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Climate change

Communicating uncertainty about climate change

By | Climate change, News, Science communication

The ways climate scientists explain their predictions about the impact of global warming can either promote or limit their persuasiveness.

The more specific climate scientists are about the uncertainties of global warming, the more the American public trusts their predictions, according to new research by Stanford scholars.

But scientists may want to tread carefully when talking about their predictions, the researchers say, because that trust falters when scientists acknowledge that other unknown factors could come into play.

In a study in Nature Climate Change, researchers examined how Americans respond to climate scientists’ predictions about sea level rise. They found that when climate scientists include best-case and worst-case case scenarios in their statements, the American public is more trusting and accepting of their statements. But those messages may backfire when scientists also acknowledge they do not know exactly how climate change will unfold.

“Scientists who acknowledge that their predictions of the future cannot be exactly precise and instead acknowledge a likely range of possible futures may bolster their credibility and increase acceptance of their findings by non-experts,” said Jon Krosnick, a Stanford professor of communication and of political science and a co-author on the paper. “But these gains may be nullified when scientists acknowledge that no matter how confidently they can make predictions about some specific change in the future, the full extent of the consequences of those predictions cannot be quantified.”

Effects of communicating uncertainty

Predicting the future always comes with uncertainty, and climate scientists routinely recognize limitations in their predictions, note the researchers.

“In the context of global warming specifically, scientific uncertainty has been of great interest, in part because of concerted efforts by so-called ‘merchants of doubt’ to minimize public concern about the issue by explicitly labeling the science as ‘uncertain,’” said Lauren Howe, who was a postdoctoral scholar at Stanford when she conducted the research with Krosnick and is first author on the paper.

“We thought that, especially in this critical context, it was important to understand whether expressing uncertainty would undermine persuasion, or whether the general public might instead recognize that the study of the future has to involve uncertainty and trust predictions where that uncertainty is openly acknowledged more than those where it is minimized,”

Howe said.

To better understand how the public reacts to scientists’ messages about the uncertainties of climate change, the researchers presented a nationally representative sample of 1,174 American adults with a scientific statement about anticipated sea level rise.

Respondents were randomly assigned to read either a prediction of the most likely amount of future sea level rise; a prediction plus a worst-case scenario; or a robust prediction with worst-case and best-case scenarios, for example: “Scientists believe that, during the next 100 years, global warming will cause the surface of the oceans around the world to rise about 4 feet. However, sea level could rise as little as 1 foot, or it could rise by as much as 7 feet.”

The researchers found that when predictions included a best-case and worst-case scenario, it increased the number of participants who reported high trust in scientists by 7.9 percentage points compared with participants who only read a most likely estimate of sea level rise.

Changes in environmental policies, human activities, new technologies and natural disasters make it difficult for climate scientists to quantify the long-term impact of a specific change – which scientists often acknowledge in their predictions, the researchers said. They wanted to know if providing such well-intended, additional context and acknowledging complete uncertainty would help or hurt public confidence in scientific findings.

To find out, the researchers asked half of their respondents to read a second statement acknowledging that the full extent of likely future damage of sea level rise cannot be measured because of other forces, such as storm surge: “Storm surge could make the impacts of sea level rise worse in unpredictable ways.”

The researchers found that this statement eliminated the persuasive power of the scientists’ messages. When scientists acknowledged that storm surge makes the impact of sea level rise unpredictable, it decreased the number of participants who reported high trust in scientists by 4.9 percentage points compared with the participants who only read a most likely estimate of sea level rise.

The findings held true regardless of education levels and political party affiliation.

Not all expressions of uncertainty are equal, Howe said: “Scientists may want to carefully weigh which forms of uncertainty they discuss with the public. For example, scientists could highlight uncertainty that has predictable bounds without overwhelming the public with the discussion of factors involving uncertainty that can’t be quantified.”

Read the paper: Nature Climate Change

Article source: Stanford University

Author: Melissa De Witte

Image credit: Jody Davis / Pixabay

World’s biggest terrestrial carbon sinks are found in young forests

By | Climate change, Forestry, News

More than half of the carbon sink in the world’s forests is in areas where the trees are relatively young – under 140 years old – rather than in tropical rainforests, research at the University of Birmingham shows.

These trees have typically ‘regrown’ on land previously used for agriculture, or cleared by fire or harvest and it is their young age that is one of the main drivers of this carbon uptake.

Forests are widely recognised as important carbon sinks – ecosystems capable of capturing and storing large amounts of carbon dioxide – but dense tropical forests, close to the equator have been assumed to be working the hardest to soak up these gases.

Researchers at the Birmingham Institute of Forest Research (BIFoR) have carried out fresh analysis of the global biosphere using a new combination of data and computer modelling in a new study published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS). Drawing on data sets of forest age, they were able to show the amount of carbon uptake between 2001 and 2010 by old, established areas of forest.

They compared this with younger expanses of forest which are re-growing across areas that have formerly experienced human activities such as agriculture or logging or natural disturbances such as fire.

Previously it had been thought that the carbon uptake by forests was overwhelmingly due to fertilisation of tree growth by increasing levels of carbon dioxide in the atmosphere.

However, the researchers found that areas where forests were re-growing sucked up large amounts of carbon not only due to these fertilisation effects, but also as a result of their younger age. The age effect accounted for around 25 per cent of the total carbon dioxide absorbed by forests. Furthermore, this age-driven carbon uptake was primarily situated not in the tropics, but in the middle and high latitude forests.

These forests include, for example, areas of land in America’s eastern states, where settlers established farmlands but then abandoned them to move west towards the end of the 19th century. The abandoned land became part of the US National Forest, along with further tracts abandoned during the Great Depression in the 1930s.

Other significant areas of forest re-growth include boreal forests of Canada, Russia and Europe, which have experienced substantial harvest activity and forest fires. Largescale reforestation programmes in China are also making a major contribution to this carbon sink.

Dr Tom Pugh, of the Birmingham Institute of Forest Research (BIFoR), explained: “It’s important to get a clear sense of where and why this carbon uptake is happening, because this helps us to make targeted and informed decisions about forest management.”

The research highlights the importance of forests in the world’s temperate zone for climate change mitigation, but also shows more clearly how much carbon these re-growing forests can be expected to take up in the future. This is particularly important because of the transient nature of re-growth forest: once the current pulse of forest re-growth works its way through the system this important part of the carbon sink will disappear, unless further reforestation occurs.

“The amount of CO2 that can be taken up by forests is a finite amount: ultimately reforestation programmes will only be effective if we simultaneously work to reduce our emissions,” explains Dr Pugh.

Read the paper: PNAS

Article source:University of Birmingham

Image credit: CCO Public domain

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