. Overpeck, Judy R. M. Allen, Patricia M. Anderson, Julio L Betancourt, Heather A, Binnay, Simon Brewer, et al. (2018) Past and future global transformation of terrestrial ecosystems under climate change. Science. 361:920-923. DOI: 10.1126/science.aan5360

Looking Back to Look Forward

To understand the amount of change that might occur as the world continues warming, Connor Nolan and his colleagues looked to the past.  This is a common approach that, in this case, allowed the researchers to study how different things were just after the last glacial period, when the world was four to seven degrees cooler. Two different kinds of change, structure and composition, were evaluated in 594 ancient records collected from around the world. The researchers asked regional teams of experts to look at each record and assess how much change had occurred compared to the present-day landscape.

A large change in composition meant the dominant species, or the type of plants most common in the record, had been replaced by a different dominant species. In contrast, a large structural change might mean a change from forest to grassland. The experts scored each record as having changed a low, moderate, or large amount, and then ranked how confident they were based on the quality of the record. For records where the changes was moderate or large, the experts were then asked to evaluate the role of climate in these changes. If climate was sufficient to explain the change, then it was assessed as large. If climate was one of several factors that might explain the change observed from the record, it was considered moderate. If climate was not likely a factor, it was assessed as low.

Experts determined that climate played a significant role in roughly two thirds of the sites that experienced large change and climate played a significant role in roughly one third of sites experiencing a moderate amount of change. Sites at the equator experienced less change than sites closer to the poles.

Did the experts get it right?

Did the climate actually change in places experts said it was probably the driver of change?

To answer this question, the researchers compiled an independent map of the local increase in the average temperature between the time the historical records were collected and the present day. They found that in general, places where the structure had changed the most were also where the largest temperature changes had occurred. Composition change, from one dominant species to another, occurred at smaller levels of temperature change. This makes sense because there are usually many different species that are well-suited to a particular climate; for example, maple trees and oak trees are found in temperate regions. Sites in North America and Europe that were close to the edge of the ice sheets experienced both large change in temperature and also large change in the structure and composition of the ecosystems in the historical record. In other places around the world, much smaller temperature changes also resulted in ecosystem changes.

What does all of this mean for the future?

Based on their analysis of the past, the researchers suggest that the same pattern will likely occur in the future. That is to say, the largest changes in ecosystem composition and structure are likely to occur in places where the changes in local temperature are greatest. To give readers an idea of where that will happen, the researchers built a model based on their historical data set to predict the probability of change in the landscape.

This probability is dependent on the amount of global climate change that occurs. Based on this study, that means if humans can limit emissions and the climate only warms 2 or 3 degrees (climate scenario RCP* 2.6), the probability of wide spread landscape change is less than 50% around the globe. But, if the climate warms 4 to 8 degrees (climate scenarios RCP*s 4.5, 6.0 & 8.5), then the chance of changes in the composition and structure of the landscapes we see around us are much more likely.

So, what will the landscape look like in 50 or 100 years? Will you still live in a forest, or a newly formed desert? It appears the answer, in part, lies in how we respond to the warming world.


* Note: “RCP” stands for “representative concentration pathways”: the short-hand name used by the International Panel on Climate Change (IPCC) for the various emissions scenarios used in the global climate models to project future climate.


Cover image references:

Rainforest, Source: Wikipedia

Desert, Source: Wikipedia

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E.M.B. Doran

E.M.B. Doran

Dr. Doran is a Postdoctoral Associate with the VT EPSCoR Basin Resilience to Extreme Events (BREE) project where she is conducting research at the interface of land use and land cover (LULC) change, water quality, and human decision making and policy. Her other research interests include urban climate, energy use and using systems science and modeling techniques to inform decision making under uncertainty.

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